Author name code: feldman
ADS astronomy entries on 2022-09-14
author:"Feldman, Uri" 
------------------------------------------------------------------------  

Title: Transition Region Abundance Measurements During Impulsive
    Heating Events
Authors: Warren, Harry P.; Brooks, David H.; Doschek, George A.;
   Feldman, Uri
Bibcode: 2016ApJ...824...56W
Altcode: 2015arXiv151204447W
  It is well established that elemental abundances vary in the solar
  atmosphere and that this variation is organized by first ionization
  potential (FIP). Previous studies have shown that in the solar corona,
  low-FIP elements such as Fe, Si, Mg, and Ca, are generally enriched
  relative to high-FIP elements such as C, N, O, Ar, and Ne. In this paper
  we report on measurements of plasma composition made during impulsive
  heating events observed at transition region temperatures with the
  Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. During these
  events the intensities of O IV, v, and VI emission lines are enhanced
  relative to emission lines from Mg v, VI, and vii and Si VI and vii,
  and indicate a composition close to that of the photosphere. Long-lived
  coronal fan structures, in contrast, show an enrichment of low-FIP
  elements. We conjecture that the plasma composition is an important
  signature of the coronal heating process, with impulsive heating leading
  to the evaporation of unfractionated material from the lower layers of
  the solar atmosphere and higher-frequency heating leading to long-lived
  structures and the accumulation of low-FIP elements in the corona.

Title: Anomalous Relative Ar/Ca Coronal Abundances Observed by the
    Hinode/EUV Imaging Spectrometer Near Sunspots
Authors: Doschek, G. A.; Warren, H. P.; Feldman, U.
Bibcode: 2015ApJ...808L...7D
Altcode:
  In determining the element abundance of argon (a high first ionization
  potential; FIP element) relative to calcium (a low FIP element) in
  flares, unexpectedly high intensities of two Ar xiv lines (194.40,
  187.96 Å) relative to a Ca xiv line (193.87 Å) intensity were
  found in small (a few arcseconds) regions near sunspots in flare
  spectra recorded by the Extreme-ultraviolet Imaging Spectrometer
  on the Hinode spacecraft. In the most extreme case the Ar xiv line
  intensity relative to the Ca xiv intensity was 7 times the value
  expected from the photospheric abundance ratio, which is about 30
  times the abundance of argon relative to calcium in active regions,
  i.e., the measured Ar/Ca abundance ratio is about 10 instead of 0.37
  as in active regions. The Ar xiv and Ca xiv lines are formed near 3.4
  MK and have very similar contribution functions. This is the first
  observation of the inverse FIP effect in the Sun. Other regions show
  increases of 2-3 over photospheric abundances, or just photospheric
  abundances. This phenomenon appears to occur rarely and only over
  small areas of flares away from the regions containing multi-million
  degree plasma, but more work is needed to quantify the occurrences
  and their locations. In the bright hot regions of flares the Ar/Ca
  abundance ratio is coronal, i.e., the same as in active regions. In
  this Letter we show three examples of the inverse FIP effect.

Title: Assessing atomic data accuracy along isoelectronic sequences
Authors: Young, Peter R.; Feldman, Uri
Bibcode: 2014AAS...22410603Y
Altcode:
  The CHIANTI atomic database provides radiative decay rates and electron
  excitation rates for modeling collisionally-excited emission lines from
  242 ions. We present a new method for assessing atomic data accuracy
  whereby level populations for specific atomic levels are plotted
  along isoelectronic sequences. Results are presented for the helium
  through fluorine isoelectronic sequences. Generally a smooth variation
  of population with atomic number is found and so anomalies, often due
  to problems with atomic data, can be identified. One exception is for
  the iron ions, which can show level populations an order of magnitude
  larger than neighboring ions. These can be demonstrated to be due to
  the much larger atomic models that are typically run for iron ions.

Title: Ultraviolet and X-ray Spectroscopy of the Solar Atmosphere
Authors: Phillips, Kenneth J. H.; Feldman, Uri; Landi, Enrico
Bibcode: 2012uxss.book.....P
Altcode:
  1. The solar atmosphere; 2. Fundamentals of solar radiation;
  3. Fundamentals of atomic physics; 4. Mechanisms of formation of the
  solar spectrum; 5. Plasma diagnostic techniques; 6. Ultraviolet and
  X-ray emission lines; 7. Spectrometers and imagers for observing the
  solar ultraviolet and X-ray spectrum; 8. Quiet Sun and coronal holes;
  9. Active regions; 10. Solar flares; 11. Element abundances; Appendices;
  References; Index.

Title: The Ne VII 465.22 Å to Ca IX 466.23 Å Intensity Ratio
    Abundance Diagnostic in Solar Observations
Authors: Widing, K. G.; Feldman, U.
Bibcode: 2011ApJ...742...71W
Altcode:
  The Ne VII 465.22 Å, and the Ca IX 466.23 Å, lines appear side by
  side in spectra of solar atmosphere regions. Although the two ions are
  formed at nearly the same temperature, the relative intensities of the
  two lines show great variations from typical cases where Ne VII 465.23
  Å is 20-30 times stronger than Ca IX 466.23 Å to spectra where the two
  lines are almost equal. The relative Ne VII/Ca IX intensity variation
  is correlated with the presence of the first ionization potential
  effect on elemental abundances in the outer solar atmosphere. Using
  published observational results, we derive the abundances of a number
  of regions and show that on occasion the enrichment of Ca in the solar
  atmosphere exceeds a factor of 30.

Title: Redshifts, Widths, and Radiances of Spectral Lines Emitted
    by the Solar Transition Region
Authors: Feldman, U.; Dammasch, I. E.; Doschek, G. A.
Bibcode: 2011ApJ...743..165F
Altcode:
  A long-standing problem in understanding the physics of the transition
  region has been the ubiquitous redshifts of transition region
  ultraviolet spectral lines relative to chromospheric emission lines,
  a result known since the Skylab era. Extended spectral scans performed
  for various regions of the solar disk by the Solar Ultraviolet
  Measurements of Emitted Radiation spectrometer on the Solar and
  Heliospheric Observatory contain thousands of line profiles per study
  and allow a thorough investigation of the redshift phenomenon. In using
  these data from seven distinct disk areas made in lines spanning the
  chromosphere to coronal temperature range, we derive a relationship
  between Doppler wavelength shifts and radiances and a relationship
  between line widths and radiances. While chromospheric and coronal
  lines emitted by very bright plasmas may in some cases show pronounced
  redshifts, transition-region lines predominantly show redshifts
  everywhere in the quiet Sun and in active regions. In coronal holes,
  however, they display a reduced shift, which at times altogether
  disappears. The observations and the findings will be described,
  and possible explanations will be considered.

Title: Forbidden and Intercombination Lines of RR Telescopii:
    Wavelength Measurements and Energy Levels
Authors: Young, P. R.; Feldman, U.; Lobel, A.
Bibcode: 2011ApJS..196...23Y
Altcode: 2011arXiv1102.3101Y
  Ultraviolet and visible spectra of the symbiotic nova RR Telescopii
  are used to derive reference wavelengths for many forbidden and
  intercombination transitions of ions +1 to +6 of elements C, N, O,
  Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, and Ca. The wavelengths are then
  used to determine new energy values for the levels within the ions'
  ground configurations or first excited configuration. The spectra
  were recorded by the Space Telescope Imaging Spectrograph of the
  Hubble Space Telescope and the Ultraviolet Echelle Spectrograph of the
  European Southern Observatory in 2000 and 1999, respectively, and cover
  1140-6915 Å. Particular care was taken to assess the accuracy of the
  wavelength scale between the two instruments. An investigation of the
  profiles of the emission lines reveals that the nebula consists of at
  least two plasma components at different velocities. The components
  have different densities, and a simple model of the lines' emissions
  demonstrates that most of the lines principally arise from the high
  density component. Only these lines were used for the wavelength study.

Title: Atomic Data for Solar Corona Studies
Authors: Feldman, Uri
Bibcode: 2011AIPC.1344..239F
Altcode:
  In recent years due to the increased sophistication of space
  instrumentation ever more detailed observations of a large variety
  of coronal structures became available. Nevertheless, thus far no
  credible model emerged that describes the means by which the solar upper
  atmosphere is created and maintained. Nevertheless, while interpreting
  such spectra, some unexpected properties of coronal plasmas were
  discovered. Although there are many cases where agreements between
  observations and calculations are found, there are cases were clear
  discrepancies do exist. I discuss some of the unexpected observational
  results that were recently discovered, and suggest some observations
  that if successfully executed could help explain the processes that
  form and maintain the solar upper atmosphere.

Title: TOPICAL REVIEW The solar UV-x-ray spectrum from 1.5 to 2000 Å
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 2010JPhB...43w2001D
Altcode:
  This review illustrates the potential of UV-x-ray spectroscopy
  for determining the physical conditions in the solar chromosphere,
  transition region and corona, and how spectroscopy can be used as a
  tool to understand the physical mechanisms governing the atmosphere. It
  also illustrates the potential for understanding transient events
  such as solar flares. This is a vast topic, and therefore the review
  is necessarily not complete, but we have tried to be as general as
  possible in showing in particular how solar spectra are currently being
  used to understand the solar upper atmosphere. The review is intended
  for non-solar physicists with an interest in spectroscopy as well as
  for solar physicists who are not specialists in spectroscopy.

Title: Spectroscopy of positron annihilation gamma rays from
    laser-exited media
Authors: Szabo, C. I.; Feldman, U.; Seely, J.; Hudson, L.; Chen, Hui;
   Tommasini, R.; Hazi, A.; Shepherd, R.; Zulick, C.; Dollar, F.; Falk,
   K.; Murphy, C. D.
Bibcode: 2010APS..DPPXO6014S
Altcode:
  Motivated by calculations for gamma ray yields and results of positron
  beam measurements from laser irradiated high Z targets [1], a Gamma-ray
  Crystal Spectrometer (GCS) was built by Artep Inc. and fielded at the
  Titan laser facility of LLNL. The spectrometer is equipped with heavy
  shielding around a cylindrically bent Ge crystal in a transmission
  geometry. The Bremsstrahlung continuum and the 511 keV annihilation
  gamma rays are dispersed by the Ge(440) crystal and detected by an
  image plate placed on the Rowland circle. The gamma rays originate
  inside the thick target material (1 to 3 mm Au disks) where positrons
  are produced in the intense field of the high energy (350 J) short
  pulse (10 ps) laser irradiation. In addition to the spectrometer,
  two different electronic detection systems also recorded the gamma
  ray spectra using the single hit per pixel technique. The first gamma
  ray spectra recorded with the crystal spectrometer and the electronic
  detectors will be reported. [4pt] [1] Hui Chen et al., PRL 105, 015003
  (2010)

Title: Elemental Abundance Variations in a Decaying EUV-Bright Region
Authors: Ko, Yuan-Kuen; Landi, E.; Feldman, U.; Young, P.
Bibcode: 2010AAS...21640515K
Altcode: 2010BAAS...41..891K
  The EIS instrument on Hinode observed an EUV-bright region at N15 as it
  evolved during a course of four days on December 7-11, 2009. Although
  containing no sunspots, this region was associated with a weak magnetic
  concentration and exhibited large variations in loop and footpoint
  brightening. It was in a decay phase with dispersing magnetic field
  and weakening high-temperature emission. We present the variations of
  elemental abundances in this region among different spatial structures
  and with time. Implications in factors that can be associated with
  the First Ionization Potential (FIP) effect will be discussed.

Title: A new approach for deriving the solar irradiance from
    nonflaring solar upper atmosphere plasmas at 2 × 10<SUP>4</SUP>
    ≤ T ≤ 2 × 10<SUP>7</SUP> K
Authors: Feldman, U.; Brown, C. M.; Seely, J. F.; Dammasch, I. E.;
   Landi, E.; Doschek, G. A.; Colgan, J.; Abdallah, J.; Fontes, C. J.;
   Sherrill, M. E.
Bibcode: 2010JGRA..115.3101F
Altcode: 2010JGRA..11503101F
  We propose a new approach for deriving the solar irradiance due to the
  emission by solar upper atmosphere plasmas at 2 × 10<SUP>4</SUP> ≤
  T ≤ 2 × 10<SUP>7</SUP> K for wavelengths shorter than 800 Å. Our
  approach is based on a new understanding of the properties of the solar
  upper atmosphere; specifically, the discovery that the majority of
  emission from the nonflaring solar upper transition region and corona in
  the temperature range 3 × 10<SUP>5</SUP> ≤ T ≤ 3 × 10<SUP>6</SUP>
  K arises from isothermal plasmas that have four distinct temperatures:
  0.35, 0.9, 1.4, and 3 × 10<SUP>6</SUP> K. Although the lower transition
  region (2 × 10<SUP>4</SUP> ≤ T ≤ 2 × 10<SUP>5</SUP> K) of coronal
  holes, quiet regions or active regions, is multithermal and variable
  in brightness, the shape of emission measure versus temperature curves
  in this region is almost constant. At any given time, flaring plasmas
  are for the most part isothermal, although their emission measure and
  temperature continuously change. In this paper we review these recent
  results and propose a set of simple spectrometers for recording the
  solar spectrum in several narrow bands. The solar emission measure,
  average plasma temperature, and composition can be derived using the
  measured line fluxes. By combining the emission measure and other
  plasma properties with the output of a suite of atomic physics codes,
  which are also described here, the solar irradiance at wavelengths
  shorter than 800 Å can be calculated.

Title: The Effect of Hot Coronal Electrons on Extreme-Ultraviolet
    Spectral Lines of He II Emitted by Solar Transition Region Plasmas
Authors: Feldman, U.; Ralchenko, Yu.; Doschek, G. A.
Bibcode: 2010ApJ...708..244F
Altcode:
  The cause of the lower intensities of extreme-ultraviolet (EUV) He II
  lines emitted by coronal hole (CH) plasmas compared with quiet Sun
  (QS) plasmas has been the subject of many studies dating back over
  half a century. In this paper, we study the effect of small amounts
  of "hot" electrons at coronal temperatures (T<SUB>e</SUB> = 1.4 ×
  10<SUP>6</SUP> K) on the intensities of EUV He II lines, as well
  as on the intensities of EUV lines of C III, C IV, O III, and O IV
  emitted by 1.5 × 10<SUP>4</SUP> K-1.5 × 10<SUP>5</SUP> K (4.2 &lt;=
  log T<SUB>e</SUB> &lt;= 5.2) plasmas in the QS. We show that although
  the influence of a fraction as small as 10<SUP>-4</SUP>-10<SUP>-3</SUP>
  of hot electrons on the intensities of the C and O lines is noticeable,
  the effect on the intensities of the He lines is much larger, to the
  extent that it could explain the excess brightness of He II lines
  emitted by QS regions relative to CH plasmas.

Title: The thermal structure of the solar upper atmosphere
Authors: Landi, Enrico; Feldman, Uri
Bibcode: 2009AIPC.1161..142L
Altcode:
  In the present work we review the thermal structure of the solar
  atmosphere. We first discuss the main diagnostic techniques used
  to measure it, outlining their pitfalls and limitations. Then, we
  review the recent measurements of the thermal structure of the solar
  atmosphere carried out with the SOHO spectrometers CDS and SUMER. The
  review shows that the solar upper atmosphere is made by an ensemble of
  few, nearly isothermal plasmas with fixed temperatures, disconnected
  from the colder, thermally continuous lower atmosphere.

Title: Can the Composition of the Solar Corona Be Derived from
    Hinode/Extreme-Ultraviolet Imaging Spectrometer Spectra?
Authors: Feldman, U.; Warren, H. P.; Brown, C. M.; Doschek, G. A.
Bibcode: 2009ApJ...695...36F
Altcode:
  Elemental abundances appear to be the same everywhere in the
  photosphere, but in the solar corona they vary in different
  regions. Abundances in quiet Sun (closed) flux tubes are different from
  those in coronal hole (CH, open) magnetic field regions, and therefore
  abundance variations might possibly be used to determine locations of
  slow and fast solar wind in the corona. In active regions, abundances
  can change from region to region and can vary with the age of the
  region. In the present paper, we evaluate the feasibility of determining
  relative elemental abundances in the corona using spectra acquired by
  the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode. As test
  cases, we attempt to evaluate the coronal composition above the limb
  in an equatorial quiet region and in a polar CH. We also determine
  the elemental composition of coronal regions with moderate activity on
  the disk and at the limb. To estimate the accuracy of the instrumental
  calibration and the atomic physics used in the calculations, we compare
  the derived composition with earlier derivations from spectra recorded
  by the Solar Ultraviolet Measurements of Emitted Radiation spectrometer
  in similar regions. We find that EIS can be used to determine relative
  abundance variations in the inner solar corona. The determination of
  absolute abundances can also be attempted after additional calibrations
  in space are accomplished.

Title: The Emission Measure of the Solar Lower Transition Region
    (2 × 10<SUP>4</SUP>-2 × 10<SUP>5</SUP> K)
Authors: Feldman, U.; Dammasch, I. E.; Landi, E.
Bibcode: 2009ApJ...693.1474F
Altcode:
  We analyze Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
  spectra in the 750-790 Å wavelength range from 12 different solar
  regions on the disk to measure the thermal structure of the lower
  transition region (LTR). We considered four coronal hole (CH), four
  quiet Sun (QS), and four active region (AR) data sets observed by
  SUMER during the rising phase of the solar cycle, and we analyzed the
  emission of seven different ions formed between 2 × 10<SUP>4</SUP>
  and 2 × 10<SUP>5</SUP> K. We study the spatial variation of line
  radiances along the slit within each observation, as well as their
  relative radiances in different data sets. We also use them to determine
  the differential emission measure of the LTR. We find that all lines
  behave in the same way both along the slit within the same observation,
  and between different data sets from different regions of the Sun. We
  also find that while the absolute value of the differential emission
  measure of LTR plasmas changes from region to region, its distribution
  with temperature is fairly constant, suggesting that the thermal
  structure of LTR plasmas is the same in CH, QS, and AR regions, and as
  a function of time along the solar cycle. We discuss the implications
  of our results for studies of coronal heating and of the solar cycle.

Title: Radiative Losses of Solar Coronal Plasmas
Authors: Colgan, J.; Abdallah, J., Jr.; Sherrill, M. E.; Foster, M.;
   Fontes, C. J.; Feldman, U.
Bibcode: 2008ApJ...689..585C
Altcode:
  A comprehensive set of calculations of the radiative losses of solar
  coronal plasmas is presented. The Los Alamos suite of atomic structure
  and collision codes is used to generate collisional data for 15 coronal
  elements. These data are used in the Los Alamos plasma kinetics code
  ATOMIC to compute the radiative power loss as a function of electron
  temperature. We investigate the sensitivity of the loss curves to
  the quality of the atomic data and changes in the coronal elemental
  abundances, and we compare our results with previous work.

Title: High-resolution imaging spectrometer for recording absolutely
    calibrated far ultraviolet spectra from laser-produced plasmas
Authors: Brown, Charles M.; Seely, John F.; Feldman, Uri; Holland,
   Glenn E.; Weaver, James L.; Obenschain, Steven P.; Kjornrattanawanich,
   Benjawan; Fielding, Drew
Bibcode: 2008RScI...79j3109B
Altcode:
  An imaging spectrometer was designed and fabricated for recording far
  ultraviolet spectra from laser-produced plasmas with wavelengths as
  short as 155 nm. The spectrometer implements a Cassegrain telescope
  and two gratings in a tandem Wadsworth optical configuration that
  provides diffraction limited resolution. Spectral images were
  recorded from plasmas produced by the irradiation of various target
  materials by intense KrF laser radiation with 248 nm wavelength. Two
  pairs of high-resolution gratings can be selected for the coverage
  of two wavebands, one grating pair with 1800 grooves/mm and covering
  approximately 155-175 nm and another grating pair with 1200 grooves/mm
  covering 230-260 nm. The latter waveband includes the 248 nm KrF
  laser wavelength, and the former waveband includes the wavelength
  of the two-plasmon decay instability at 23 the KrF laser wavelength
  (165 nm). The detection media consist of a complementary metal
  oxide semiconductor imager, photostimulable phosphor image plates,
  and a linear array of 1 mm<SUP>2</SUP> square silicon photodiodes
  with 0.4 ns rise time. The telescope mirrors, spectrometer gratings,
  and 1 mm<SUP>2</SUP> photodiode were calibrated using synchrotron
  radiation, and this enables the measurement of the absolute emission
  from the laser-produced plasmas with temporal, spatial, and spectral
  resolutions. The spectrometer is capable of measuring absolute spectral
  emissions at 165 nm wavelength as small as 5×10<SUP>-7</SUP> J/nm
  from a plasma source area of 0.37 mm<SUP>2</SUP> and with 0.4 ns
  time resolution.

Title: Solar Observations of High-Temperature Emission with the
    Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Warren, Harry P.; Feldman, Uri; Brown, Charles M.
Bibcode: 2008ApJ...685.1277W
Altcode:
  We present an analysis of solar coronal emission lines formed above 2.5
  MK observed with the Extreme-Ultraviolet Imaging Spectrometer on Hinode
  during a small flare. Our main purpose is to evaluate the internal
  consistency of the atomic data available for the observed emission. We
  find that the observed emission from high-temperature Ca lines (Ca XIV,
  XV, XVI, and XVII) is generally consistent with the available atomic
  data. The observed Fe XVII emission at these wavelengths, in contrast,
  is more difficult to reconcile with current atomic calculations. The
  energy levels tabulated in the CHIANTI atomic physics database generally
  do not correspond to the observed wavelengths. After associating the
  calculated emissivities with the observed emission by hand, we find
  that the observed intensities are roughly consistent with what is
  predicted. However, the intensity of the strongest unblended line, Fe
  XVII 254.87 Å, is not consistent with the intensities of the other Fe
  XVII lines at these wavelengths. Several of the Ca XV emission lines,
  which are formed at about 4 MK, form density-sensitive line ratios in
  the range log n<SUB>e</SUB> = 9-11 cm<SUP>-3</SUP>. Density measurements
  at these temperatures are potentially important for understanding
  the coronal heating mechanism. Our initial analysis suggests that
  high-temperature active region plasma is underdense relative to the
  predictions of steady heating models.

Title: Nonthermal Electron Measurements in Solar Flares with
    Hinode EIS
Authors: Feldman, Uri; Ralchenko, Yuri; Landi, Enrico
Bibcode: 2008ApJ...684..707F
Altcode:
  The spectral range of the Hinode EIS (EUV Imaging Spectrometer)
  instrument is 170-211 Å and 245-291 Å lines emitted by low-energy
  levels in highly ionized Mn, Fe, Co, and Ni, as well as the very
  energetic 1s2s<SUP>3</SUP>S<SUB>1</SUB>-1s2p<SUP>3</SUP>P<SUB>2</SUB>
  transition in Fe XXV, appear in the EIS range. In this paper, we
  investigate the use of these lines for detecting the presence of
  nonthermal, high-energy electrons in flares. We first calculate line
  fluxes among the various lines expected in the EIS range, assuming
  that the electron velocity distribution is strictly Maxwellian. Then,
  we calculate line fluxes using a velocity distribution composed of a
  Maxwellian distribution plus an additional population of electrons with
  a temperature of 10 keV (1.2 × 10<SUP>8</SUP> K) providing 1%, 2%, 4%,
  7%, and 10% of the total free electrons. The calculations indicate that
  flux ratios between the highly excited Fe XXV line and lines originating
  in low-lying levels of other highly ionized ions in the EIS range could
  shed light on the electron velocity distribution in hot flare plasmas.

Title: Ultraviolet and X-ray Spectroscopy of the Solar Atmosphere
Authors: Phillips, Kenneth J. H.; Feldman, Uri; Landi, Enrico
Bibcode: 2008uxss.book.....P
Altcode:
  1. The solar atmosphere; 2. Fundamentals of solar radiation;
  3. Fundamentals of atomic physics; 4. Mechanisms of formation of the
  solar spectrum; 5. Plasma diagnostic techniques; 6. Ultraviolet and
  X-ray emission lines; 7. Spectrometers and imagers for observing the
  solar ultraviolet and X-ray spectrum; 8. Quiet Sun and coronal holes;
  9. Active regions; 10. Solar flares; 11. Element abundances; Appendices;
  References; Index.

Title: Wavelengths and Intensities of Spectral Lines in the 171-211
    and 245-291 Å Ranges from Five Solar Regions Recorded by the
    Extreme-Ultraviolet Imaging Spectrometer (EIS) on Hinode
Authors: Brown, C. M.; Feldman, U.; Seely, J. F.; Korendyke, C. M.;
   Hara, H.
Bibcode: 2008ApJS..176..511B
Altcode:
  We present spectral line wavelengths, identifications, and intensities
  in the 171-211 and 245-291 Å ranges from five solar plasma regions
  recorded by the Extreme-Ultraviolet Imaging Spectrometer (EIS)
  on Hinode. The recorded data were emitted from a quiet region,
  two active areas on the solar disk, a limb region, and a region
  20'' above the limb. The line list contains 500 lines of which 55%
  were identified with previously known transitions. Although the EIS
  spectral coverage is limited to two ranges approximately 40 Å wide,
  the identified lines belong to a total of 56 ions from 15 elements.

Title: Line Intensity Ratios in the EIS Range Sensitive to Electron
    Densities in 10<SUP>7</SUP> K Plasmas
Authors: Feldman, U.; Landi, E.; Doschek, G. A.
Bibcode: 2008ApJ...679..843F
Altcode:
  Electron density variations during the rise, maximum, and decay phases
  of flaring plasmas at T simeq 10 MK are important quantities to be
  used to test flare models. To date, electron density values measured
  in solar flares are, with few exceptions, only lower limits. With the
  launch of the EUV Imaging Spectrometer (EIS) on Hinode, it has become
  possible for the first time to measure electron densities and their
  time evolution during flares. In this paper we discuss electron density
  diagnostics in the 10<SUP>10</SUP>-10<SUP>13</SUP> cm<SUP>-3</SUP>
  range by means of intensity ratios of lines emitted by Ti, Cr, and Mn
  ions within the Hinode/EIS wavelength range.

Title: The temperature structure of solar coronal plasmas
Authors: Feldman, Uri; Landi, Enrico
Bibcode: 2008PhPl...15e6501F
Altcode:
  In the early 1940s it was at last accepted that the temperature of
  the solar corona is at least 1 MK and varies considerably from region
  to region throughout the solar activity cycle. It was recognized that
  during solar minimum periods the electron temperatures of plasmas in
  polar regions do not exceed 1 MK, but during solar maximum periods
  the plasma temperatures of highly active regions could be as high as 3
  MK. Nevertheless, until recently the consensus among the solar physics
  community was that coronal temperatures vary among the different
  regions in a continuous manner. In the present paper we review the
  evidence showing that solar coronal plasmas (T<SUB>e</SUB>&gt;0.7 MK)
  are isothermal and their temperature can have only a small set of
  fixed values.

Title: Ultra-Hot Plasma in Active Regions Observed by the
    Extreme-ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Warren, H. P.; Feldman, U.
Bibcode: 2008AGUSMSP43C..01D
Altcode:
  The Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
  spacecraft obtains high resolution spectra of the solar atmosphere in
  two wavelength ranges: 170 - 210 and 250 — 290 Angstroms. These
  wavelength regions contain a wealth of emission lines covering
  temperature regions from the chromosphere/transition region (e.g.,
  He II, Si VII) up to soft X-ray flare temperatures (Fe XXIII,
  Fe XXIV). EIS can obtain line profiles and intensities for the
  spectral lines in these wavelength regions. Of particular interest
  for understanding coronal heating is a line of Ca XVII, formed near
  a temperature of 6 MK. This line is blended with lines of Fe XI and O
  V. However, by using unblended lines of these ions, the Ca XVII line
  can be deconvolved from the blended emission. EIS has obtained many
  raster observations of active regions by stepping the slit in small
  increments across the active region, producing monochromatic images
  of the active region. The Ca XVII blend has been included in many of
  these rasters. In this paper we discuss the appearance and frequency
  of 6 MK plasma in active regions in the absence of strong flaring
  activity. This temperature region is not well-observed by normal
  incidence imaging spectrometers and therefore the EIS data shed light
  on higher temperature areas of active regions than normally available
  from imaging instruments alone. We discuss how to deconvolve the blend
  and show examples of 6 MK plasma emission in several active regions.

Title: An EUV narrow band imaging technique for diagnosing 10-30
    keV ITER plasmas
Authors: Feldman, U.; Seely, J. F.; Landi, E.; Ralchenko, Y.
Bibcode: 2008AIPC..988..205F
Altcode:
  In this paper we investigate the use of lines from tungsten (W)
  ions to measure the properties of W impurities in ITER plasmas. We
  calculate the intensities of the brightest spectral lines expected to
  be radiated by W ions with wavelengths longer than 45 Å, abundance of
  10<SUP>-4</SUP> and at densities of 10<SUP>20</SUP> m<SUP>3</SUP>. Using
  the calculated wavelengths and intensities we propose a concept for
  segmented multilayer-coated imaging telescopes that could be used to
  investigate the properties of W impurities as a function of time and
  space using spectral lines from highly ionized W

Title: Calcium-to-Argon and Nickel-to-Argon Abundance Ratios as
    Tracers of the Source Region of Postflare Loop System Material
Authors: Widing, K. G.; Feldman, U.
Bibcode: 2008ApJ...675..863W
Altcode:
  Intensities of abundance diagnostic lines of Ca XV, Ca XVI, Ni XVII,
  Ar XIII, and Ar XV have been derived for a classic flare loop system
  observed during the Skylab mission. These have been used to test
  for photospheric or coronal origin of the flare loop material. The
  resulting FIP-bias factors are between 1.7 and 4.6 with a majority of
  the values around 4.5 indicating a source with material modified by the
  FIP effect. The loop system bias factors are similar to those observed
  in a sample of Skylab prominences, suggesting that the disrupted mass
  of the preflare embedded filament provided the loop system material.

Title: The Thermal Structure of an Active Region Observed Outside
    the Solar Disk
Authors: Landi, E.; Feldman, U.
Bibcode: 2008ApJ...672..674L
Altcode:
  In the present work we analyze an extensive active region spectrum
  observed by the SUMER instrument on board SOHO with the aim of
  determining the thermal structure of the emitting plasma. We found
  that the plasma is made of three distinct, isothermal components,
  whose physical properties are similar to coronal hole, quiet-Sun,
  and active region plasmas. The temperatures of the coronal hole-like
  and quiet-Sun-like plasmas are in excellent agreement with previous
  measurements obtained outside active regions. We also used a DEM
  diagnostic technique to check the robustness of our results and
  found that the DEM curves are compatible with the presence of three
  distinct nearly isothermal plasmas if the individual DEM measurements
  are smoothed over a small temperature interval. Larger intervals lead
  the resulting DEM curves to a more multithermal behavior, raising the
  question of whether multithermal active region DEM curves available in
  the literature are real or an artifact of oversmoothing. The results
  are compared with measurements of the temperature of individual loop
  structures in the literature and discussed in light of a new picture
  of the solar corona.

Title: A proposed new method for the determination of the solar
    irradiance at EUV wavelength range
Authors: Feldman, Uri; Doschek, G. A.; Seely, J. F.; Landi, E.;
   Dammasch, I.
Bibcode: 2008cosp...37..866F
Altcode: 2008cosp.meet..866F
  The solar irradiance in the far ultraviolet (FUV) and extreme
  ultraviolet (EUV) and its time variability are important inputs to
  geospace models. It provides the primary mechanism for heating the
  earth's upper atmosphere and creating the ionosphere. Understanding
  various space weather phenomena requires reliable detailed knowledge
  of the solar EUV irradiance. Ideally one would like to have a single
  well-calibrated, high-resolution spectrometer that can continuously
  monitor the solar irradiance over the relevant wavelengths range. Since
  this is much too difficult to accomplish, a number of monitoring
  instruments were constructed in the past, each covering a fraction
  of the required wavelength range. Assembling solar irradiance from
  measurements by a number of instruments is extremely difficult and
  is usually plagued by large uncertainties. To overcome some of the
  difficulties resulting from such procedures, empirical models have
  been developed that rely in large part on solar activity levels as
  proxies. In recent years a different approach has been established for
  the determination of the solar irradiance, an approach independent
  of irradiance observations. The new approach is based on the line
  intensities calculated from emission measure (EM) distributions across
  the solar surface. The EM distributions are derived from spatially and
  spectrally resolved measurements of line intensities and describe the
  temperature and density structure of the basic large scale features of
  the solar atmosphere, specifically coronal holes, quiet Sun, and active
  regions. Recently, as a result of detailed analysis of solar upper
  atmosphere (SUA) spectra recorded by SUMER/SoHO it was discovered that,
  in contrast to earlier beliefs, the solar EM in 3x105 -4x106 K plasmas
  does not appear to vary continuously with temperature as previously
  assumed. Instead it appears to be composed of isothermal structures
  where each can attain but one of the following four main temperatures:
  5x105 , 9x105 , 1.4x106 and 3x106 K. At the transition region (2x104
  -2x105 K) where the structures are not isothermal the slopes of the
  emission measure vs. temperature stay the same independent of the solar
  activity. In our talk we will propose a variation to the EM method for
  the determination of the solar irradiance described above. The modified
  method will be based on line intensity calculations from the actual
  solar EM values at the above specified discrete temperatures. The
  EM in those temperatures could in principle be derived from solar
  observations spanning a fairly limited wavelengths range.

Title: Observations of the Sun at Vacuum-Ultraviolet Wavelengths
from Space. Part II: Results and Interpretations
Authors: Wilhelm, Klaus; Marsch, Eckart; Dwivedi, Bhola N.; Feldman,
   Uri
Bibcode: 2007SSRv..133..103W
Altcode:
  In Part I of this review, the concepts of solar vacuum-ultraviolet
  (VUV) observations were outlined together with a discussion of
  the space instrumentation used for the investigations. A section on
  spectroradiometry provided some quantitative results on the solar VUV
  radiation without considering any details of the solar phenomena leading
  to the radiation. Here, in Part II, we present solar VUV observations
  over the last decades and their interpretations in terms of the plasma
  processes and the parameters of the solar atmosphere, with emphasis
  on the spatial and thermal structures of the chromosphere, transition
  region and corona of the quiet Sun. In addition, observations of
  active regions, solar flares and prominences are included as well as
  of small-scale events. Special sections are devoted to the elemental
  composition of the solar atmosphere and theoretical considerations on
  the heating of the corona and the generation of the solar wind.

Title: Wavelength Determination for Solar Features Observed by the
    EUV Imaging Spectrometer on Hinode
Authors: Brown, Charles M.; Hara, Hirohisa; Kamio, Suguru; Feldman,
   Uri; Seely, John F.; Doschek, George A.; Mariska, John T.; Korendyke,
   Clarence M.; Lang, James; Dere, Kenneth P.; Culhane, Len; Thomas,
   Roger J.; Davila, Joseph M.
Bibcode: 2007PASJ...59S.865B
Altcode:
  A wavelength calibration of solar lines observed by the high
  resolution EUV Imaging Spectrometer (EIS) on the Hinode satellite
  is reported. Spectral features of the quiet sun and of two mildly
  active areas were measured and calibrated. A listing of the stronger
  observed lines with identification of the leading contributor ions
  is presented. 41 lines are reported, with 90% identified. Wavelength
  precisions (2σ) of ±0.0031Å for the EIS short band and ±0.0029Å
  for the EIS long band are obtained. These lines, typical of 1-2
  ×10<SUP>6</SUP> K plasmas, are recommended as standards for the
  establishment of EIS wavelength scales. The temperature of EIS varies
  by about 1D.5 C around the orbit and also with spacecraft pointing. The
  correlation of these temperature changes with wavelength versus pixel
  number scale changes is reported.

Title: Comparison of solar spectra from the Hinode extreme-ultraviolet
    imaging spectrometer (EIS) to preflight calibrations
Authors: Seely, John; Feldman, Uri; Brown, Charles; Doschek, George;
   Hara, H.
Bibcode: 2007SPIE.6688E..0WS
Altcode: 2007SPIE.6688E..29S
  The Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode
  satellite records high-resolution solar spectra in the 170-210 Å
  and 246-290 Å wavelength ranges. The EIS optics operate at near
  normal incidence and consist of an off-axis parabolic mirror, a
  toroidal diffraction grating, two CCD detectors, and two thin aluminum
  filters. To increase the normal incidence efficiency, high-reflectance
  multilayer interference coatings were deposited on the mirror and the
  grating. Prior to launch, each of the optical components was calibrated
  using synchrotron radiation, and the spectral and spatial resolution
  of the complete instrument were measured. In this paper, we compare the
  preflight calibrations with the first-light spectra recorded in space.

Title: Improved low-lying energy levels determined from solar coronal
    forbidden and spin-forbidden lines in the 500 1500 Å range
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 2007ADNDT..93..779F
Altcode:
  We list observed parity-forbidden and spin-forbidden lines in
  the 500 1600 Å range emitted by solar coronal plasmas and derive
  improved energy levels from their wavelengths. The lines, emitted
  by astrophysical abundant elements, belong to transitions within the
  ground configurations of the type ns<SUP>2</SUP>np<SUP>k</SUP>, for n
  = 2, 3 and k = 0 5, and between the lowest term of the first excited
  configuration 2s2p<SUP>k+1</SUP> and the 2s<SUP>2</SUP>2p<SUP>k</SUP>
  ground configurations for k = 0, 1, 2. For each line we give the newly
  measured wavelength, and the measured or predicted wavelength from
  the NIST Atomic Spectra Database (ASD) (which except for a few cases
  includes the previously reported compilation of Kaufman and Sugar
  [J. Phys. Chem. Ref. Data 15 (1986) 321]), and the values of the
  transition probability taken from the ASD and CHIANTI database. The
  list contains measured wavelengths of 136 lines of which over 100 were
  not available for the Kaufman and Sugar compilation. In addition we
  provide energy levels that were derived from the reported lines.

Title: Spectroscopic Measurement of Coronal Compositions
Authors: Feldman, U.; Widing, K. G.
Bibcode: 2007SSRv..130..115F
Altcode: 2007SSRv..tmp...94F
  Although the elemental composition in all parts of the solar photosphere
  appears to be the same this is clearly not the case with the solar
  upper atmosphere (SUA). Spectroscopic studies show that in the corona
  elemental composition along solar equatorial regions is usually
  different from polar regions; composition in quiet Sun regions is
  often different from coronal hole and active region compositions and
  the transition region composition is frequently different from the
  coronal composition along the same line of sight. In the following two
  issues are discussed. The first involves abundance ratios between the
  high-FIP O and Ne and the low-FIP Mg and Fe that are important for
  meaningful comparisons between photospheric and SUA compositions and
  the second involves a review of composition and time variability of
  SUA plasmas at heights of 1.0≤ h≤1.5 R <SUB>⊙</SUB>.

Title: Diagnostics of Suprathermal Electrons in Active-Region Plasmas
    Using He-like UV Lines
Authors: Feldman, U.; Landi, E.; Doschek, G. A.
Bibcode: 2007ApJ...660.1674F
Altcode:
  In the present paper we use UV lines emitted by He-like ions as a
  tool to test the presence of nonthermal high-energy electrons and
  to quantify their number and energy. The He-like lines we consider
  are the He-like 1s2s<SUP>3</SUP>S-1s2p<SUP>3</SUP>P lines observed
  in the UV, and their use capitalizes on the high excitation energies
  for the 1s2p<SUP>3</SUP>P levels and on the near-unity ion abundances
  of the He-like ions for large temperature ranges. We investigate the
  presence of nonthermal high-energy electrons in solar active regions,
  placing upper limits on the presence of electrons capable of exciting
  the upper levels of Ne IX, Mg XI, and Si XIII.

Title: Neon and Oxygen Absolute Abundances in the Solar Corona
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
Bibcode: 2007ApJ...659..743L
Altcode:
  In the present work we use the UV spectrum of a solar
  flare observed with SOHO SUMER to measure the absolute
  abundance of Ne in the solar atmosphere. The measurement
  is carried out using the intensity ratio between the allowed
  1s2s<SUP>3</SUP>S<SUB>1</SUB>-1s2p<SUP>3</SUP>P<SUB>2</SUB> Ne IX
  line at 1248.28 Å and the free-free continuum radiation observed
  close to the Ne IX line. We find a value of the absolute Ne abundance
  A<SUB>Ne</SUB>=8.11+/-0.12, in agreement with previous estimates
  but substantially higher than the very recent estimate by Asplund et
  al. based on the oxygen photospheric abundance and the Ne/O relative
  abundance. Considering our measured A<SUB>Ne</SUB> value, we argue
  that the absolute oxygen abundance of Asplund et al. is too low by a
  factor 1.9. This result has important consequences for models of the
  solar interior based on helioseismology measurements, as well as on
  the FIP bias determination of the solar upper atmosphere, solar wind,
  and solar energetic particles.

Title: Is There a High-Energy Particle Population in the Quiet
    Solar Corona?
Authors: Ralchenko, Yu.; Feldman, U.; Doschek, G. A.
Bibcode: 2007ApJ...659.1682R
Altcode:
  A study of spectra emitted by the quiet solar corona indicates that
  the majority of line intensities originating in low-lying levels
  are consistent with isothermal plasma of ~1.3×10<SUP>6</SUP>
  K. Nevertheless, a number of line intensities and, in particular,
  those belonging to ions that are typical of higher temperatures
  are brighter than expected. We show in this paper that the excess
  brightness of the hotter lines may be satisfactorily accounted for by
  a two-Maxwellian electron distribution function. We have calculated
  the effects on the line intensities and ionization balance under the
  assumption of both single- and two-Maxwellian electron distribution
  functions. One Maxwellian is characterized by a temperature of about 110
  eV (1.35×10<SUP>6</SUP> K). The second Maxwellian is assumed to be a
  high-energy component ranging in temperatures between 150 and 1000 eV,
  with electron fractions relative to the total electron density that
  vary from 0.5% to 10%. We found that a good match to the quiet-Sun
  intensities could be achieved by adding ~5% electrons with a 300-400
  eV Maxwellian temperature to the cooler component at 110 eV. We also
  found that the calculated line intensities become inconsistent with the
  quiet solar corona measurements if more than 3% of a T<SUB>e</SUB>=500
  eV plasma or more than 1% of a T<SUB>e</SUB>=1000 eV plasma is added
  to the cooler Maxwellian.

Title: Spectroscopic Measurement of Coronal Compositions
Authors: Feldman, U.; Widing, K. G.
Bibcode: 2007coma.book..115F
Altcode:
  Although the elemental composition in all parts of the solar photosphere
  appears to be the same this is clearly not the case with the solar
  upper atmosphere (SUA). Spectroscopic studies show that in the corona
  elemental composition along solar equatorial regions is usually
  different from polar regions; composition in quiet Sun regions is
  often different from coronal hole and active region compositions and
  the transition region composition is frequently different from the
  coronal composition along the same line of sight. In the following two
  issues are discussed. The first involves abundance ratios between the
  high-FIP O and Ne and the low-FIP Mg and Fe that are important for
  meaningful comparisons between photospheric and SUA compositions and
  the second involves a review of composition and time variability of
  SUA plasmas at heights of 1.0≤h≤1.5R <SUB>⊙</SUB>.

Title: Plasma Diagnostics of the Large-Scale Corona with SUMER
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
Bibcode: 2006ESASP.617E..12L
Altcode: 2006soho...17E..12L
  No abstract at ADS

Title: Plasma Diagnostics of the Large-Scale Corona with
    SUMER. I. Measurements at the West Limb
Authors: Landi, E.; Feldman, U.; Doschek, G. A.
Bibcode: 2006ApJ...643.1258L
Altcode:
  In the present work we analyze the physical properties of the quiet-Sun
  plasma measured in a 0.5×1.8 R<SUB>solar</SUB> region above the west
  solar limb (R<SUB>solar</SUB>=solar radius). We make use of large
  scans obtained with the SUMER spectrometer on board SOHO to construct
  two-dimensional spatial maps of line intensities, electron temperature,
  emission measure, element abundances, line widths and nonthermal
  velocities, and photoexcitation effects covering the entire field
  of view. Electron densities were measured in a more limited portion
  of the field of view. The aim of the paper is to identify tracers of
  coronal hole and quiet-Sun plasma at high altitudes that allow us to
  measure the position of the coronal hole/quiet-Sun boundaries, and
  to provide a comprehensive, empirical picture of the off-limb solar
  corona that can provide theoreticians with experimental constraints
  to their models of the large-scale coronal structure, coronal heating,
  and solar wind acceleration.

Title: X-Ray Observations of Solar Long-Duration Flares
Authors: Phillips, K. J. H.; Feldman, U.; Harra, L. K.
Bibcode: 2005ApJ...634..641P
Altcode:
  Yohkoh X-ray observations during the several-hour decay of six
  large solar flares show that the main emitting region is in the
  form of a bright loop-top source whose spatial extent well after
  the impulsive stage explains most of the broadening of S XV and Ca
  XIX X-ray lines, which would otherwise imply nonthermal velocities
  of 100 km s<SUP>-1</SUP> or more. During the decay of each event,
  the electron temperature and emission measure decline slowly. For the
  nearly disk center event of 1992 February 27, the volume increases and
  the deduced lower limit to the electron density N<SUB>e</SUB> decreases
  from ~10<SUP>11</SUP> cm<SUP>-3</SUP> to just below 10<SUP>10</SUP>
  cm<SUP>-3</SUP>. The nonuniform emission along the loops indicates
  that Spitzer heat conduction does not operate. If radiation is the
  only or main energy-loss mechanism, the lower limits to N<SUB>e</SUB>
  imply upper limits to radiation cooling times of up to 10 hr, less
  than the flare decay time, so necessitating a continuing energy
  input. Although magnetic reconnection of previous broken open loops
  (the Kopp-Pneuman model) has been widely regarded as the source of
  energy in such flares, the small nonthermal velocities-only 20-50
  km s<SUP>-1</SUP> as indicated by SUMER observations-and the lack of
  spectroscopic indicators of large inflows or outflows argue against
  it. Other flare models must also explain the relatively small nonthermal
  velocities. An alternative picture of loop oscillations recently seen
  in TRACE and Yohkoh data is proposed for the production of observed
  nonthermal velocities.

Title: A new method for in-flight intensity calibration of
    high-resolution EUV and FUV spectrometers
Authors: Feldman, U.; Landi, E.; Doschek, G. A.; Mariska, J. T.
Bibcode: 2005A&A...441.1211F
Altcode:
  We introduce a new technique for the measurement of the in-flight
  relative intensity calibration of high resolution spectrometers. This
  technique makes use of the free-free radiation in hot, dense active
  regions and flares, and combines it with spectral line intensities
  in an iterative procedure. After a few iterations, the relative
  intensity calibration and the temperature of the emitting plasma are
  determined. The application of this technique to the EIS instrument
  on board the Solar-B satellite (launch in 2006) is discussed.

Title: Evidence for In Situ Heating in Active Region Loops
Authors: Curdt, W.; Landi, E.; Wang, T. J.; Feldman, U.
Bibcode: 2005ESASP.592..475C
Altcode: 2005soho...16E..85C; 2005ESASP.592E..85C
  No abstract at ADS

Title: On the nature of the unidentified solar emission near 117 nm
Authors: Wilhelm, K.; Schühle, U.; Curdt, W.; Hilchenbach, M.;
   Marsch, E.; Lemaire, P.; Bertaux, J. -L.; Jordan, S. D.; Feldman, U.
Bibcode: 2005A&A...439..701W
Altcode:
  Spectral observations of the Sun in the vacuum-ultraviolet wavelength
  range by SUMER on SOHO led to the discovery of unusual emission
  features - called humps here - at 116.70 nm and 117.05 nm on either
  side of the He i 58.43 nm line. This resonance line is seen in the
  second order of diffraction, whereas the humps are recorded in the
  first order with the SUMER spectrometer. In its spectra both orders
  are superimposed. Two less pronounced humps can be detected at 117.27
  nm and near 117.85 nm. After rejecting various possibilities of an
  instrumental cause of the humps, they are studied in different solar
  regions. Most of the measurements, in particular those related to the
  limb-brightening characteristics, indicate that the humps are not part
  of the background continuum. An assembly of spectrally-unresolved atomic
  or ionic emission lines might be contributing to the hump at 117.05
  nm, but no such lines are known near 116.7 nm. It is concluded that we
  detect genuine radiation, the generation of which is not understood. A
  two-photon emission process, parametric frequency down conversion,
  and molecular emissions are briefly considered as causes of the humps,
  but a final conclusion could not be reached.

Title: On the sources of fast and slow solar wind
Authors: Feldman, U.; Landi, E.; Schwadron, N. A.
Bibcode: 2005JGRA..110.7109F
Altcode: 2005JGRA..11007109F
  The slow speed solar wind as measured at the Earth orbit and beyond
  is characterized by its velocity of ≃400 km s<SUP>-1</SUP>, by its
  coronal composition and by its frozen-in temperature (from carbon
  charge-states) of 1.4-1.6 × 10<SUP>6</SUP> K. In contrast the
  fast speed solar wind is characterized by its velocity of ≃750
  km s<SUP>-1</SUP>, its nearly photospheric composition and its
  frozen-in temperature of ≃8 × 10<SUP>5</SUP> K. The solar wind is
  believed to originate very close to the solar surface, but since it
  is accelerated significantly above the solar surface, its velocity
  cannot be correlated with remote observations to trace its origin. In
  contrast, elemental abundances and freeze-in temperatures can be used
  as tracers for locating the sources from which the slow and fast solar
  winds emerge. By comparing remote observations with properties of the
  solar wind observed in situ, the most likely structures from which solar
  wind plasmas emerge can be identified. In the present paper we review
  the current understanding of the morphological features present in the
  solar upper atmosphere and their physical properties such as electron
  temperature, electron density and elemental abundances. In addition, we
  discuss these observations in the context of recent theories describing
  the emergence of new magnetic flux to power the solar wind, and more
  traditional models that treat the background field and solar wind as
  a steady phenomenon.

Title: Properties of the Solar Corona Outside the West Solar Limb
Authors: Doschek, G. A.; Feldman, U.; Landi, E.
Bibcode: 2005AGUSMSP21B..08D
Altcode:
  We discuss the analysis of 36 spectral observations recorded by the
  SUMER spectrometer on SOHO on April 22-23, 1998, at the onset of the
  new solar cycle. The observations were made with the 4" x 300" slit,
  and are distributed over the west hemisphere between 1.02 and 1.5 solar
  radii along the equatorial direction and between -0.9 solar radii south
  of the equator and +0.9 solar radii north of it. At the far corners of
  the studied region the solar distance was 1.74 solar radii. We have
  found that the physical characteristics of the central part of the
  region are typical of quiet Sun coronal plasmas. The regions furthest
  from the equator resemble coronal hole plasmas and the intermediate
  regions are consistent with a transition between the two. We believe
  that this is the most comprehensive work of its kind undertaken thus
  far using UV spectral lines. We use the recorded line intensities
  and line shapes to describe, as a function of coronal position,
  electron temperatures, electron densities, elemental abundances,
  line-of-sight emission measures (EM), nonthermal mass motions, and
  mass dependent elemental settling. By using intensity ratios between
  the two component resonance lines of Li-like O VI, Ne VIII and Mg X,
  we determine the fractional excitation in the Li-like lines produced
  by electron collisions and the fractional excitation produced by
  photo-excitation of transition region radiation emitted just above
  the photosphere.

Title: Coronal Element Comparison Observed by SOHO SUMER in the
    Quiet Southeast and Northwest Limb Regions at 1.04 R<SUB>solar</SUB>
    above the Solar Disk
Authors: Widing, K. G.; Landi, E.; Feldman, U.
Bibcode: 2005ApJ...622.1211W
Altcode:
  The composition in an isothermal region at 1.04 R<SUB>solar</SUB> above
  a diffuse, quiet coronal region on the northwest limb is studied and
  compared with a similar region above the southeast limb analyzed by
  Warren in 1999. Elemental abundances relative to H in the corona are
  measured and normalized to the abundance ratios in the photosphere. The
  enrichment factors of the low first ionization potential elements are
  comparable above both limbs, but are significantly smaller than the
  factor of 4 in SUMER spectra obtained 2 years earlier at solar minimum
  in a diffuse, quiet equatorial region.

Title: Helium Abundance in High-Temperature Solar Flare Plasmas
Authors: Feldman, U.; Landi, E.; Laming, J. M.
Bibcode: 2005ApJ...619.1142F
Altcode:
  In the present work we use emission from dense plasmas late in the decay
  phase of flares, while the plasmas are still hot [(2-4)×10<SUP>6</SUP>
  K], to determine the absolute helium abundance in flaring solar
  corona. To achieve this, we make use of intensity ratios of H I
  and He II lines and of intensity ratios between the He II lines
  and the bremsstrahlung continuum radiation emitted by the local
  postflare plasmas. These ratios are very sensitive to the electron
  temperature, which is measured by using two different techniques:
  intensity ratios from lines emitted by heavier elements and from the
  line width of H I and He II lines. The latter method is made possible
  by the low atomic weight of H and He and by the high temperature of
  the plasma, which causes the widths of these lines to exceed 0.6 Å
  (He) and 1.1 Å (H). Such values significantly exceed the broadening
  due to nonthermal mass motions, so line widths can provide accurate
  temperature measurements. The average helium absolute abundance was
  found to be 12.2%+/-2.4%.

Title: In-Situ Heating in Active Region Loops
Authors: Curdt, W.; Landi, E.; Wang, T.; Feldman, U.
Bibcode: 2005HvaOB..29..157C
Altcode:
  We report new observational results and insights in the energy release
  during transient events on sub-flare level in active region coronal
  loops. Our work is based on multi-temperature observations obtained
  high above the limb by the SUMER spectrometer on SOHO. We conclude
  that the energy is impulsively injected into the loop system from
  one and only one foot point. This asymmetric injection does not seem
  to be connected with any bulk flow and there is no indication that
  the plasma in the loop is replenished or replaced. Therefore the
  chromospheric evaporation model is not applicable for this type of
  events. The electron density, N<SUB>e</SUB>, however, increases by up
  to two orders of magnitude during such events. If no new material is
  added to the local plasma, then the N<SUB>e</SUB> increase can only be
  explained by a rapid volume decrease, i.e., by a in-situ pinch effect,
  compressing and heating the affected plasma.

Title: The SUMER spectral atlas of solar coronal features
Authors: Curdt, W.; Landi, E.; Feldman, U.
Bibcode: 2004A&A...427.1045C
Altcode:
  We present a spectral atlas of the solar corona in the far-ultraviolet
  (FUV) and extreme ultraviolet (EUV) wavelength range. The atlas is based
  on observations obtained between 670 Å and 1609 Å in first order of
  diffraction and between 465 and 670 Å in second order with the SUMER
  (Solar Ultraviolet Measurements of Emitted Radiation) spectrograph
  on SOHO (Solar and Heliospheric Observatory). This paper complements
  the SUMER Spectral Atlas of Solar Disk Features, also published in
  A&amp;A. The atlas contains off-limb spectra of the corona above a
  coronal hole, a quiet region, the active corona, and a flare. We provide
  wavelengths of all detected lines and identification, if available; 311
  out of 507 coronal emission lines could be identified or reconfirmed,
  including several new identifications. Brief descriptions of the
  data reduction and calibration procedures are given. The spectral
  radiances are determined with a relative uncertainty of 0.15 to 0.40
  (1σ) and the wavelength scale is accurate to typically ≃30 mÅ. The
  atlas is also available in a machine readable format. <P />Table
  \ref{tab3} and Fig. \ref{fig3} are only available in electronic form
  at http://www.edpsciences.org

Title: Role of Closed Magnetic Fields in Solar Wind Flow
Authors: Woo, Richard; Habbal, Shadia Rifai; Feldman, Uri
Bibcode: 2004ApJ...612.1171W
Altcode:
  In this paper we demonstrate how closed magnetic fields appear to be
  playing a significant role in solar wind flow. Confinement or trapping
  of plasma is the physical process, while confinement duration, as
  characterized by the first ionization potential (FIP) bias, is the
  attribute that divides the fast- and slow-wind regions. The trapped
  plasma is released along ubiquitous and predominantly radial open
  field lines, presumably by continual reconnection at the base of the
  corona, with evidence for this process coming from the appearance of
  the imprint of polar coronal holes, quiet Sun, and active regions
  in the outer corona and interplanetary space. When trapping is not
  long enough to enrich the elemental abundance (FIP bias near 1), the
  coronal radial density gradient is steep, coronal temperature is low,
  and a fast wind flows in the overlying corona. However, the presence of
  closed fields still influences the flow of the fast wind, as revealed
  by the fact that flow speed is anticorrelated with, or characterized
  by, the density at the base of the corona. When trapping is long
  enough to enrich the abundance (FIP bias &gt; 1), a slow wind flows,
  and FIP bias characterizes its properties. Enhanced FIP bias gives
  rise to a decreased coronal radial density gradient, as manifested
  by the extension of coronal streamers in white-light coronal images,
  increased coronal temperature, and decreased solar wind speed in the
  overlying corona.

Title: Resolving X-Ray Sources from B Stars Spectroscopically:
    The Example of μ Leporis
Authors: Behar, Ehud; Leutenegger, Maurice; Doron, Rami; Güdel,
   Manuel; Feldman, Uri; Audard, Marc; Kahn, Steven M.
Bibcode: 2004ApJ...612L..65B
Altcode: 2004astro.ph..7338B
  We present high-resolution X-ray observations of the chemically peculiar
  late-type B star μ Lep. However, we find spectroscopic and astrometric
  evidence, which shows that the X-rays are not traced back to the B
  star itself but rather to a previously unresolved companion, μ Lep-B,
  whose X-ray spectrum resembles that of a coronally active source. We
  discuss the possibility that μ Lep-B is a pre-main-sequence companion,
  most likely of the nonaccreting magnetically active type.

Title: Models for Solar Magnetic Loops. IV. On the Relation between
    Coronal and Footpoint Plasma in Active Region Loops
Authors: Landi, E.; Feldman, U.
Bibcode: 2004ApJ...611..537L
Altcode:
  In the present work we analyze several SUMER intensity maps of active
  region solar loops in order to compare the relative brightnesses of
  the footpoints and the coronal section of active region loops. We
  find that the former are barely distinguishable from the background
  emission of the active region, while the coronal emission of loops is
  confined in well-identifiable structures that are significantly brighter
  than the background. This result means that the vast majority of the
  active region emission in chromospheric and transition region lines
  is generated by plasma not directly connected with the coronal plasma
  that constitutes the observed coronal loops. We determine the observed
  intensities of coronal lines relative to the observed transition
  region and chromospheric emission and compare them with predictions
  from loop models having uniform cross section and different heating
  functions. We find that the loop models overestimate the footpoint
  emission by orders of magnitude. We discuss the discrepancy in light
  of the heating function and of the loop cross section. We speculate
  that nonuniformity in the loop cross section, more specifically a
  significant decrease of the cross section near the footpoints, is the
  most likely solution to the discrepancy.

Title: Observations Indicating That ~1 × 10<SUP>7</SUP> K Solar
    Flare Plasmas May Be Produced in Situ from ~1 × 10<SUP>6</SUP>
    K Coronal Plasma
Authors: Feldman, U.; Dammasch, I.; Landi, E.; Doschek, G. A.
Bibcode: 2004ApJ...609..439F
Altcode:
  We discuss a set of flare observations obtained at a position of
  0.10 R<SUB>solar</SUB> above the solar northwest limb. The data
  were acquired by the Solar Ultraviolet Measurement of Emitted
  Radiation (SUMER) spectrometer on the Solar and Heliospheric
  Observatory (SOHO). We derive time-dependent comparisons of
  physical properties, such as electron temperature and density,
  between flare plasma and background coronal plasma observed along
  the same lines of sight. In addition to temperature and density,
  we discuss emission measures, elemental abundances, nonthermal mass
  motions (from line widths), and bulk mass motions (from Doppler
  shifts). The observations appear to indicate that the flaring plasmas
  (4×10<SUP>6</SUP>K&lt;=T<SUB>e</SUB>&lt;=1×10<SUP>7</SUP>K)
  along the lines of sight were formed by in situ heating
  and possibly by compression of the ambient coronal material
  (T<SUB>e</SUB>&lt;=2×10<SUP>6</SUP> K).

Title: Newly Identified Forbidden Transitions within the Ground
    Configuration of Ions of Very Low Abundance P, Cl, K, and Co
Authors: Feldman, U.; Landi, E.; Curdt, W.
Bibcode: 2004ApJ...607.1039F
Altcode:
  Forbidden lines from transitions within the ground configuration
  of highly ionized atoms occupy an important role in diagnosing the
  properties of astrophysical plasmas. In this paper we report the
  identification of forbidden lines in the 500-1500 Å range from
  transitions within the ground configuration of highly ionized ions
  of the very low abundance phosphorus, chlorine, potassium, and
  cobalt recorded by SOHO SUMER. For the newly identified lines we
  provide upper level fractional populations multiplied by relevant
  spontaneous decay rates. Aided by the newly identified lines, the
  coronal composition of elements with photospheric abundances of
  5×10<SUP>-7</SUP>-1×10<SUP>-8</SUP> relative to hydrogen could
  be established.

Title: Observations of the Sun at Vacuum- Ultraviolet Wavelengths
from Space. Part I: Concepts and Instrumentation
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.; Marsch, Eckart; Feldman,
   Uri
Bibcode: 2004SSRv..111..415W
Altcode:
  Studies of the high-temperature solar atmosphere are to a large extent
  based on spectroscopic observations of emission lines and continuum
  radiation in the vacuum-ultraviolet (VUV) wavelength range of the
  electromagnetic spectrum. In addition, important contributions stem
  from soft X-ray measurements. Most of the VUV radiation is produced
  by transitions of atoms and ions. The resulting atomic and ionic
  spectral lines have formation temperatures between 10 000 K and 20 MK,
  representative of the chromosphere, transition region, corona, and
  solar flares. Some molecular lines and the continua originate in cooler
  regions of the Sun, around and below the temperature minimum between
  the photosphere and the chromosphere. Radiation at VUV wavelengths
  is strongly absorbed by the Earth's atmosphere. Consequently, it can
  only be detected with instruments on sounding rockets and spacecraft
  operating above the atmosphere. The progress in this field of research,
  in particular over the last 25 years, will be presented in the first
  part of this review by describing the concepts and instrumentation
  of modern spectrographs and imaging telescopes. This presentation
  is accompanied by some examples of high-resolution solar images
  and a discussion of radiometric-calibration aspects and wavelength
  measurements. A second part will follow in the near future, summarizing
  important results obtained on the plasma conditions in the solar
  atmosphere.

Title: Properties of the Lower Transition Region: The Widths of
    Optically Allowed and Intersystem Spectral Lines
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 2004ApJ...600.1061D
Altcode:
  The widths of spectral lines in the ultraviolet (UV) and extreme
  ultraviolet (EUV) spectral regions that are formed in the solar
  transition region and corona are usually greater than the optically
  thin widths due to thermal Doppler broadening calculated under the
  assumption of ionization equilibrium. Although opacity can explain the
  widths of some lines, there are a host of optically thin lines for which
  the excess widths are attributed to nonthermal motions. Interest in
  these motions for coronal heating theories has led to the measurement
  and comparison of spectral line profiles/widths throughout the solar
  UV and EUV spectrum. We find that for the quiet Sun the widths of some
  optically allowed lower transition region lines, deduced from spectra
  obtained by the Solar Ultraviolet Measurements of Ultraviolet Radiation
  (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO)
  spacecraft, are considerably larger than predicted from simply scaling
  previously measured wavelengths of other lines from the same ion. For
  example, the O III lines of the multiplet near 834 Å are considerably
  wider than predicted from the previously measured (from Skylab) width of
  the optically thin O III 1666.15 Å intersystem line. The excess widths
  are not due to nonthermal motions, as these are already included in
  the width of the 1666.15 Å line. In this paper, we analyze the widths
  of some prominent optically allowed lines and discuss possible causes
  for discrepancies with previous measurements of intersystem lines.

Title: What do Measurements of Abundance Variations Tell us About
    the Origin and Evolution of the Solar Wind
Authors: Woo, R.; Habbal, S. R.; Feldman, U.
Bibcode: 2003AGUFMSH41B0470W
Altcode:
  Connections between the Sun and solar wind have recently been made based
  on observations of density, velocity, and magnetic field. These have
  led to fundamental changes in our understanding of coronal magnetic
  topology and the origin and evolution of the solar wind. During solar
  minimum, polar coronal holes are neither the only regions of open
  magnetic field lines nor the sole source of fast solar wind. Instead,
  open magnetic field lines thread the entire corona, and solar wind
  flowing along them carries the imprint of coronal holes, quiet Sun, and
  active regions into interplanetary space. The purpose of this paper is
  to show how measurements of abundance variations in the corona and solar
  wind reinforce and complete this picture, providing key insight into
  where and how the solar wind, especially the slow wind, is produced.

Title: New Identifications of Mn VI and Fe VII Vacuum Ultraviolet
    Lines
Authors: Ekberg, J. O.; Feldman, U.
Bibcode: 2003ApJS..148..567E
Altcode:
  The Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
  spectrometer aboard the Solar and Heliospheric Observatory (SOHO)
  recorded a large number of spectra in the 500-1600 Å region. Although
  many of the detected lines have already been identified, the origins
  of a substantial fraction of the lines remain unknown. In this paper
  we report on a study of Mn VI and Fe VII in laboratory-generated
  vacuum spark spectra. Some of the Fe VII identified lines belonging
  to transitions of the type 3d4s-3d4p and 3d4p-3d4d were also observed
  in SUMER quiet-Sun and sunspot spectra. Because of the much lower
  manganese abundance in the solar atmosphere, none of the Mn VI lines
  were observed in the SUMER spectra.

Title: New Identifications of Mn VII and Fe VIII Lines Belonging
    to Transitions of the Type 3p<SUP>6</SUP>4p-3p<SUP>6</SUP>4d and
    3p<SUP>5</SUP>3d<SUP>2</SUP>-3p<SUP>6</SUP>4d
Authors: Ekberg, J. O.; Feldman, U.
Bibcode: 2003ApJ...595..517E
Altcode:
  The Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
  spectrometer aboard the Solar and Heliospheric Observatory (SOHO)
  recorded a large number of spectra in the 500-1600 Å region. Many of
  the detected spectral lines have been identified as transitions in ions
  from elements with low-to-moderate atomic numbers (Z&lt;=20). However,
  a substantial number of lines remained unidentified. We postulated
  that some of the unidentified lines are transitions between excited
  configurations in Fe<SUP>+7</SUP>. Unfortunately, Cr<SUP>+5</SUP> was
  the last ion in the K I isoelectronic sequence where the envisioned
  types of transitions were previously identified. In this paper we report
  new identifications, in laboratory-generated spectra, of transitions
  between excited configurations in Mn<SUP>+6</SUP> and Fe<SUP>+7</SUP>,
  two additional ions along the K I isoelectronic sequence. Since the
  elemental abundance of manganese in the solar atmosphere is very low,
  no Mn VII lines were identified in the SUMER spectra; however, the
  laboratory-identified Fe VIII lines were found to be present in the
  SUMER quiet-Sun spectra recorded above the solar limb and in sunspot
  spectra recorded on the solar disk.

Title: Free-Free Emission in the Far-Ultraviolet Spectral Range:
    A Resource for Diagnosing Solar and Stellar Flare Plasmas
Authors: Feldman, U.; Landi, E.; Doschek, G. A.; Dammasch, I.;
   Curdt, W.
Bibcode: 2003ApJ...593.1226F
Altcode:
  We report the detection of free-free (bremsstrahlung) emission near 1200
  Å from a flare at the solar limb observed with the Solar Ultraviolet
  Measurements of Emitted Radiation (SUMER) spectrometer on the Solar
  and Heliospheric Observatory (SOHO) spacecraft. The observations
  consist of a time series of slit spectra at a fixed pointing that
  lasted almost 2 hr, during which the observed solar region produced
  a C8 flare. Using the free-free continuum intensities in conjunction
  with intensities of high-temperature (10<SUP>6</SUP>-10<SUP>7</SUP>
  K) emission lines that appear in the same wavelength range, we
  derive the flare plasma electron density, electron temperature,
  emission measure, and nonthermal mass motions before, during, and
  after the flare. We describe a new diagnostic method for determining
  the temperature of cooling plasmas. Because the free-free radiation
  is emitted primarily by the interaction of electrons with nuclei of
  H and He atoms, we are also able to derive the Fe/H, Al/H, and Ca/H
  abundance ratios from the line intensities of highly ionized Fe, Al,
  and Ca lines and the intensities of the free-free emission, assuming
  a He abundance. The present work demonstrates the exceptional plasma
  diagnostic potential of ultraviolet free-free continuum radiation when
  coupled with emission-line intensities. We demonstrate that a similar
  technique could be employed to diagnose plasma properties of stellar
  flares using a high-resolution spectrometer with a sufficiently large
  effective collecting area.

Title: Properties of Solar Plasmas near Solar Maximum above Two
    Quiet Regions at Distances of 1.02-1.34 R<SUB>solar</SUB>
Authors: Landi, E.; Feldman, U.
Bibcode: 2003ApJ...592..607L
Altcode:
  In the present work we have analyzed the spectra emitted by two quiet
  solar regions observed off the solar disk by the SUMER instrument on
  board the SOHO satellite. The two complete spectra were recorded when
  the SOHO north-south axis was rotated relative to the Sun north-south
  axis by ~=150° clockwise. As a result, the SUMER slit could be placed
  so that it is perpendicular to the solar limb in an intermediate
  orientation between the equator and the poles. The SUMER fields of
  view consisted of two 1" wide radial strips of the solar corona from
  1.02 to 1.34 R<SUB>solar</SUB>. The aim of the present work was to
  measure the physical properties of the emitting plasma, namely, the
  electron density and temperature, the plasma emission measure, and
  the nonthermal mass motions, as a function of the distance from the
  solar limb. The measurement of the plasma absolute element abundances
  is deferred to a future paper. In measuring the nonthermal velocities
  of both source regions, we have discovered a residual instrumental
  systematic effect to line widths. The plasma in the SUMER field of
  view is nearly isothermal. The measurements of electron density and
  temperature allow us to check the hydrostatic assumption commonly
  adopted in the literature and to find that the plasma is denser than
  predicted. The wide wavelength range covered by the SUMER instrument
  includes several Li-like ions, allowing us to investigate the relative
  contribution of the radiative and collisional excitation mechanisms
  in the Li-like resonance doublet formation. We confirm the earlier
  findings that a significant radiative excitation occurs for O VI and
  Ne VIII resonance lines even at low altitudes.

Title: The Variability of the Solar Coronal Helium Abundance: Polar
    Coronal Holes Compared to the Quiet Sun
Authors: Laming, J. Martin; Feldman, Uri
Bibcode: 2003ApJ...591.1257L
Altcode:
  We report on measurements of the abundance ratio He/H in solar polar
  coronal holes and neighboring quiet coronal regions, using the SUMER
  spectrometer on board SOHO. In coronal holes we find He abundances
  smaller than or equal to the value found in the fast solar wind,
  5% by number relative to H, suggesting that the flow speed of He up
  into the wind is equal to or greater than the flow speed for H in the
  regions we observe. Going to regions above quiet solar corona, we find
  similar He abundances at altitudes of 50" or more, with some indication
  that the He abundance is increased toward its photospheric value of
  8.5% relative to H lower down. We take this to indicate that the He
  abundance in open-field regions of the corona is never higher than 5%
  (as observed in the solar wind), but that in low-lying, closed magnetic
  field regions higher abundances may result.

Title: Elemental Abundances in the Solar Upper Atmosphere Derived
    by Spectroscopic Means
Authors: Feldman, U.; Widing, K. G.
Bibcode: 2003SSRv..107..665F
Altcode:
  The composition of the solar photosphere is believed to be
  uniform. Indeed a quantity that does not vary with solar surface
  location or with a particular solar feature, i.e., no observational
  evidence is available to indicate that the photospheric composition near
  the solar equator is different from the photospheric composition near
  the solar poles or that the photospheric composition in quiet regions
  is different from the composition in active regions. In contrast, the
  composition of the solar upper atmosphere is not well defined. Solar
  composition work in recent decades has brought the recognition that
  there are systematic differences between the composition of the
  corona and the photosphere and revealed evidence for spatial and time
  variability in the composition of various coronal features. We review
  the spectroscopic techniques used and the progress that was made in
  recent years in deriving the plasma compositions of various solar
  upper atmosphere structures.

Title: Temperature Measurements in the Solar Transition Region Using
    N III Line Intensity Ratios
Authors: Doron, R.; Doschek, G. A.; Laming, J. M.; Feldman, U.;
   Bhatia, A. K.
Bibcode: 2003ApJ...590.1121D
Altcode:
  UV emission from B-like N and O ions offers a rather rare opportunity
  for recording spectral lines in a narrow wavelength range that can
  potentially be used to derive temperatures relevant to the solar
  transition region. In these ions, the line intensity ratios of the type
  (2s2p<SUP>2</SUP>-2p<SUP>3</SUP>)/(2s<SUP>2</SUP>2p-2s2p<SUP>2</SUP>)
  are very sensitive to the electron temperature. In addition, the lines
  involving the ratios fall within a range of only ~12 Å in N III
  the lines fall in the 980-992 Å range, and in O IV in the 780-791
  Å range. In this work, we explore the use of these atomic systems,
  primarily in N III, for temperature diagnostics of the transition
  region by analyzing UV spectra obtained by the Solar Ultraviolet
  Measurement of Emitted Radiation spectrometer flown on the Solar and
  Heliospheric Observatory. The N III temperature-sensitive line ratios
  are measured in more than 60 observations. The mean measured ratios are
  lower by ~30% than those predicted in the typical quiet Sun. Assuming
  an isothermal plasma, most of the measured ratios correspond to
  temperatures in the range 5.7×10<SUP>4</SUP>-6.7×10<SUP>4</SUP>
  K. This range is considerably lower than the calculated temperature of
  maximum abundance of N III, which is ~7.6×10<SUP>4</SUP> K. Detailed
  analysis of the spectra further indicates that the measured ratios
  are probably somewhat overestimated because of resonant scattering
  effects in the 2s<SUP>2</SUP>2p-2s2p<SUP>2</SUP> lines and small
  blends in the 2s2p<SUP>2</SUP>-2p<SUP>3</SUP> lines. Actual lower
  ratios would only increase the discrepancy between the ionization
  balance calculations and present temperature measurements based on
  a collisional excitation model. In the case of the O IV spectra,
  we determine that because of the close proximity in wavelength of the
  weak line (2s2p<SUP>2</SUP>-2p<SUP>3</SUP> transitions) to a strong Ne
  VIII line, sufficiently accurate ratio measurements cannot be obtained.

Title: Images of the solar upper atmosphere from SUMER on SOHO
Authors: Feldman, Uri; Dammasch, Ingolf E.; Wilhelm, Klaus; Lemaire,
   Philippe; Hassler, Donald M.; Battrick, Bruce
Bibcode: 2003ESASP1274.....F
Altcode: 2003isua.book.....F
  During the first year of SOHO operations and later in 1999, SUMER
  acquired several thousand images of the solar upper atmosphere. This
  atlas includes most of the full-Sun images that SUMER recorded
  and the majority of its images acquired during the Whole-Sun Month
  campaign. One of our main tasks while selecting the atlas format has
  been the implementation of our desire to maintain the high spatial
  resolution that SUMER achieved. In particular we hope that people
  with average vision will be able to see the finest details of the
  plasma structures that SUMER can resolve. Thus the page size has
  been chosen such that the finest resolution element in the images
  corresponds to approximately 250 μm in this atlas. The images in
  the atlas were recorded in spectral lines or in continuum radiation
  emitted by plasmas spanning the electron temperature domain from
  1×10<SUP>4</SUP>K to 1.4×10<SUP>6</SUP>K. Some of the images were
  recorded simultaneously in radiation emitted by plasmas of different
  temperatures. Due to substantial differences of the plasma properties
  from which the radiation originated, the atlas provides a unique source
  for studying many aspects of the solar upper atmosphere.

Title: Nonthermal Mass Motions within the High-Temperature Plasmas
    above a Complex Solar Active Region
Authors: Feldman, U.; Landi, E.; Curdt, W.
Bibcode: 2003ApJ...585.1087F
Altcode:
  We report on mass motions in high-temperature plasmas at
  radial distances of 1.06-1.20 R<SUB>solar</SUB> corresponding
  to 3.3×10<SUP>4</SUP>-1.3×10<SUP>5</SUP> km above the west
  solar limb. The observations were conducted over a 53 hr time
  period while a complex active region moved across the west
  solar limb. We found that the nonthermal mass motions in the
  2.6×10<SUP>6</SUP>-6.6×10<SUP>6</SUP> K plasmas that were
  imaged along the slit were in the 20-35 km s<SUP>-1</SUP>
  velocity range. The magnitude of the nonthermal mass motions
  was independent of the plasma temperature or its height above the
  limb. We also found that the emission measure distribution within the
  2.6×10<SUP>6</SUP>-6.6×10<SUP>6</SUP> K plasma regimes did not change
  during most of the observations, an indication that on the average
  the temperature distribution among the various plasma volumes along
  the line of sight stayed unchanged.

Title: Mass Motions and Plasma Properties in the 10<SUP>7</SUP>
    K Flare Solar Corona
Authors: Landi, E.; Feldman, U.; Innes, D. E.; Curdt, W.
Bibcode: 2003ApJ...582..506L
Altcode:
  In the present work, we analyze Solar Ultraviolet Measurement of
  Emitted Radiation (SUMER) observations of a solar limb flare that
  occurred on 1999 May 9. The analyzed data cover a time span of around
  6.4 hr, during which an M-7.6 flare erupted and decayed in the field of
  view. Two selected regions along the SUMER slit have been considered
  for quantitative analysis. The main purpose of the present analysis
  is to measure the mass motions and the nonthermal velocities of the
  postflare plasmas and their temporal evolution. To achieve this we
  use lines having formation temperatures in the 2.5×10<SUP>6</SUP>
  to 2×10<SUP>7</SUP> K range from which we derive net mass motions
  and nonthermal velocities and compare them with the properties of the
  surrounding plasma not affected by the flare activity. To understand
  the physical conditions of the flaring plasma and of the surrounding
  material, we derive electron temperature, electron density, and emission
  measures of the emitting plasma. We find that bulk motions, initially
  of the order of several hundreds of kilometers per second in both
  directions, decay within 10 minutes from the flare onset; nonthermal
  velocities decay to preflare values of around 30 km s<SUP>-1</SUP> in
  less than 2 hr from the maximum value of around 100 km s<SUP>-1</SUP>
  at flare onset. The measured electron density does not seem to change
  during activity, while the flare plasma temperature steadily decays
  to preflare values. The temperature evolution is consistent with a
  radiatively cooling plasma, although the uncertainties associated to
  the measurement of the variation of thermal energy of the flare plasma
  prevent a definitive conclusion on possible continuous heating of the
  flaring plasma.

Title: The X-ray Spectra Predicted to Be Emitted From Hot
    Astrophysical Plasmas Abnormally Enriched With High-Z Elements -
    The Case of Mercury
Authors: Doron, R.; Feldman, U.; Doschek, G. A.; Bar-Shalom, A.
Bibcode: 2002ASPC..277..461D
Altcode: 2002sccx.conf..461D
  No abstract at ADS

Title: The Effect of High-Lying Configurations and Ionization and
    Recombination Processes on Analyses of Solar and Stellar Coronal
    Spectra
Authors: Doron, Rami; Behar, Ehud; Doschek, George A.; Feldman, Uri
Bibcode: 2002AIPC..636..125D
Altcode:
  This work addresses two topics important for the appropriate
  interpretation of astrophysical spectra. The first is the effect
  of high-lying levels on the atomic models and the second is the
  importance of ionization and recombination processes in forming
  line emission. In the first part of the work we study the influence
  of high-lying configurations on the calculated intensities of UV
  lines, particularly of O-like ions, observed by the Solar Ultraviolet
  Measurements of Emitted Radiation (SUMER) spectrometer aboard the SOHO
  satellite. The high-lying configurations alter the line intensities
  through radiative cascades and configuration interaction effects. We
  find that cascades can significantly enhance the intensities of
  some lines of the considered ions by up to 65% at temperatures
  of the ion maximum fractional abundance. The enhancement due to
  cascades increases with increasing temperature and charge state. The
  configuration mixing effects can either enhance or reduce the line
  intensities. In a second study, we calculate the theoretical intensities
  of the soft X-ray Fe16+ lines arising from 2l-3l' transitions using a
  three-ion collisional-radiative model that includes the contribution of
  recombination and ionization processes to line formation. Dielectronic
  recombination is found to be particularly important. The newly
  calculated line intensities can explain the high values of the 2p-3s
  / 2p-3d intensity ratios, which are often obtained in astrophysical
  observations. Observed intensity ratios among the 2p-3s lines are also
  better reproduced.

Title: A Comparison between Coronal Emission Lines from an Isothermal
    Spectrum Observed with the Coronal Diagnostic Spectrometer and
    CHIANTI Emissivities
Authors: Landi, E.; Feldman, U.; Dere, K. P.
Bibcode: 2002ApJ...574..495L
Altcode:
  The present paper compares off-disk spectral observations of the
  solar corona in the ranges 307-379 and 513-633 Å with theoretical
  emissivities calculated using the CHIANTI database. The observed spectra
  were recorded by the Coronal Diagnostic Spectrometer instrument on
  board the Solar and Heliospheric Observatory using the normal-incidence
  portion of the instrument. Using line-ratio techniques, we first measure
  the electron temperature and density in the emitting region, verifying
  that it is nearly isothermal. Next, we use an emission-measure analysis
  to compare measured spectral line intensities with predictions from the
  CHIANTI database. This comparison allows us to assess the quality of
  the CHIANTI data for the brightest coronal lines in the 307-379 and
  513-633 Å spectral ranges. As a result, we are able to (1) select
  lines and ions for which the agreement between theory and observation
  is good, (2) identify a few lines that are blended, and (3) stress
  inconsistencies between a few lines and theory, thus showing where
  improvements to atomic data and transition probabilities are necessary.

Title: The Effect of High-lying Levels on Atomic Models Relevant to
    Spectroscopic Analyses of Solar Extreme-Ultraviolet Spectra
Authors: Doron, R.; Doschek, G. A.; Feldman, U.; Bhatia, A. K.;
   Bar-Shalom, A.
Bibcode: 2002ApJ...574..504D
Altcode:
  In this work we investigate the effect of including high-lying
  configurations in the collisional-radiative models used to calculate
  spectral line intensities recorded by the Solar Ultraviolet
  Measurement of Emitted Radiation (SUMER) spectrometer on board the
  SOHO satellite. Many of the emission lines observed by SUMER are
  attributed to transitions within the L and M electronic shells of
  ions isoelectronic to sequences from Li I to Na I. By using atomic
  data that are mostly generated by the Hebrew University Lawrence
  Livermore Atomic Code (HULLAC), we incorporate in the atomic models
  configurations from higher shells and systematically study their effect
  on the calculated line intensities in selected ions. The high-lying
  configurations alter the line intensities through radiative cascades
  and configuration interaction effects. We find that cascades can
  significantly enhance the line intensities of the considered ions by
  up to 60% at temperatures of the ion maximum fractional abundance. The
  enhancement due to cascades increases with increasing temperature and
  charge state. The configuration mixing effects can either enhance or
  reduce the line intensities. Generally, the mixing effect becomes less
  important for higher charge states.

Title: The new picture of the transition region and corona from SUMER
Authors: Feldman, U.
Bibcode: 2002ESASP.508..531F
Altcode: 2002soho...11..531F
  The solar upper atmosphere (SUA) is defined as the volume above the
  photosphere occupied by plasmas at electron temperatures greater than
  2×10<SUP>4</SUP>K. Until the Skylab era, little was known about
  the morphology of the SUA. As a result, the early models assumed
  a continuous atmosphere in which the temperature increased with
  height. With the advances in spectroscopic measurements it became
  apparent that most of the radiation from plasmas at temperatures of
  3×10<SUP>4</SUP> - 6×10<SUP>5</SUP>K is not coming from the interface
  between the chromosphere and corona but rather from unrelated plasma
  structures that I chose to name Unresolved Fine Structures (UFS). Recent
  results obtained by instruments on SOHO and on TRACE support the earlier
  conclusions and provide additional insight into the makeup of the SUA
  plasma structures of quiet Sun and coronal-hole regions.

Title: SOHO/SUMER Measurements of the Solar Coronal Helium Abundance
Authors: Laming, J. M.; Feldman, U.
Bibcode: 2002AAS...200.5716L
Altcode: 2002BAAS...34R.739L
  We report on the progress of work to measure the helium abundance in
  various regions of the solar corona. Concentrating on polar coronal
  holes, we find similar helium abundances to those measured in the fast
  solar wind, i.e. 4-5% by number relative to hydrogen at an altitude
  approximately 100 arcseconds above the limb. This suggests that the
  flows of hydrogen and helium up into the fast solar wind must be locked
  together, presumably by plasma waves, since otherwise large variations
  of the He/H abundance ratio could result. This work is supported by
  the NRL/ONR Solar Magnetism and the Earth's Environment 6.1 Research
  Option and by NASA Contract S137836.

Title: An Inquiry into the Nature of Spectra from Hot Astrophysical
    Plasma Abnormally Enriched with Mercury
Authors: Doron, R.; Feldman, U.; Doschek, G. A.; Bar-Shalom, A.
Bibcode: 2002ApJS..139..297D
Altcode:
  Observatories such as Chandra, XMM-Newton, and more likely future
  instruments with higher effective collecting area of radiation will
  offer the opportunity to study the nature of chemically peculiar
  sources using observations in the X-ray and EUV range. In the present
  work we explore the possibility to observe the spectral signature
  of highly stripped Hg ions that might be present in possible coronae
  or winds of HgMn stars. A systematic theoretical survey of the most
  intense X-ray spectral features predicted to be emitted by H-like to
  Pd-like Hg ions (Hg<SUP>+79</SUP>-Hg<SUP>+34</SUP>) is performed. The
  calculated intensities (photons s<SUP>-1</SUP> ion<SUP>-1</SUP>)
  of the various spectral features of the Hg ions are compared to the
  intensities calculated for the lines of Fe ions that may be observed
  in the same range of the X-ray spectrum, but not necessarily from the
  same temperature domain. Fe lines corresponding to transitions from the
  L electronic shell were already observed in the coronae of stars, e.g.,
  by Chandra in Capella. Assuming a similar abundance for Hg and Fe ions,
  many of the calculated Hg lines are found to be of comparable intensity
  to the Fe lines and in some cases stronger by about a factor of 20. We
  also discuss possible density and temperature diagnostic applications
  for some of the Hg lines.

Title: CHIANTI-An Atomic Database for Emission Lines. V. Comparison
    with an Isothermal Spectrum Observed with SUMER
Authors: Landi, E.; Feldman, U.; Dere, K. P.
Bibcode: 2002ApJS..139..281L
Altcode:
  CHIANTI is a database consisting of critically evaluated atomic data and
  transition probabilities necessary to analyze spectral observations
  of optically thin plasmas. Previous papers described the content
  of the database and compared it to a solar active region spectrum
  between 170 and 450 Å. The aim of the present paper is to compare
  CHIANTI predictions to off-disk spectral observations of the solar
  corona between 500 and 1500 Å. The observed spectra were recorded by
  the SUMER instrument on board the Solar and Heliospheric Observatory
  using the full spectral range allowed by the instrument. Earlier works
  have demonstrated that the particular emitting plasma is isothermal
  at a temperature of 1.35×10<SUP>6</SUP> K, making it ideal for the
  assessment of the accuracy of the CHIANTI database. This assessment of
  the CHIANTI database allowed us (1) to select lines and ions for which
  the agreement between theory and observation is good, (2) to identify
  several lines which are blended, and (3) to stress inconsistencies
  between a few lines and theory, thus showing where improvements to
  atomic data and transition probabilities are necessary.

Title: A review of the first ionization potential effect on elemental
    abundances in the solar corona and in flares
Authors: Feldman, U.; Widing, K. G.
Bibcode: 2002PhPl....9..629F
Altcode:
  The elemental composition of solar upper atmosphere plasmas was
  studied from spectra obtained by instruments aboard all major
  solar observatories that were launched into space in the last three
  decades. The studies show that the first ionization potential (FIP)
  of the elements has a profound effect on their abundance in the various
  solar upper atmosphere regions. In this paper we review properties of
  the FIP effect as they relate to coronal holes, quiet regions, active
  regions and flares and we show that although the derived compositions
  vary considerably with the type of plasma observed regularities in
  their behavior are emerging. The observed behavior may help identify
  the energy deposition mechanism that fuels the corona and solar flares.

Title: Electric Currents as the Main Cause of Coronal and Flare
    Activity in the Sun and in Many Late-Type Stars
Authors: Feldman, U.
Bibcode: 2002PhyS...65..185F
Altcode:
  Coronal temperatures of late type stars are hundreds to thousands of
  times higher than the temperatures of their photospheres. Attempts
  to account for the existence of high coronal temperature in the Sun,
  by invoking wave heating of various kinds and/or by the annihilation
  of parts of the magnetic field above the surface and using the resulted
  energy to heat coronal activity, seem to be unsuccessful. In this paper,
  I suggest that electric currents are the means by which the Sun and
  most likely many late type stars produce their coronal activity. To
  support this idea, I bring evidence from observations occurring in
  solar and stellar upper atmosphere plasmas that resemble in their
  appearance phenomena that are the consequence of electric currents
  flowing in highly ionized plasmas.

Title: The Solar Helium Abundance in Polar Coronal Holes as Measured
    by SOHO/SUMER
Authors: Laming, J. M.; Feldman, U.
Bibcode: 2001AAS...199.8806L
Altcode: 2001BAAS...33.1434L
  The solar helium abundance measured in situ in the fast solar wind is
  typically 0.05 by number relative to hydrogen, whereas in the solar
  envelope it is measured by helioseismology to be 0.085. We report on
  analyses of spectra taken by SOHO/SUMER of solar polar coronal holes
  to determine the abundance of helium by emission line spectroscopy. In
  comparison with our earlier measurement in an equatorial streamer,
  coronal hole spectra are less intense, which makes determining
  the intensities of hydrogen lines to adequate precision much more
  difficult. Using other strong lines in the spectrum, e.g. C IV, N V,
  O VI we find helium abundance values more consistent with those in the
  fast solar wind than the photospheric value. This work is supported by
  the NRL/ONR Solar Magnetism and the Earth's Environment 6.1 Research
  Option and by NASA Contract S137836.

Title: The SUMER spectral atlas of solar-disk features
Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi,
   B. N.; Schühle, U.; Lemaire, P.
Bibcode: 2001AIPC..598...45C
Altcode: 2001sgc..conf...45C
  A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas
  of the Sun between 670 Å and 1609 Å in first order of diffraction
  has been derived from observations obtained with the SUMER (Solar
  Ultraviolet Measurements of Emitted Radiation) spectrograph on
  the spacecraft SOHO (Solar and Heliospheric Observatory) [1]. The
  atlas contains spectra of the average quiet Sun, a coronal hole and
  a sunspot on disk. Different physical parameters prevalent in the
  bright network (BN) and in the cell interior (CI)-contributing in a
  distinct manner to the average quiet-Sun emission-have their imprint
  on the BN/CI ratio, which is also shown for the entire spectral
  range. With a few exceptions, all major lines are given with their
  identifications and wavelengths. Lines that appear in second order
  are superimposed on the first order spectra, but below 500 Å the
  responsivity of the normal-incidence optical system is very low. The
  spectra include emissions from atoms and ions in the temperature range
  6 10<SUP>3</SUP> K to 2 10<SUP>6</SUP> K, i.e., continua and mission
  lines emitted from the lower chromosphere to the corona. This spectral
  atlas, with its broad wavelength coverage, provides a rich source
  of new diagnostic tools for studying the physical parameters in the
  chromosphere, the transition region and the corona. In particular,
  the wavelength range below 1100 Å as observed by SUMER represents
  a significant improvement over the spectra produced in the past. In
  view of the manifold appearance and temporal variation of the solar
  atmosphere it is obvious that our atlas can only be a-hopefully
  typical-snapshot. The spectral radiances are determined with a
  relative uncertainty of 0.15 to 0.30 (1σ), and the wavelength scale
  is accurate to typically 10 mÅ, which is the level achievable with
  semi-automatic processing. The SUMER solar-disk spectral atlas will
  be published in the near future by Curdt et al. [2]. It includes
  profiles of the average quiet Sun, an equatorial coronal hole, and
  a sunspot. As an example we show in Fig. 1 the spectral range from
  1300 Å to 1342 Å with the prominent O I and C II lines. Resolved
  emission lines are indicated by a mark, the measured wavelength in
  angstrom, and the identification, if available. Marks point to line
  lists available in the literature, where additional information about
  a specific line can be found [3-7]. New lines or identifications
  are indicated. Lines observed in first order and in second-order of
  diffraction are distinguished. Only the three least-significant digits
  of the wavelength values are given. If available, unidentified lines
  are characterized by the temperature classification defined in [3] (a:
  T<SUB>e</SUB>&lt;3 10<SUP>5</SUP> b: T<SUB>e</SUB>~3 10<SUP>5</SUP> c:
  T<SUB>e</SUB>~4 10<SUP>5</SUP> d: 6 10<SUP>5</SUP>&lt;T<SUB>e</SUB>
  &lt;9 10<SUP>5</SUP> e: T<SUB>e</SUB>~1.4 10<SUP>6</SUP> f:
  T<SUB>e</SUB>~1.8 10<SUP>6</SUP>). The vertical axes are scaled
  to spectral radiance in units of mW sr<SUP>-1</SUP> m<SUP>-2</SUP>
  Å<SUP>-1</SUP> on the left the radiometric calibration for first
  order lines is given, on the right for second order lines. Note,
  that second order lines are always superimposed on a first order
  background. We have taken care of the type of photocathode (bare or KBr)
  when applying the radiometric calibration to different sections of the
  spectrum. Also displayed in green is the BN/CI ratio in an attempt
  to characterize the quiet-Sun chromospheric network structure. A
  pre-print of the SUMER spectral atlas and a line list is available at
  http://www.linmpi.mpg.de/~curdt. .

Title: On the Unresolved Fine Structures of the Solar Upper
    Atmosphere. IV. The Interface with the Chromosphere
Authors: Feldman, U.; Dammasch, I. E.; Wilhelm, K.
Bibcode: 2001ApJ...558..423F
Altcode:
  An important objective of the solar physics community is the
  unambiguous determination of the morphology of the fine structures of
  the solar upper atmosphere in quiet-Sun and coronal hole regions and
  the relationship of the cold chromosphere to the hot corona. Recently
  the Solar Ultraviolet Measurements of Emitted Radiation spectrometer
  on board the Solar and Heliospheric Observatory succeeded in obtaining
  observations that can be used to achieve this goal. In this paper
  we study the spatial relationship between previously unresolved fine
  structures and the chromospheric emissions that underlie them. The main
  result is that looplike structures seen in transition region lines
  with length scales of 10"-20" straddle the chromospheric network and
  have no chromospheric counterpart near their apparent footpoints.

Title: Intensity Ratios between the 2s<SUP>2</SUP>
    <SUP>1</SUP>S<SUB>0</SUB>-2s2p <SUP>3</SUP>P<SUB>1</SUB>
    and 2s<SUP>2</SUP>p <SUP>1</SUP>P<SUB>1</SUB>-2p<SUP>2</SUP>
    <SUP>1</SUP>D<SUB>2</SUB> Transitions in Be-like Ions as Electron
    Temperature Indicators for Solar Upper Atmosphere Plasmas
Authors: Landi, E.; Doron, R.; Feldman, U.; Doschek, G. A.
Bibcode: 2001ApJ...556..912L
Altcode:
  We investigate the relative intensities of
  the two moderately bright Be-like 2s<SUP>2</SUP>
  <SUP>1</SUP>S<SUB>0</SUB>-2s2p <SUP>3</SUP>P<SUB>1</SUB> and 2s2p
  <SUP>1</SUP>P<SUB>1</SUB>-2p<SUP>2</SUP> <SUP>1</SUP>D<SUB>2</SUB>
  lines as a function of electron temperature. We show that the intensity
  ratios of the lines in the beryllium isoelectronic sequence from C
  III to Ni XXV ions can serve as sensitive temperature indicators for
  a large variety of solar plasmas. While the C III-Ne VII lines can be
  used to diagnose unresolved fine structures in relatively cold solar
  atmosphere plasmas [(1-5)×10<SUP>5</SUP> K], the Na VIII-Ar XV ions
  can be used to diagnose coronal plasmas [(0.8-3)×10<SUP>6</SUP>
  K], and Ca XVII-Ni XXV lines are useful to measure the temperature
  in flaring plasmas [(5-16)×10<SUP>7</SUP> K]. We investigate the
  effects on the temperature determination caused by varying the number of
  energy levels that are included in the atomic model for the considered
  ions. It is found that a model that includes the 2l2l<SUP>'</SUP>
  and 2l3l<SUP>'</SUP> configurations is sufficient for adequately
  describing the relevant level populations of the Be-like ions in
  coronal conditions. We compare theoretical ratios obtained using
  collisional cross section and transition probability values derived
  by different theoretical methods. The atomic data are obtained from
  the CHIANTI database, the Hebrew University Lawrence Livermore Atomic
  Code (HULLAC) suite of programs, and other available sources in the
  literature. Finally, we use spectra of an apparently isothermal
  coronal plasma observed by the Solar Ultraviolet Measurement of
  Emitted Radiation instrument on the Solar and Heliospheric Observatory
  to determine the electron temperature of streamer plasma using the
  HULLAC and CHIANTI atomic data sets. The result is compared with the
  temperature derived in an earlier study using different methods.

Title: The SUMER spectral atlas of solar-disk features
Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi,
   B. N.; Schühle, U.; Lemaire, P.
Bibcode: 2001A&A...375..591C
Altcode:
  A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas of
  the Sun between 670 Å and 1609 Å in the first order of diffraction
  has been derived from observations obtained with the SUMER (Solar
  Ultraviolet Measurements of Emitted Radiation) spectrograph on the
  spacecraft SOHO (Solar and Heliospheric Observatory). The atlas contains
  spectra of the average quiet Sun, a coronal hole and a sunspot on the
  disk. Different physical parameters prevalent in the bright network (BN)
  and in the cell interior (CI) - contributing in a distinct manner to
  the average quiet-Sun emission - have their imprint on the BN/CI ratio,
  which is also shown for almost the entire spectral range. With a few
  exceptions, all major lines are given with their identifications and
  wavelengths. Lines that appear in second order are superimposed on the
  first order spectra. These lines are clearly marked in the atlas. The
  spectra include emissions from atoms and ions in the temperature range
  6*E<SUP>3</SUP> K to 2*E<SUP>6</SUP> K, i.e., continua and emission
  lines emitted from the lower chromosphere to the corona. This spectral
  atlas, with its broad wavelength coverage, provides a rich source of new
  diagnostic tools to study the physical parameters in the chromosphere,
  the transition region and the corona. In particular, the wavelength
  range below 1100 Å as observed by SUMER represents a significant
  improvement over the spectra produced in the past. In view of the
  manifold appearance and temporal variation of the solar atmosphere,
  it is obvious that our atlas can only be a - hopefully typical -
  snapshot. Brief descriptions of the data reduction and calibration
  procedures are given. The spectral radiances are determined with a
  relative uncertainty of 0.15 to 0.30 (1sigma ) and the wavelength
  scale is accurate to typically 10 mÅ. The atlas is also available
  in a machine readable form. Table A.1 is only available in electronic
  form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
  or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/375/591

Title: On the Rate of Abundance Modifications versus Time in Active
    Region Plasmas
Authors: Widing, K. G.; Feldman, U.
Bibcode: 2001ApJ...555..426W
Altcode:
  Four emerging and developing active regions observed on Skylab
  spectroheliograms (300-600 Å) have been studied over intervals of 3
  to 7 days to determine the change in their Mg/Ne abundance ratio. The
  Mg/Ne abundance ratio is used as a measure of the FIP effect on element
  abundances in the solar upper atmosphere. Mg/Ne abundance ratios were
  derived from diagnostic intensity ratios of Mg VI lines at 400 Å
  relative to adjacent Ne VI lines. Intensity ratios were estimated from
  the active region images in the Skylab Atlas of Extreme-Ultraviolet
  Spectroheliograms. The resulting abundance ratios expressed in terms
  of the FIP bias β (see text) are plotted as a function of elapsed
  time since emergence. After emergence the newborn region shows
  photospheric composition: i.e., the abundance ratio of Mg/Ne=0.296,
  β=1. Thereafter, the developing regions show a progressive increase
  in the Mg/Ne abundance ratio with the value of β reaching after 2
  days coronal-type abundances: Mg/Ne=1.43, β~4.8. In the later stages,
  the bias increases to values between 7 and 9 after 3 to 7 days. Some
  implications of the abundance modifications are briefly discussed.

Title: VizieR Online Data Catalog: SUMER Spectral Atlas of Solar
    Disk Features (Curdt+, 2001)
Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi,
   B. N.; Schuhle, U.; Lemaire, P.
Bibcode: 2001yCat..33750591C
Altcode:
  List of spectral lines in the wavelength range from 668Å to 1611Å
  identified in SUMER (Solar Ultraviolet Measurements of Emitted
  Radiation, spectrograph on the spacecraft SOHO) spectra of the average
  quiet Sun (QS), a coronal hole (CH) and a sunspot on disk (SS). Spectral
  lines observed in second order of diffraction which are also given
  here, extend the lower wavelength limit to below 500Å. For each entry
  we give the observed wavelengths in angstrom, the identification,
  the transition, the peak of spectral radiance, L<SUP>peak</SUP>, in
  mW/(sr*m<SUP>2</SUP>*Å) (incl. background), and a cross-reference
  to other line lists available in the literature (cf., Sect. 5.1). For
  second-order lines radiance entries are generally not provided, since
  the background separation in both orders of diffraction is a non-trivial
  task, which can not be automated. Only a few radiance values of strong
  second-order lines with negligible first-order contribution are given,
  which are marked by an asterisk (*). (1 data file).

Title: FIP Effect Measurements in the Solar Corona and in Flares
Authors: Feldman, U.
Bibcode: 2001AGUSM..SH52C04F
Altcode:
  The compositions of solar upper atmosphere plasmas were studied from
  spectra obtained by instruments aboard all major solar observatories
  that were launched into space in the last three decades. During my talk
  I will review FIP effect results that were obtained from instruments
  on some of the observatories as they relate to coronal holes, quiet
  regions, active regions and flares. I will shaw that although the
  derived compositions vary considerably with the type of plasma observed
  some regularities in their behavior begin to emerge.

Title: The Solar Helium Abundance in the Outer Corona Determined
    from Observations with SUMER/SOHO
Authors: Laming, J. M.; Feldman, U.
Bibcode: 2001ApJ...546..552L
Altcode: 2000astro.ph..8427L
  At altitudes of about 1.05 R<SUB>solar</SUB> or more, the corona above
  quiet solar regions becomes essentially isothermal. This obviates many
  of the difficulties associated with the inverse problem of determining
  emission measure distributions and allows for fairly straightforward
  relative element abundance measurements. We present new values for the
  He abundance. The first is based on a reanalysis of the He/O ratio
  studied previously using data acquired by SUMER. A more thorough
  evaluation of the atomic physics for He II, including a detailed
  treatment of radiative recombination, increases the predicted emission
  in the He II Balmer series compared with earlier analyses. We use a
  recently revised value of the O abundance to derive an He/H abundance
  ratio of 0.038 (mass fraction, Y=0.13), with an error of ~17% coming
  mainly from the O abundance uncertainty. We demonstrate that this result
  may be affected by gravitational settling of O relative to He. We also
  derive an abundance for He by direct comparison with emission lines of
  the H I Lyman series, with the result He/H=0.052+/-0.005 (Y=0.17), a
  value similar to He abundances determined in the slow-speed solar wind.

Title: Spectroscopic features in the EUV emission of a M8 flare
    observed by SUMER
Authors: Curdt, W.; Landi, E.; Feldman, U.; Innes, D.; Dwivedi, B.;
   Wilhelm, K.
Bibcode: 2001IAUS..203..260C
Altcode:
  On May 9, 1999 a flare of size M8 occurred while SUMER obtained a
  spectral scan above the active region NOAA 8537 at the west limb. We
  recorded spectra during the pre-flare phase, at flare onset, and during
  the decay phase. More than 60 flare lines were observed during this
  event, which include Fe XVIII - Fe XXIII lines that provide evidence
  of 10<SUP>7</SUP> K plasmas. We also recorded lines from He-like ions,
  such as Ne IX, Na X, Mg XI or Si XIII. Accurate wavelength measurements
  of such lines are of interest in basic atomic physics studies. Using
  plasma diagnostic techniques, we investigated the temporal evolution
  of the electron densities and temperatures during the event. Since
  the spectra contain lines from many different elements, we were able
  to determine elemental abundances in the flaring plasma.

Title: Properties of Solar Polar Coronal Hole Plasmas Observed above
    the Limb
Authors: Doschek, G. A.; Feldman, U.; Laming, J. M.; Schühle, U.;
   Wilhelm, K.
Bibcode: 2001ApJ...546..559D
Altcode:
  We determine the line-of-sight emission measure distribution and
  nonthermal motions as a function of height above the limb in the
  north and south polar coronal holes. These quantities are derived from
  extreme-ultraviolet (EUV) spectra obtained from the Solar Ultraviolet
  Measurements of Emitted Radiation (SUMER) spectrometer on the Solar
  and Heliospheric Observatory (SOHO) spacecraft. The SUMER slit was
  oriented along the north-south direction for all the observations,
  and the spatial resolution is about 1". The spectra were obtained
  from a number of different types of observations in 1996. We select
  a group of emission lines for analysis for which, under the usual
  assumption of ionization equilibrium, the maximum emissivities span
  the temperature range from about 3×10<SUP>5</SUP> K up to about
  1.1×10<SUP>6</SUP> K. We compare our results with recently published
  similar observations of a west limb quiet-Sun streamer region, with
  other coronal hole results based on SUMER spectra, and with earlier
  observations of the quiet Sun and coronal holes obtained from Skylab
  and rocket spectra. We find that the electron temperature in the polar
  holes increases with height above the limb, that the emission measure
  distribution of plasma located at line-of-sight heights less than
  about 60" peaks at a temperature of about 9×10<SUP>5</SUP> K, and that
  nonthermal motions sometimes, but not always, increase slightly with
  height above the limb. When observed, these increases level off above
  the limb at about 120". We speculate that the increases with height
  above the limb may be a manifestation of the fast solar wind. They
  may also be due to the reduction in transition region structures with
  increasing limb height. We also discuss wave heating as a cause of
  the line width increases.

Title: Identification of Spectral Lines in the 500-1600 Å Wavelength
    Range of Highly Ionized Ne, Na, Mg, Ar, K, Ca, Ti, Cr, Mn, Fe, Co,
    and Ni Emitted by Flares (T<SUB>e</SUB>&gt;=3×10<SUP>6</SUP> K)
    and Their Potential Use in Plasma Diagnostics
Authors: Feldman, U.; Curdt, W.; Landi, E.; Wilhelm, K.
Bibcode: 2000ApJ...544..508F
Altcode:
  On 1999 May 9 the Solar Ultraviolet Measurements of Emitted Radiation
  (SUMER) spectrometer on the Solar and Heliospheric Observatory
  (SOHO) recorded spectra from a high-temperature region located
  in the solar corona above the west limb. These spectra contain
  lines from rather less-abundant elements in solar plasmas. In
  this paper we present identifications of the high-temperature
  (T<SUB>e</SUB>&gt;=3×10<SUP>6</SUP> K) Ne, Na, Mg, Ar, K, Ca, Ti,
  Cr, Mn, Fe, Co, and Ni lines that were detected in the 500-1600 Å
  spectral range of SUMER. In addition, accurate wavelength measurements
  have been obtained with uncertainties varying between 0.015 and 0.040
  Å (1 σ). Making use of the newly measured wavelengths, we derive
  energy levels in the ground configuration of a number of highly
  charged ions. We present intensity ratio calculations of lines in
  the SUMER range that could be used to measure electron densities in
  high-temperature solar plasmas. We also provide emissivities for Ca
  XIII-Ca XV and Fe XVIII-Fe XXIII lines that could be used to determine
  emission measures and electron temperatures of high-temperature
  plasmas. We discuss a method for measuring elemental abundance
  variations in high-temperature solar plasmas using lines presented
  in the paper. A list of spectral lines spanning the 300-30000 Å
  wavelength range and their branching ratios that are suitable for
  efficiency calibration of space-borne spectrographs is provided.

Title: The Morphology of the Solar Upper Atmosphere During the
    Sunspot Minimum
Authors: Feldman, U.; Dammasch, I. E.; Wilhelm, K.
Bibcode: 2000SSRv...93..411F
Altcode:
  The solar upper atmosphere (SUA) is defined as the volume above the
  photosphere occupied by plasmas with electron temperatures, T_e,
  above ~ 2×10^4 K. Until the Skylab era, only little was known about
  the morphology of the SUA, while the quality of the spectroscopic
  observations was continually improving. A spherically symmetric
  atmosphere was assumed at that time, in which the temperature increased
  with height. With advances in the observational techniques, it became
  apparent that the morphology of the SUA was very complex even during the
  minimum of the magnetic activity cycle. In particular, spectroscopic
  measurements with high spectral and spatial resolution, which were
  made in the light of ultraviolet emission lines representing a variety
  of temperatures, led to the conclusion that most of the radiation
  from the solar transition region could not be explained by assuming
  a continuous chromosphere-corona interface, but rather by a region of
  unresolved fine structures. Recent observational results obtained by
  modern instruments, such as the Extreme-ultraviolet Imaging Telescope
  (EIT), the Large Angle Spectroscopic Coronagraph (LASCO), and the
  Solar Ultraviolet Measurements of (SUMER) spectrograph on the Solar and
  Heliospheric Observatory (SOHO), as well as the Transition Region and
  Coronal Explorer (TRACE), and their interpretations will be presented
  in this review of our understanding of the morphology of the SUA.

Title: Wavelength measurements of heliumlike 1s2s
    <SUP>3</SUP>S<SUB>1</SUB>-1s2p <SUP>3</SUP>P<SUB>0,2</SUB>
    transitions in Ne<SUP>8+</SUP>, Na<SUP>9+</SUP>, Mg<SUP>10+</SUP>,
    and Si<SUP>12+</SUP> emitted by solar flare plasmas
Authors: Curdt, W.; Landi, E.; Wilhelm, K.; Feldman, U.
Bibcode: 2000PhRvA..62b2502C
Altcode:
  With the Solar Ultraviolet Measurements of Emitted Radiation
  instrument-a high-resolution normal-incidence telescope and spectrometer
  on board the Solar and Heliospheric Observatory-heliumlike 1s2s
  <SUP>3</SUP>S<SUB>1</SUB>-1s2p <SUP>3</SUP>P<SUB>0,2</SUB> transitions
  in the highly ionized species Ne<SUP>8+</SUP>, Na<SUP>9+</SUP>,
  Mg<SUP>10+</SUP>, and Si<SUP>12+</SUP> were observed. The spectral
  lines were emitted by high-temperature solar flare plasmas. In this
  paper, we report on wavelength measurements of the He-like lines
  identified in the recorded spectra. The wavelength uncertainties
  we obtained from the solar measurements are &lt;=20 mÅ(1σ),
  and in one case &lt;=30 mÅ. This is comparable to or better than
  the best determinations so far achieved for these heliumlike 1s2s
  <SUP>3</SUP>S<SUB>1</SUB>-1s2p <SUP>3</SUP>P<SUB>0,2</SUB> transitions
  with instrumentation in the laboratory. For the Na<SUP>9+</SUP>
  <SUP>3</SUP>S<SUB>1</SUB>-<SUP>3</SUP>P<SUB>2</SUB> transition we
  report what is to our knowledge the first wavelength measurement. The
  knowledge of the accurate wavelengths can provide important checks on
  atomic structure calculations.

Title: Wavelengths of Forbidden Transitions Arising from Levels Within
    the Fe<SUP>+19</SUP> 2S<SUP>2</SUP>2P<SUP>3</SUP> Ground Configuration
Authors: Kucera, T. A.; Feldman, U.; Widing, K. G.; Curdt, W.
Bibcode: 2000ApJ...538..424K
Altcode:
  In this paper we report the identification of all remaining unidentified
  forbidden lines arising from transitions within levels of the
  Fe<SUP>+19</SUP> ground configuration. These lines were identified using
  data from the SOHO/SUMER spectrograph and Skylab. Adjusted wavelength
  values are also given for some previously observed lines. Forbidden
  lines that are the result of transitions within levels of the ground
  configuration of a highly ionized astrophysically abundant element
  generally have longer wavelengths than resonance lines emitted by
  the same ion. Many of these forbidden lines are fairly prominent in
  low-density plasmas and traditionally have been used in determining
  properties of high-temperature astrophysical plasmas. The identified
  Fe<SUP>+19</SUP> forbidden lines span the 300-2665 Å wavelength
  range. Since spontaneous decay rates of forbidden transitions arising
  from the same upper level are known quite accurately, these lines can
  be used for calibrating spectrometers over wide wavelength ranges.

Title: The EUV Spectrum of Sunspot Plumes Observed by SUMER on SOHO
Authors: Curdt, W.; Dwivedi, B. N.; Feldman, U.
Bibcode: 2000JApA...21..397C
Altcode:
  No abstract at ADS

Title: The solar helium abundance in the outer corona determined
    from observations with SUMER/SOHO.
Authors: Laming, J. M.; Feldman, U.
Bibcode: 2000BAAS...32Q.815L
Altcode:
  No abstract at ADS

Title: Properties of Solar Polar Coronal Hole Plasmas Observed Above
    the Limb
Authors: Doschek, G. A.; Feldman, U.; Laming, J. M.
Bibcode: 2000SPD....31.1307D
Altcode: 2000BAAS...32Q.846D
  We discuss nonthermal motions, line-of-sight emission measures, and
  relative element abundances as a function of height in the solar polar
  coronal holes. The data pertain to the upper transition region and
  coronal regions of the atmosphere at heights ranging from the solar limb
  to about 150'' above the limb. The spatial resolution is 1\arcsec. The
  physical quantities are derived from spectral line intensities and
  profiles obtained by the Solar Ultraviolet Measurements of Emitted
  Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory
  (SOHO) spacecraft. The line width information is important for wave
  theories of coronal heating. We find that the electron temperature
  in the polar holes increases with height above the limb, that the
  emission measure distribution of plasma at line-of-sight heights less
  than 60'' peaks at a temperature of about 9 x 10<SUP>5</SUP> K, and
  that nonthermal motions sometimes, but not always, increase slightly
  with height above the limb. When observed, these increases level off
  above the limb at about 120\arcsec. We speculate that the line width
  increases with height above the limb may be a manifestation of the
  fast solar wind. Finally, we find that increases of a Mg VI/Ne VI
  line ratio with height above the north polar limb are probably due
  to the increase of electron temperature with height, and not due to
  a relative element abundance variation caused by the first ionization
  potential (FIP) effect. This work was supported by NASA SR&amp;T Grant
  W-19,329 and by the ONR/NRL Research Option, Solar Magnetism and the
  Earth's Environment.

Title: The Solar Helium Abundance in the Outer Corona Determined
    from Observations with SUMER/SOHO
Authors: Laming, J. M.; Feldman, U.
Bibcode: 2000SPD....31.0224L
Altcode:
  At altitudes of about 1.05 solar radii or more, the corona above quiet
  solar regions becomes essentially isothermal. This obviates many of
  the difficulties associated with the inverse problem of determining
  emission measure distributions, and allows for fairly straightforward
  relative element abundance measurements. We present new values for
  the He abundance. The first is based on a reanalysis of the He/O ratio
  studied by previously by Feldman (1998) using data acquired by SUMER. We
  use a revised value of the O abundance, and a more thorough evaluation
  of the atomic physics for He II to derive an He/H abundance ratio of
  0.092, (mass fraction, Y=0.27), with an error of ~ 17% coming mainly
  from the O abundance uncertainty. We demonstrate that this result
  may be affected by gravitational settling of O relative to He. We
  also derive an abundance for He by direct comparison to emission
  lines of the H I Lyman series, with the result He/H =0.083 +/- 10%
  (Y=0.25). Gravitational settling, if present, has the opposite effect
  on this result to that above. Combining the two measurements leads
  to a final result of He/H =0.084+/- 0.008. This work was supported by
  the NRL/ONR Solar Magnetism and the Earth's Environment 6.1 Research
  Option and by NASA Contract W19473. The SUMER project is financially
  supported by DARA, CNES, NASA and the ESA PRODEX program (Swiss
  contribution). SUMER is a part of SOHO, the Solar and Heliospheric
  Observatory, of ESA and NASA.

Title: Newly Discovered Fe XX lines in Flares Observed by SOHO/SUMER
    and Skylab.
Authors: Kucera, T. A.; Feldman, U.; Widing, K. G.; Curdt, W.; Khan,
   J. I.
Bibcode: 2000SPD....31.0264K
Altcode: 2000BAAS...32..822K
  We have used UV spectra from solar flares observed with SOHO/SUMER and
  Skylab to identify all of the all remaining unidentified forbidden
  lines arising from transitions within levels of the Fe XX ground
  configuration. We have also obtained more accurate wavelengths for
  previously observed lines. Forbidden lines resulting from transitions
  within levels of the ground configuration of highly ionized elements
  generally have longer wavelengths than resonance lines emitted by
  the same ions. Many of these forbidden lines are fairly prominent in
  low-density plasmas, and have traditionally been used in determining
  properties of high temperature astrophysical plasmas. The identified Fe
  XX forbidden lines span the 300-2665 Angstroms wavelength range. Since
  spontaneous decay rates of forbidden transitions arising from the same
  upper level are known quite accurately, these lines can be used for
  calibrating spectrometers over wide wavelength ranges.

Title: Observations: The case for unresolved fine structures
Authors: Feldman, U.
Bibcode: 2000SPD....31.1201F
Altcode: 2000BAAS...32..843F
  The solar upper atmosphere (SUA) is defined as the volume above the
  photosphere occupied by plasma with electron temperature above 20,000
  K. Until the Skylab era, only little was known about the morphology
  of the SUA. As a result early models assumed a continuous atmosphere
  in which the temperature increased with height. With the advances in
  spectroscopic measurements it became apparent that most of the radiation
  from the 30,000-500,000 K temperature region could not be explained as
  coming from a continuous chromosphere-corona interface, but rather from
  unrelated plasma structures named unresolved fine structures. Recent
  results obtained by the Extreme Ultraviolet Imaging telescope (EIT),
  the Solar Ultraviolet Measurements of Emitting Radiation (SUMER) and
  the Transition Region and Coronal Explorer (TRACE) support the earlier
  conclusions. An account of observations that were made, over the last
  three decades, to identify the morphology of the 30,000-500,000 K plasma
  structures above quiet and coronal hole regions will be given. This
  work was supported by the NRL/ONR Solar Magnetism and the Earth's
  Environment 6.1 Research Option.

Title: Element Abundances in the Upper Atmospheres of the Sun and
Stars: Update of Observational Results
Authors: Feldman, U.; Laming, J. M.
Bibcode: 2000PhyS...61..222F
Altcode:
  We review observational progress in the determination of element
  abundances in the solar corona, largely due to the new capabilities
  offered by the instrumentation on the SOHO satellite. Many new facets
  to coronal abundance anomalies with respect to the photosphere are
  revealed. This includes new results on the FIP (First Ionization
  Potential) Effect, whereby elements with FIP &lt; 10 eV are enriched
  in the corona by a factor ∼4 with respect to the photosphere, and
  the first evidence for gravitational settling of heavy elements in the
  corona. Advances in EUV and X-ray astronomy instrumentation have also
  yielded the first spectra of stellar coronae of sufficient quality to
  allow element abundance measurements. We survey these new results and
  compare the various stellar cases to the solar corona.

Title: Erratum: Morphology of the Quiet Solar Upper Atmosphere in
    the 4 W 104 &lt; Te &lt; 1.4 W 106 K Temperature Regime
Authors: Feldman, U.; Widing, K. G.; Warren, H. P.
Bibcode: 2000ApJ...529.1145F
Altcode:
  No abstract at ADS

Title: Extreme-Ultraviolet Spectral Line Widths in Quiet-Sun Coronal
    Plasmas at Distances of 1.03&lt;=R<SUB>solar</SUB>&lt;=1.45 along
    the Solar Equatorial Plane
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 2000ApJ...529..599D
Altcode:
  We measure the full width at half-maximum intensity (FWHM)
  of extreme-ultarviolet (EUV) spectral line profiles as a function
  of height in the Sun's equatorial west limb streamer region using
  EUV spectra recorded by the Solar Ultraviolet Measurements of Emitted
  Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory
  (SOHO) spacecraft. The spectra were recorded on 1996 November 21 and
  22, during a special ``roll'' maneuver in which the SUMER slit was
  oriented in the east-west direction. Because the SUMER spectrometer
  is stigmatic along the slit length, the spectra are spatially resolved
  in the east-west direction. The spectra we discuss cover an effective
  distance range outside the west limb from 1.03 to 1.45 R<SUB>solar</SUB>
  the maximum spatial resolution is 1<SUP>''</SUP>. We select a group of
  emission lines for analysis that under the usual ionization equilibrium
  assumption have maximum fractional abundances at temperatures ranging
  from 3×10<SUP>5</SUP> up to 2×10<SUP>6</SUP> K. We determine
  nonthermal motions as a function of position in the streamer region
  from the FWHMs under the assumption that the ion temperature equals the
  electron temperature of the streamer plasma. The electron temperature
  was derived previously by Feldman and coworkers.

Title: Radiometric Calibration of the Vacuum-Ultraviolet Spectrograph
    SUMER on the SOHO Spacecraft with the B Detector
Authors: Schühle, Udo; Curdt, Werner; Hollandt, Jörg; Feldman, Uri;
   Lemaire, Philippe; Wilhelm, Klaus
Bibcode: 2000ApOpt..39..418S
Altcode:
  The Solar Ultraviolet Measurement of Emitted Radiation (SUMER)
  vacuum-ultraviolet spectrograph was calibrated in the laboratory
  before the integration of the instrument on the Solar and Heliospheric
  Observatory (SOHO) spacecraft in 1995. During the scientific operation
  of the SOHO it has been possible to track the radiometric calibration
  of the SUMER spectrograph since March 1996 by a strategy that employs
  various methods to update the calibration status and improve the
  coverage of the spectral calibration curve. The results for the A
  Detector were published previously Appl. Opt. 36, 6416 (1997) . During
  three years of operation in space, the B detector was used for two
  and one-half years. We describe the characteristics of the B detector
  and present results of the tracking and refinement of the spectral
  calibration curves with it. Observations of the spectra of the stars and
  Leonis permit an extrapolation of the calibration curves in the range
  from 125 to 149.0 nm. Using a solar coronal spectrum observed above
  the solar disk, we can extrapolate the calibration curves by measuring
  emission line pairs with well-known intensity ratios. The sensitivity
  ratio of the two photocathode areas can be obtained by registration of
  many emission lines in the entire spectral range on both KBr-coated and
  bare parts of the detector s active surface. The results are found to be
  consistent with the published calibration performed in the laboratory
  in the wavelength range from 53 to 124 nm. We can extrapolate the
  calibration outside this range to 147 nm with a relative uncertainty
  of 30% (1 ) for wavelengths longer than 125 nm and to 46.5 nm with 50%
  uncertainty for the short-wavelength range below 53 nm.

Title: Relationships among the Intensities of LI-, BE-, and NA-like
    Resonance Lines in Collisionally Ionized Astrophysical Plasmas
    (10<SUP>5</SUP>&lt;=T<SUB>e</SUB>&lt;=10<SUP>7</SUP> K)
Authors: Laming, J. M.; Feldman, U.
Bibcode: 1999ApJ...527..461L
Altcode:
  The strongest lines emitted from optically thin collisionally ionized
  astrophysical plasmas are usually those of the Li-, Be-, and Na-like
  sequences. When numerous other weaker lines are also measurable in the
  spectrum, the derivation of relative element abundances is reasonably
  straightforward. However, for many sources only the strongest lines
  will be observed, so here we explore under what conditions it may be
  possible to determine relative element abundances in this case. We find
  that several temperature regions exist in which the ratios of these
  strong lines can be fairly insensitive to temperature. We discuss
  applications to solar/stellar coronae, the interstellar medium, and
  SN 1987A. Additionally under certain conditions in the solar corona
  ratios of Li-like line intensities to those of He II are found to
  allow relatively straightforward determinations of the He abundance.

Title: SOHO EIT Observations of Coronal Holes
Authors: Norton, H.; Newmark, J. S.; Feldman, U.
Bibcode: 1999ESASP.446..509N
Altcode: 1999soho....8..509N
  We present a study of coronal holes (not including the polar holes)
  using observations from SOHO EIT during 1996 and 1997. EIT obtains
  daily full disk observations of the Sun at spectral emission lines from
  FeIX,X (171 A), FeXII (195 A), FeXV (284 A), and HeII (304 A). Previous
  studies (mainly He I 10830 A and ground based magnetograms) have
  demonstrated the role that bipolar magnetic regions play in their
  evolution as well as rotation rates for recurrent coronal holes. We
  further the correlation between coronal holes and bipolar fields by
  presenting definitive symbiotic relationships between coronal holes
  and active regions. Comparisons of EUV observations and magnetograms
  plus potential field extrapolations are shown.

Title: Molecular Hydrogen Lines Observed with SUMER in the Spectrum
    of a Sunspot
Authors: Schüehle, U.; Brown, C. M.; Curdt, W.; Feldman, U.
Bibcode: 1999ESASP.446..617S
Altcode: 1999soho....8..617S
  No abstract at ADS

Title: Measuring the Solar He Abundance in the Outer Corona with
    SUMER.
Authors: Laming, J. Martin; Feldman, Uri
Bibcode: 1999ESASP.446..405L
Altcode: 1999soho....8..405L
  We outline new spectroscopic methods for measuring relative element
  abundances in the solar corona, with special emphasis on the He
  abundance. At altitudes of about 1.05 solar radius or more, the solar
  corona becomes essentially isothermal. This is not unexpected in view
  of the quiescent nature of the plasma at these heights, and the long
  radiative cooling times at densities below log n<SUB>e</SUB> = 8.0. The
  isothermal nature of the plasma obviates many of the difficulties
  associated with the inverse problem of determining an emission
  measure distribution. This is particularly true in the cases of Li-
  and Na-like ions whose ionization balance fractions have long tails
  extending to high temperatures, making the inversion problem especially
  difficult. We present new calculations of intensity ratios as a function
  of temperature that can be used to determine element abundance ratios in
  the solar corona. The He abundance may be determined from He II lines
  relative to, for example, O VI, and we present an extensive analysis
  of the He II spectrum. In order to predict accurate line intensities,
  large close-coupling calculations are required. One special feature
  is that in order to get the excitation cross sections correct, impact
  ionization channels also need to be included in the calculation,
  for the temperatures relevant to the solar corona. The model ion also
  needs to include the many highly excited levels from which the Balmer
  series originates.

Title: Morphology of the Quiet Solar Upper Atmosphere in the
    4×10<SUP>4</SUP>&lt;T<SUB>e</SUB>&lt;1.4×10<SUP>6</SUP> K
    Temperature Regime
Authors: Feldman, U.; Widing, K. G.; Warren, H. P.
Bibcode: 1999ApJ...522.1133F
Altcode:
  Studies on the morphology of the solar upper atmosphere began over
  three decades ago. Early models assumed that the temperature structure
  of the solar upper atmosphere was continuous with a thin transition
  region connecting the chromosphere with the corona. Over the years
  it became apparent that the original depiction of the solar upper
  atmosphere was too simplistic. In this paper we present a morphological
  study of the solar upper atmosphere over a wide range of temperatures
  (4×10<SUP>4</SUP>&lt;=T<SUB>e</SUB>&lt;=1.4×10<SUP>6</SUP> K)
  using high-resolution images (1<SUP>''</SUP>-2<SUP>''</SUP>)
  taken by TRACE, the SUMER spectrometer on SOHO, and the NRL
  spectroheliograph on Skylab. The images clearly show that the
  4×10<SUP>4</SUP>&lt;=T<SUB>e</SUB>&lt;=1.4×10<SUP>6</SUP>
  K temperature domain of the solar upper atmosphere consists
  of a hierarchy of isothermal loop structures. While at the
  T<SUB>e</SUB>&lt;8×10<SUP>5</SUP> K temperature regime the looplike
  structures are more abundant along the chromospheric network, at higher
  temperatures (T<SUB>e</SUB>&gt;9×10<SUP>5</SUP> K) no association
  between them and the chromospheric network is apparent. The hottest
  (T<SUB>e</SUB>~1.4×10<SUP>6</SUP> K), which are also the longest among
  the quiet-Sun loop structures, form a canopy over the lower temperature
  loop structures. We discuss in the paper possible relationships between
  the morphology of the solar upper atmosphere, its elemental abundance,
  and ideas regarding the origin of the slow-speed solar wind.

Title: A Comparison of Measurements of Solar Extreme-Ultraviolet
    Spectral Line Intensities Emitted by C, N, O, and S Ions with
    Theoretical Calculations
Authors: Doschek, E. E.; Laming, J. M.; Doschek, G. A.; Feldman, U.;
   Wilhelm, K.
Bibcode: 1999ApJ...518..909D
Altcode:
  Atomic data for ionized atoms are important for many astrophysical
  applications. The launch of the Solar Ultraviolet Measurements of
  Emitted Radiation (SUMER) extreme-ultraviolet (EUV) spectrometer aboard
  the Solar and Heliospheric Observatory (SOHO) allows us to test the
  accuracy of certain computed relative excitation rate coefficients
  and transition probabilities for a number of important astrophysical
  ions. We use spectral line intensity ratios derived from SUMER spectra
  to compare these quantities with the best available theoretical
  calculations for transitions within the ions C II, N III, N IV, O III,
  O IV, O V, S III, S IV, and S V. The results of this work are important
  for many current and upcoming NASA astrophysics missions. In addition
  to the published atomic data, we calculate some new atomic data using
  the Hebrew University Lawrence Livermore Atomic Code (HULLAC). Our
  comparison of measured intensity ratios with theoretical predictions
  reveals significant discrepancies between the predicted and measured
  intensity ratios for several ions, particularly for S III, S IV, and
  S V. S III and S IV produce strong line emission in the Io torus. We
  discuss the methods we used to ensure that our ratios are accurate,
  the possible effects of Lyman continuum absorption on our data, and the
  ramifications of ignoring dielectronic capture resonances in certain
  transitions as a possible explanation for some of the discrepancies.

Title: The Off-Limb Behavior of the First Ionization Potential Effect
    in T&gt;5×10<SUP>5</SUP> K Solar Plasmas
Authors: Laming, J. M.; Feldman, U.; Drake, J. J.; Lemaire, P.
Bibcode: 1999ApJ...518..926L
Altcode:
  We investigate the behavior of the solar first ionization potential
  (FIP) effect (the abundance enhancement of elements with first
  ionization potential of less than 10 eV in the corona with respect
  to photospheric values) with height above the limb in a region of
  diffuse quiet corona observed by the SUMER instrument on SOHO, with
  emphasis on so-called upper transition region lines. Previous disk
  observations have shown different abundance patterns in emission
  from lines at temperatures above and below ~8×10<SUP>5</SUP> K,
  with an FIP effect clearly visible at the higher temperatures and
  less so at the lower temperatures. Our initial aim is to determine
  whether such a difference is also visible in off-limb observations. We
  find a low-FIP element enhancement of a factor of 3-4 indicated in
  all line ratios. The Mg VII 868.11/Ne VII 895.17 ratio is also seen
  to decrease toward a photospheric value when tracked down from the
  corona to the limb. This is markedly different from the behavior of
  higher temperature line ratios and may be related to the differing
  heating and mass supply mechanisms for plasmas at temperatures above
  and below ~8×10<SUP>5</SUP> K. <P />An additional unexpected feature
  of our observations is that in low-FIP/high-FIP line ratios formed
  at temperatures close to the freeze-in temperature of the fast solar
  wind (~10<SUP>6</SUP> K), there is also a small diminution of the FIP
  enhancement at the highest altitudes observed in this study. We discuss
  the possible relevance of this to the origin of the fast solar wind.

Title: Properties of Quiet-Sun Coronal Plasmas at Distances of
    1.03&lt;=R<SUB>solar</SUB>&lt;=1.50 along the Solar Equatorial Plane
Authors: Feldman, U.; Doschek, G. A.; Schühle, U.; Wilhelm, K.
Bibcode: 1999ApJ...518..500F
Altcode:
  We determine the physical properties, i.e., electron temperature,
  density, line-of-sight emission measure, and element-abundance variation
  with height, in the Sun's equatorial west limb streamer region from
  extreme-ultraviolet (EUV) spectra recorded by the Solar Ultraviolet
  Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and
  Heliospheric Observatory (SOHO) spacecraft. The spectra were recorded
  on 1996 November 21-22 during a special ``roll'' maneuver in which
  the SUMER slit was oriented in the east-west direction. Because the
  SUMER spectrometer is stigmatic along the slit length, the spectra are
  spatially resolved in the east-west direction. The spectra we discuss
  cover an effective distance range outside the west limb from 1.03 to
  1.50 solar radii (R<SUB>solar</SUB>) the maximum spatial resolution is
  1<SUP>''</SUP>. We select a group of emission lines for analysis that
  under the usual ionization equilibrium assumption span the temperature
  range from 3×10<SUP>5</SUP> up to 2×10<SUP>6</SUP> K. However,
  we note that above the limb a major fraction of a line intensity may
  arise at a temperature that is far from the temperature of maximum
  emitting efficiency in ionization equilibrium. In this paper we assume
  ionization equilibrium in deriving plasma parameters. Readers can redo
  our analysis without this assumption if desired, because the line
  intensities we present in this paper are simply the measured photon
  production rates in the lines. Assuming ionization equilibrium, we
  determine the electron temperature, electron density, line-of-sight
  emission measure, and abundance variation with height above the limb
  from the line intensities and line intensity ratios. The spatial
  resolution has allowed us to detect an apparent element-abundance
  variation as a function of height above the west limb that is strong
  evidence for gravitational settling of ``heavy'' elements.

Title: Properties of the Quiet Sun Corona in the West Limb Equatorial
    Streamer Region
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1999AAS...19410005D
Altcode: 1999BAAS...31..997D
  We determine physical properties, such as electron temperature and
  density, in the Sun's west limb equatorial streamer region from spectra
  recorded by the SUMER spectrometer on SOHO. The spectra were recorded
  on 1996 November 21-22 during a special roll maneuver in which the
  stigmatic SUMER slit was oriented in the east-west direction. Results
  are obtained as a function of height from close to the limb out to about
  1.5 solar radii. We find that the streamer region is well-represented
  by an isothermal plasma at 1.3 x 10(6) K between 1.03 and 1.5 solar
  radii. The electron density falls from 1.8 x 10(8) cm(-3) near the limb
  to about 1.6 x 10(7) cm(-3) at 1.3 solar radii. For ions with similar
  atomic weights, we find that the typical quiet Sun FIP enhancement of
  about a factor of 4 does not vary with height above the limb. Perhaps
  of most interest, we find strong evidence for gravitational settling
  of Fe relative to the lighter elements such as Ne, Mg, and Si. This
  adds a complicating factor in determining physical parameters in
  the corona. The above results are discussed in detail in Feldman et
  al. 1999, ApJ, 518, June 10 issue. We also measure the full width at
  half maximum intensity of spectral line profiles for lines of several
  upper transition region and coronal ions formed in the streamer. If we
  adopt our measured electron temperature and assume that the electron
  and ion temperatures are equal, we obtain typical nonthermal speeds of
  about 33 km s(-1) and in addition find that the speed does not increase
  with height between about 1.03 and 1.3 solar radii. The line profile
  results are discussed in detail in Doschek &amp; Feldman 1999, ApJ,
  submitted. This work was funded by the 6.1 NRL/ONR Solar Magnetism
  and the Earth's Environment Research Option.

Title: New Identifications of Si VIII and S X Lines in the Solar
    Coronal Spectrum Measured by SOHO/SUMER
Authors: Kink, I.; Engström, L.; Feldman, U.
Bibcode: 1999ApJ...512..496K
Altcode:
  This paper reports the identification of 14 lines
  in the solar coronal spectrum as high-excitation
  2s<SUP>2</SUP>2p<SUP>2</SUP>3s-2s<SUP>2</SUP>2p<SUP>2</SUP>3p
  and 2s<SUP>2</SUP>2p<SUP>2</SUP>3p-2s<SUP>2</SUP>2p<SUP>2</SUP>3d
  transitions in Si VIII and S X (N I isoelectronic sequence). The
  analysis combines solar spectra, recorded by the SUMER (Solar
  Ultraviolet Measurement of Emitted Radiation) instrument on board the
  Solar and Heliospheric Observatory (SOHO) satellite, with laboratory
  data obtained with the beam-foil technique. Theoretical gA values
  and branching ratios for the observed lines, based on semiempirical
  calculations, are also presented. Intensity ratios between the newly
  identified high-excitation transitions and known forbidden transitions
  within the 2s<SUP>2</SUP>2p<SUP>3</SUP> ground configuration can be
  used in determining coronal plasma temperatures in the 70-120 eV range.

Title: On the Ability of an Extreme-Ultraviolet Multilayer
    Normal-Incidence Telescope to Provide Temperature Information for
    Solar Plasmas
Authors: Feldman, U.; Laming, J. M.; Doschek, G. A.; Warren, H. P.;
   Golub, L.
Bibcode: 1999ApJ...511L..61F
Altcode:
  In recent years, multilayer-coated optics have been used in solar-soft
  X-ray and extreme-ultraviolet telescopes to record high-resolution,
  full Sun images. The multilayer coatings reflect efficiently over rather
  narrow wavelength bands that are selected to contain spectral emission
  lines considered to have plasma diagnostic importance for determining
  approximate electron temperatures. The purpose of this Letter is to
  discuss the effect of continuum emission on the response of multilayer
  passbands and the effect of this response on temperature determinations
  in the 4×10<SUP>6</SUP>-2×10<SUP>7</SUP> K range. Significant effects
  are largely confined to continuum emission from flare plasma. The
  flare free-free continuum in the EUV range is nearly temperature and
  wavelength insensitive and dominates the emission in passbands that
  are centered on quiet- to active-Sun coronal lines emitted by ions
  such as Fe IX-Fe XV.

Title: On the Unresolved Fine Structures of the Solar
    Atmosphere. III. Elemental Abundances Consideration
Authors: Feldman, Uri
Bibcode: 1998ApJ...507..974F
Altcode:
  Results from high-quality solar upper atmosphere observations in the
  10<SUP>4</SUP>-10<SUP>6</SUP> K range contradict predictions made
  by models that assume that a single class of structures stretching
  throughout the entire temperature domain, from the cold chromosphere
  to the hot corona, is responsible for all the radiation we see. As a
  result, I proposed that new types of structures--the unresolved fine
  structures (UFSs)--are responsible for most of the detected emission in
  the 3 × 10<SUP>6</SUP> &lt;= T<SUB>e</SUB> &lt;= 8 × 10<SUP>6</SUP>
  K. In a recent paper Wikstøl, Judge, &amp; Hansteen challenged the
  presence of UFSs by claiming that the interpretation of the data
  in terms of UFSs is not unique and is likely to be incorrect in the
  presence of plasmas with unresolved dynamics. Further, they claim that
  most or all of the evidence that was brought in support of the UFSs is
  amenable to a different, equally reasonable interpretation in which the
  transition region emission is at all times formed in the time-varying
  thermal interface between the corona and chromosphere. In this paper I
  discuss some of the assertions made by Wikstøl and collaborators. I
  also bring evidence from elemental abundance studies that would
  be difficult to support with the Wikstøl model. In contrast, the
  existence of UFSs is not contradicted by any of the new observations.

Title: The Electron Pressure in the Solar Lower Transition Region
    Determined from O V and Si III Density-sensitive Line Ratios
Authors: Doschek, G. A.; Feldman, U.; Laming, J. M.; Warren, H. P.;
   Schüle, U.; Wilhelm, K.
Bibcode: 1998ApJ...507..991D
Altcode:
  We determine the electron density at the temperatures of formation
  of O<SUP>+4</SUP> and Si<SUP>+2</SUP> ions, which are about 2.5 ×
  10<SUP>5</SUP> and 3.2 × 10<SUP>4</SUP> K in ionization equilibrium,
  respectively. These temperatures occur in the lower transition
  region of the Sun's atmosphere and allow a test of the often invoked
  assumption of constant pressure in quiet-Sun models. The O<SUP>+4</SUP>
  density is determined from a density-sensitive spectroscopic O V
  line ratio involving 2s2p<SUP>3</SUP>P-2p<SUP>2</SUP><SUP>3</SUP>P
  transitions that fall near 760 Å. The Si<SUP>+2</SUP> density is
  determined from a density-sensitive Si III line ratio within the
  3s3p<SUP>3</SUP>P-3p<SUP>2</SUP><SUP>3</SUP>P multiplet near 1300
  Å. There are few available line ratio techniques for determining
  the density and hence electron pressure in the quiet-Sun and coronal
  hole transition regions using lines emitted by the same ion, and
  determining these quantities is the principal motivation for this
  work. The spectra used in our analysis were obtained from the Solar
  Ultraviolet Measurements of Emitted Radiation (SUMER) experiment on the
  Solar and Heliospheric Observatory (SOHO). We determine the electron
  density and pressure in typical quiet-Sun/coronal hole regions, and
  densities in active region brightenings and in an explosive event. Our
  O V and Si III results indicate that constant pressure is valid or
  nearly valid in quiet-Sun lower transition regions, although there
  are complications arising from the weakness of a key Si III line in
  the quiet-Sun disk spectra. We also discuss our results in light of
  other density measurements and theories regarding the structure and
  heating of the transition region.

Title: Coronal Composition above the Solar Equator and the North Pole
    as Determined from Spectra Acquired by the SUMER Instrument on SOHO
Authors: Feldman, U.; Schühle, U.; Widing, K. G.; Laming, J. M.
Bibcode: 1998ApJ...505..999F
Altcode:
  Using spectra obtained by the SUMER instrument on the Solar and
  Heliospheric Observatory (SOHO) we have determined the composition of
  the bulk of the coronal plasma in the vicinity of the solar surface
  over a polar coronal hole and an equatorial region. Our measurements
  show that although low first ionization potential (FIP) elements are
  enriched by about a factor of 4 in the corona above the quiet equatorial
  region, little or no enrichment exists above the north polar coronal
  hole. These observations are in good agreement with the Ulysses in
  situ observations in both fast speed and slow speed winds.

Title: The Si/Ne Abundance Ratio in Polar Coronal Hole and Quiet-Sun
    Coronal Regions
Authors: Doschek, G. A.; Laming, J. M.; Feldman, U.; Wilhelm, K.;
   Lemaire, P.; Schühle, U.; Hassler, D. M.
Bibcode: 1998ApJ...504..573D
Altcode:
  Using spectra obtained from the Solar Ultraviolet Measurements
  of Emitted Radiation (SUMER) spectrometer flown on the Solar and
  Heliospheric Observatory (SOHO) spacecraft, we determine the Si/Ne
  abundance ratio in diffuse, interplume polar coronal hole regions,
  as well as the ratio relative to quiet-Sun coronal regions. Ne has
  the second highest first ionization potential (FIP) of solar abundant
  elements, and Si is a low-FIP element. Thus the Si/Ne ratio is a
  sensitive indicator of abundance variations due to the FIP effect. We
  develop new spectroscopic diagnostics for the determination of the
  Si/Ne abundance ratio. Assuming ionization equilibrium, we find that
  the Si/Ne abundance ratio in interplume polar coronal hole regions is
  about a factor of 2 greater than the photospheric value and is close
  to or the same as in coronal quiet-Sun regions. This result pertains
  to the electron temperature range 5-8 × 10<SUP>5</SUP> K. However,
  the combined atomic physics, instrumental, and statistical uncertainty
  in this result is about a factor of 2, and therefore this observed
  enhancement is consistent with no enhancement in the polar hole
  abundances. Nevertheless, our results follow the same trend, i.e., a
  greater than photospheric abundance ratio of low-FIP elements in the
  corona relative to high-FIP elements, as found from other abundance
  measurements in the corona that involve different atomic physics and
  different instruments. Therefore we feel that our results reflect
  an actual abundance enhancement, despite being within an uncertainty
  level bar that encompasses photospheric abundances. We also examine
  the Ne/Mg abundance ratio over a 24.5 hr observation and find no
  significant abundance variations. (Mg is a low-FIP element.) Thus,
  no large transient abundance variations appear to occur on timescales
  shorter than about a day, although this result is based on only
  one observation. From lines of Mg VII, Mg VIII, Mg IX, and Mg X we
  find that the electron temperature along the line of sight increases
  with height above the limb over the polar coronal holes, as has been
  previously reported. We determine the emission measure distribution as
  a function of height from Mg VII, Mg VIII, and Mg X lines. We determine
  average temperatures along the line of sight over the polar holes from
  Ne VIII/Ne VII, Mg VIII/Mg VII, and Si VIII/Si VII line ratios. We also
  discuss the temperature properties of the coronal hole and quiet-Sun
  regions using forbidden lines of Fe X and Fe XI. We comment on the
  possibility that ionization equilibrium is not valid in polar coronal
  hole regions, a possible scenario in light of recent observations that
  show outflows in coronal holes beginning at about the temperature of
  formation of Ne VIII.

Title: High-Temperature Lines in SUMER Spectra Recorded Above a
    Bright Solar Active Region
Authors: Feldman, U.; Curdt, W.; Doschek, G. A.; Schühle, U.; Wilhelm,
   K.; Lemaire, P.
Bibcode: 1998ApJ...503..467F
Altcode:
  We identify spectral lines emitted by solar abundant elements due
  primarily to transitions within the 2s<SUP>2</SUP>2p<SUP>k</SUP> and
  3s<SUP>2</SUP>3p<SUP>k</SUP> (where k = 1, 5) ground configurations
  of ions that are formed in ionization equilibrium between 2 ×
  10<SUP>6</SUP> and 8 × 10<SUP>6</SUP> K. The transitions were
  identified in spectra of a bright active region recorded 1997
  September 6, by the Solar Ultraviolet Measurements of Emitted Radiation
  Spectrometer (SUMER) flown on the Solar and Heliospheric Observatory
  (SOHO). Some of these lines provide useful plasma diagnostic tools
  for measuring the physical conditions in the solar corona.

Title: A Compact Spectral Range and Matching Extreme-Ultraviolet
    Spectrometer for the Simultaneous Study of 1 × 10<SUP>4</SUP>-2 ×
    10<SUP>7</SUP> K Solar Plasmas
Authors: Feldman, U.; Brown, C. M.; Laming, J. M.; Seely, J. F.;
   Doschek, G. A.
Bibcode: 1998ApJ...502..997F
Altcode:
  An EUV spectral range of less than 100 Å in first order has been found
  that includes sufficient spectral lines and critical combinations
  of lines in first and second order to permit dynamic and diagnostic
  investigations of the solar atmosphere with a relatively simple
  spectrometer. An optical design of such a spectrometer, based on the
  performance of the Solar Ultraviolet Measurements of Emitted Radiation
  (SUMER) spectrometer on the Solar and Heliospheric Observatory
  (SOHO) spacecraft, and sample stigmatic solar spectra for the range
  1334-1428 Å from SUMER are presented to illustrate the utility of
  this range. Lines of almost all abundant solar elements except H and He
  are present within this wavelength band in first or second order. The
  lines cover the large temperature range from 1 × 10<SUP>4</SUP> K
  (chromosphere) to 2 × 10<SUP>7</SUP> K (flares). The spectrometer's
  resolution is sufficiently high to permit measuring line profiles and
  wavelength shifts which allows plasma dynamical studies of individual
  solar structures from the chromosphere up into the corona. In addition,
  electron density diagnostics are available within the spectral range
  that cover the temperature range from 8 × 10<SUP>4</SUP> to 1 ×
  10<SUP>6</SUP> K and an electron density range from 10<SUP>8</SUP>
  to 10<SUP>13</SUP> cm<SUP>-3</SUP>.

Title: FIP Effect in the Solar Upper Atmosphere: Spectroscopic Results
Authors: Feldman, U.
Bibcode: 1998SSRv...85..227F
Altcode:
  Recent spectroscopic measurements from instruments on the Solar and
  Heliospheric Observatory (SOHO) find that the coronal composition above
  a polar coronal hole is nearly photospheric. However, similar SOHO
  observations show that in coronal plasmas above quiet equatorial regions
  low-FIP elements are enhanced by a factor of ≈ 4. In addition, the
  process of elemental settling in coronal plasmas high above the solar
  surface was shown to exist. Measurements by the Ulysses spacecraft,
  which are based on non-spectroscopic particle counting techniques,
  show that, with the exception of He, the elemental composition of
  the fast speed solar wind is similar to within a factor of 1.5 to
  the composition of the photosphere. In contrast, similar measurements
  in the slow speed wind show that elements with low first ionization
  potential (FIP &lt; 10 eV) are enhanced, relative to the photosphere,
  by a factor of 4-5. By combining the SOHO and Ulysses results, ideas
  related to the origin of the slow speed solar wind are presented. Using
  spectroscopic measurements by the Solar Ultraviolet Measurement of
  Emitted Radiation (SUMER) instrument on SOHO the photospheric abundance
  of He was determined as 8.5 ± 1.3% (Y = 0.248).

Title: The Neon-to-Magnesium Abundance Ratio as a Tracer of the
    Source Region of Prominence Material
Authors: Spicer, D. S.; Feldman, U.; Widing, K. G.; Rilee, M.
Bibcode: 1998ApJ...494..450S
Altcode:
  A survey of all 1000 spectroheliograms in the Skylab spectroheliograph
  plate collection was made to identify prominences above the limb and
  prominence-like features. The Ne/Mg abundance ratios obtained from
  the measurements have been determined from relative intensities of Ne
  VI and Mg VI lines at 400 Å of seven prominences and prominence-like
  features observed above the solar limb. The derived abundance ratios
  have values intermediate between the photosphere and corona, while none
  are as low as the ratio of 0.7 expected in the corona, which implies
  that the material found in prominences is photospheric in origin. The
  significance of these results for the formation of prominences is
  briefly discussed.

Title: The Magnetic Reconnection Explorer (MAGREX)
Authors: Schühle, U.; Antionchos, S. K.; Barbee, T. W., Jr.; Bixler,
   J. V.; Brown, C. M.; Carter, P. H., II; Curdt, W.; Davila, J. M.;
   Doschek, G.; Feldman, U.; Goldstein, W. H.; Kordas, J.; Lemaire, P.;
   Mariska, J. T.; Marsch, E.; Moses, J. D.; Seely, J. F.; Wilhelm, K.;
   Woods, T. N.
Bibcode: 1998ESASP.417..289S
Altcode: 1998cesh.conf..289S
  No abstract at ADS

Title: Using the YOHKOH BCS to Check Element Abundances and Ionization
    Fractions
Authors: Phillips, K. J. H.; Feldman, U.
Bibcode: 1998ASSL..229..341P
Altcode: 1998opaf.conf..341P
  No abstract at ADS

Title: FIP Effect in the Solar Upper Atmosphere: Spectroscopic Results
Authors: Feldman, U.
Bibcode: 1998sce..conf..227F
Altcode:
  No abstract at ADS

Title: The solar disk spectrum between 660 and 1175 Anstroms (first
    order) obtained by SUMER on SOHO
Authors: Curdt, W.; Feldman, U.; Laming, J. M.; Wilhelm, K.; Schuehle,
   U.; Lemaire, P.
Bibcode: 1997A&AS..126..281C
Altcode:
  SUMER -- Solar Ultraviolet Measurements of Emitted Radiation -- onboard
  of SOHO -- Solar and Heliospheric Observatory -- obtained its first
  spectrum on January 25, 1996 near the north polar limb. The range
  from 660 Angstroms to 1175 Angstroms which has never before been
  observed with such a good spectral resolution contains a wealth of
  spectroscopic details. Identification of about 400 lines in this
  spectral range is given. We list the wavelengths of identified
  transitions and provide their absolute peak intensities. General
  spectral features of the most abundant elements H, He, C, N, O,
  Ne, Mg, Si, S, Ar, and Fe are described. In this spectral range
  many density- and temperature-sensitive line pairs are found. It is
  shown in examples how they can be used as diagnostic tools. Table
  1 and Fig.nearlimb are also available in digital form at the CDS
  via anonymous ftp to cdsarc.u-strasbg. fr (130.79.128.5) or via
  http://cdsweb.u-strasbg.fr/Abstract.html

Title: The Off-Limb Behaviour of the Solar Transition Region FIP
    Effect
Authors: Laming, J. M.; Feldman, U.; Drake, J. J.; Schuhle, U.; Curdt,
   W.; Wilhelm, K.; Lemaire, P.
Bibcode: 1997AAS...191.7301L
Altcode: 1997BAAS...29.1320L
  We investigate the behaviour of the solar FIP effect (the abundance
  enhancement of elements with first ionization potential &lt; 10 eV by
  factor of 3-4 in the corona with respect to photospheric values) with
  height above the limb in a region of diffuse quiet corona observed
  by the SUMER instrument on SOHO. Line ratios formed at log T &gt;
  5.8 show coronal abundances for all heights. Line ratios formed at
  lower temperatures are consistent with coronal abundances well off the
  limb, with the apparent magnitude of the FIP enhancement decreasing
  by a factor of 1.5 - 2 as one approaches the solar limb. Thus our
  observations support a spatial variation in the quiet sun transition
  region FIP effect inferred previously from studies of the full disk
  solar spectrum (Laming, Drake, &amp; Widing 1995, ApJ, 443, 416
  and references therein). This result adds to the probability that
  emission from the solar disk transition region and corona originates
  from qualitatively different structures for values of log T {&lt;atop
  &gt;} 5.8, having different FIP effects.

Title: A Coronal Spectrum in the 500--1610 Angstrom Wavelength Range
    Recorded at a Height of 21,000 Kilometers above the West Solar Limb
    by the SUMER Instrument on Solar and Heliospheric Observatory
Authors: Feldman, U.; Behring, W. E.; Curdt, W.; Schühle, U.; Wilhelm,
   K.; Lemaire, P.; Moran, T. M.
Bibcode: 1997ApJS..113..195F
Altcode:
  We present a solar coronal spectrum recorded by the extreme UV
  spectrometer SUMER on the Solar and Heliospheric Observatory. The
  spectrum was taken between 21:28 UT on 1996 June 25 and 02:47 UT on
  1996 June 26, at a height of 21,000 km above the west equatorial limb
  with the slit oriented in the north-south direction. At the time of
  the observations the Sun was rather quiet, and the west limb appeared
  ``devoid of any activity.'' The spectrum, which covers the 500-1610
  Å wavelength range, originates from plasmas with temperatures
  ranging between 1.5 × 10<SUP>4</SUP> and 1.5 × 10<SUP>6</SUP>
  K. Identification of lines originating from different temperature
  regimes is facilitated by the appearance of their intensity along the
  300" long slit. <P />Well over 800 lines have been found, many of which
  were not previously observed. We present the entire spectrum and discuss
  line identifications. A table of the wavelengths of lines observed,
  with their identifications and peak intensities, is provided. Although
  we have identified lines previously detected in laboratory plasmas and
  a number of new lines not previously observed, over 40% of the SUMER
  lines remain unidentified. Among the newly detected lines, some have
  a potential as plasma density diagnostics.

Title: Laboratory Identification of Temperature Diagnostic Si VII and
    S IX Lines Present in the Solar Coronal Spectra Measured by SUMER/SOHO
Authors: Kink, I.; Jupén, C.; Engström, L.; Feldman, U.; Laming,
   J. M.; Schühle, U.
Bibcode: 1997ApJ...487..956K
Altcode:
  The solar coronal spectrum between 500 and 1610 Å and at a
  height of 21,000 km above the west equatorial limb has recently
  been recorded by the SUMER instrument on SOHO. Using laboratory
  spectra obtained with the beam-foil technique, we report
  the identification of 32 lines observed in this spectrum as
  2s<SUP>2</SUP>2p<SUP>3</SUP>3s-2s<SUP>2</SUP>2p<SUP>3</SUP>3p and
  2s<SUP>2</SUP>2p<SUP>3</SUP>3p-2s<SUP>2</SUP>2p<SUP>3</SUP>3d
  transitions in Si VII and S IX. Theoretical gA-values
  and branching ratios for the observed lines, obtained from
  semiempirical configuration interaction calculations, are also
  presented. Intensity ratios between the 2s<SUP>2</SUP>2p<SUP>4</SUP>
  <SUP>3</SUP>P<SUB>1</SUB>-2s<SUP>2</SUP>2p<SUP>4</SUP>
  <SUP>1</SUP>S<SUB>0</SUB> forbidden transition and transition from
  the newly identified high-excitation lines that appear in the same
  wavelength range are temperature sensitive. Calculations of the
  intensity ratios between the forbidden line and the high-excitation
  lines for three temperatures are presented. A comparison between the
  calculations and some of the SUMER observations is provided.

Title: Radiometric calibration of SUMER: refinement of the laboratory
    results under operational conditions on SOHO
Authors: Wilhelm, Klaus; Lemaire, Philippe; Feldman, Uri; Hollandt,
   Jörg; Schühle, Udo; Curdt, Werner
Bibcode: 1997ApOpt..36.6416W
Altcode:
  No abstract at ADS

Title: Electron Density Diagnostics for the Solar Upper Atmosphere
    from Spectra Obtained by SUMER/SOHO
Authors: Laming, J. M.; Feldman, U.; Schühle, U.; Lemaire, P.; Curdt,
   W.; Wilhelm, K.
Bibcode: 1997ApJ...485..911L
Altcode:
  We evaluate the electron density in various solar regions above the
  limb observed by the Solar Ultraviolet Measurement of Emitted Radiation
  (SUMER) instrument on SOHO. We find in general good agreement among
  line ratios from Be-, B-, N-, and Mg-like ions, giving densities of
  order 10<SUP>8</SUP> cm<SUP>-3</SUP>.

Title: Turbulent Velocities and Ion Temperatures in the Solar Corona
    Obtained from SUMER Line Widths
Authors: Seely, J. F.; Feldman, U.; Schühle, U.; Wilhelm, K.; Curdt,
   W.; Lemaire, P.
Bibcode: 1997ApJ...484L..87S
Altcode:
  Turbulent plasma velocities and ion temperatures were determined from
  the line widths recorded by the Solar Ultraviolet Measurements of
  Emitted Radiation instrument on the Solar and Heliospheric Observatory
  spacecraft. From the widths of the lines of five light elements
  (Ne, Na, Mg, Si, and S) and a heavy element (Fe), it was possible
  to determine the contributions of turbulent plasma motion and ion
  thermal motion to the line widths. The results indicated that the
  turbulent velocity was approximately 22 km s<SUP>-1</SUP> at 30"
  above the limb and decreased to less than 10 km s<SUP>-1</SUP> at 109"
  and 209" above the limb. At 30" above the limb, the ion temperatures
  of the hotter lines were comparable to the electron temperatures for
  ionization equilibrium. The ion temperatures of the cooler lines were
  higher than the ionization equilibrium temperatures; at 109" and 209"
  above the limb, the ion temperatures were at least a factor of 2.5
  higher than the ionization equilibrium temperatures.

Title: VizieR Online Data Catalog: Solar disk spectrum (660-1175A)
    (Curdt+ 1997)
Authors: Curdt, W.; Feldman, U.; Laming, J. M.; Wilhelm, K.; Schuehle,
   U.; Lemaire, P.
Bibcode: 1997yCat..41260281C
Altcode:
  The near-limb quiet-Sun spectrum recorded on January 25, 1996
  near the solar North pole is presented in tabular form and in
  graphical form. Table 1 - the line list - lists all lines found
  in the spectrum providing absolute peak intensities, measured and
  literature wavelengths, identification, and classification of the
  transition. Fig. 4 is a display the composite spectrum. The most
  prominent lines are labelled. In this figure intensities are given in
  instrumental units and logarithmic scale. (1 data file).

Title: Yohkoh Observations as a Means of Checking S, Ca, and Fe
    Coronal Abundances and He-like Ionization Fractions
Authors: Phillips, K. J. H.; Feldman, U.
Bibcode: 1997ApJ...477..502P
Altcode:
  Electron temperatures are derived from X-ray spectra observed by
  the Bragg crystal spectrometer on board the Yohkoh satellite during
  long-duration solar flares, and it is found that in the late stages
  of such events the emitting plasma is nearly isothermal. This fact
  enables us to examine the accuracy of the fractional abundances of
  He-like S, Ca, and Fe ions, as well as the ratios of coronal element
  abundances. Using currently accepted values for ionization fractions
  and our own values of element abundances, we find that adjustments of
  50% or less are needed.

Title: The Occurrence Rate of Soft X-Ray Flares as a Function of
    Solar Activity
Authors: Feldman, U.; Doschek, G. A.; Klimchuk, J. A.
Bibcode: 1997ApJ...474..511F
Altcode:
  In this paper we investigate the occurrence rate of soft X-ray
  solar flares observed by the Geostationary Operational Environmental
  Satellites (GOES). The analysis includes all flares classified as equal
  to or brighter than A1 and covers the time period from 1993 November
  to 1995 July. We find a power-law relationship between the number of
  flares per hour and peak X-ray brightness in the 1-8 Å range. The
  average power-law index for dN/dF, where N is the number of events
  per hour and F, the GOES flux, is about -1.88 +/- 0.21. A similar
  result was found from previous work based on uncollimated GOES-type
  observations concerning flares brighter than about C2. This index is
  independent of the background flux level (which is related to the solar
  activity level) to within our statistical uncertainties. We obtain the
  FWHM distribution of flare lifetimes from our sample and find that the
  distribution is independent of X-ray brightness class. We extrapolate
  the soft X-ray flare occurrence rate obtained for the Sun to other
  very active solar-like stars.

Title: First Results of the SUMER Telescope and Spectrometer on SOHO -
    I. Spectra and Spectroradiometry
Authors: Wilhelm, K.; Lemaire, P.; Curdt, W.; Schühle, U.; Marsch, E.;
   Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Huber,
   M. C. E.; Vial, J. -C.; Kühne, M.; Siegmund, O. H. W.; Gabriel, A.;
   Timothy, J. G.; Grewing, M.; Feldman, U.; Hollandt, J.; Brekke, P.
Bibcode: 1997SoPh..170...75W
Altcode:
  SUMER - the Solar Ultraviolet Measurements of the Emitted Radiation
  instrument on the Solar and Heliospheric Observatory (SOHO) - observed
  its first light on January 24, 1996, and subsequently obtained a
  detailed spectrum with detector B in the wavelength range from 660
  to 1490 Å (in first order) inside and above the limb in the north
  polar coronal hole. Using detector A of the instrument, this range
  was later extended to 1610 Å. The second-order spectra of detectors
  A and B cover 330 to 805 Å and are superimposed on the first-order
  spectra. Many more features and areas of the Sun and their spectra
  have been observed since, including coronal holes, polar plumes and
  active regions. The atoms and ions emitting this radiation exist at
  temperatures below 2 × 10<SUP>6</SUP> K and are thus ideally suited
  to investigate the solar transition region where the temperature
  increases from chromospheric to coronal values. SUMER can also be
  operated in a manner such that it makes images or spectroheliograms
  of different sizes in selected spectral lines. A detailed line profile
  with spectral resolution elements between 22 and 45 mÅ is produced for
  each line at each spatial location along the slit. From the line width,
  intensity and wavelength position we are able to deduce temperature,
  density, and velocity of the emitting atoms and ions for each emission
  line and spatial element in the spectroheliogram. Because of the high
  spectral resolution and low noise of SUMER, we have been able to detect
  faint lines not previously observed and, in addition, to determine
  their spectral profiles. SUMER has already recorded over 2000 extreme
  ultraviolet emission lines and many identifications have been made on
  the disk and in the corona.

Title: Properties of thermal flare plasmas (3 × 10<SUP>6</SUP>-3
× 10<SUP>7</SUP> K): Observational results
Authors: Feldman, Uri
Bibcode: 1996PhPl....3.3203F
Altcode:
  One of the most violent while best observed phenomena occurring in
  the solar upper atmosphere is flare emission in the 3×10<SUP>6</SUP>
  to 3×10<SUP>7</SUP> K temperature range. This emission, commonly
  called thermal flare emission, can vary in intensity by more than
  five orders of magnitude, and exhibits regular and predictable
  properties. A wealth of observational data regarding thermal solar
  flares has been collected. Through these data the morphological
  properties of thermal flares have been determined. Plasma properties
  such as electron temperatures, electron densities, mass motions, and
  variations in elemental abundances during the course of the flare are
  well established. Observational data have also been used to determine
  relationships between peak fluxes and maximum flare temperatures as
  well as general properties of the light curve of flares.

Title: Electron Temperature, Emission Measure, and X-Ray Flux in A2
    to X2 X-Ray Class Solar Flares
Authors: Feldman, U.; Doschek, G. A.; Behring, W. E.; Phillips,
   K. J. H.
Bibcode: 1996ApJ...460.1034F
Altcode:
  In this paper we present a statistical analysis of soft X-ray flare
  class and emission measure as a function of electron temperature
  determined for the time of maximum flare X-ray flux. The study includes
  868 flares of X-ray class A2 to X2. Our work shows that their properties
  are very different, although large and small flares as seen by the 1-8
  Å detector aboard the Geostationary Operational Environmental Satellite
  (GOES) records have similar appearances. The peak temperature of intense
  (major) flares is much higher than the peak temperature of weak (minor)
  flares. This finding has important implications on the nature of the
  flare-heating mechanism. For example, if a flare is a collection of
  elementary bursts, the plasma properties of the elementary-bursts
  occurring during peak emission of large flares and small flares must
  be different. <P />Using the relationship between electron temperature
  and emission measure in solar flares, we provide an estimate of the
  electron temperature during the peak emission of large stellar flares.

Title: Electron Temperature and Emission Measure Determinations of
    Very Faint Solar Flares
Authors: Feldman, U.; Doschek, G. A.; Behring, W. E.
Bibcode: 1996ApJ...461..465F
Altcode:
  We have studied 28 flares in the X-ray magnitude range of A2-A9
  using high-resolution Bragg crystal spectrometer data obtained from
  instrumentation flown on the Yohkoh spacecraft. Flares in the A-class
  category can be detected in spectral lines of He-like ions formed
  at low temperatures. Their average temperature is approximately 5 x
  10<SUP>6</SUP> K, and their emission measure as determined from the S
  XV resonance line near 5 Å varies between 2 x 10<SUP>46</SUP> and 1
  x 10<SUP>48</SUP> cm<SUP>-3</SUP>.

Title: The Temperature of the Bright Knots at the Tops of Solar
    Flare Loops
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1996ApJ...459..773D
Altcode:
  The Japanese Yohkoh spacecraft has revealed the pervasive presence
  of confined bright regions at the tops of solar flare magnetic
  flux tubes. The physical parameters in the bright regions, such as
  temperature and density, are of considerable interest for attempting
  to understand the nature and longevity of these regions. We have
  found an example of such a source in spectroheliograms of a flare
  observed by the Naval Research Laboratory slitless spectroheliograph on
  Skylab. This instrument offers better temperature discrimination than
  possible with a broadband X-ray telescope such as flown on Yohkoh We
  determine the temperature of the Skylab source using the most recent
  atomic data. From the Skylab extreme-ultraviolet images of this flare
  in spectral lines of Fe XXII, Fe XXIII, and Fe XXIV, we find that the
  confined bright region can be described as an isothermal source at a
  temperature of about 11 x 106 K. However, this conclusion generally
  contradicts temperatures measured from uncollimated Bragg crystal
  spectrometer spectra from Yohkoh and other spacecraft for similar
  X-ray class flares. There is also emission at the same location from
  Ca XVII ions formed at about 6 x 106 K, implying that the source might
  be multithermal A multithermal source would indicate that the bright
  regions are composed of structures below the spatial resolution of
  the Skylab and Yohkoh instrumentation and could possibly resolve the
  discrepancies between Bragg spectrometer and imaging data.

Title: Ultra Low Temperature Sulfur X-Ray Spectra
Authors: Doschek, G. A.; Feldman, U.; Dubau, J.
Bibcode: 1996ASPC..111..122D
Altcode: 1997ASPC..111..122D
  The BCS experiment on Yohkoh was designed to be about an order of
  magnitude more sensitive than previously flown Bragg crystal X-ray
  spectrometers. Because of this sensitivity the authors have attempted
  to detect X-ray sulfur line emission emitted from temperatures as
  low as 2×10<SUP>6</SUP>K. This attempt failed, in part because of
  possible scattered radiation from cosmic X-ray sources! Nevertheless,
  the authors investigated the plasma diagnostic possibilities and
  present some preliminary results.

Title: Properties of Thermal Flares (4-30 MK) Derived from
Observations: Does a Reconnection Mechanism Have a Role in the
    Flare Process?
Authors: Feldman, U.
Bibcode: 1996ASPC..111..145F
Altcode: 1997ASPC..111..145F
  One of the most violent and best observed phenomena occurring in the
  solar upper atmosphere is flare emission in the 4 - 30 MK temperature
  range. This emission can vary in intensity by more than five orders
  of magnitude, yet exhibits regular and predictable properties. A
  wealth of observational data regarding 4 - 30 MK solar flares has been
  collected. Any credible flare model must account for the observations
  described.

Title: Possibility of infrared coronal line laser emission in
    Seyfert nuclei.
Authors: Greenhouse, M. A.; Smith, H. A.; Feldman, U.
Bibcode: 1996amli.conf..295G
Altcode:
  The following topics were dealt with: stimulated emission in Seyfert
  Nuclei, population inversions and gain lengths, observational tests.

Title: Relationship between Cold and Hot Post-Flare Loops and the
    Impact on the Reconnection Flare Model
Authors: Seely, J. F.; Feldman, U.
Bibcode: 1996mpsa.conf..517S
Altcode: 1996IAUCo.153..517S
  No abstract at ADS

Title: Properties of cool flare with GOES class B5 to C2.
Authors: Phillips, K. J. H.; Feldman, U.
Bibcode: 1995A&A...304..563P
Altcode:
  Observed parameters for 208 small flares with GOES classification
  B5 to C2 are discussed using data from the broad-band detectors
  on the Geostationary Operational Environmental Satellites (GOES)
  and the Bragg Crystal Spectrometer (BCS) on the Yohkoh solar flare
  spacecraft. Peak temperatures derived from He-like sulfur spectra are in
  the range 8+/-2x10^6^K and are similar to those derived from the ratio
  of the 1-8A and 0.5-4A GOES channels, but a little less than those
  from He-like calcium spectra, showing that even these small flares
  are non-isothermal. The absence of He-like iron emission shows that
  the temperatures are less than 14x10^6^K. There is a slight positive
  correlation between temperature and emission measure from the calcium
  and sulfur data. Differences in this distribution and that derived
  for larger flares in a separate study can be reconciled in terms of
  the fact that temperatures were measured from He-like iron spectra for
  the larger flares. The emission measure of the flares in our sample are
  correlated with GOES class. A detailed study of a subset of 20 flares
  shows that the temperatures generally reach peak flux slightly before
  (up to 30s) or coincident with the light curve maximum. It is found
  that even small flux enhancements which are frequently present are
  associated with temperature enhancements.

Title: The Correlation of Solar Flare Temperature and Emission
    Measure Extrapolated to the Case of Stellar Flares
Authors: Feldman, U.; Laming, J. M.; Doschek, G. A.
Bibcode: 1995ApJ...451L..79F
Altcode:
  We discuss an extrapolation of a recently discovered correlation
  between temperature and emission measure derived from X-ray spectra
  for the peak of solar flares to temperatures and emission measures
  characteristic of stellar flares. We find surprisingly good agreement
  between the parameters derived for stellar flares by various authors
  and the extrapolation of the results from the survey of solar flares.

Title: Relationships between Temperature and Emission Measure in
    Solar Flares Determined from Highly Ionized Iron Spectra and from
    Broadband X-Ray Detectors
Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T.; Brown, C. M.
Bibcode: 1995ApJ...450..441F
Altcode:
  We compare the electron temperature and emission measure of flares at
  the time of maximum soft X-ray intensity derived using two different
  techniques: (1) from the ratio of a dielectronic Fe XXIV line to
  the resonance line of Fe XXV, combined with the absolute intensity
  of the Fe XXV line, and (2) from the ratio of the 0.5-4.0 Å and 1-8
  Å broadband X-ray fluxes, combined with the absolute flux in one of
  the broadband spectral regions. The high-resolution Fe spectra are
  obtained with the Bragg Crystal Spectrometer experiment flown on
  the Japanese Yohkoh spacecraft. The broadband fluxes are obtained
  from Geostationary Operational Environmental Satellites (GOES). A
  data set of 540 X-ray magnitude C2 or brighter flares, observed by
  both spacecraft, is used for the analysis. Both techniques assume an
  isothermal plasma. The broadband temperatures are substantially lower
  than the Fe xxv temperatures. We find that the maximum temperature
  of flares brighter than MS exceeds 2 × 10<SUP>7</SUP> K and that the
  maximum temperature of flares fainter than C4 is substantially lower
  than 2 × 10<SUP>7</SUP> K. We find that the Fe XXV emission measure
  is linearly proportional to the GOES flux in the 0.5-4.0 Å detector.

Title: Relationship between Cold and Hot Post--Solar Flare Loops
    and the Impact on the Reconnection Flare Model
Authors: Feldman, U.; Seely, J. F.
Bibcode: 1995ApJ...450..902F
Altcode:
  The relationship between cold and hot postflare loops has been studied
  using the 1973 September 7 and 1974 January 15 flare images recorded
  by the Skylab S082 spectroheliograph. The images are of intense
  emission lines in the extreme ultraviolet region that span the 1 ×
  10<SUP>4</SUP> (He I) to 3.2 × 10<SUP>6</SUP> K (Ni XVIII) temperature
  range. The analysis of the images does not support the widely held
  notion that cold loops are always smaller than hot loops, lie below
  hot loops, and are similar in shape. It is found that the coldest and
  hottest loops often differ significantly in size and shape. Based on
  the analysis of a time sequence of Skylab images of cold and hot loops,
  there is no evidence that the loop system expands in a discontinuous
  manner, as would be the case if higher loops were sequentially formed
  and activated by reconnection of the magnetic field. It is found
  that the individual coronal loops expand in a gradual manner. These
  conclusions are consistent with images of postflare loop systems in the
  10<SUP>7</SUP> K range that were recorded by the soft X-ray telescope
  on the Yohkoh spacecraft. Previous observations and interpretations of
  postflare loop systems, which led to the formulation of the reconnection
  flare model, are reexamined. In light of recent high-quality imagery
  that spans the temperature range from 10<SUP>4</SUP> to 10<SUP>7</SUP>
  K, it is concluded that the observations do not support all aspects
  of the reconnection flare model as presently articulated. Elements
  of the reconnection flare model that are inconsistent with the modern
  observations should be reconsidered.

Title: Infrared Coronal Emission Lines and the Possibility of Their
Laser Emission in Seyfert Nuclei: Erratum
Authors: Greenhouse, Matthew A.; Feldman, Uri; Smith, Howard A.;
   Klapisch, Marcel; Bhatia, Anand K.; Bar-Shalom, Avi
Bibcode: 1995ApJS...99..743G
Altcode:
  In the paper "Infrared Coronal Emission Lines and the Possibility of
  Their Laser Emission in Seyfert Nuclei" by Matthew A. Greenhouse, Uri
  Feldman, Howard A. Smith, Marcel Klapisch, Anand K. Bhatia, and Avi
  Bar- Shalom (ApJS, 88,23-48[1993]), the wavelength of the 2s2ρ^3^P1-
  ^3^P_2_ transition of Ne VII is listed incorrectly as 10.6 microns. The
  correct value is 10.06 microns. This error is typographical and does
  not affect the results of the paper.

Title: Morphology and Physical Parameters for Two Long-Duration
Solar Flares: Observations from YOHKOH
Authors: Feldman, U.; Seely, J. F.; Doschek, G. A.; Brown, C. M.;
   Phillips, K. J. H.; Lang, J.
Bibcode: 1995ApJ...446..860F
Altcode:
  We have analyzed the Yohkoh soft X-ray telescope images and Bragg
  crystal spectrometer spectra of two long-duration X-class events (LDEs),
  obtained from instruments on the Japanese Yohkoh spacecraft. The two
  events are a limb flare that occurred on 1992 November 2 near 03 UT
  and a disk flare that occurred on 1992 February 27 near 10 UT. The
  spatial resolution of the images is about 2"5, and the time resolution
  is 2 s. The emission originates from plasma at temperatures ≥
  10<SUP>7</SUP> K. <P />The morphology of the LDEs is quite complicated,
  but the most intense emission consists of a small number of loops
  (usually one or two prominent loops). The brightest emission regions
  are located at the tops of loops for most of the flares' duration,
  as was found in earlier studies of compact flares observed by Yohkoh
  In the case of the 1992 November 2 limb flare, the brightening at
  the loop top is visible for a period of 24 hr after flare onset. This
  implies that the heating mechanism must act over a period of tens of
  hours for these long-duration events, that the energy is deposited at
  the top of the loop, and that the hot plasma is confined at the top
  of the loop. <P />We derive emission measures and temperatures from
  the soft X-ray telescope and Bragg crystal spectrometer data. Lower
  limit estimates of electron density of the bright regions at the loop
  tops are derived from the morphology of the regions and the emission
  measures. Fractional ion abundances for highly ionized iron are deduced
  from the spectrometer data. <P />We relate the Yohkoh observations to
  previous observations from the solar instruments on the Skylab manned
  space station.

Title: VizieR Online Data Catalog: Cool X-ray flares of Sun with GOES
    (Phillips+, 1995)
Authors: Phillips, K. J. H.; Feldman, U.
Bibcode: 1995yCat..33040563P
Altcode:
  Observed parameters for 208 small flares with GOES classification B5
  to C2 are discussed using data from the broad-band detectors on the
  Geostationary Operational Environmental Satellites (GOES) and the Bragg
  Crystal Spectrometer (BCS) on the Yohkoh solar flare spacecraft. Peak
  temperatures derived from He-like sulfur spectra are in the range
  8+/-2x10<SUP>6</SUP>K and are similar to those derived from the ratio
  of the 1-8A and 0.5-4A GOES channels, but a little less than those
  from He-like calcium spectra, showing that even these small flares
  are non-isothermal. The absence of He-like iron emission shows that
  the temperatures are less than 14x10<SUP>6</SUP>K. There is a slight
  positive correlation between temperature and emission measure from
  the calcium and sulfur data. Differences in this distribution and that
  derived for larger flares in a separate study can be reconciled in terms
  of the fact that temperatures were measured from He-like iron spectra
  for the larger flares. The emission measure of the flares in our sample
  are correlated with GOES class. A detailed study of a subset of 20
  flares shows that the temperatures generally reach peak flux slightly
  before (up to 30s) or coincident with the light curve maximum. It is
  found that even small flux enhancements which are frequently present
  are associated with temperature enhancements. (1 data file).

Title: Abundance Ratios of Oxygen, Neon, and Magnesium in Solar
Active Regions and Flares: The FIP Effect
Authors: Widing, K. G.; Feldman, U.
Bibcode: 1995ApJ...442..446W
Altcode:
  Relative abundances of oxygen, neon, and magnesium have been
  derived for a sample of nine solar active regions, flares, and
  an erupting prominance by combining plots of the ion differential
  emission measures. The observations were photographed in the 300-600
  A range by the Naval Research Laboratory (NRL) spectroheliograph on
  Skylab. Methods for deriving the Mg/Ne abundance ratio-which measures
  the separation between the low- first ionization potential (FIP) and
  high-FIP abundnace plateaus-have been described in previous papers. In
  this paper we describe the spectroscopic methods for deriving the
  O/Ne abundance ratio, which gives the ratio between two high-FIP
  elements. The plot of the O/Ne ratio versus the Mg/Ne ratio in the
  sample of nine Skylab events is shown. The variation in the Mg/Ne ratio
  by a factor of 6 is associated with a much smaller range in the O/Ne
  ratio. This is broadly consistent with the presence of the standard
  FIP pattern of abundances in the outer atmosphere of the Sun. However,
  a real change in the relative abundances of oxygen and neon by a factor
  of 1.5 cannot be excluded.

Title: Can the state of ionization equilibrium in the solar upper
    atmosphere be determined by means of atomic physics?
Authors: Feldman, U.
Bibcode: 1995CoAMP..31...11F
Altcode:
  The solar upper atmosphere (SUA) is an intriguing body of plasma
  spanning the 3×10<SUP>4</SUP>≤T<SUB>e</SUB>≤2×10<SUP>7</SUP>K
  electron temperature and
  1×10<SUP>9</SUP>≤n<SUB>e</SUB>≤1×10<SUP>13</SUP>cm<SUP>-3</SUP>
  electron density ranges. After some fifty years of research into
  the mechanism sustaining the SUA, no satisfactory solution has been
  found. It seems that some of the assumptions describing SUA properties
  are invalid, in particular the assumption stating that SUA plasmas
  are in steady state coronal ionization equilibrium (SSCIE) is in
  question. Atomic physics properties of the SUA based on the state of
  ionization equilibrium are reviewed. Discrepancies between predictions
  based on SSCIE calculations and observations are presented. It is
  shown that by assuming transient ionization conditions some of the
  discrepancies disappear.

Title: On the Absence of a Relationship between the Properties of
    the T E &gt;=10 6 K and the Properties of the T E &lt;=7 x10 5 K
    Solar Plasmas
Authors: Feldman, U.; Laming, J. M.
Bibcode: 1994ApJ...434..370F
Altcode:
  When accounting for coronal heat losses (based on previous models)
  three mechanisms are considered: (1) radiation by coronal plasma;
  (2) thermal conductivity between the 10<SUP>6</SUP> K corona and the
  10<SUP>4</SUP> K chromosphere and (3) mass motions, mostly into the
  solar wind. According to these models, thermal conductivity is the
  most efficient among the coronal heat loss mechanisms. In this paper,
  we describe studies of the relationships between structures having
  temperatures of T<SUB>e</SUB> greater than or = 1 x 10<SUP>6</SUP> and
  those with temperatures of T<SUB>e</SUB> less than 7 x 10<SUP>5</SUP>
  K. We show that effects of thermal conduction between the hot and cold
  regions are not seen at the expected levels, implying that unimpaired
  continuity is not being maintained between the 10<SUP>6</SUP> and
  10<SUP>4</SUP> K plasma regions. As a consequence of these findings,
  we stress that no conclusion on the properties of T<SUB>e</SUB> greater
  than or = 1 x 10<SUP>6</SUP> K plasmas can be drawn from properties
  of the so-called transition region (3 x 10<SUP>4</SUP> less than or =
  T<SUB>e</SUB> less than or = 7 x 10<SUP>5</SUP> K) plasmas.

Title: Morphology of the 10 Million Degree Plasma in Solar Flares
    and the Failure of the Chromospheric Evaporation Model
Authors: Seely, J. F.; Feldman, U.; Doschek, G. A.; Strong, K. T.;
   Acton, L. W.; Uchida, Y.; Tsuneta, S.
Bibcode: 1994kofu.symp..177S
Altcode:
  The SXT images of over fifty C, M, and X type flares which occurred
  between October 1991 and February 1993 were analyzed. For each flare,
  the 10 million degree emitting region was typically found to be located
  at the loop top in the first well-exposed flare image recorded during
  the rise phase (within 1 to 2 minutes after flare onset), in images
  recorded near the intensity peak, and in images recorded during most of
  the decay phase. For the November 2 1992 limb flare, the loop top was
  bright for 24 hours. For a few flares, the brightness of the footpoints
  in the onset images was comparable to the brightness of the loop top,
  but the loop top brightness rapidly increased relative to the footpoints
  and remained intense for the duration of the flare. The brightest region
  at the loop top was very small throughout the flare, often as small as
  a single pixel (1800x1800 km). The conclusions are that the energy is
  deposited in a small volume at the top of the flaring loop structure,
  the heating mechanism acts over a period of up to tens of hours, and
  the hot plasma is confined at the top of the loop structure. These
  results are not explained by the traditional chromospheric evaporation
  model of solar flares.

Title: The plasma properties of the solar upper atmosphere determined
    from high resolution observations and the nature of the physical
    processes sustaining it
Authors: Feldman, Uri
Bibcode: 1994PhPl....1.1390F
Altcode:
  Half a century ago, it was established that the temperature of the
  ``quiescent'' solar corona is ≊10<SUP>6</SUP> K (≊100 eV). Wave
  theories have been used to explain the means by which the Sun
  keeps the corona about 200 times hotter than the 5000 K (≊0.5 eV)
  photosphere. In recent years, it has been suggested that a mechanism
  other than wave dissipation heats the ``quiescent'' corona and other
  transient phenomena that occur in the upper solar atmosphere. It is
  postulated by some that the solar upper atmosphere is heated by small
  bursts of energy resulting from magnetic reconnection. In this paper,
  the plasma properties of the upper solar atmosphere, a domain that,
  when flares are included, encompasses about three orders of magnitude
  in temperature (3×10<SUP>4</SUP>-3×10<SUP>7</SUP> K) and four orders
  of magnitude in electron density (3×10<SUP>8</SUP>—3×10<SUP>12</SUP>
  cm<SUP>-3</SUP>), are described. It is shown that conventional scenarios
  based on magnetic reconnections may not adequately explain the observed
  plasma properties of the solar upper atmosphere. However, a model,
  consisting of electric currents flowing along magnetic field lines may
  have a better chance simulating the observed properties. For quiescent
  solar upper atmosphere phenomena, constant currents are needed to
  simulate the observations, while for flares, currents supplied by an
  exponentially decaying storage media are required.

Title: The Solar Abundance of Helium Determined from a Redshifted
    Plasma Flow over a Sunspot
Authors: Laming, J. M.; Feldman, U.
Bibcode: 1994ApJ...426..414L
Altcode:
  The ultraviolet spectrum of a redshifted plasma flow appearing over a
  sunspot in data obtained during the Naval Research Laboratory (NRL) High
  Resolution Telescope and Spectrograph (HRTS I) flight is interpreted
  as a radiatively cooling plasma. For most lines emitted from this
  plasma, the assumption of ionization equilibrium during the cooling
  is good; however, for He II this is not the case. In order to get the
  helium abundance by comparison with other lines, one must integrate
  differential equations for the various He ionization fractions, and
  the temperature, and then calculate the radiation emitted. Our result
  for the solar helium abundance is in the range 0.078-0.22 relative
  to hydrogen, with the uncertainty arising from lack of knowledge of
  model parameters.

Title: The Morphology of the 10 7 K Plasma in Solar
    Flares. I. Nonimpulsive Flares
Authors: Feldman, U.; Seely, J. F.; Doschek, G. A.; Strong, K. T.;
   Acton, L. W.; Uchida, Y.; Tsuneta, S.
Bibcode: 1994ApJ...424..444F
Altcode:
  In this paper we have analyzed images of 48 C-, M-, and X-type
  flares which occurred between 1991 October and 1993 February. The
  images were recorded by the soft X-ray telescope (SXT) flown on the
  Japanese Yohkoh spacecraft. The spatial resolution of the recorded
  images is about 2.5 sec. In each of the recorded flares the brightest
  regions emitting the 10<SUP>7</SUP> K radiation were analyzed and
  evaluate. The 10<SUP>7</SUP> K emitting region was found to be located
  at loop tops in the first well-exposed flare image recorded during the
  rise phase (within 1-2 minutes after flare onset), in images recorded
  near intensity peak, and in those recorded during most of the decay
  phase. Occasionally, in the begining of the event when the total
  flare intensity is low, the brightness of the footpoints may rival the
  brightness of the loop top. However, in these cases it is expected that
  the temperature of the loop top is considerably higher. The emitting
  region, even during flare peak, is very small (often smaller than a
  single SXT pixel 1800 x 1800 km).

Title: Very Impulsive Solar Flares Observed with the YOHKOH Spacecraft
Authors: Feldman, U.; Hiei, E.; Phillips, K. J. H.; Brown, C. M.;
   Lang, J.
Bibcode: 1994ApJ...421..843F
Altcode:
  Using X-ray data from two instruments aboard the Yohkho spacecraft,
  launched in 1991 August to study solar high-energy phenomena, some 38
  extremely impulsive flares of X-ray importance greater than C1 have
  been identified and studied. Electron temperatures of these flares,
  derived from Yohkoh Bent Crystal Spectrometer data, appear to decline
  immediately after the intensity maximum is attained, implying that
  energy input into the flaring plasma is reduced or possibly ceases
  after this time. Images of these flares with the high-resolution Yohkoh
  Soft X-ray Telescope show that, contrary to expectation if thermal
  conduction is a significant cooling mechanism, the emitting regions of
  tiny pointlike sources (volumes less than or = 3 x 10<SUP>24</SUP>cc)
  within a loop structure. With mass loss along field lines eliminated
  also, from a previous study, the chief energy-loss mechanism is
  likely to be radiation, and if so a lower limit for the electron
  density of approximately 10<SUP>12</SUP>/cc is imposed. This is only
  compatible with values of the emission measure if the flare volume
  is 3 x 10<SUP>24</SUP>cc, corresponding to a sphere of only 1790 km
  in diameter.

Title: Absorption spectroscopy of radiatively-heated low-Z foils
Authors: Seely, J. F.; Feldman, U.; Brown, C. M.; Hammel, B. A.;
   Back, C. A.; Hsieh, E.; Lee, R. W.
Bibcode: 1994JQSRT..51..349S
Altcode:
  High-resolution absorption spectra of radiatively-heated low-Z foils
  (CH and BN) have been recorded at the Nova II laser facility by a
  grazing-incidence spectrograph. Using a calibration curve for Kodak
  101 photographic plates, the plate density was converted to relative
  intensity transmitted by the foil. Absorption spectra are presented
  for the elements B, C, and N. The absoprtion features near the nickel
  L edge in the wavelength region 11-15 A are also presented.

Title: Infrared Coronal Emission Lines and the Possibility of their
    Laser Emission in Seyfert Nuclei
Authors: Greenhouse, Matthew A.; Feldman, Uri; Smith, Howard A.;
   Klapisch, Marcel; Bhatia, Anand K.; Bar-Shalom, Avi
Bibcode: 1994IAUS..159..447G
Altcode:
  No abstract at ADS

Title: Very Impulsive Flares Observed with YOHKOH
Authors: Feldman, U.; Hiei, E.; Phillips, K. J. H.; Lang, J.; Brown,
   C. M.
Bibcode: 1994xspy.conf..269F
Altcode:
  No abstract at ADS

Title: Very Impulsive Flares Observed with Yohkoh
Authors: Lang, J.; Feldman, U.; Hiei, E.; Phillips, K. J. H.; Brown,
   C. M.
Bibcode: 1994emsp.conf..191L
Altcode:
  No abstract at ADS

Title: What have we Learned from YOHKOH about Flares and what Should
    BE done from Solar B
Authors: Feldman, U.
Bibcode: 1994xspy.conf..139F
Altcode:
  No abstract at ADS

Title: Solar Coronal Abundances of Elements with Low First Ionization
Potential: Chromium, Calcium, and Aluminum
Authors: McKenzie, D. L.; Feldman, U.
Bibcode: 1994ApJ...420..892M
Altcode:
  We have used X-ray spectra obtained by the SOLEX spectrometers on the
  P78-1 satellite to study coronal abundances of three elements with low
  first ionization potential (FIP): Cr, Ca, and Al. The Cr/O abundance
  ratio was determined from the ratio of the Cr XV 2p<SUP>6</SUP>
  (1)S<SUB>0</SUB>-2p<SUP>5</SUP> 3d (1)P<SUB>1</SUB> line to the O VIII
  1s (2)S-2p (2)P unresolved doublet, a ratio that is almost independent
  of temperture. In a scenario in which the ratio of an element's
  coronal to its photospheric abundance is largely determined by its
  FIP, the Cr/O ratio should be reflective of the absolute Cr abundance,
  because the FIPs of O and H are nearly equal. We find that the Cr/O
  abundance ratio in coronal active regions varies by a factor of 2.7
  and is probably always enhanced by at least a factor of 3 over the
  photospheric ratio. The Ca/O abundance ratio was determined from the
  ratio of a blend of Ca XV lines at around 22.75 A to the O VIII 1s
  (2)S-2P (2)P doublet. Because this ratio is temperature dependent,
  only lower limits are derived for the Ca/O abundance ratio. The lower
  limits range from 3.0 to 9.7 times the photospheric ratio. Hence, it
  is likely that both Ca and Cr are always enriched by at least a factor
  of 3 in coronal active regions and flares. The Al/Mg abundance ratio
  determination was based on the line ratio (Al XII 1 S<SUP>2</SUP>
  (i)S<SUB>0</SUB>-s2p (1)P<SUB>1</SUB>/(Mg XI 1s<SUP>2</SUP>
  (1)S<SUB>0</SUB>-1s 3p (1)P<SUB>1</SUB>). Because this ratio is
  temperature sensitive and we have only six Al/Mg spectra, the results
  of this study are somewhat equivocal. The evidence indicates that Al
  is enriched in coronal active regions, but it is uncertain whether,
  as expected, it is enriched as much as is Ca, which has a slightly
  higher FIP. In order to account for these observations, as well as
  previously reported determinations of the Fe/O, O/Ne, and Fe/Mg coronal
  abundance ratios, in terms of a mechanism that moves ions much more
  easily than neutrals form the chromosphere to the corona, we have
  calculated the fraction of ionization for the abundant elelments
  in the chromosphere. Photoionization by blackbody radiaiton from
  just below the temperature minimum region, by locally produced Ly
  alpha radiation, and by line and continuum radiation emitted at high
  temperatures play and important role in determining the chromospheric
  ionization structure. In particular, photoionization of O I by EUV
  radiation from above must be invoked to account for variations in
  the coronal O/Ne abundance ratio. Because H I strongly absorbs this
  radiation, O is unionized at chromospheric depths of more than a few
  hundred kilometers. The ionization pattern, as a function of FIP,
  in the part of the upper chromosphere where the temperature is in
  the range 6000-8000 K, may account for the observed coronal abundance
  variations and enrichments. A mechanism that imparts a few tens of eV
  to ions, but not to neutrals, in this region could be responsible for
  the coronal enrichment of low-FIP elements.

Title: High-resolution EUV spectroscopy: performance of spherical
    multilayer-coated gratings operated at near normal incidence
Authors: Kowalski, Michael P.; Seely, John F.; Cruddace, Raymond G.;
   Rife, Jack C.; Brown, C. M.; Doschek, G. A.; Feldman, Uri; Barbee,
   Troy W.; Hunter, William R.; Holland, G. E.; Boyer, Craig N.
Bibcode: 1993SPIE.1945..164K
Altcode:
  A program is underway at the Naval Research Laboratory (NRL) to develop
  a high-resolution spectrometer for the study of astrophysical sources
  at EUV/soft X-ray wavelengths. The spectrometer design is simple in
  that the sole optic is a multilayer-coated spherical grating or mosaic
  of co-aligned gratings used at near-normal incidence, allowing large
  effective collecting area without the strict tolerance requirements
  of grazing incidence optics. Therefore, both high resolution and high
  throughput can be obtained over several selected narrow bandpasses. We
  present efficiency and resolving power measurements of spherical
  gratings which have parameters similar to that intended for our flight
  instrument. Two gratings were replicated from the same ruled master
  and then coated with a multilayer of molybdenum and silicon. A third
  sister grating was used as a control and over-coated with gold.

Title: Nonphotospheric Abundances in a Solar Active Region
Authors: Widing, K. G.; Feldman, U.
Bibcode: 1993ApJ...416..392W
Altcode:
  Element abundances have been determined for a solar active region
  observed to have a highly nonphotospheric Ne/Mg abundance ratio
  associated with an open magnetic field. This active region is an
  example of a class of relatively inconspicuous features with open
  magnetic fields which contrast with brighter, more compact emission
  regions with less anomalous abundance ratios. The study is based
  on images of the active region in Ne VI, VII, Mg VI-VIII, Na VIII,
  Si VIII, and Ca VIII, IX photographed in the 300-600 Å range by the
  NRL spectroheliograph on Skylab. <P />Element abundances relative to
  magnesium were determined by combining plots of the ion differential
  emission measures. The electron density was bracketed in the range 4 ×
  10<SUP>9</SUP> to 2 × 10<SUP>10</SUP> cm<SUP>-3</SUP>, and ionization
  equilibrium was assumed. The Ne/Mg abundance ratio was also derived
  from the Ne VI to Mg VI intensity ratios observed at 400 Å. <P />We
  find that the Ne/Mg abundance ratio is 15 times smaller than in the
  photosphere, whereas the abundances of Na, Si, and Ca relative to
  magnesium are not different by more than a factor of 2 from the ratios
  in the photosphere. From other evidence we conclude that the abundances
  of the low first ionization potential group of elements (Na, Mg, Si,
  and Ca) are enriched more than tenfold relative to high FIP neon in
  this region with open magnetic fields. Properties of a similar group
  of solar features are summarized.

Title: Infrared Coronal Emission Lines and the Possibility of Their
    Laser Emission in Seyfert Nuclei
Authors: Greenhouse, Matthew A.; Feldman, Uri; Smith, Howard A.;
   Klapisch, Marcel; Bhatia, Anand K.; Bar-Shalom, Avi
Bibcode: 1993ApJS...88...23G
Altcode:
  Infrared coronal emission lines are providing a new window for
  observation and analysis of highly ionized gas in such Galactic
  and extragalactic sources as Seyfert nuclei and classical novae
  shells. These lines are expected to be primary coolants in colliding
  galaxies, galaxy cluster cooling flows, cometary-compact H II regions,
  and supernova remnants. In this paper, we compile a complete list
  of infrared (λ &gt; 1 micron) lines due to transitions within
  the ground configurations 2S^2^2p^k^ and 3S^2^3p^k^ (k = 1-5) or
  the first excited configurations 2s2p and 3s3p of highly ionized
  (χ &gt;= 100 eV) astrophysically abundant [n(X)/n(H) &gt;= 10^-6^]
  elements. Included are approximately 74 lines in ions of O, Ne, Na,
  Mg, Al, Si, S, Ar, Ca, Fe, and Ni spanning a wavelength range of
  approximately 1-280 microns. We present results from detailed balance
  calculations, critical densities for collisional deexcitation, intrinsic
  photon rates, branching ratios, and excitation temperatures for the
  majority of the compiled transitions. The temperature and density
  parameter space for dominant cooling via infrared coronal lines is
  presented, and the relationship of infrared and optical coronal lines
  is discussed. We find that under physical conditions found in Seyfert
  nuclei, 14 of 70 transitions examined have significant population
  inversions in levels that give rise to infrared coronal lines. Laser
  gain lengths and corresponding column densities are calculated for
  dense [10^6^ &lt;= n_e_ (cm^-3^) &lt;= 10^9^] collisionally ionized
  plasmas. Application of these results to cooler plasmas photoionized
  by power-law continuum radiation fields is also discussed. We find that
  several infrared coronal line transitions have laser gain lengths that
  correspond to column densities of 10^24-25^ cm^-2^ which are modeled
  to exist in Seyfert nuclei. Observations that can reveal inverted level
  populations and laser gain in infrared coronal lines are also suggested.

Title: Elemental Abundances in the Upper Solar Atmosphere of Quiet
    and Coronal Hole Regions (T E 4.3 X 10 5 K)
Authors: Feldman, U.; Widing, K. G.
Bibcode: 1993ApJ...414..381F
Altcode:
  Detailed examination of the sun's upper atmosphere reveals that
  elemental abundances vary between different solar regions. Some solar
  regions exhibit the well-established photospheric abundances, while in
  other regions the abundances of some elements diverge from photospheric
  by an order of magnitude, and perhaps even more. Elemental abundances
  in the solar wind (SW) are also different from elemental abundances
  in the photosphere. It is postulated that elemental abundances in the
  SW reflect the elemental abundances of their place of origin near the
  solar surface. The solar surface is covered, predominantly, by quiet
  and coronal hole regions. In this paper we measure the intensities of
  limb-brightening rings over quiet and coronal hole regions in lines
  of Mg VI and Ne VI (Te is approximately equal to 4.3 x 10 exp 5 K) and
  determine the relative elemental abundances of the features producing
  the rings. The rings are formed by a plasma component occupying only
  a small fraction of the immediate volume above the solar surface.

Title: Is It Justified to Assume that ``Everywhere in the Sun's
    Photosphere-Corona Domain the Electric Conductivity Is High''?; or,
    What Drives the Solar Upper Atmosphere?
Authors: Feldman, Uri
Bibcode: 1993ApJ...411..896F
Altcode:
  For many years, solar scientists have recognized the extreme complexity
  of the upper solar atmosphere. However, in order to construct a valid
  theoretical model they have formulated a set of simplified assumptions
  governing the makeup of the sun's upper atmosphere. In previous papers
  a number of assumptions used to construct the models were shown not
  to be valid. In this Paper I bring evidence to question the validity
  of the last and most important of the assumptions, the assertion that
  'Everywhere in the photosphere-corona domain the electric conductivity
  is HIGH'. The consequences of the finding are briefly discussed. A
  laboratory measurement of the electrical conductivity versus temperature
  in a gas with photospheric composition would resolve this important
  issue and seem to be feasible.

Title: Non-Photospheric Abundances in a Solar Active Region
Authors: Widing, K. G.; Feldman, U.
Bibcode: 1993BAAS...25.1201W
Altcode:
  No abstract at ADS

Title: Atomic Transition Probabilities of Fe II Lines Determined from
    Solar Emission Spectra. I. The 2000--2800 Angstrom Wavelength Range
Authors: Ekberg, J. O.; Feldman, U.
Bibcode: 1993ApJS...86..611E
Altcode:
  Intensities of Fe II lines were measured at a number of positions
  above the white light limb of the quiet sun, using photographic spectra
  obtained by the Naval Research Laboratory normal incidence spectrometer
  on Skylab. With the aid of experimental spontaneous decay rates
  previously published in the scientific literature we have calculated the
  spontaneous decay rates of over 550 Fe II transitions in the 2000-2800 A
  wavelength range. Two-hundred twenty of the measured spontaneous decay
  rates are published for the first time. It was determined that the Fe
  II levels in the solar chromosphere achieve a Boltzmann population
  corresponding to a about 0.78 eV temperature. The accuracy of the
  new rates is comparable to the accuracy of the previously published
  experimental rates.

Title: The He II 1640 Angstrom Multiplet Observed from Solar
Prominences: Erratum
Authors: Laming, J. M.; Feldman, U.
Bibcode: 1993ApJ...409..869L
Altcode:
  No abstract at ADS

Title: A Burst Model for Line Emission in the Solar Atmosphere. III. A
    Reassessment of the Assumptions of Constant Pressure and Steady
    State Coronal Equilibrium in the Solar Transition Region
Authors: Feldman, U.; Laming, J. M.
Bibcode: 1993ApJ...404..799F
Altcode:
  We investigate the temperature dependence of the electron densities
  inferred from various spectral line diagnostics for the quiet sun,
  two active regions, and the 1973 June 15 flare, all observed by
  NRL instruments on Skylab. We find that the common assumption of
  constant pressure in these solar regions is very poor, especially
  for the quiet sun and the active regions, and that a constant density
  assumption is much closer to the observations. Such a conclusion is not
  contradicted by the morphology of these regions, as observed by the
  HRTS instrument. We also investigate the variation of the nonthermal
  mass motion with departures of the line formation temperature from
  that corresponding to ionization equilibrium.

Title: On the Absolute Abundance of Calcium in Solar Flares
Authors: Sterling, Alphonse C.; Doschek, George A.; Feldman, Uri
Bibcode: 1993ApJ...404..394S
Altcode:
  The abundance of calcium relative to hydrogen in soft X-ray-emitting
  solar flare plasmas is determined. Results were obtained for 25
  flares. An average calcium-to-hydrogen abundance of about 5 x 10
  exp -6, which is about a factor of 2 greater than measured for the
  photosphere, is found. This result is consistent with an enhancement
  of low first ionization elements in soft X-ray flare plasmas. For
  one flare, the calcium abundance was higher, at about 1.6 times the
  average results. It is inferred that the calcium abundance can vary
  among flares. Significant variations of the calcium abundance during
  the course of a flare were not detected.

Title: Infrared coronal emission lines and the possibility of their
    maser emission in Seyfert nuclei
Authors: Greenhouse, Matthew A.; Feldman, Uri; Smith, Howard A.;
   Klapisch, Marcel; Bhatia, Anand K.; Bar-Shalom, Abi
Bibcode: 1993egte.conf..303G
Altcode:
  Energetic emitting regions have traditionally been studied via x-ray,
  UV and optical emission lines of highly ionized intermediate mass
  elements. Such lines are often referred to as 'coronal lines' since
  the ions, when produced by collisional ionization, reach maximum
  abundance at electron temperatures of approx. 10(exp 5) - 10(exp 6)
  K typical of the sun's upper atmosphere. However, optical and UV
  coronal lines are also observed in a wide variety of Galactic and
  extragalactic sources including the Galactic interstellar medium,
  nova shells, supernova remnants, galaxies and QSOs. Infrared coronal
  lines are providing a new window for observation of energetic emitting
  regions in heavily dust obscured sources such as infrared bright
  merging galaxies and Seyfert nuclei and new opportunities for model
  constraints on physical conditions in these sources. Unlike their
  UV and optical counterparts, infrared coronal lines can be primary
  coolants of collisionally ionized plasmas with 10(exp 4) less than
  T(sub e)(K) less than 10(exp 6) which produce little or no optical or
  shorter wavelength coronal line emission. In addition, they provide
  a means to probe heavily dust obscured emitting regions which are
  often inaccessible to optical or UV line studies. In this poster,
  we provide results from new model calculations to support upcoming
  Infrared Space Observatory (ISO) and current ground-based observing
  programs involving infrared coronal emission lines in AGN. We present
  a complete list of infrared (lambda greater than 1 micron) lines due to
  transitions within the ground configurations 2s(2)2p(k) and 3s(2)3p(k)
  (k = 1 to 5) or the first excited configurations 2s2p and 3s3p of highly
  ionized (x greater than or equal to 100 eV) astrophysically abundant
  (n(X)/n(H) greater than or equal to 10(exp -6)) elements. Included
  are approximately 74 lines in ions of O, Ne, Na, Mg, Al, Si, S, Ar,
  Ca, Fe, and Ni spanning a wavelength range of approximately 1 - 280
  microns. We present new results from detailed balance calculations,
  new critical densities for collisional de-excitation, intrinsic photon
  rates, branching ratios, and excitation temperatures for the majority
  of the compiled transitions. The temperature and density parameter
  space for dominant cooling via infrared coronal lines is presented,
  and the relationship of infrared to optical coronal lines is discussed.

Title: The He II 1640 Angstrom Multiplet Observed from Solar
    Prominences
Authors: Laming, J. M.; Feldman, U.
Bibcode: 1993ApJ...403..434L
Altcode:
  We describe an analysis of EUV spectra of solar prominences taken with
  the SO82-B instrument on Skylab, with special attention to the 1640 A
  2l-3l arcmin multiplet of He II. It appears that the line intensities
  emitted from plasma at temperatures between 2 x 10 exp 4 and 4 x 10 exp
  4 K can be explained by an ionization equilibrium model, incorporating
  photoexcitation and photoionization by incident radiation from the
  solar disk. With this interpretation, the data are consistent with an
  abundance for He of 0.1 relative to H. Some problems remain, however,
  in predicting the relative intensities of the components of the 1640
  A multiplet.

Title: Highly ionized atoms: what do they teach us about the solar
    atmosphere?
Authors: Feldman, U.
Bibcode: 1993PhST...47..128F
Altcode:
  Solar atmosphere models are based primarily on six assumptions designed
  to describe the properties and the fashion by which solar plasmas
  behave. Over the years atomic physics methods were used to investigate
  the above assumptions. In the course of this paper comments on each
  of the six assumptions will be made and conclusions will be drawn.

Title: Highly ionized atoms in space; or highly ionized atoms,
    what are they teaching us about the solar coronal heating processes?
Authors: Feldman, U.
Bibcode: 1993PhST...46...34F
Altcode:
  Dedicated to Professor Bengt Edlén on the 50. anniversary of the
  publication of his paper on the identification of the solar coronal
  lines.

Title: Helium-Like Sulphur Emission Lines in Solar Active Regions
    and Their Sub-C Class Variability
Authors: Watanabe, Tetsuya; Hiei, Eijiro; Lang, James; Culhane,
   J. Leonard; Bentley, Robert D.; Doschek, George A.; Bromage, Barbara
   J. I.; Brown, Charles M.; Feldman, Uri; Fludra, Andrzej; Kato, Takako;
   Payne, Jeffrey
Bibcode: 1992PASJ...44L.141W
Altcode:
  Helium-like sulphur spectra (formation temperature, T_m ~ 18times
  10(6) K) from coronal active regions are being obtained by the Bragg
  Crystal Spectrometer onboard the Yohkoh mission. The average electron
  temperatures of the quiescent active regions deduced from the full-disk
  integrated sulphur spectra are 3.5--4 times 10(6) K. The temporal
  behavior of the emission lines in the sub-C level events shows that
  hot plasmas (T &gt; 10(7) K) can be produced in these weak events.

Title: The Morphology of 20times 10(6) K Plasma in Large Non-Impulsive
    Solar Flares
Authors: Acton, Loren W.; Feldman, Uri; Bruner, Marilyn E.; Doschek,
   George A.; Hirayama, Tadashi; Hudson, Hugh S.; Lemen, James R.;
   Ogawara, Yoshiaki; Strong, Keith T.; Tsuneta, Saku
Bibcode: 1992PASJ...44L..71A
Altcode:
  We have examined images of 10 flares observed by the Soft X-ray
  Telescope on-board the Yohkoh spacecraft. These images show that the
  hottest portion of the soft X-ray flare is located in compact regions
  that appear to be situated at the tops of loops. These compact regions
  form at, or shortly after, flare onset, and persist well into the decay
  phase of the flares. In some cases, the compact regions are only a
  few thousand kilometers in size and are small compared to the lengths
  of flaring loops. This is inconsistent with the smoother intensity
  distribution along the loops expected from models of chromospheric
  evaporation.

Title: A Burst Model for Line Emission in the Solar
    Atmosphere. II. Coronal Extreme Ultraviolet Lines
Authors: Feldman, U.; Laming, J. M.; Mandelbaum, P.; Goldstein, W. H.;
   Osterheld, A.
Bibcode: 1992ApJ...398..692F
Altcode:
  We review the spectroscopic evidence for explosive events - bursts -
  occurring in solar coronal plasmas. Problems in the interpretation
  of extreme ultraviolet spectra from Mg-like ions, particularly Fe XV
  in solar flares can be obviated to certain extent if these ions are
  produced in an ionizing plasma, with the 3s3p 3P levels being excited
  directly by inner shell ionization of the Al-like ion. We believe that a
  similar mechanism should apply to Be-like ions. The excitation following
  inner shell ionization can become important compared to electron impact
  excitation at a temperature corresponding to approximately twice the
  ionization potential of the ion concerned, but to be properly effective,
  it requires some deviation of the electron distribution function from
  a Maxwellian. The model we present produces a coronal heating rate
  from these bursts that is somewhat larger than current estimates.

Title: Thickness Variations along Coronal Loops Observed by the Soft
    X-Ray Telescope on YOHKOH
Authors: Klimchuk, James A.; Lemen, James R.; Feldman, Uri; Tsuneta,
   Saku; Uchida, Yutaka
Bibcode: 1992PASJ...44L.181K
Altcode:
  It has been suggested that observed coronal loops have constant
  thicknesses. However, if plasma loops coincide with magnetic loops,
  then we might expect many loops to be significantly broader at their
  tops than at their footpoints (since, on average, magnetic fields
  must diverge with height in the solar corona). It is important to
  understand how the thicknesses of loops vary along their lengths, since
  such a variation is related to the distribution of electric currents
  in the corona and is therefore relevant to solar flares and coronal
  heating. We here present preliminary results of our investigation of
  thickness variations along coronal loops observed with the Soft X-ray
  Telescope (SXT) on board the Yohkoh satellite.

Title: YOHKOH Bragg Crystal Spectrometer Observations of the Dynamics
    and Temperature Behavior of a Soft X-Ray Flare
Authors: Doschek, George A.; Mariska, John T.; Watanabe, Tetsuya;
   Hiei, Eijiro; Lang, James; Culhane, J. Leonard; Bentley, Robert D.;
   Brown, Charles M.; Feldman, Uri; Phillips, Andrew T.; Phillips,
   Kenneth J. H.; Sterling, Alphonse C.
Bibcode: 1992PASJ...44L..95D
Altcode:
  We describe X-ray spectra of an M1.5 flare that occurred on 1991
  November 9, starting at about 0313 UT. This flare is unusual in that
  very intense blueshifted components are observed in the resonance
  lines of Fe XXV, Ca XIX, and S XV. During the onset of the flare,
  the resonance lines of Ca XIX and Fe XXV are primarily due to
  this blueshifted component, which from the Doppler effect indicates
  line-of-sight speeds and turbulent motions that in combination extend
  up to 800 km s(-1) .

Title: Infrared Coronal Emission Lines and the Possibility of Their
    Maser Emission In Seyfert Nuclei
Authors: Greenhouse, M. A.; Feldman, U.; Smith, H. A.; Klapisch, M.;
   Bhatia, A. K.; Bar-Shalom, A.
Bibcode: 1992AAS...181.9803G
Altcode: 1992BAAS...24.1274G
  No abstract at ADS

Title: Elemental abundances in the upper solar atmosphere
Authors: Feldman, Uri
Bibcode: 1992PhST...46..202F
Altcode:
  A previous reassessment of spectroscopic abundance measurements from
  high temperature solar plasmas showed that, on the average, the solar
  upper atmosphere possesses a composition that is similar in nature to
  the composition of the solar wind and solar energetic particles. In
  recent years, an examination of spectra of the upper solar atmosphere
  has confirmed these results and proceeded to demonstrate that elemental
  substances change from region to region by as much as an order of
  magnitude. An account of these changes, a description of the regions
  in which they occur, and a possible elemental enrichment model are
  presented.

Title: Elemental abundances in the upper solar atmosphere.
Authors: Feldman, U.
Bibcode: 1992PhyS...46..202F
Altcode:
  Elemental abundances in the solar wind (SW) and in solar energetic
  particles (SEP) are different from abundances in the photosphere. A
  reassessment of spectroscopic abundance measurements from high
  temperature solar plasmas showed that, indeed, on the average, the solar
  upper atmosphere possesses a composition which is similar in nature
  to the composition of SW and SEP's. In the last few years a detailed
  examination of spectra of the upper solar atmosphere has confirmed the
  above results and proceeded to show that elemental abundances change
  from region to region by as much as an order of magnitude. An account
  of these changes, a description of the regions in which the changes
  occur, and a possible elemental enrichment model is given.

Title: Observation of Upflows during Soft X-Ray Solar Flares
Authors: Seely, J. F.; Feldman, Uri
Bibcode: 1992ApJ...394..697S
Altcode:
  Upflows of the soft X-ray emission regions of four flares located near
  sun center have been determined from the blueshift of the absolute
  wavelength of the Ca XIX resonance lines recorded by the SOLFLEX
  spectrometer on the P-78 spacecraft. Peak upward velocities were 35-90
  km/s and occurred during the time of gradual increase in the Ca XIX
  count rate and prior to the peak H-alpha emission. Rises in altitude
  of 7000-80,000 km were inferred from the upward velocities.

Title: Absolute O and O <SUB>2</SUB> concentrations in the
    thermosphere from SKYLAB occultation data
Authors: Meier, R. R.; Feldman, U.; Brown, C. M.; Picone, J. M.
Bibcode: 1992P&SS...40.1153M
Altcode:
  High resolution far u.v. spectra of the Sun observed during the
  SKYLAB mission exhibited both broadband extinction by O <SUB>2</SUB>
  and narrowband self-absorption by O as the spacecraft passed through
  sunset. The data were analyzed using Discrete Inverse Theory to retrieve
  the O <SUB>2</SUB> and O concentrations. Excellent agreement with the
  MSIS-86 model was found for O <SUB>2</SUB> and moderate agreement
  for O. Both determinations were made with high absolute accuracy,
  thereby demonstrating the power of absorption experiments.

Title: The Potential for Plasma Diagnostics from Stellar
    Extreme-Ultraviolet Observations
Authors: Feldman, U.; Mandelbaum, P.; Seely, J. F.; Doschek, G. A.;
   Gursky, H.
Bibcode: 1992ApJS...81..387F
Altcode:
  A description of the lines from the most abundant ions in the EUV
  spectrum in the range 50-500 A that have special diagnostic significance
  is presented. These lines are from plasmas in the temperature
  range from 10 exp 5 to 10 exp 7 K. Their utility for determining
  temperature, density, and abundances is demonstrated. An objective
  grating spectrometer, based on the Skylab slitless spectrograph, for
  making celestial observations in the EUV spectral region with high
  spectral resolution is also described. Such an instrument, if equipped
  with a multilayer grating, can achieve efficiencies over limited
  EUV wavelength ranges that rival much larger telescope-spectrometer
  instruments for the observation of stars and other celestial objects.

Title: Element Abundances and Plasma Properties in a Coronal Polar
    Plume
Authors: Widing, K. G.; Feldman, U.
Bibcode: 1992ApJ...392..715W
Altcode:
  The paper determines element abundances in a coronal polar plume
  previously observed to have a low Ne/Mg abundance ratio associated with
  an open magnetic field. This study is based on images of the plume in
  Ne VI, VII, Mg VI-VIII, Na VIII, and Ca IX, X photographed between 300
  and 600 A by the NRL spectroheliograph on Skylab. The density variation
  with height derived from MG VIII 436.7 A is satisfactorily fitted with
  a temperature of 843,000 K in hydrostatic equilibrium, close to the
  temperature expected in ionization equilibrium. The electron density
  derived from the MG VIII doublet ratio is 1 x 10 exp 9/cu cm. Element
  abundances relative to magnesium at several altitudes are derived
  by combining plots of the ion differential emission measures. The
  relative abundances of Na, Mg, and Ca in the plume are found to be the
  same (within a factor of 2) as those in the photosphere, whereas the
  abundance of neon relative to magnesium is only 1/10 of this ratio in
  the photosphere.

Title: Thickness Variations Along Coronal Loops Observed by Yohkoh
Authors: Klimchuk, J. A.; Kluge, K.; Lemen, J. R.; Feldman, U.;
   Uchida, Y.
Bibcode: 1992AAS...180.2304K
Altcode: 1992BAAS...24Q.760K
  No abstract at ADS

Title: The variability of elemental abundances in the upper solar
    atmosphere
Authors: Feldman, Uri
Bibcode: 1992AIPC..257..171F
Altcode:
  Coronal elemental abundances are found to change by as much as
  an order of magnitude relative to those present in the solar
  photosphere. Observations of modifications in coronal elemenal
  abundances are reviewed and a tentative model governing the changes
  is discussed.

Title: Variations in the Relative Elemental Abundances of Oxygen,
    Neon, Magnesium, and Iron in High-Temperature Solar Active-Region
    and Flare Plasmas
Authors: McKenzie, D. L.; Feldman, U.
Bibcode: 1992ApJ...389..764M
Altcode:
  X-ray line ratios that are weakly dependent on temperature are
  used here to search for coronal abundance variations of O, Ne, Mg,
  and Fe. Significant variations are found for the following abundance
  ratios: Fe/Ne (a factor of 4.1-4.3), Fe/O (2.4-3.1), and O/Ne(2.4). The
  mechanism, that enhances the coronal abundances of low first ionization
  potential (FIP) elements apparently operates to a decreasing extent with
  increasing FIP up to at least 13.6 eV, the FIP of oxygen. The data also
  indicate that significant abundance changes in the course of a flare
  are rare, but that changes on a time scale of days are not unusual. It
  is argued that the minimum observed coronal abundance ratios of Fe/Ne,
  Fe/O, and O/Ne should be no lower than the photospheric ratios, unless a
  process that favors the population of the corona with high-FIP elements
  over lower FIP elements is operative.

Title: A Burst Model for Line Emission in the Solar Atmosphere. I. XUV
    Lines of He i and He II in Impulsive Flares
Authors: Laming, J. M.; Feldman, U.
Bibcode: 1992ApJ...386..364L
Altcode:
  A model in which the solar chromosphere is heated by explosive events
  is developed and used to interpret XUV spectra of He I and He II in
  impulsive flares observed by the Skylab spectroheliograph. From a
  comparison of relative line intensities from He I and He II emitted
  within the flares, the model establishes sizes, durations, and
  frequencies for the individual events and, by comparison with lines
  from other elements observed in the same flares, is demonstrated to
  be consistent with a helium abundance relative to hydrogen of 0.1 for
  burst temperatures of 15-18 eV.

Title: Transitions from Metastable Levels Emitted during
Short-Duration Bursts: How Valid Are Their Calculated Intensities?
Authors: Feldman, Uri
Bibcode: 1992ApJ...385..758F
Altcode:
  Recent spectroscopic studies of the quiescent and transient phenomena
  that take place in the sun's atmosphere suggest that short-duration
  bursts may play a significant role in the heating processes of
  the upper solar atmosphere. Accepting bursts as working processes,
  concepts of electron density diagnostics in the upper solar atmosphere,
  and element abundance determinations, methods which are based mostly
  on line ratios formed in steady state coronal equilibrium are being
  reexamined. A review of the Fe IX density diagnostics and the effects
  of high-temperature short-lived bursts on this unique atomic system
  is given. An account of some of the metastable emission lines used
  in solar plasma diagnostics, and the electron densities at which they
  may become affected as a result of short-lived bursts, is also given.

Title: Elemental abundances and their variations in the upper solar
    atmosphere
Authors: Widing, K. G.; Feldman, U.
Bibcode: 1992sws..coll..405W
Altcode:
  In the standard FIP pattern of element abundances observed in the bulk
  corona and solar wind, elements with first ionization potential (FIP)
  below about 10 eV are enriched relative to elements with higher FIP. We
  have surveyed element abundances in a variety of emitting structures
  on the sun using imaged spectra of the sun in the 200-600 A range
  from SKYLAB and diagnostic flux ratios of soft X-ray lines between
  10 and 20 A. The resulting element abundances show the imprint of the
  FIP effect, but the characteristics of this pattern are variable and
  greatly enhanced in some features, and are correlated with the magnetic
  morphology. The enrichment factor reaches values of 10 to 15 in diffuse
  features with open magnetic fields. The O/Ne abundance ratio is constant
  in the SKYLAB sample (in agreement with the standard FIP pattern), but
  shows variations up to a factor of two in soft X-ray flares. Soft X-ray
  abundance ratios involving Fe suggest that the photospheric abundance
  of iron is equal to the meteoritic rather than the spectroscopic ratio.

Title: Fe II Emission Lines. II. Excitation Mechanisms in Cool Stars
Authors: Judge, P. G.; Jordan, C.; Feldman, U.
Bibcode: 1992ApJ...384..613J
Altcode:
  Excitation mechanisms are discussed for the 'resonance' transitions
  (between the 3d(6)4s, 3d7, and 3d(6)4p configurations) of Fe II observed
  in emission in the near-UV spectra of cool stars. The analysis is
  based upon: (1) emission measure analysis of previously measured
  lines in IUE spectra of cool giants; (2) discussion of the behavior
  of Fe II lines observed above the solar limb from Skylab spectra; (3)
  approximate radiative-transfer calculations in a 59 level Fe-II model
  atom using mean escape probabilities and a parameterization of optical
  radiation fields; and (4) accurate radiative transfer calculations in
  a smaller atomic model. The solar spectra show unambiguous evidence
  that electron collisions are responsible for most of the Fe-II emission
  observed above the white-light limb. The terms leading to UV multiplets
  3-6, 34-36, and 61-64 are excited by electron excitation of metastable
  quartet terms below about 4 eV, followed by photoexcitation in lines at
  optical wavelengths by photospheric radiation. A 'cool-star' diagnostic
  diagram is constructed showing the regimes in which electron collisions
  and continuum photoexcitation are important in the chromospheres of
  cool stars.

Title: The Bragg Crystal Spectrometer for SOLAR-A
Authors: Culhane, J. L.; Hiei, E.; Doschek, G. A.; Cruise, A. M.;
   Ogawara, Y.; Uchida, Y.; Bentley, R. D.; Brown, C. M.; Lang, J.;
   Watanabe, T.; Bowles, J. A.; Deslattes, R. D.; Feldman, U.; Fludra,
   A.; Guttridge, P.; Henins, A.; Lapington, J.; Magraw, J.; Mariska,
   J. T.; Payne, J.; Phillips, K. J. H.; Sheather, P.; Slater, K.;
   Tanaka, K.; Towndrow, E.; Trow, M. W.; Yamaguchi, A.
Bibcode: 1991SoPh..136...89C
Altcode:
  The Bragg Crystal Spectrometer (BCS) is one of the instruments which
  makes up the scientific payload of the SOLAR-A mission. The spectrometer
  employs four bent germanium crystals, views the whole Sun and observes
  the resonance line complexes of H-like FeXXVI and He-like FeXXV,
  CaXIX, and SXV in four narrow wavelength ranges with a resolving power
  (λ/Δλ) of between 3000 and 6000. The spectrometer has approaching
  ten times better sensitivity than that of previous instruments thus
  permitting a time resolution of better than 1 s to be achieved. The
  principal aim is the measurement of the properties of the 10 to 50
  million K plasma created in solar flares with special emphasis on the
  heating and dynamics of the plasma during the impulsive phase. This
  paper summarizes the scientific objectives of the BCS and describes
  the design, characteristics, and performance of the spectrometers.

Title: The Iron-to-Calcium Abundance Ratio in the 20 X 10 6 K Plasma
    of Medium and Large Solar Flares
Authors: Phillips, K. J. H.; Feldman, U.
Bibcode: 1991ApJ...379..401P
Altcode:
  The iron-to-calcium abundance ratio during several flares observed
  by instruments on the P78-1 and Solar Maximum Mission spacecraft are
  determined using the intensity ratio of a dielectronic satellite line
  of Fe XXIV and the resonance line of Ca XIX. Values of A(Fe)/A(Ca)
  equal to 6.8 +/- 1.0 and 6.0 +/- 1.5 were derived from these data sets,
  respectively, the small difference being attributable to errors in the
  calculated instrument sensitivities. These values fall between two other
  determinations from X-ray spectra, but are less than the photospheric
  value. They are fairly constant from flare to flare, contrasting with
  other recent work which indicates strong flare-to-flare variations.

Title: Analysis of the Solar O ii/O III Multiplets at 834 Angstrom :
    Implications for the Emission Measure Distribution in the Vicinity
    of 40,000 K
Authors: Meier, R. R.; Widing, K. G.; Feldman, U.
Bibcode: 1991ApJ...369..570M
Altcode:
  A previously unpublished very high resolution solar spectrum has
  been analyzed to determine the relative contributions of O II and
  O III at 834 Å. The resulting ratio of O II to O III emissions is
  found to be 0.35, which is lower than derived from lower resolution
  data or expected from calculations based on standard emission measure
  theory. In order to reproduce the ratio observed in the high-resolution
  spectrum, it is proposed to lower the emission measure in the vicinity
  of 40,000 K by a factor of 2. This would also reconcile differences
  among apparently discrepant lines of C II and is consistent with the
  physical interpretation that the emission measure between 10<SUP>4</SUP>
  and 10<SUP>5</SUP> K is comprised of components arising from physically
  different regimes in the solar atmosphere.

Title: Element Abundances in a Coronal Polar Plume
Authors: Widing, K. G.; Feldman, U.
Bibcode: 1991BAAS...23.1046W
Altcode:
  No abstract at ADS

Title: Intensities of the neonlike iron
    (Fe<SUP>16+</SUP>) 2p<SUP>5</SUP>3s-2p<SUP>5</SUP>3p and
    2p<SUP>5</SUP>3p-2p<SUP>5</SUP>3d transitions in solar-flare spectra
Authors: Doschek, G. A.; Feldman, U.; Bhatia, A. K.
Bibcode: 1991PhRvA..43.2565D
Altcode:
  We present relative spectral line intensities for 16 3s-3p and 3p-3d
  transitions in the neonlike ion Fe<SUP>16+</SUP>, obtained from
  solar-flare spectra. The spectra were obtained by a Naval Research
  Laboratory slitless spectrograph flown on the Skylab manned space
  station. The results are of relevance to x-ray-laser experiments
  involving collisional pumping of excited states of neonlike ions,
  and to the analysis of solar-flare spectra. The relative line
  intensities are measured to an accuracy of about 30%. The measured line
  intensities are compared with theoretical line intensities calculated
  assuming electron collisional excitation within the Fe<SUP>16+</SUP>
  ion followed by deexcitation and radiative decay. The measured and
  theoretical intensities agree to within less than a factor of 2 for all
  but one line. The important J=0 lines (3 <SUP>1</SUP>S<SUB>0</SUB>-3s
  <SUP>1</SUP>P<SUB>1</SUB>,3s <SUP>3</SUP>P<SUB>1</SUB>) at 254.87 and
  204.65 Å are about a factor of 1.4 weaker than predicted, which is
  almost within experimental error. The 3s <SUP>3</SUP>P<SUB>2</SUB>-3p
  <SUP>3</SUP>S<SUB>1</SUB> line at 409.69 Å is 2.3 times weaker than
  predicted, and this is unexplained.

Title: The Solar Spectrum between 914 and 1177 Angstrom
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1991ApJS...75..925F
Altcode:
  A spectral line list with wavelengths and identifications for the
  914-1177 A region is presented. The list is based on a Naval Research
  Laboratory (NRL) solar spectrum obtained from a rocket flight in 1966
  and on spectra recorded by the NRL S082-B slit spectrograph flown
  in 1973 on the Skylab manned space station as part of the Apollo
  Telescope Mount. Three Skylab spectra were used for this work: a limb
  spectrum recorded at a position of arcsec outside the white-light
  limb, and two flare spectra. The wavelength list should be useful in
  analyzing some spectra to be obtained from the planner NASA Lyman Far
  Ultraviolet Spectroscopic Explorer mission. A separate table listing
  observed or predicted forbidden lines that fall in the 914-1177 A
  range is presented, and some of the plasma diagnostic possibilities
  for spectral lines in this range are discused.

Title: Wavelengths and Energy Levels for the Na I Isoelectronic
    Sequence Y<SUP>28+</SUP> through U<SUP>81+</SUP>
Authors: Seely, J. F.; Brown, C. M.; Feldman, U.; Ekberg, J. O.;
   Keane, C. J.; MacGowan, B. J.; Kania, D. R.; Behring, W. E.
Bibcode: 1991ADNDT..47....1S
Altcode:
  Na-like transitions from the n = 3, 4, and 5 excited levels of the
  ions Cd <SUP>37+</SUP>, In <SUP>38+</SUP>, Sn <SUP>39+</SUP>, and Gd
  <SUP>53+</SUP> were identified in the extreme ultraviolet spectra from
  plasmas produced by one or two beams of the Nova laser at the Lawrence
  Livermore National Laboratory. The currently observed wavelengths and
  the previously observed wavelengths for lower Z ions were compared with
  the wavelengths calculated using Grant's multiconfiguration Dirac-Fock
  program. Based on this comparison, semiempirical corrections to the
  wavelengths were made, and the corrected wavelengths were determined
  for the ions Y <SUP>28+</SUP> through U <SUP>81+</SUP>. The excitation
  energies for the n = 3, 4, and 5 levels and the ionization energies
  of the ground states were also derived for the ions Y <SUP>28+</SUP>
  through U <SUP>81+</SUP>.

Title: The beam driven chromospheric evaporation model of large
solar flares: a model getting ``no respect'' from the sun
Authors: Feldman, Uri
Bibcode: 1991LNP...387..146F
Altcode: 1991fpsa.conf..146F
  Since before the last solar maximum, theoretical and to some extent
  observational, flare physics were dominated by beam driven chromospheric
  evaporation models. Comparisons between theoretical predictions and
  observations from soft and hard X-ray radiations point to major model
  inconsistencies. An account of some of the inconsistencies as well as
  the requirements for a better soft X-ray model are presented.

Title: The SOLAR-A Bragg Crystal Spectrometer (Extended Abstract)
Authors: Culhane, J. L.; Hiei, E.; Bentley, R. D.; Brown, C. M.;
   Doschek, G. A.; Feldman, U.; Lang, J.; Watanabe, T.
Bibcode: 1991LNP...387...22C
Altcode: 1991fpsa.conf...22C
  No abstract at ADS

Title: Plasma diagnostics with the Solar-A Bragg Crystal Spectrometer
Authors: Culhane, J. L.; Hiei, E.; Bentley, R. D.; Brown, C. M.;
   Doschek, G. A.; Feldman, U.; Lang, J.; Watanabe, T.
Bibcode: 1991AdSpR..11e..77C
Altcode: 1991AdSpR..11...77C
  A Bragg Crystal spectrometer is one of the instruments on the Solar-A
  mission. Using bent crystals, the spectrometer will observe the
  resonance line complexes of the H-like Fe XXVI, and He-like Fe XXV
  and Ca XIX ions with a sensitivity 5 to 10 times that of the SMM Bent
  Crystal Spectrometer. It will also study the lower temperature lines
  of He-like S XV. The improved sensitivity will allow observations
  much earlier in the impulsive phase of flares than has previously been
  possible. The new observations should help to answer questions about
  plasma heating and dynamics. As well as providing information on line
  profiles and shifts, the selected spectral lines will also provide
  electron temperature and emission measure estimates over a range from
  5 to 50 MK. The onboard microprocessor will permit spectral resolution
  to be traded against time resolution during an observation.

Title: On the Anomalous Abundances of the 2 x10 4--2 10 5 K Solar
    Atmosphere above a Sunspot
Authors: Feldman, U.; Widing, K. G.; Lund, P. A.
Bibcode: 1990ApJ...364L..21F
Altcode:
  The EUV spectrum (1175-1710 A) of a sunspot is compared with the EUV
  spectrum of two nearby plage regions. The observations were obtained
  during the July 21, 1975 rocket flight of the Naval Research Laboratory
  High Resolution Telescope and Spectrograph (HRTS). It is shown that
  the silicon-to-carbon elemental abundance ratios in the 20,000-200,000
  K temperature regions observed in the plage are enhanced by a factor
  of about 3 relative to the same ratios in the sunspot. By comparing
  lines from C II, Si II, and Si III with H I Ly-alpha and O I, it is
  shown that above active regions the abundance of ionized silicon is
  enhanced relative to its value in the photosphere.

Title: Photospheric Abundances of Oxygen, Neon, and Argon Derived
    from the XUV Spectrum of an Impulsive Flare
Authors: Feldman, U.; Widing, K. G.
Bibcode: 1990ApJ...363..292F
Altcode:
  Relative elemental abundances of O, Ne, Na, Mg, Ar, and Ca are
  determined from detailed analysis of XUV spectra emitted by an
  impulsive flare. The electron density measured from three diagnostic
  line ratios is 2-3 x 10 to the 12th/cu cm. It was found that the
  relative abundances in the flare are similar to values obtained from
  or proposed for photospheric material. The ratios of O/Mg, Ne/Mg,
  and Ar/Mg are about four times higher in the impulsive flare than the
  values typically observed in the average corona. It is suggested that
  electric fields above the photosphere may be responsible for the order
  of magnitude variations between the abundances of the group of elements
  with high first ionization potentials (FIP) and the group with low FIP.

Title: The Beam-driven Chromospheric Evaporation Model of Solar
Flares: A Model Not Supported by Observations from Nonimpulsive
    Large Flares
Authors: Feldman, U.
Bibcode: 1990ApJ...364..322F
Altcode:
  Most large solar flares exhibit hard X-ray emission which is usually
  impulsive, as well as thermal soft X-ray emission, which is gradual. The
  beam-driven chromospheric evaporation model of solar flares was proposed
  to explain the origin of the soft X-ray emitting flare plasma. A careful
  evaluation of the issue under discussion reveals contradictions between
  predictions from the theoretical chromospheric evaporation model and
  actual observations from a set of large X- and M-type flares. It is
  shown that although the soft X-ray and hard X-ray emissions are a
  result of the same flare, one is not a result of the other.

Title: Spectral Line Intensities for the Carbon Isoelectronic Sequence
    (Kr XXXI through Xe IL)
Authors: Seely, J. F.; Feldman, U.; Rozzi, S.; Goldstein, W. H.;
   Klapisch, M.
Bibcode: 1990ADNDT..45..321S
Altcode:
  The intensities of transitions in the C-like ions Kr XXXI, Sr XXXIII,
  Zr XXXV, Mo XXXVII, Ru XXXIX, Pd XLI, Cd XLIII, Sn XLV, Te XLVII,
  and Xe IL have been calculated. Included in the calculation were the
  46 levels of the configurations 2 s<SUP>2</SUP>2 p<SUP>2</SUP>, 2 s2
  p<SUP>3</SUP>, 2 p<SUP>4</SUP>, 2 s<SUP>2</SUP>2 p3 s, 2 s<SUP>2</SUP>2
  p3 p, and 2 s<SUP>2</SUP>2 p3 d. The intensities were calculated for
  the electron densities 10 <SUP>12</SUP>, 10 <SUP>13</SUP>, and 10
  <SUP>14</SUP> cm <SUP>-3</SUP> that are appropriate for tokamak plasmas.

Title: High-Resolution X-Ray Spectra of Solar Flares. IX. Mass Upflow
    in the Long-Duration Flare of 1979 June 5
Authors: Doschek, G. A.; Feldman, U.; Seely, J. F.; McKenzie, D. L.
Bibcode: 1989ApJ...345.1079D
Altcode:
  Blueshifted X-ray spectral line components in Fe and Ca spectra of a
  large long-duration flare observed on June 5, 1979. It is found that
  blueshifted emission exists for a time interval of at least 28 minutes
  indicating upflowing plasma at about 250 km/s. Emission measures for
  both the blueshifted and stationary plasma are derived and the results
  are interpreted in terms of chromospheric evaporation. The total amount
  of hot upflowing plasma during the flare rise time exceeds the amount
  of stationary plasma contained in the loop close to the time of the
  peak of the flare. This result contradicts the simplest version of the
  evaporation model. Evaporation can account for the observations only
  if some of the upflowing plasma cools on time scales much shorter than
  the rise time of the event, which was about 40 minutes.

Title: Measurement of relative electron-impact-excitation cross
    sections for Fe(24+)
Authors: Brown, C. M.; Feldman, U.; Doschek, G. A.; Seely, J. F.;
   Lavilla, R. E.
Bibcode: 1989PhRvA..40.4089B
Altcode:
  We present measurements of the relative
  electron-impact-excitation cross sections for the 1s<SUP>2</SUP>
  <SUP>1</SUP>S<SUB>0</SUB>-1s2p <SUP>1</SUP>P<SUB>1</SUB>, 1s<SUP>2</SUP>
  <SUP>1</SUP>S<SUB>0</SUB>-1s2p <SUP>3</SUP>P<SUB>2</SUB>, 1s<SUP>2</SUP>
  <SUP>1</SUP>S<SUB>0</SUB>-1s2p <SUP>3</SUP>P<SUB>1</SUB>, and
  1s<SUP>2</SUP> <SUP>1</SUP>S<SUB>0</SUB>-1s2s <SUP>3</SUP>S<SUB>1</SUB>
  transitions for the He-like ion, Fe<SUP>24+</SUP>. The measurements
  were made at two electron energies: 6.86 and 9.94 keV. The cross-section
  measurements are compared with theoretical calculations.

Title: Abundance Variations in the Outer Solar Atmosphere Observed
    in SKYLAB Spectroheliograms
Authors: Widing, K. G.; Feldman, U.
Bibcode: 1989ApJ...344.1046W
Altcode:
  Relative abundances of neon, magnesium, silicon, and oxygen have
  been derived from emission measure analyses of a prominence, flare,
  and active region observed in the 315-625 A range on NRL Skylab
  spectroheliograms. The neon-to-magnesium abundance ratio changes from
  a value of 2.2 in the prominence to 0.64 in the active region, while
  the magnesium to silicon ratio does not vary, suggesting that neon is
  the variable element. Neon-to-magnesium abundance ratios in a larger
  sample of solar features have been estimated using eye estimates of
  line ratios in the Ne VI and Mg VI multiplets at 400 A. The abundance
  variations are strongly correlated with the magnetic field morphology,
  ranging from Ne/Mg = 0.1 or 0.2 in some diffuse, open-field structures
  to values of 2 or 3 in some active, closed-field structures. Large
  Ne/Mg ratios of approximately 3 observed in impulsive flares may be
  representative of the abundance distribution in the photosphere. It
  is suggested that the well-known weakening of helium lines in coronal
  holes may be caused by an abundance deficiency of helium, similar to
  the abundance of depletions of neon observed in open-field regions.

Title: Photospheric Abundances of Oxygen, Neon, and Argon Derived
    from XUV Spectra of an Impulsive Flare
Authors: Feldman, U.; Widing, K. G.
Bibcode: 1989BAAS...21.1151F
Altcode:
  No abstract at ADS

Title: Mass Upflow in the Long Duration Flare of 5 June 1979
Authors: Doschek, G. A.; Feldman, U.; Seely, J. F.; McKenzie, D. L.
Bibcode: 1989BAAS...21..850D
Altcode:
  No abstract at ADS

Title: Element Abundances in the Sun Observed on SKLAB
    Spectroheliograms
Authors: Widing, K. G.; Feldman, U.
Bibcode: 1989BAAS...21..833W
Altcode:
  No abstract at ADS

Title: Erratum: Solar spectroscopy in the far-ultraviolet-x-ray
wavelength regions: status and prospects: errata
Authors: Feldman, Uri; Doschek, G. A.; Seely, John F.
Bibcode: 1989JOSAB...6..379F
Altcode: 1989OSAJB...6..379F
  No abstract at ADS

Title: Atomic Data and Spectral Line Intensities for the Nitrogen
    Isoelectronic Sequence (Ar XII through Kr XXX)
Authors: Bhatia, A. K.; Seely, J. F.; Feldman, U.
Bibcode: 1989ADNDT..43...99B
Altcode:
  Oscillator strengths, radiative decay rates, and electron collision
  strengths have been calculated for the N-like ions Ar XII, Ti XVI,
  Fe XX, Zn XXIV, and Kr XXX. Included in the calculation are the 72
  levels of the configurations 2 s<SUP>2</SUP>2 p<SUP>3</SUP>, 2 s2
  p<SUP>4</SUP>, 2 p<SUP>5</SUP>, 2 s<SUP>2</SUP>2 p<SUP>2</SUP>3 s,
  2 s<SUP>2</SUP>2 p<SUP>2</SUP>3 d. and 2 s<SUP>2</SUP>2 p<SUP>2</SUP>3
  d. The level populations are calculated for the electron densities 10
  <SUP>13</SUP>, 10 <SUP>14</SUP>, and 10 <SUP>15</SUP> cm <SUP>-3</SUP>,
  and the spectral line intensities of the transitions from these levels
  are presented. The calculated intensities are in good agreement with
  the relative intensities observed in the spectra from the PLT tokamak.

Title: Wavelengths and Energy Levels for the Cu I Isoelectronic
    Sequence Ru<SUP>15+</SUP> through U<SUP>63+</SUP>
Authors: Seely, J. F.; Brown, C. M.; Feldman, U.
Bibcode: 1989ADNDT..43..145S
Altcode:
  The observed wavelengths for the 18 strongest transitions of types
  n = 4-4 and n = 4-5 in the Cu I isoelectronic sequence were compared
  to the wavelengths calculated using the optimal-level option of the
  multiconfiguration Dirac-Fock program of Grant et al. On the basis
  of this comparison semiempirical corrections to the wavelengths were
  made, and corrected wavelengths for the ions Ru <SUP>15+</SUP> through U
  <SUP>63+</SUP> were determined. The semiempirically corrected excitation
  energies for all of the n = 4 and n = 5 levels were also derived.

Title: Solar spectroscopy in the far-ultraviolet - X-ray wavelength
regions:status and prospects.
Authors: Feldman, U.; Doschek, G. A.; Seely, J. F.
Bibcode: 1988JOSAB...5.2237F
Altcode: 1988OSAJB...5.2237F
  The authors review the status and prospects of solar spectroscopy in
  the far-UV - X-ray wavelength regions between approximately 1.7 and 2000
  Å. They divide the solar spectrum into a number of wavelength regions,
  determined by characteristics of spectroscopic instrumentation. The
  quality of the available spectra obtained in each region is discussed,
  concentrating on spectral resolution, wavelength coverage and accuracy,
  and line intensity and line-profile information.

Title: Generation of XUV Spectra by Powerful Picosecond Laser
Authors: Nam, C. H.; Tighe, W.; Suckewer, S.; Feldman, U.; Seely, J.
Bibcode: 1988JPhys..49..203N
Altcode: 1988IAUCo.102..203N
  No abstract at ADS

Title: On the Unresolved Fine Structures of the Solar
    Atmosphere. II. The Temperature Region 2 x10 5 K--5 x10 5 K
Authors: Feldman, U.
Bibcode: 1987ApJ...320..426F
Altcode:
  It was shown previously (Feldman, 1983) that the 30,000-200,000 K
  temperature solar plasmas behave differently than the chromosphere and
  corona, and it was concluded that while a small part of the emission
  detected may consist of 'classical' transition zone plasma, most of
  the emissions from these temperatures belong to a different entity
  termed 'unresolved fine structures'. In this paper these conclusions
  are extended to plasma emitted at higher temperatures, in the range of
  Te between 200,000 to 500,000 K. Using the Skylab spectrometer data on
  the Lyman continuum, C II, C III, O IV, O VI, and Mg X, it is shown that
  the properties of the solar atmosphere in these two temperature regions
  (30,000-200,000 K and 200,000-500,000 K, respectively) are similar.

Title: Observations of Nonthermal Energy Distributions during the
    Impulsive Phase of Solar Flares
Authors: Seely, J. F.; Feldman, U.; Doschek, G. A.
Bibcode: 1987ApJ...319..541S
Altcode:
  The Fe XXV resonance line and dielectronic satellite intensities
  have been measured as functions of time for several flares recorded
  by the Naval Research Laboratory crystal spectrometer (SOLFLEX) flown
  on the US Air Force P78-I spacecraft. The intensity ratios of the Fe
  XXV resonance line, the Fe XXIV n = 2 satellite line j, and the Fe
  XXIV n = 3 satellite line d13 indicate that nonthermal electron energy
  distributions occur during the impulsive phase of the flares. For the
  electron energies at which the j and d13 satellites are formed (4.7 and
  5.8 keV, respectively), the electron energy distributions during the
  impulsive phase are observed to have a bump or to be nearly flat. For
  all of the flares that were studied, hard X-ray bursts occurred near
  the time of the nonthermal distributions observed in the SOLFLEX data.

Title: Ultraviolet AL III Emission Lines and the Physics of the
    Solar Transition Region
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1987ApJ...315L..67D
Altcode:
  Two lines of the solar UV spectrum were identified as due to 3p-3d
  Al III transitions near 1612 A; the ratios of these lines to the
  3s-3p Al III doublet near 1855 A were found to be very sensitive to
  temperature. Thus, the temperatures of formation of the Al III lines
  could be determined by using one of the line ratios in two quiet
  sun regions, a coronal hole, and an active region. The results were
  found to be consistent with expectations based on the assumption of
  ionization equilibrium for Al III. It is suggested that S III lines
  near 1350 A and 1200 A may also serve as a temperature diagnostic.

Title: The Temperature of Solar Flares Determined from X-Ray Spectral
    Line Ratios
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1987ApJ...313..883D
Altcode:
  The effect on derived solar flare plasma temperatures of (1) a power-law
  distribution of emission measure as a function of temperature, (2)
  a high-temperature isothermal source coupled to a low-temperature
  power-law distribution of emission measure, and (3) two isothermal
  sources is calculated for line ratios involving the ions S XV, Ca
  XIX, Ca XX, Fe XXV, Ni XXVII, and Fe XXVI. It is shown that if the
  Fe XXV temperature is less than about 25 million K, as is true for
  the majority of flares, then about 75 percent or more of the emission
  measure is produced by plasma at temperatures equal to or less than the
  Fe XXV temperature plus about 3 million K. If the Fe XXV temperature
  is 20 million K or higher, this percentage can be larger. This result
  is obtained even if a superhot component exists that extends up to
  several hundred million degrees. Temperatures determined from Fe XXVI
  demonstrate the presence of a superhot component.

Title: Atomic Data and Spectral Line Intensities for the Carbon
    Isoelectronic Sequence (Ar XIII through Kr XXXI)
Authors: Bhatia, A. K.; Seely, J. F.; Feldman, U.
Bibcode: 1987ADNDT..36..453B
Altcode:
  Oscillator strengths, radiative decay rates, and electron collision
  strengths have been calculated for the C-like ions Ar XIII, Ti XVII,
  Fe XXI, Zn XXV, Se XXIX, and Kr XXXI. The corresponding atomic data
  for the ions Ca XV, Cr XIX, Ni XXIII, and Ge XXVII are determined by
  interpolation. The configurations included in the calculation are 2
  s<SUP>2</SUP>2 p<SUP>2</SUP>, 2 s2 p<SUP>3</SUP>, 2 p<SUP>4</SUP>,
  2 s<SUP>2</SUP>2 p3 s, 2 s<SUP>2</SUP>2 p3 p, and 2 s<SUP>2</SUP>2 p3
  d. The populations of the 46 levels belonging to these configurations
  are calculated for electron densities equal to 10 <SUP>13</SUP>,
  10 <SUP>14</SUP>, and 10 <SUP>15</SUP> cm <SUP>-3</SUP>, and the
  spectral line intensities of the transitions from these levels are
  also presented.

Title: Atlas of extreme ultraviolet spectroheliograms from 170 to
    625 A. Volume 1; Volume 2
Authors: Feldman, Uri
Bibcode: 1987aeus.book.....F
Altcode:
  No abstract at ADS

Title: The Extreme-Ultraviolet Spectrum (300--630 Angstrom ) of an
    Errupting Prominence Observed from SKYLAB
Authors: Widing, K. G.; Feldman, U.; Bhatia, A. K.
Bibcode: 1986ApJ...308..982W
Altcode:
  The eruptive-spray event of 1974 January 17 observed from Skylab was
  an energetic limb event in which the expansion of a prominence arch
  with velocities of the order of 400 km s<SUP>-1</SUP> was accompanied
  by heating to coronal temperatures. The authors have studied the
  prominence images photographed in the 300 - 630 Å wavelength range by
  the NRL spectroheliograph on Skylab. From the spectrum they have derived
  thermal properties for the brightest portion of the nearly straightened
  leg of the arch. Wavelengths, identifications, and intensities are
  presented for approximately 90 emission lines formed at temperatures
  between 10<SUP>5</SUP>K and 10<SUP>6</SUP>K. The emission measure
  plot is similar to those observed for the quiet Sun. From this plot
  the authors derive a neon to magnesium abundance ratio of 2.2 and an
  oxygen to neon ratio of 8.

Title: Measurement of Wavelengths and Lamb Shifts for Inner-Shell
    Transitions in Fe xviii--xxiv
Authors: Seely, J. F.; Feldman, U.; Safronova, U. I.
Bibcode: 1986ApJ...304..838S
Altcode:
  The wavelengths of inner-shell 1s-2p transitions in the ions Fe
  XVIII-XXIV have been measured in solar flare spectra recorded by the
  Naval Research Laboratory crystal spectrometer (SOLFLEX) on the Air
  Force P78-1 spacecraft. The measurements are compared with previous
  measurements and with recently calculated wavelengths. It is found that
  the measured wavelengths are systematically larger than the wavelengths
  calculated using the Z-expansion method by up to 0.65 mA. For the more
  highly charged ions, these differences can be attributed to the QED
  contributions to the transition energies that are not included in the
  Z-expansion calculations.

Title: Measured wavelengths for N = 4 to 2 transitions in Fe XXIV
    and Fe XXIII
Authors: Seely, J. F.; Feldman, U.
Bibcode: 1986PhyS...33..110S
Altcode:
  Accurate wavelength measurements for Fe XXIV and Fe XXIII
  transitions near 8 A and of the type N = 4 to 2 from solar spectra
  are presented. The resonance transition in the hydrogenlike ion Mg
  XII is used as a reference. The measured wavelengths are compared with
  previous ones and with ab initio and semiempirical calculations that
  include screening parameters in the nonrelativistic, relativistic,
  and radiative terms.

Title: Atomic Data and Spectral Line Intensities for the Beryllium
    Isoelectronic Sequence (Ar XV through Kr XXXIII)
Authors: Bhatia, A. K.; Feldman, U.; Seely, J. F.
Bibcode: 1986ADNDT..35..449B
Altcode:
  Oscillator strengths, radiative decay rates, and electron collision
  strengths are calculated for the ions Ar XV, Ti XIX, Ni XXV, Ge XXIX,
  and Kr XXXIII in the Be I isoelectronic sequence. The corresponding
  atomic data for the ions Ca XVII, Cr XXI, Fe XXIII, Zn XXVII, and Se
  XXXI are determined by interpolation. The configurations included
  in the calculation of the atomic data are 2 s<SUP>2</SUP>, 2 s2 p,
  2 p<SUP>2</SUP>, 2 s3 s, 2 s3 p, 2 s3 d, 2 p3 s, 2 p3 p, and 2 p3
  d. The intensities for transitions between the lowest 20 levels of
  these configurations are calculated for an electron temperature equal
  to half the ionization potential and for electron densities equal to 10
  <SUP>13</SUP>, 10 <SUP>14</SUP>, and 10 <SUP>15</SUP> cm <SUP>-3</SUP>.

Title: Atomic Data and Spectral Line Intensities for the Boron
    Isoelectronic Sequence (Ar XIV through Kr XXXII)
Authors: Bhatia, A. K.; Feldman, U.; Seely, J. F.
Bibcode: 1986ADNDT..35..319B
Altcode:
  We have calculated the oscillator strengths, radiative decay rates,
  and the electron collision strenghts for the B-like ions Ar XIV, Ti
  XVIII, Fe XXII, Ge XXVIII, and Kr XXXII. The corresponding atomic data
  for the ions Ca XVI, Cr XX, Ni XXIV, Zn XXVI, and Se XXX are determined
  by interpolation. The configurations included in the calculation are 2
  s<SUP>2</SUP>2 p, 2 s2 p<SUP>2</SUP>, 2 p<SUP>3</SUP>, 2 s<SUP>2</SUP>3
  s, 2 s<SUP>2</SUP>3 p, and 2 s<SUP>2</SUP>3 d. Using both the computed
  and the interpolated atomic data, we calculated the populations of
  the 20 levels belonging to these configurations. The intensities of
  the transitions are presented for electron densities of interest for
  the diagnosis of tokamak plasmas (10 <SUP>13</SUP>, 10 <SUP>14</SUP>,
  and 10 <SUP>15</SUP> cm <SUP>-3</SUP>).

Title: High-resolution observations of X-ray transitions in Fe
    XXV-XXIII
Authors: Seely, J. F.; Feldman, U.
Bibcode: 1985JPhB...18L.797S
Altcode:
  The wavelengths of X-ray transitions in Fe XXV-XXIII have been measured
  using a high-resolution spectrum reflected from the Ge(13-1) planes. A
  number of transitions have been resolved for the first time in solar
  flare spectra, and the contributions of the Fe XXIV n = 3 satellites
  to the Fe XXV parent lines are discussed. The QED contributions to
  the wavelengths of the Fe XXIV n = 3 satellite transitions have been
  determined.

Title: Element abundances from solar flare spectra
Authors: Doschek, G. A.; Feldman, U.; Seely, J. F.
Bibcode: 1985MNRAS.217..317D
Altcode:
  Ratios of solar element abundances are determined for Ar/Ca, K/Ca,
  and Ca/Fe, from high-resolution solar flare X-ray spectra obtained from
  Bragg spectrometers flown on the P78-1 spacecraft. Values of the ratios
  are: Ar/Ca = 0.65, K/Ca = 0.10, and Ca/Fe = 0.10. If the abundance
  of iron is taken to be coronal, i.e. log A(Fe) = 7.65 log A(H) = 12,
  then the abundances are: log A(Ca) = 6.62, log A(Ar) = 6.44, log A(K)
  = 5.62. If the iron abundance is assumed to be photospheric, i.e.,
  log A(Fe) = 7.50, then the abundances are: log A(Ca) = 6.47, log A(Ar)
  = 6.29, log A(K) = 5.47. The uncertainties in abundance ratios are +
  or - 25 percent. The abundance results are discussed in terms of the
  possibility of varying abundances in the solar atmosphere.

Title: High-resolution X-ray spectra of solar flares. VII - A
    long-duration X-ray flare associated with a coronal mass ejection
Authors: Kreplin, R. W.; Doschek, G. A.; Feldman, U.; Sheeley, N. R.,
   Jr.; Seely, J. F.
Bibcode: 1985ApJ...292..309K
Altcode:
  It has been recognized that very long duration X-ray events
  (lasting several hours) are frequently associated with coronal mass
  ejection. Thus, Sheeley et al. (1983) found that the probability of the
  occurrence of a coronal mass ejection (CME) increases monotonically
  with the X-ray event duration time. It is pointed out that the
  association of long-duration, or long-decay, X-ray events (LDEs) with
  CMEs was first recognized from analysis of solar images obtained by
  the X-ray telescopes on Skylab and the Naval Research Laboratory (NRL)
  slitless spectroheliograph. Recently high-resolution Bragg crystal
  X-ray spectrometers have been flown on three spacecraft, including the
  Department of Defense P78-1 spacecraft, the NASA Solar Maximum Mission
  (SMM), and the Japanese Hinotori spacecraft. In the present paper,
  P78-1 X-ray spectra of an LDE which had its origin behind the solar
  west limb on November 14, 1980 is presented. The obtained data make
  it possible to estimate temperatures of the hottest portion of the
  magnetic loops in which the emission arises.

Title: Relative intensities of 2s<SUP>2</SUP>2p<SUP>k</SUP>-2s2p<SUP>k
    + 1</SUP> transitions in F i- to B i-like Ti, Cr, Fe, Ni, and Ge in
a tokamak plasma: A comparison of experiment and theory
Authors: Stratton, B. C.; Moos, H. W.; Suckewer, S.; Feldman, U.;
   Seely, J. F.; Bhatia, A. K.
Bibcode: 1985PhRvA..31.2534S
Altcode:
  Measured relative intensities of a number of allowed
  2s<SUP>2</SUP>2p<SUP>k</SUP>-2s2p<SUP>k+1</SUP> transitions (60-200
  A&amp;#778) in the F i- to B i-like ions of titanium, chromium, iron,
  nickel, and germanium are compared with values from level-population
  calculations. The measurements are from Princeton Large Torus (PLT)
  tokamak plasmas with electron densities of ~2.5×10<SUP>13</SUP>
  cm<SUP>-3</SUP>. For titanium and chromium, data from plasmas
  with densities of ~5×10<SUP>12</SUP> cm<SUP>-3</SUP> are also
  presented; a number of density-dependent line-intensity ratios are
  found. The spectra were obtained with use of a grazing-incidence
  time-resolving spectrograph which was radiometrically calibrated with
  use of synchrotron radiation from the National Bureau of Standards
  Synchrotron Ultraviolet Radiation Facility (SURF II). The measured
  relative intensities are therefore reliable. For the majority of the
  observed lines, agreement between the measured and calculated relative
  intensities is within 30%, the estimated accuracy of the measurements;
  significant discrepancies are found in the titanium ions at the
  low density. The discrepancies, some of which are due to blends,
  are discussed. Thus, the level-population calculations may be used
  with some confidence for spectroscopic plasma diagnostics. In the C
  i-like ions, there is some evidence that calculations which include
  proton-collisional excitation and deexcitation between the levels of
  the ground configuration are in better agreement with the measurements
  than those that do not, indicating that proton collisions should be
  included in the calculations for these ions.

Title: The solar coronal X-ray spectrum 5.5-12 A
Authors: McKenzie, D. L.; Landecker, P. B.; Feldman, U.; Doschek, G. A.
Bibcode: 1985STIN...8528908M
Altcode:
  Solar X-ray spectra in the wavelength range 5.5-12 a have been measured
  by the SOLEX spectrometers aboard the USAF p78-1 satellite. The
  spectra were measured under a variety of flaring and nonflaring
  conditions. High sensitivity, attained by summing data from several
  successive spectral scans, enabled the detection of 85 lines, 22 of
  which remain unidentified, in this wavelength range. In addition,
  observations of many strong lines were possible with individual scans
  during the course of the flare evolution. This capability, coupled with
  the availability of nonflare spectra, facilitated the identification
  of several lines. The lines of Fe XXII-XXIV are especially important
  in this wavelength range. For many of these lines, theoretical and
  observed line strengths

Title: Element Abundances from Solar Flare Spectra
Authors: Doschek, G. A.; Feldman, U.; Seely, J. F.
Bibcode: 1985BAAS...17..629D
Altcode:
  No abstract at ADS

Title: Precision measurement of transition energies and Lamb shifts
    in two-electron argon and potassium in solar-flare spectra
Authors: Seely, J. F.; Feldman, U.
Bibcode: 1985PhRvL..54.1016S
Altcode:
  The wavelengths of 1s<SUP>2</SUP> <SUP>1</SUP>S<SUB>0</SUB>-1snp
  <SUP>1</SUP>P<SUB>1</SUB> transitions in the two-electron ions Ar
  xvii and K xviii have been measured in solar-flare spectra. The QED
  contributions to the transition energies are determined by comparison
  of the measured transition energies to the calculated values. The
  ionization limit of Ar xvii is also determined.

Title: Population mechanisms for the He(+) N = 3 levels determined
    from measurements of the solar 1640 A emission
Authors: Seely, J. F.; Feldman, U.
Bibcode: 1985MNRAS.213..417S
Altcode:
  The intensities of the 3s-2p, 3p-2s, and 3d-2p components of the He II
  1640 Å line have been measured from solar data taken by the NRL slit
  spectrograph on Skylab. The relative and absolute population densities
  of the 3s, 3p, and 3d levels of He<SUP>+</SUP> are determined near
  the white-light limb in various solar regions (coronal hole, quiet
  Sun, active regions, and a prominence) and in a flare region on the
  solar disc. The population density measurements are interpreted using
  a rate equation model for the He<SUP>+</SUP> ion. It is found that
  self-absorption of the 3p-1s radiation contributes to the population
  of the 3p level in all the solar regions that are studied and is
  particularly important in the active regions, the prominence and the
  flare. Recombination contributes to the population of the 3d level in
  the active regions near the limb and in the prominence. In all the
  solar regions that are studied, the 3p-2s component of the 1640 Å
  line is more intense than the 3d-2p and 3s-2p components.

Title: New identifications of Fe XVII spectral lines in solar flares
Authors: Feldman, U.; Doschek, G. A.; Seely, J. F.
Bibcode: 1985MNRAS.212P..41F
Altcode:
  The authors review the identifications of Fe XVII transitions between
  the 2s<SUP>2</SUP>2p<SUP>5</SUP>3s, 3p, and 3d configurations
  recently published by Jupén. The review is based on examining
  spectroheliograms of solar flares obtained by a Naval Research
  Laboratory instrument on Skylab (S082-A). The authors agree with
  the majority of identifications given by Jupén, but find different
  wavelengths for a few of the lines. The relative intensities of
  the lines are qualitatively in agreement with calculations. The
  authors also identify a broad line at 1153.20 Å with the
  2p<SUP>5</SUP>3s<SUP>3</SUP>P<SUB>0</SUB>→2p<SUP>5</SUP>3s<SUP>3</SUP>P<SUB>1</SUB>
  forbidden transition of Fe XVII. This line was found in flare spectra
  obtained by the NRL slit spectrograph on Skylab (S082-B).

Title: The solar coronal X-ray spectrum from 5.5 to 12 A
Authors: McKenzie, D. L.; Landecker, P. B.; Feldman, U.; Doschek, G. A.
Bibcode: 1985ApJ...289..849M
Altcode:
  A compilation of spectral lines in the 5.5-12 A wavelength region
  is presented from observations under a variety of solar conditions,
  including flare onset, flares, and nonflaring active regions. The
  line fluxes and wavelengths of Fe XXII-XXIV are compared with theory,
  and the results for Fe XXIII-XXIV are shown to agree with theoretical
  determinations. When only the strongest lines are considered, some
  relative strengths agree with theory and some do not. Diagnostically
  useful line ratios of Mg XI, Al XII, and Si XIII are also examined. The
  density-sensitive line ratio R measured for Mg XI and Si XIII agree with
  theoretical calculations of R(0) the low-density limit of R. For Mg XI
  in a flare-onset spectrum, R is lower than R(0), but the statistical
  significance of the result is not high.

Title: Atomic Data and Spectral Line Intensities for the Neon
    Isoelectronic Sequence (Si V through Kr XXVII)
Authors: Bhatia, A. K.; Feldman, U.; Seely, J. F.
Bibcode: 1985ADNDT..32..435B
Altcode:
  The electron impact collision strengths and the spontaneous radiative
  decay rates are presented for the following ions of the Ne isoelectronic
  sequence: Si V, Ar IX, Ti XIII, Fe XVII, Ge XXIII and Kr XXVII. Data are
  given for the 27 levels that belong to four different configurations
  (2 s<SUP>2</SUP>2 p<SUP>6</SUP>, 2 s<SUP>2</SUP>2 p<SUP>5</SUP>3 s,
  2 s<SUP>2</SUP>2 p<SUP>5</SUP>3 p, and 2 s<SUP>2</SUP>2 p<SUP>5</SUP>3
  d). By use of the atomic data calculations of the above-mentioned
  ions, the atomic data for all the ions with 14 ⩽ Z ⩽ 36 have
  been interpolated. Energy levels and level populations are presented
  for all the even- Z ions with 14 ⩽ Z ⩽ 36 (Si V, S VII, Ar IX,
  Ca XI, Ti XIII, Cr XV, Fe XVII, Ni XIX, Zn XXI, Ge XXIII, Se XXV,
  and Kr XXVII). The level populations are given for the three electron
  densities 10 <SUP>13</SUP>, 10 <SUP>14</SUP>, and 10 <SUP>15</SUP>
  cm <SUP>-3</SUP>. Spectral line intensities are also presented for
  all transitions with intensities within two orders of magnitude of
  the most intense line in each ion.

Title: Spectral Line Intensities for the O I, N I, C I, B I, and Be
    I Isoelectronic Sequences, Z = 26-36
Authors: Feldman, U.; Seely, J. F.; Bhatia, A. K.
Bibcode: 1985ADNDT..32..305F
Altcode:
  The spectral line intensities for the O I, N I, C I, B I, and Be
  I isoelectronic sequences and for Z = 26, 28, 30, 32, 34, and 36
  are presented. The transitions are of the types 2 s<SUP>2</SUP>2
  p<SUP>k</SUP>-2 s2 p<SUP>k+1 </SUP>, 2 s2 p<SUP>k+1 </SUP>-2 p<SUP>k+2
  </SUP>, 2 s<SUP>2</SUP>2 p<SUP>k</SUP>-2 s<SUP>2</SUP>2 p<SUP>k</SUP>,
  and 2 s2 p<SUP>k+1 </SUP>-2 s2 p<SUP>k+1 </SUP>. The simulated spectra
  are useful for the identification of allowed and forbidden transitions
  in the wavelength range 40 to 2300 Å in tokamak plasmas. The
  line intensities are calculated for an electron density of 2.5 ×
  10 <SUP>13</SUP> cm <SUP>-3</SUP> and for an electron temperature
  approximately equal to the temperature for maximum abundance of each
  ion in the case of coronal equilibrium.

Title: The relation of electron temperature to emission measure and
    limits of increase in emission measure in soft X-ray flares
Authors: Denton, R. E.; Feldman, U.
Bibcode: 1984ApJ...286..359D
Altcode:
  A sample of 126 soft X-ray flares (ranging in X-ray class from C3
  up to X3) is studied in order to look for possible correlations
  between various parameters of the flare plasma. It is found that
  the emission measure (N2V) correlates positively with the electron
  temperature (T) determined from the Ca XIX resonance line and nearby
  satellites. Measured values of the maximum value of T (TM) range
  from 8 to 18 x 10 to the 6th K. Increases in N2V of no more than a
  factor of 400 from X-ray onset to soft X-ray maximum are observed. The
  largest increases result from the most intense flares. The limit on
  the increase of N2V may be important in determining the relative roles
  of chromospheric evaporation and compression in producing the observed
  high densities in soft X-ray flare plasmas.

Title: The Large Flare November 7, 1980: A Test of Chromospheric
    Evaporation Theories?
Authors: Karpen, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1984BAAS...16.1003K
Altcode:
  No abstract at ADS

Title: Direct measurement of the increase in altitude of the soft
    X-ray emission region during a solar flare
Authors: Seely, J. F.; Feldman, U.
Bibcode: 1984ApJ...280L..59S
Altcode:
  The upward motions of the hot thermal regions of several large (M
  type) solar flares have been determined from the soft X-ray spectral
  data recorded by the scanning spectrometer (SOLFLEX) on the P78-1
  spacecraft. For the limb flares that are studied, the centroid of the
  Ca XIX emission region moves to a higher altitude with an apparent
  speed of 20-40 km/s for a period of 20-30 minutes following onset of
  the flare and reaches an altitude of 30,000-40,000 km. Although brief
  periods of downward motion of the emission centroid are observed,
  substantial decreases in altitude are not observed in any of the flares.

Title: On the rate of energy input in thermal solar flares
Authors: Feldman, U.; Doschek, G. A.; McKenzie, D. L.
Bibcode: 1984ApJ...276L..53F
Altcode:
  The rise phases of solar soft X-ray flares observed by X-ray crystal
  spectrometers on P78-1 are discussed in terms of the rate of change of
  X-ray flux as a function of time. It is shown that the flux increases
  exponentially over most of the rise time. The e-folding time (tau) has
  a cutoff at approximately 13 s. Soft X-ray flares with smaller values
  of tau are not observed. It is suggested that this phenomenon is due
  to the ability of the solar atmosphere to absorb the input energy and
  convert it into a typical soft X-ray flare, when the value of tau is
  greater than about 13 s. For energy input rates with tau greater than
  about 13 s, the temperature attained by the plasma is typically around
  2 x 10 to the 7th K, but for values of tau less than 13 s, the gas is
  heated to much higher temperatures (about 10 to the 8th K), producing
  a certain class of hard X-ray flares.

Title: Measurement of Wavelengths and Abundances from Solar Flare
    X-Ray Spectra
Authors: Seely, J. F.; Feldman, U.; Doschek, G. A.
Bibcode: 1984uxsa.coll..151S
Altcode: 1984IAUCo..86..151S; 1984uxsa.conf..151S
  No abstract at ADS

Title: Measurement of the Increase in Altitude of the Soft X-Ray
    Emission Regions of Solar Flares (short Abstract)
Authors: Seely, J. F.; Feldman, U.
Bibcode: 1984uxsa.coll...12S
Altcode: 1984IAUCo..86...12S; 1984uxsa.conf...12S
  No abstract at ADS

Title: Transitions of the Type 2s-2p in Highly-Ionized CA Through RB
Authors: Behring, W. E.; Cohen, L.; Seely, J. F.; Feldman, U.;
   Goldsmith, S.; Richardson, M.
Bibcode: 1984uxsa.coll..225B
Altcode: 1984uxsa.conf..225B; 1984IAUCo..86..225B
  No abstract at ADS

Title: Relative Intensities of Lines in Fi-Bi ti, cr, fe, ni, and Ge:
    a Comparison of Theory and Experiment
Authors: Stratton, B. C.; Moos, H. W.; Feldman, U.; Seely, J. F.;
   Suckewer, S.; Finkenthal, M.
Bibcode: 1984uxsa.coll..175S
Altcode: 1984uxsa.conf..175S; 1984IAUCo..86..175S
  No abstract at ADS

Title: On the unresolved fine structures of the solar atmosphere in
    the 30,000-200,000 K temperature region
Authors: Feldman, U.
Bibcode: 1983ApJ...275..367F
Altcode:
  The solar atmospheres from the chromosphere through the transition
  zone and all the way up into the corona usually are considered to be
  parts of one continuous structure. Now that stellar measurements in the
  far-ultraviolet have become available, an attempt is being made to apply
  solar physics ideas to solar type stars. The intention of this paper is
  to reexamine the experimental facts concerning the relations between the
  solar chromosphere, transition zone, and corona. Experimental evidence
  is presented to argue that the solar plasma in the temperature region
  40,000-220,000 K occurs in structures magnetically isolated from the
  chromosphere and corona. It is suggested that while a small part of the
  emission detected in the 40,000-220,000 K region consists of the 'true'
  transition zone plasma, i.e., the interface between chromospheric and
  coronal temperature, most of it belongs to an altogether different
  entity. It is also suggested that this particular entity be called
  unresolved fine structures.

Title: On the rate of energy input in thermal solar flares
Authors: Feldman, U.; Doschek, G. A.; McKenzie, D. L.
Bibcode: 1983STIN...8423548F
Altcode:
  The rise phases of solar soft X-ray flares observed by X-ray crystal
  spectrometers on p78-1 are discussed in terms of the rate of change of
  X-ray flux as a function of time. It is shown that the flux increased
  exponentially over most of the rise time. The e-folding time TAU has a
  cut-off at 13 s. Soft X-ray flares with smaller values of TAU are not
  observed. It is suggested that this phenomenon is due to the ability
  of the solar atmosphere to absorb the input energy and convert it into
  a typical soft X-ray flare. For energy input rates that are below
  a certain critical value the temperature attained by the plasma is
  around 20,000,000 K, but for values above the critical value, the
  gas is heated to much higher temperatures T<SUB>e</SUB> &gt; or =
  10 to the 8th K, producing a certain class of hard X-ray events.

Title: Lines of Fe XII sensitive to coronal electron density
Authors: Feldman, U.; Doschek, G. A.; Cohen, L.
Bibcode: 1983ApJ...273..822F
Altcode:
  Lines of Fe XII sensitive to coronal electron density are discussed. The
  lines appear in solar spectra obtained by the Naval Research
  Laboratory (NRL) slit spectograph flown on Skylab. These lines are
  due to transitions between levels of the 3s 2 3p 3 configuration and
  fall at the wavelengths 1242.03 A, 1349.38 A, 2169.03 A, 2405.71 A,
  and 2565.99 A. It is shown that the line at 2169.03 A is severely
  blended by a line of Ni II at heights less than 12 arcsec outside the
  solar limb. Above 12 arcsec the lines at 2169.03 and 2405.71 A are
  apparently unblended and can be used to derive electron densities. An
  average coronal electron pressure of 6 x 10 to the 14th/cu cm K is
  obtained. However, the emitting path lengths of the Fe XII lines,
  deduced using the electron densities and absolute intensities, are
  unrealistically large. The reason for this difficulty is unclear.

Title: He D3 as a diagnostic for the hard and soft X-rays from
    solar flares
Authors: Feldman, U.; Liggett, M.; Zirin, H.
Bibcode: 1983ApJ...271..832F
Altcode:
  The time comparison of He D3 and X-ray emission has been studied
  in a number of medium-sized flares. In most cases there is a good
  agreement between the time histories of the He D3 emission and the
  high-temperature (about 2 keV) thermal source. The most intense He D3
  emission comes from two small regions on either side of the neutral
  line, which are identified with the footpoints of magnetic structures
  in which a hot (2.3 x 10 to the 7th K) thermal plasma is formed. The
  impulsive X-ray event is marked by the transient brightening of a
  number of (usually weaker) He D3 sources. The two types of sources are
  well displaced from each other, which is an indication that they are
  produced in two different volumes. In some cases a long-lived third
  He D3 source is seen.

Title: X-Rays from Laboratory and Astrophysical Plasmas
Authors: Feldman, U.
Bibcode: 1982AIPC...94..447F
Altcode:
  X-ray spectra of highly ionized elements are widely used in diagnosing
  high temperature plasmas from astrophysical as well as from laboratory
  sources. The emission lines in the X-ray region are produced primarily
  from two different types of transitions. One type involves the
  transitions 1s-2p in hydrogen-like ions, helium-like ions and their
  associated satellites. The second type involves the transitions 2l - nl'
  for n &gt; 2. These transitions are sensitive to electron temperature,
  electron density and the ionization balance. High quality spectrometers
  in the X-ray region have instrumental line widths that in many cases
  are significantly less than the true line widths. As a result, it is
  quite convenient to use the physical information in the line profiles to
  determine additional properties of the plasma under investigation. <P
  />In the course of my talk I will describe results from recent
  experiments concerning solar plasmas as well as laboratory sources.

Title: High-resolution X-ray spectra of solar flares. VI - Impulsive
    soft X-ray flares
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.
Bibcode: 1982ApJ...260..885F
Altcode:
  Doschek et al. (1980) and Feldman et al. (1980) have discussed
  high-resolution soft X-ray spectra of solar flares. The present
  investigation is concerned with the characteristics of the impulsive
  events as observed in soft X rays and the cooling of the flare plasma in
  terms of energy loss processes. A class of intense, short-lived solar
  flares which appear to be characterized by very high densities at high
  temperatures is found. For the 1979 November 6 event, the cooling time
  is so rapid that the density obtained may be a lower limit. The main
  cooling mechanism for the flares is found to be radiative. Two of the
  events are associated with strong gamma-ray emission and both of these
  events are very unusual in their soft X-ray emission. The 1979 November
  9 flare shows extremely broad X-ray emission lines during the rise
  phase, indicative of nonthermal velocities of the order of 300 km/s.

Title: Observational constraints for a theoretical model describing
    the soft X-ray flare
Authors: Feldman, U.; Cheng, C. -C.; Doschek, G. A.
Bibcode: 1982ApJ...255..320F
Altcode:
  High-resolution solar flare X-ray spectra have recently been obtained
  from X-ray spectrometer experiments flown on an Air Force spacecraft
  (P78-1) launched on 1979 February 24. Interpretation of the spectra
  has produced new results concerning the physical conditions and time
  behavior of the thermal soft X-ray emitting plasma at temperatures
  near 20,000,000 K. It is argued that soft and hard X-ray events
  are not causally related to each other, but are simply two different
  manifestations of flare energy release. They probably occur in different
  plasma volumes. The source of the preflare plasma appears to be in the
  cooler parts of the solar atmosphere, perhaps transition region loops
  with initial temperatures of 100,000 K and densities of 10 to the 11th
  per cu cm. Continuous energy input, rather than sequential activation
  of loops, is required to explain the observations. Compression coupled
  with chromospheric ablation may produce the high densities in coronal
  flare loops.

Title: Doppler wavelength shifts of ultraviolet spectral lines in
    solar active regions
Authors: Feldman, U.; Doschek, G. A.; Cohen, L.
Bibcode: 1982ApJ...255..325F
Altcode:
  Doppler shifts are measured for solar UV emission lines formed in the
  lower transition region of active regions. Doppler shifts in different
  regions at the same solar location, variations of Doppler shift with
  position of an active region on the disk, and variations of Doppler
  shift with time at the same solar location in the same active region
  were studied. Observations were made with the NRL slit spectrograph on
  Skylab. Excluding flare and flare-related phenomena, only redshifts
  are found whose magnitudes correspond to downflow velocities between
  about 4 and 17 km/s. Shifts are largest for lines formed between about
  50,000 and 100,000 K, and are distinctly less for lines formed above
  100,000 K. The shifts persist out to the limb, but not above it. There
  is no obvious change in redshift for lines measured at the same solar
  location over time intervals of about 20 minutes.

Title: Ultraviolet continuum absorption /less than about 1000 A/
    above the quiet sun transition region
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1982ApJ...254..371D
Altcode:
  Lyman continuum absorption shortward of 912 A in the quiet sun solar
  transition region is investigated by combining spectra obtained from
  the Apollo Telescope Mount experiments on Skylab. The most recent
  atomic data are used to compute line intensities for lines that fall
  on both sides of the Lyman limit. Lines of O III, O IV, O V, and S
  IV are considered. The computed intensity ratios of most lines from
  O IV, O V, and S IV agree with the experimental ratios to within a
  factor of 2. However, the discrepancies show no apparent wavelength
  dependence. From this fact, it is concluded that at least part of the
  discrepancy between theory and observation for lines of these ions
  can be accounted for by uncertainties in instrumental calibration and
  atomic data. However, difficulties remain in reconciling observation
  and theory, particularly for lines of O III, and one line of S IV. The
  other recent results of Schmahl and Orrall (1979) are also discussed
  in terms of newer atomic data.

Title: Electron densities in a solar flare derived from X-ray spectra
Authors: McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge,
   H. R.; Young, R. M.; Doschek, G. A.; Feldman, U.
Bibcode: 1982STIN...8325647M
Altcode:
  A major solar flare was observed with the RAP crystal of the SOLEX
  B spectrometer. The spectra were obtained by scanning back and forth
  between Bragg angles of 17.4 deg and 61.7 deg (7.8 to 23 A) at a rate of
  0.525 degrees-.15. A full scan took 84.5 sec. A line list identifying
  more than 100 lines observed in this flare was compiled. Measurements
  of the density sensitive O 7 lines near 22 A are discussed.

Title: On ionization equilibrium in solar flares as determined from
    X-ray emissionlines of CA XVIII and CA XIX
Authors: Doscher, G. A.; Feldman, U.
Bibcode: 1981ApJ...251..792D
Altcode:
  A diagnostic capable of determining the state of ionization equilibrium
  in flare plasmas is important for the determination of the physical
  conditions in flares. An experiment on the Air Force satellite P78-1
  has provided high-resolution X-ray spectra which make it possible
  to determine the state of the ionization equilibrium in coronal flare
  plasmas. The considered investigation has the objective to show that the
  interpretation of the calcium results is complicated by several possible
  blends to line q, and to point out a variation in the observed ratios
  which seems difficult to account for. Possible explanations for the
  observations are discussed, taking into account the possibility that
  the ionization equilibrium calculations have to be improved. Another
  possible explanation is related to a suggestion made by Urnov (1981)
  and Karev et al. (1980) concerning the effects produced by the presence
  of high-energy nonthermal electrons.

Title: A Solar Extreme Ultraviolet Telescope and Spectrograph for
    Shuttle / Spacelab
Authors: Neupert, W. M.; Epstein, G. L.; Thomas, R. J.; Feldman, U.
Bibcode: 1981SSRv...29..425N
Altcode:
  An instrument for advanced studies of the solar corona is described. Its
  optical system provides nearly stigmatic imaging of selected portions
  of the Sun over the spectral range from 22.5 to 44.0 nm. Both
  spectroheliograms and emission line profiles of coronal features will
  be obtained over a wide range of coronal temperatures.

Title: Solar observations and atomic data for the 3s2 1s0-3s3p 3P1
    transition in S V
Authors: Feldman, U.; Doschek, G. A.; Bhatia, A. K.
Bibcode: 1981ApJ...250..799F
Altcode:
  High resolution solar observations of the S v intersystem line at
  1199.18 A are available from Skylab. This line is potentially useful
  as a density diagnostic for high density plasmas expected in solar
  flares. S v lines are also prominent in solar spectra at wavelengths
  below 1000 A. Collision strengths and radiative decay rates are
  calculated for levels of the configurations 3 s2, 3s3p, 3p2, and
  3s3d. Level populations for the five lowest energy levels have been
  calculated as a function of electron density. These calculations are
  carried out assuming the temperature at which S v is most abundant
  in solar plasmas. The calculated population of the 3s3p 3P1 level
  reaches a pseudo-Boltzmann equilibrium at a density which is about
  five times higher than is derived from solar spectra and previous
  density determinations. It is believed that the discrepancy is due
  to a significant contribution from resonances to the 3s2-3s3p 3P
  excitation rate coefficient. It is suggested that the contribution of
  the resonances to the S v excitation rate coefficient can be estimated
  from a comparison of the experimental results and the theoretical
  calculations.

Title: High resolution solar flare X-ray spectra - The temporal
    behavior of electron density, temperature, and emission measure for
    two class M flares
Authors: Doschek, G. A.; Feldman, U.; Landecker, P. B.; McKenzie, D. L.
Bibcode: 1981ApJ...249..372D
Altcode:
  High resolution soft X-ray flare spectra recorded by Naval Research
  Laboratory (NRL) and Aerospace Corporation Bragg crystal spectrometers
  flown on an orbiting spacecraft (P78-1) are combined and analyzed. The
  instruments were launched on t979 February 24 by the U.S. Air Force,
  and the data discussed in this paper cover the wavelength ranges,
  1.82-1.97 Å, 3.143.24 Å, and 18.423.0 Å. The NRL experiment (SOLFLEX)
  covers the two short wavelength ranges (highly ionized Fe and Ca lines)
  and the Aerospace experiment (SOLEX) covers the t8.4-23.O Å range,
  which includes the Lyα O VIII line and the resonance, intercombination,
  and forbidden lines of O VII. We analyze the spectra of two flares which
  occurred on 1980 April 8 and May 9. Temporal coverage is fairly complete
  for both flares, including the rise and decay phases. Measurements of
  electron density N<SUB>e</SUB> with rather high time resolution (about
  1 minute) have been obtained throughout most of the lifetimes of the
  two flares. These measurements were obtained from the O VII lines and
  pertain to flare plasma at temperatures near 2 × 10<SUP>6</SUP> K. Peak
  density seems to occur slightly before the times of peak X-ray flux in
  the resonance lines of Fe XXV, Ca XIX, and O VII, and for both flares
  the peak density is about 10<SUP>12</SUP> cm<SUP>-3</SUP>. Electron
  temperature T<SUB>e</SUB> as a function of time is determined from
  the Fe and Ca spectra. Peak temperature for both flares is about 18 ×
  10<SUP>6</SUP> K. Differential emission measures and volume emission
  measures are determined from the resonance lines of O VII, Ca XIX,
  and Fe XXV. The number of electrons N<SUB>e</SUB>ΔV and the volume
  ΔV over which the O VII lines are formed are determined from the
  O VII volume emission measure N<SUB>e</SUB><SUP>2</SUP>ΔV and the
  density N<SUB>e</SUB>. These quantities are determined as a function
  of time. The relationship of the low and high temperature regions
  is discussed.

Title: The use of spectral emission lines in the diagnostics of hot
    solar plasma.
Authors: Feldman, U.
Bibcode: 1981PhyS...24..681F
Altcode:
  A summary of spectroscopic and atomic physics results that were
  obtained in the last 30 years and are closely related to diagnostics
  of solar plasmas will be presented. The article will not review the
  very extensive work that was done on the theoretical determinations of
  energy levels, transition probabilities, or calculations of excitation
  ionization and recombination cross sections, but with the end results of
  these calculations. In other words it deals with line intensities, line
  shapes and their changes as a result of the properties of the plasma
  from which they are emitted. The emission lines under discussion are
  optically thin and the spectral range covered is primarily from 2000
  A down to 1.8 A. The review is divided into several sections according
  to the typical wavelength ranges covered by the different spectrometers.

Title: A discussion of theoretical ionization equilibrium calculations
    based on solar flare X-ray spectra
Authors: Feldman, U.; Doschek, G. A.; Cowan, R. D.
Bibcode: 1981MNRAS.196..517F
Altcode:
  Several sets of ionization equilibrium calculations exist for use
  in interpreting X-ray and EUV spectra of astrophysical plasmas. In
  particular, the calculations of Jordan (1969, 1970), Jacobs et
  al. (1977, 1978) and Summers (1974) are well known. The temperatures
  of maximum fractional abundance calculated by Summers for the more
  highly ionized and heavier elements such as iron are about a factor
  of two higher than the temperatures calculated by Jordan and Jacobs
  et al. By the use of recently obtained X-ray spectra of solar flares,
  it is shown that the temperatures calculated by Summers (1974) for
  iron are incorrect. The temperatures calculated by Jordan or Jacobs
  et al. should be used until further improvements become available.

Title: High resolution solar flare X-ray spectra: The temporal
    behavior of electron density, temperature, and emission measure for
    two class M flares
Authors: Doschek, G. A.; Feldman, U.; Landecker, P. B.; McKenzie, D. L.
Bibcode: 1981STIN...8225073D
Altcode:
  High resolution soft X-ray flare spectra recorded by crystal
  spectrometers flown on an orbiting spacecraft (P78-1) are combined
  and analyzed. The spectra of two flares are analyzed. Temporal
  coverage for both flares, including the rise and decay phases, is
  discussed. Measurements of electron density were obtained throughout
  most of the lifetimes of the two flares. Electron temperature as a
  function of time is determined from the Fe and Ca spectra. Differential
  emission measures and volume emission measures are determined for the
  low and high temperature (Fe, Ca) plasma. The relationship of the low
  and high temperature regions is discussed.

Title: On the relationship between soft X-rays and H-alpha-emitting
    structures during a solar flare
Authors: Zirin, H.; Feldman, U.; Doschek, G. A.; Kane, S.
Bibcode: 1981ApJ...246..321Z
Altcode:
  Based on data obtained during a solar flare on March 31, 1979, soft
  X-ray (SXR) and hard X-ray (HXR) bursts are analyzed and compared with
  other available data in order to identify structures in H-alpha that
  may correspond to the SXR-emitting site. Measurements taken with the
  X-ray telescope and the XUV spectroheliograph flown on Skylab, have
  shown that the SXR emission from many flares comes from rather small
  structures of about 10-20 arcsec across. These structures appear to
  be loops that cross the magnetic neutral line. Understanding of the
  morphology of SXR was based on data of the solar flare of June 15, 1973,
  observed from Skylab, and the work of Moore et al., (1980). Dense,
  highly emissive coronal structures, not suggested to be the X-ray
  source, were forming, lost energy rapidly by emission and conduction,
  and finally formed the loops. It is concluded that bright H-alpha
  loops form rapidly as the SXR emission rises, and the overall decay
  (cooling rate) of SXR emission is much slower than the formation time
  of individual loops.

Title: High resolution X-ray spectra of solar flares. V -
    Interpretation of inner-shell transitions in Fe XX-Fe XXIII
Authors: Doschek, G. A.; Feldman, U.; Cowan, R. D.
Bibcode: 1981ApJ...245..315D
Altcode:
  The paper examines high-resolution solar flare iron line spectra
  recorded between 1.82 and 1.97 A by a spectrometer flown by the Naval
  Research Laboratory on an Air Force spacecraft launched on 1979 February
  24. The emission line spectrum is due to inner-shell transitions in the
  ions Fe XX-Fe XXV. Using theoretical spectra and calculations of line
  intensities obtained by methods discussed by Merts, Cowan, and Magee
  (1976), electron temperatures as a function of time for two large class
  X flares are derived. These temperatures are deduced from intensities
  of lines of Fe XXII, Fe XXIII, and Fe XXIV. The determination of the
  differential emission measure between about 12-million and 20-million K
  using these temperatures is considered. The possibility of determining
  electron densities in flare and tokamak plasmas using the inner-shell
  spectra of Fe XXI and Fe XX is discussed.

Title: Mass motions in optically thin solar transition zone lines
Authors: Doschek, G. A.; Mariska, John T.; Feldman, U.
Bibcode: 1981MNRAS.195..107D
Altcode:
  The widths of optically thin EUV spectral lines formed at temperatures
  between ≃ 3 × 10<SUP>4</SUP> and 2 × 10<SUP>5</SUP> K in the
  solar transition zone are larger than expected assuming ionization
  equilibrium. This result has been interpreted as due to non-thermal
  mass motions, characterized by a parameter ξ(km s<SUP>-1</SUP>) In
  this paper we discuss observations of spectral line recorded mostly at
  +2 arcsec outside the limb of the north and south polar coronal holes,
  and compare the derived values of ξ to values deduced from spectra of
  quiet Sun regions. These spectra were recorded by the NRL spectrograph
  on Skylab (1100-2000 Å). Systematic differences in line widths between
  coronal holes and quiet Sun region spectra are probably no larger than
  0.01 Å, for the optically thin lines used in the analysis. -sight
  path lengths of the emitting plasma at 2 arc sec above the limb are
  calculated from the intensity ratios of optically thick lines of C IV,
  N V, Al III, and Si IV. These ratios should be 2:1 in the optically thin
  limit, but they are around 1.5 at 2 arcsec above the solar limb. The
  derived path lengths range from ≃1000 to 5000km.

Title: What produces the high densities observed in solar flare
    plasmas
Authors: Cheng, C. -C.; Feldman, U.; Doschek, G. A.
Bibcode: 1981A&A....97..210C
Altcode:
  Attention is drawn to the implications of the high densities observed in
  flare plasmas in the wide temperature range from 10 to the 4th K to more
  than 10 to the 7th K. The chromospheric evaporation theory for the decay
  phase is discussed, and it is found that it is not consistent with the
  observations. It is pointed out that all the flare mechanisms proposed
  so far, e.g., magnetic field reconnection in various geometries, have
  entirely ignored the fundamental problem of how the high densities
  arise in the first place, and, in fact, they are unable to answer this
  question. It is suggested that compressional heatings of a flaring loop
  might be responsible for the density and emission measure (EM) increases
  observed in flare plasmas. Chromospheric evaporation associated with
  local heating in the initial rising phase of the flare, in distinction
  to the existing evaporation theory which assumes a coronal heating
  source, is also discussed. Possible observational tests, utilizing
  the newly launched Solar Maximum Mission (SMM) satellite, are presented.

Title: Solar flare X-ray spectra between 7.8 and 23.0 angstroms
Authors: McKenzie, D. L.; Landecker, P. B.; Broussard, R. M.; Rugge,
   H. R.; Young, R. M.; Feldman, U.; Doschek, G. A.
Bibcode: 1981STIN...8225072M
Altcode:
  High resolution X-ray spectra taken during a large solar flare on
  10 June 1979 are presented. Many lines of highly ionized iron were
  resolved and identified for the first time in solar spectra. Lines
  with a wide range of excitation temperatures are found to have a
  similar time development during the flare's rapid rise phase. The
  density-sensitive line ratios in Fe(XXI) and Fe(XXII) are discussed.

Title: The detection of companion stars to the Cepheid variables
    Eta Aquilae and T Monocerotis.
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1981NASCP2171..209M
Altcode: 1981NASCP3171..209M; 1980IUE80......209M; 1981uviu.nasa..209M
  Ultraviolet spectra of the classical Cepheid variables eta Aq1
  and T Mon at several phases in their periods were obtained with
  IUE. For eta Aq1 significant ultraviolet emission is detected at
  wavelengths less than 1600 A, where little flux is expected from
  classical Cepheids. Furthermore, the emission at wavelengths less
  than about 1600 A does not vary with phase. Comparison with model
  atmosphere flux distributions shows that the nonvariable emission is
  consistent with the flux expected from a main sequence companion star
  with an effective temperature of about 9500 K (AO V - A1 V). For T Mon
  a nonvarying component to the ultraviolet emission is observed for
  wavelengths less than 2600 A. Comparison with model atmosphere flux
  distributions suggests that the companion has an effective temperature
  of around 10,000 K (AO) and is near the main sequence.

Title: The detection of a companion star to the Cepheid variable
    T Monocerotis
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1980ApJ...242.1083M
Altcode:
  We have obtained ultraviolet spectra with the International Ultraviolet
  Explorer (IUE) spacecraft of the classical Cepheid T Mon at several
  phases in the 27 day period. Significant ultraviolet emission is
  detected at wavelengths less than 1600 A, where little flux is expected
  from classical Cepheids. Furthermore, the emission at wavelengths
  less than about 1900 A does not vary with phase. Comparison with model
  atmosphere flux distributions shows that the emission is consistent with
  the flux expected from a companion star with an effective temperature
  of about 10,000 K (approximately A0) near the main sequence.

Title: High-resolution X-ray spectra of solar flares. IV - General
    spectral properties of M type flares
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.; Mariska, J. T.
Bibcode: 1980ApJ...241.1175F
Altcode:
  The spectral characteristics in selected narrow regions of the X-ray
  spectrum of class M solar flares are analyzed. High-resolution spectra
  in the ranges 1.82-1.97, 2.98-3.07, 3.14-3.24 and 8.26-8.53 A, which
  contain lines important for the determination of electron temperature
  and departure from ionization equilibrium, were recorded by spaceborne
  Bragg crystal spectrometers. Temperatures of up to 20,000,000 K are
  obtained from line ratios during flare rise phases in M as well as X
  flares, while in the decay phase the calcium temperature can be as low
  as 8,000,000 K, which is significantly lower than in X flares. Large
  nonthermal motions (on the order of 130 km/sec at most) are also
  observed in M as well as X flares, which are largest during the soft
  X-ray rise phase. Finally, it is shown that the method proposed by
  Gabriel and Phillips (1979) for detecting departures of electrons
  from Maxwellian velocity distributions is not sufficiently sensitive
  to give reliable results for the present data.

Title: Solar flare X-ray spectra between 7.8 and 23.0 Angstroms.
Authors: McKenzie, D. L.; Landecker, P. B.; Broussard, R. M.; Rugge,
   H. R.; Young, R. M.; Feldman, U.; Doschek, G. A.
Bibcode: 1980ApJ...241..409M
Altcode:
  The high-resolution X-ray spectra taken during a large solar flare
  on 1979 June 10 are presented. Many lines of highly ionized iron are
  resolved and identified for the first time in solar spectra. Lines with
  a wide range of excitation temperatures have similar time development
  during the flare's rapid rise phase. The density sensitive line ratios
  in Fe XXI and Fe XXII are discussed.

Title: Simultaneous Observations of Solar Flares Obtained by the
    SOLEX AND SOLFLEX High Resolution X-Ray Spectrometers
Authors: Landecker, P. B.; McKenzie, D. L.; Doschek, G. A.; Feldman, U.
Bibcode: 1980BAAS...12Q.906L
Altcode:
  No abstract at ADS

Title: Physical conditions in the solar atmosphere above an active
    region
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1980ApJ...240..300M
Altcode:
  From a series of EUV spectra obtained at several heights above the
  limb in a solar active region, the volume emission measure is derived
  as a function of the electron temperature in the temperature range
  70,000-1,500,000 K and the electron density at two locations. The
  emission measure from the coronal material (temperature greater than
  700,000 K) is nearly the same everywhere and represents most of the
  material in the line of sight, while the emission measure from the
  transition region material (temperature between 70,000 and 250,000
  K) fluctuates by two orders of magnitude from position to position
  above the active region. This is in agreement with the picture of
  this active region as consisting of a number of well-defined loops
  or lower portions of loops at transition region temperatures that
  are inhomogeneously distributed in much larger and more diffuse loop
  structures at coronal temperatures. The coronal data are in reasonable
  agreement with simple coronal models. Emission measures near 1,000,000
  K evaluated using different ions differ by a factor of 4, suggesting
  difficulties with the atomic physics data.

Title: High-resolution X-ray spectra of solar flares. III - General
    spectral properties of X1-X5 type flares
Authors: Doschek, G. A.; Feldman, U.; Kreplin, R. W.; Cohen, L.
Bibcode: 1980ApJ...239..725D
Altcode:
  High-resolution X-ray spectra of six class X1-X5 solar flares are
  discussed. The spectra were recorded by spaceborne Bragg crystal
  spectrometers in the ranges 1.82-1.97, 2.98-3.07 and 3.14-3.24
  A. Electron temperatures derived from dielectronic satellite line to
  resonance line ratios for Fe XXV and Ca XIX are found to remain fairly
  constant around 22,000,000 and 16,000,000 K respectively during the
  rise phase of the flares, then decrease by approximately 6,000,000 K
  during the decay phase. Nonthermal motions derived from line widths
  for the April 27, 1979 event are found to be greatest during the rise
  phase (approximately 130 km/sec) and decrease to about 60 km/sec during
  decay. Volume emission measures for Fe XXV, Ca XIX and Ca XX are derived
  from photon fluxes as a function of temperature, and examination of the
  intensity behavior of the Fe K alpha emission as a function of time
  indicates that it is a result of fluorescence. Differences between
  the present and previous observations of temperature variation are
  discussed, and it is concluded that the flare plasmas are close to
  ionization equilibrium for the flares investigated.

Title: Atomic data for S IV and solar observations of the 3x/2/3p
    /2/P-3s3p/2/ /4/P multiplet
Authors: Bhatia, A. K.; Doschek, G. A.; Feldman, U.
Bibcode: 1980A&A....86...32B
Altcode:
  High resolution observations of intersystem lines of S IV near 1400
  A are available from Skylab. These lines are potentially useful
  as density diagnostics for the solar atmosphere. Energy levels,
  transition probabilities and collision strengths have, therefore, been
  calculated for S IV, including the configurations 3x(2)3p, 3s3p(2), and
  3s(2)3d. Line intensities and level populations have been calculated as
  a function of electron density. The calculated population of the 3s3p(2)
  (4)P(5/2) level is found to reach a pseudo-Boltzmann equilibrium at a
  density which is four times higher than is inferred from solar spectra
  and level population calculations of lighter ions such as O IV.

Title: Observations of the O I 1355.6 A and C I 1355.8 A lines in
    solar flares
Authors: Cheng, C. C.; Feldman, U.; Doschek, G. A.
Bibcode: 1980A&A....86..377C
Altcode:
  The paper presents observations of the intersystem line O I 1355.6
  A and the allowed line C I 1355.8 A in solar flares. In flares,
  the intersystem O I line is weaker than the allowed C I line and
  the intensity ratio O I/C I is 0.3-0.7. On the other hand, in active
  regions, O I line is stronger than the C I line and O I/C I is about
  1-2, while in quiet sun regions, the O I line is much stronger than
  the C I line and O I/C I not in excess of 20. The variation of the
  intensity ratio from quiet sun region to flares may be due to an
  electron density enhancement of a factor of about 50 in flares.

Title: The detection of a companion star to the Cepheid variable
    eta Aql.
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1980ApJ...238L..87M
Altcode:
  Ultraviolet spectra have been obtained with IUE of the classical Cepheid
  Eta Aquilae at several phases in the 7.18 day period. Significant
  ultraviolet emission is detected at wavelengths less than 1600 A,
  where little flux is expected from classical Cepheids. Furthermore,
  the emission at wavelengths less than about 1600 A does not vary with
  phase. Comparison with model atmosphere flux distributions shows that
  the nonvariable emission is consistent with the flux expected from a
  main-sequence companion star with an effective temperature of about
  9500 K (A0 V). The observed ultraviolet flux and spectral type are
  used to compute a distance of 300 pc to the system, in agreement with
  the distance predicted using the period luminosity relation.

Title: High-resolution X-ray spectra of the 1979 March 25 solar flare
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.
Bibcode: 1980ApJ...238..365F
Altcode:
  High-resolution X-ray spectra of a solar flare that occurred on
  1979 March 25 are discussed. The spectra were obtained from four
  Bragg crystal spectrometers (SOLFLEX = solar flare X-rays) flown by
  NRL on a spacecraft launched by the Air Force. The wavelength ranges
  discussed here are: 1.82-1.97 A, 2.98-3.07 A, and 3.14-3.24 A. Electron
  temperatures ranging between 12 x 10 to the 6th K and 30 x 10 to the 6th
  K are derived from dielectronic satellite to resonance line ratios. The
  apparent departure from ionization equilibrium indicated by intensities
  of other satellite lines is discussed. Wavelengths and identifications
  are given for the strongest lines observed. It is proposed that the
  soft X-ray flare radiation is caused by the slow compression of a
  single or multiple set of magnetic flux tubes. Experimental methods
  of confirming or refuting this hypothesis are given.

Title: Electron densities in a solar flare derived from X-ray spectra
Authors: McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge,
   H. R.; Young, R. M.; Doschek, G. A.; Feldman, U.
Bibcode: 1980ApJ...238L..43M
Altcode:
  A major solar flare was observed with the rubidium acid phthalate
  crystal of the satellite-borne SOLEX B spectrometer and high-resolution
  solar X-ray spectra were obtained during the rising phase of the
  flare. Measurements of the density-sensitive line ratio of the O
  VII 1s2 1S(0) - 1s2s 3S(1) (22.10 A) flux to the O VII 1s2 1S(0) -
  1s2p 3P(1) (21.80 A) flux indicate that the density of the plasma at
  around 2,000,000 K exceeded 10 to the 11th per cu cm near the peak of
  the flare. This corresponds to an electron pressure of about 30 dynes
  per sq cm.

Title: Mass Motions in the Transition Zone of Coronal Holes
Authors: Doschek, G. A.; Mariska, J. T.; Feldman, U.
Bibcode: 1980BAAS...12S.518D
Altcode:
  No abstract at ADS

Title: High resolution solar flare X-ray spectra.
Authors: Feldman, U.; Doschek, G. A.; Kreplin, R. W.
Bibcode: 1980BAAS...12..529F
Altcode:
  No abstract at ADS

Title: The Detection of an Early Type Companion Star to the Classical
    Cepheid T Mon
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1980BAAS...12Q.462M
Altcode:
  No abstract at ADS

Title: Impulsive phase of solar flares
Authors: Kane, S. R.; Crannell, C. J.; Datlowe, D.; Feldman, U.;
   Gabriel, A.; Hudson, H. S.; Kundu, M. R.; Maetzler, C.; Neidig, D.;
   Petrosian, V.
Bibcode: 1980sfsl.work..187K
Altcode: 1980sofl.symp..187K
  The present understanding of the impulsive phase of a solar flare,
  characterized by short-duration bursts of impulsive hard X-ray,
  EUV, optical and radio emission indicating the release of energetic
  electrons is reviewed. Observations of the spectral distribution
  of impulsive hard X-ray bursts and of Type III and radio continuum
  bursts are presented and interpreted in terms of energetic electron
  distributions, and impulsive EUV, XUV, soft X-ray and optical
  observations, which provide a lower limit to total energy release
  during the impulsive phase, are discussed. The role of energetic
  electrons in exciting the hard X-ray, EUV and microwave emissions is
  considered, and thin-target, thick-target, partial-precipitation and
  thermal models of impulsive phase electron acceleration are evaluated
  in light of the observations. It is noted that available data do
  not allow discrimination between a thermal or a nonthermal electron
  distribution, on which depends the proportion of flare energy supplied
  by the energetic electrons, and that data favors models which permit
  at least partial electron precipitation. Future observational and
  theoretical work is indicated.

Title: The Detection of a Companion Star to the Cepheid Variable
    Eta Aquilae
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1979BAAS...11..687M
Altcode:
  No abstract at ADS

Title: Solar Flare Electron Densities Derived from X-ray Spectra
Authors: McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge,
   H. R.; Young, R. M.; Doschek, G. A.; Feldman, U.
Bibcode: 1979BAAS...11..676M
Altcode:
  No abstract at ADS

Title: SOLEX Solar Flare X-ray Spectra from 5 to 23 Å
Authors: Landecker, P. B.; McKenzie, D. L.; Broussard, R. M.; Rugge,
   H. R.; Young, R. M.; Doschek, G. A.; Feldman, U.
Bibcode: 1979BAAS...11Q.709L
Altcode:
  No abstract at ADS

Title: New atomic data for Si/6+/, S/8+/ and Ar/10+/
Authors: Bhatia, A. K.; Feldman, U.; Doschek, G. A.
Bibcode: 1979A&A....80...22B
Altcode:
  The paper gives new atomic data, populations of excited levels,
  and line intensity ratios for the ions Si VII, S IX, and Ar XI
  of the O I isoelectronic sequence. Ten levels are included in the
  calculations, i.e., the levels of the 2s/2/2p/4/ and 2s2p/5/ and
  2p/6/ configurations. It is noted that the calculations are done
  for applications to solar plasmas. The line ratios (2s/2/2p/4/3P1
  - 2s2p/5/3P0) / (2s/2/2p/4/3P1 - 2s2p/5/3P1) and (2s/2/2p/4/1D2 -
  2s2p/5/1P/1/) / (2s/2/2p/4/3P/1/ - 2s1p/5/3P/1/) are two of the ratios
  useful for electron density determination. Finally, density sensitive
  line ratios of Ca XIII and Fe XIX are also discussed.

Title: The N III and O IV intersystem multiplets as density indicators
    for solar plasmas.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1979A&A....79..357F
Altcode:
  The usefulness of the relative intensities of lines within the N III
  intersystem multiplet near 1750 A as an electron density indicator for
  solar plasmas is discussed. Although the relative intensities of lines
  in the multiplet are density sensitive, the intensity ratios should at
  present be used with caution. Errors of the order of 20% in transition
  probabilities and excitation rate coefficients can lead to order of
  magnitude errors in density determinations. It is demonstrated that the
  intensity ratio of one of the N III intersystem lines and an allowed
  line from a different ion may also be used as a density indicator in
  the 10 to the 9th to 10 to the 11th per cu cm regime.

Title: High-resolution solar flare X-ray spectra.
Authors: Doschek, G. A.; Kreplin, R. W.; Feldman, U.
Bibcode: 1979ApJ...233L.157D
Altcode:
  High-spectral-resolution solar flare spectra have been recorded
  by four Bragg crystal spectrometers flown by the Naval Research
  Laboratory on a spacecraft. The wavelength ranges are 1.82-1.97 A,
  2.98-3.07 A, and 3.14-3.24 A. Electron temperatures ranging between
  12 million and 30 million K are derived from dielectronic satellite
  to resonance-line ratios for an X9 flare that occurred on March 25,
  1979. Nonthermal motions varying between about 70 and 160 km/s are
  derived from line profiles. Equilibrium conditions in the plasma are
  investigated by using lithium-like satellite lines excited by electron
  impact excitation. Emission measures of about 5 x 10 to the 50th per
  cu cm are determined for the times of maximum X-ray flux.

Title: EUV limb spectra of a surge observed from Skylab.
Authors: Doschek, G. A.; Feldman, U.; Mason, H. E.
Bibcode: 1979A&A....78..342D
Altcode:
  The EUV spectra of a surge observed at plus 8 in. and plus 20
  in. above the white light limb from Skylab are examined. The shape of
  the differential emission measure determined at 8 in. and 20 in. is
  nearly the same as for a quiet Sun spectrum at 8 in., but the emission
  measure of the surge at 8 in. is about an order of magnitude greater
  than for the quiet Sun. At 20 in. the emission measure of the surge is
  initially close to the quiet Sun distribution, but decreases by a factor
  of 4 within 6 min. The optically thin lines formed near 10 to the 5th
  power K show nonthermal broadening at 8 in., and electron densities near
  this temperature are derived from intersystem to resonance ratios. The
  volume of the emitting plasma at 8 in. above the limb was determined,
  concluding that a continuous energy input is required to explain the
  observations.

Title: The Fe XXI lambda 1354 line in solar flares observed from
    Skylab and its implications on ionization equilibrium calculations.
Authors: Cheng, C. -C.; Feldman, U.; Doschek, G. A.
Bibcode: 1979ApJ...233..736C
Altcode:
  We have measured the line width of the forbidden line Fe xxi Al 354
  in flare spectra observed from Skylab. The measured line widths are
  examined using three sets of ionization equilibrium calculations
  by Jordan, Summers, and Jacobs et al. The results indicate that the
  ionization equilibrium temperature of Fe xxi is more likely to be 1.0
  x 10 K, a value given by Jacobs et al. and Jordan, rather than the
  higher value of 2.0 x 10 K given by Summers. Subject headings: Sun:
  flares - Sun: spectra

Title: Extreme-ultraviolet limb spectra of a prominence observed
    from Skylab.
Authors: Mariska, J. T.; Doschek, G. A.; Feldman, U.
Bibcode: 1979ApJ...232..929M
Altcode:
  Line profiles of extreme ultraviolet emission lines observed in a
  solar prominence at positions above the white-light limb with the NRL
  slit spectrograph on Skylab are discussed. Absolute line intensities
  and full widths at half-maximum are presented, and emission measures,
  electron densities, and mass motions are derived at several locations
  within the prominence. For electron temperatures less than 40,000
  K, the calculated mass motions are found to be near zero, while for
  electron temperatures greater than 40,000 K, the nonthermal velocity
  decreases with increasing height in the prominence. It is suggested
  that falling material is responsible for the fact that the measured
  electron density decreases with height less rapidly than the decrease
  predicted for a hydrostatic gas. In addition, from the He II 1640 A
  line profile, an average temperature of 27,000 K is derived for the
  region in which He II is emitted.

Title: New atomic data for O<SUP>+2</SUP>.
Authors: Bhatia, A. K.; Doschek, G. A.; Feldman, U.
Bibcode: 1979A&A....76..359B
Altcode:
  New atomic data are tabulated for the ion O(2+). Collision strengths
  are calculated for several energies of the exciting electron. The
  populations of the levels of O(2+) are calculated as a function
  of electron density under conditions appropriate for the solar
  atmosphere. The available solar data are compared with theoretical
  predictions of relative line intensities.

Title: Solar flare spectroscopic diagnostics for wavelengths less
    than 2000 angstroms
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1979nrl..reptQ....D
Altcode:
  We discuss the use of intensity ratios of emission lines for determining
  the electron density and temperature in flare plasmas. The availability
  diagnostics cover the temperature range from about 40,000 K to about
  10,000,000 K. We summarize the current work on flare density diagnostics
  and review the applications of this theory to available flare
  spectra. We discuss the importance of line profiles for determining
  nonthermal mass motions in the plasma and for estimating path lengths
  along the line of sight. We review the current information on line
  profiles in flare spectra. We comment on determining departures from
  ionization equilibrium using line ratios in the X-ray and EUV regions.

Title: On the structure of the solar transition zone and lower corona.
Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T.
Bibcode: 1979ApJ...229..369F
Altcode:
  Recent observations of the solar transition zone and corona
  obtained primarily from NRL spectrographs on Skylab are summarized
  and used to examine the structure of the transition zone. The
  transition zone is revealed to be more inhomogeneous than is
  apparent from spectroheliograms with spatial resolution of about 3
  arcsec. Transition-zone emission appears to arise in spicularlike
  structures. The effective area covered by the emitting structures at
  lower transition-zone temperatures (about 100,000 K) is only about 1%
  of the total surface area of the sun. The transition zone is highly
  inhomogeneous even over cell interior regions, where fluctuations in
  brightness by factors of 25 can occur. It is shown that homogeneous
  coronal models are not valid for the inner corona. Most of the
  higher-density inner corona is concentrated into looplike structures
  that extend down to the white-light limb. These structures are
  unrelated to the spicular-type structures that produce most of the
  transition-zone emission.

Title: Fe XXI as an electron density diagnostic in solar flares.
Authors: Mason, H. E.; Bhatia, A. K.; Doschek, G. A.; Feldman, U.
Bibcode: 1979A&A....73...74M
Altcode:
  Atomic data have been calculated for Fe XXI, and the theoretical
  intensity ratios for many transitions are tabulated. Fe XXI lines in
  wavelength regions 1-25 A, 90-200 A, and 300-2500 A are discussed with
  reference to presently available solar and laboratory spectra. It is
  found that Fe XXI is an excellent density diagnostic for solar-flare
  and tokamak plasmas, when densities are in the range from 10 to the
  11th to 10 to the 15th per cu cm. The theoretical calculations are
  applied to flare spectra obtained from OSO 5, and an electron density
  of less than 10 to the 13th per cu cm is deduced for a temperature
  of 10,000,000 K. The results are somewhat ambiguous in several cases
  because of the limited spectral and temporal resolution of these
  earlier spectrometers. However, the calculations will be important
  for forthcoming solar projects, such as the Solar Maximum Mission.

Title: High Resolution Solar Flare X-Ray Spectra
Authors: Kreplin, R. W.; Doschek, G. A.; Feldman, U.; Bell, W. D.;
   Wassam, W. W.
Bibcode: 1979BAAS...11..421K
Altcode:
  No abstract at ADS

Title: Nonthermal broadening of extreme ultraviolet emission lines
    near the solar limb.
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1979A&A....73..361M
Altcode:
  Summary. Line profiles of optically thin extreme ultraviolet emission
  lines observed in quiet-Sun regions at 8', 12', and 20' above the
  white light limb with the NRL slit spectrograph (5082-B) on Skylab are
  discussed. Random mass-motion velocities are calculated. The velocity
  is found to increase with increasing height above the white light limb
  for all the lines regardless of the temperature of formation between 4
  l0 K and 2l0 K. At +12' a typical velocity is about 33km -1 Key words:
  Sun - transition zone - EUV spectra

Title: The dynamical properties of the solar corona from intensities
    and line widths of EUV forbidden lines of Si VIII, Fe XI, and Fe XII.
Authors: Cheng, C. -C.; Doschek, G. A.; Feldman, U.
Bibcode: 1979ApJ...227.1037C
Altcode:
  We have studied the line profiles of the solar coronal forbidden lines
  Si viii 1445.76 A, Fe XI 1467.08 A, and Fe xii 1242.03 A in quiet and
  active coronal regions from a survey of available limb spectra in the
  NRL Skylab data. The results show that the line widths of these lines
  are essentially the same in quiet-Sun regions as in active regions. For
  some active regions, however, the line widths are systematically
  narrower than those in quiet-Sun regions. In addition, the line widths
  are about the same in the height range from 0" to 30 . The widths are
  wider than the thermal Doppler widths at the ionization equilibrium
  temperature given by Jordan. The additional widths correspond to
  a nonthermal mass-motion velocity of 10-25 km -1 at 1.7 x 106 K (Fe
  xii), 10-17 km -1 at 1.5 x 10 K (Fe xi), and 10-20 km -1 at 9.3 x 10 K
  (Si viii). The intensities of the forbidden lines in active regions are
  about an order of magnitude greater than those in quiet-Sun regions. The
  distribution of column density calculated for the three different lines
  indicates that more plasma is near 1.7 x 106 K than near 9.3 x 10 K
  at a given height. The observational results are discussed in terms
  of coronal heating mechanisms. The dissipation of acoustic waves does
  not provide a sufficient heating rate. The dissipation of three modes
  of hydromagnetic waves-the slow mode, the fast mode, and the AlfVe'n
  mode-also cannot satisfactorily explain the observational results. It
  is difficult for heating by hydromagnetic waves to meet simultaneously
  the requirements of a large enough heating rate, a dissipation length
  comparable to the length of a coronal loop, and a velocity amplitude
  that agrees with observations. Subject headings: line profiles - Sun:
  corona - Sun: spectra - ultraviolet: spectra

Title: L-series satellite spectra in Ti XII and Fe XVI.
Authors: Burkhalter, P. G.; Cohen, L.; Cowan, R. D.; Feldman, U.
Bibcode: 1979JOSA...69.1133B
Altcode: 1979OSAJ...69.1133B
  Transitions in Na-like Ti and Fe ions, which appear as satellites
  to 2p-3s and 2p-3d transitions in Ne-like ions, were studied. The
  soft X-ray spectra produced by a focused-laser source and a
  vacuum-spark device were obtained with the same grazing-incidence
  spectrograph. Atomic structure calculations agreed with the observed
  2p-3s spectral patterns and made possible line identifications in Ti
  XII and Fe XVI.

Title: Electron densities in the solar corona from density-sensitive
    line ratios in the N I isoelectronic sequence.
Authors: Feldman, U.; Doschek, G. A.; Mariska, J. T.; Bhatia, A. K.;
   Mason, H. E.
Bibcode: 1978ApJ...226..674F
Altcode:
  Electron densities are derived in the solar inner corona from forbidden
  lines of S x near 1100 A. The density-sensitive line ratio considered
  is (4S0312-2D0312)/(4S0312-2D0612). The ratio is calculated as a
  function of density for four ions of the N I isoelectronic sequence,
  i.e., Mg VI, Si VIII, S x, and Ar XII. The variation of the ratio
  (4S0312-2P0312)/(4S0312-2D0312) with density is also calculated. The
  results are applied to off-limb spectra recorded by the NRL Skylab
  spectrograph. Densities were found to be the same in five quiet Sun
  regions and four active regions observed at heights &gt; 8" outside
  the white-light limb. The average density derived from the S x lines
  for all regions considered is 1.0 x 10 cm -3. This result applies to
  plasma at the temperature of formation of S x, i.e., 1.3 x 106 K. At
  heights greater than 20" outside the limb the average density is 7.7 x
  108 cm -3, and between 8" and 12" above the limb the average density is
  1.0 x 10 cm 3, for both quiet Sun and active regions. Subject heading:
  Sun: corona

Title: Densities in the quiet sun and polar coronal holes from EUV
    line ratios involving O III (1666.15 Å).
Authors: Doschek, G. A.; Feldman, U.; Bhatia, A. K.; Mason, H. E.
Bibcode: 1978ApJ...226.1129D
Altcode:
  The EUV line intensity ratios C iii (1908.73 A)/o iii (1666.15 A), 0 iii
  (1666.15 A)/Si iv (1402.77 A), and C iii (1908.73 A)ISi iv (1402.77 A)
  are shown to be sensitive to variations in the electron density at
  densities typical of the quiet Sun ( 1010 cm - at 6 x 10 K). Using
  the 0 iii line, the above ratios can be normalized to observational
  data and densities in quiet-Sun regions and coronal holes can be
  determined. The average value of the density determined for three
  quiet-Sun regions is 1.9 x 1010 cm - . The densities determined from
  several observations of the north and south polar coronal holes are
  about the same as in the quiet Sun, with the exception of one set of
  observations of the north polar hole that indicates a density about
  a factor of 2 less than that of the quiet Sun. Subject headings: Sun:
  corona - Sun: spectra - ultraviolet: spectra

Title: Measurements of extreme-ultraviolet emission-line profiles
    near the solar limb.
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1978ApJ...226..698M
Altcode:
  Line profiles of optically thin extreme-ultraviolet emission
  lines observed in a quiet sun region at positions within and above
  the white-light limb with the NRL slit spectrograph (S082-B) on
  Skylab are discussed. Absolute line intensities and full widths at
  half-maximum are presented for lines formed over the temperature range
  from about 10,000 to 22,000 K. The line intensities are compared with
  the predictions of simple atmospheric models consisting of a spicule
  component and a thin spherically symmetric or network models, but can
  be explained by assuming that the emission arises from spicule-like
  inhomogeneities. Random mass-motion velocities are calculated. The
  velocity increases with increasing temperature of line formation. Near
  the limb and above about 4000 K the calculated velocity is consistent
  with the predictions of a constant acoustic flux passing through the
  transition zone. For the ions formed at temperatures not less than
  about 63,000 K, the velocity is found to increase with increasing
  height above the white-light limb.

Title: Electron densities in stellar atmospheres determined from
    IUE spectra.
Authors: Doschek, G. A.; Feldman, U.; Mariska, J. T.; Linsky, J. L.
Bibcode: 1978ApJ...226L..35D
Altcode:
  No abstract at ADS

Title: EUV spectra from Skylab (1175 - 1940 Å). Mass motions in
    the transition zone in regions of solar activity.
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1978A&A....69...11D
Altcode:
  The profiles of spectral lines in the 1100-2000-A range emitted by
  transition-zone ions in regions of solar activity are discussed. The
  data were recorded by the NRL spectrograph on Skylab. At the spatial
  resolution of the Skylab spectrograph (2 x 60 arcsec), it is shown that
  the line profiles result from the superposed emission of a number of
  physically distinct regions at different electron densities and with
  different mass motions. Although high densities are found for some
  surgelike phenomena at transition-zone temperatures, the densities can
  also be comparable to normal active-region densities. Line profiles,
  as well as spectral line intensities, must be considered if meaningful
  theoretical models of dynamic activity in the transition zone are to
  be constructed.

Title: Evolution of the coronal and transition-zone plasma in a
compact flare: the event of 1973 August 9.
Authors: Underwood, J. H.; Antiochos, S. K.; Feldman, U.; Dere, K. P.
Bibcode: 1978ApJ...224.1017U
Altcode:
  X-ray and extreme ultraviolet observations of a compact flare were
  analyzed to determine the relative importance of radiation, thermal
  conduction, and 'evaporation' in the evolution of the temperature and
  density structure of the plasma. In the event studied (1973 August 9),
  the electron density was relatively high (5 x 10 to the eleventh to 1 x
  10 to the twelfth) and radiation was evidently an important energy-loss
  and cooling mechanism. The light curves of ultraviolet lines formed at
  temperatures between 10 to the fifth to 10 to the seventh K indicate a
  time-varying emission measure gradient, and hence temperature gradient,
  during the flare. Radiative instability evidently played an important
  role in determining the steepness of these gradients during the rise
  and fall phases, and caused strong downward motions of material during
  the cooling phase. Toward the end of the event, the coronal electron
  density decreased and the temperature gradient relaxed toward that
  expected from a conduction-dominated plasma. For this flare, evaporative
  cooling did not appear to be a significant factor.

Title: Emission-line spectra of two active regions on the solar limb:
    1175 - 1940 Å.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1978ApJS...37..443F
Altcode:
  Skylab emission-line spectra (1175 to 1940 A) of two active
  regions on the solar limb are examined. Electron densities for the
  active regions are derived using the intensity ratios of selected
  intersystem and allowed lines. The intensity ratios in the active
  regions are compared with those observed previously in quiet-sun and
  coronal-hole regions. The behavior of coronal forbidden lines relative
  to transition-zone lines is discussed along with the solar continuum
  intensities near and above the limb. These continuum intensities are
  then compared with those at similar slit positions for the quiet sun
  and the previously studied coronal hole. The active-region data are
  found to be consistent with either (1) multithermal loops with the
  high-temperature plasma occupying the tops of the loops or (2) nearly
  isothermal loops with the hotter loops extending to higher altitudes.

Title: XUV spectra of the 1973 June 15 solar flare observed from
    Skylab. III. A list of spectral lines from 1000 to 1940 Å.
Authors: Cohen, L.; Feldman, U.; Doschek, G. A.
Bibcode: 1978ApJS...37..393C
Altcode:
  A wavelength list of spectral lines between 1000 and 1940 A is
  presented for the solar flare that occurred on June 15, 1973. The
  spectra were recorded by the NRL spectrograph on Skylab. The spectral
  resolution is 0.06 A. Intensities, identifications, and estimates of
  line widths are given. The intensity of the continuum is also given at
  50-A intervals between 1400 and 1900 A. The wavelength list includes
  about 1400 lines; about 30% of these lines are not indentified. Because
  of the high wavelength resolution, this line list will be useful as a
  source of identification for some stellar as well as solar spectra. In
  particular, the list should be a useful aid in the identification
  of lines in the spectra of stars with classifications close to that
  of the sun. Spectra of such stars may be obtained from the recently
  launched IUE spacecraft. It is also interesting to compare the list
  with some of the spectra of early-type stars recorded by Copernicus.

Title: The importance of spectroscopy in the 80 800 å region for
    plasma diagnostics in the solar atmosphere
Authors: Feldman, U.; Doschek, G. A.; Behring, W. E.
Bibcode: 1978SSRv...22..191F
Altcode:
  We discuss the importance of the spectral range from about 80 to 800
  Å for determining physical conditions in different regions of the
  solar atmosphere. We give examples of line ratios that may be used to
  determine electron densities in quiet Sun regions, active regions,
  and flares. We discuss the possibility of determining electron
  temperatures from line ratios in the EUV. We show that profiles as
  well as intensities of spectral lines must be obtained for a proper
  interpretation of the spectra. We give approximate parameters for a
  solar grazing incidence spectrograph suitable for the study of the 80
  800 Å wavelength region.

Title: The electron density at 10<SUP>5</SUP>K in different regions
    of the solar atmosphere derived from an intersystem line of O IV.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1978A&A....65..215F
Altcode:
  Summary. Electron densities are derived for typical solar active
  regions and flares from EUV spectral lines of 0 IV, N V, C iv and
  Si iv. The densities pertain to electron temperatures near 10 K. The
  spectra were recorded by the NRL spectrograph flown on Skylab. Typical
  densities found for active regions are 1011 . The density in flares
  can range from 1011 to above 1013 . The volumes of high density
  emitting plasma in active regions and flares are quite small, with
  values ranging from 1.5 1(Y cm3 to less than 2.2 1020 cm3. Also, the
  density in a polar coronal hole is about one-half of the density in
  a typical quiet Sun region, at a temperature near 6 1 K. Key words:
  Sun-transition zone-electron density

Title: Nonthermal Broadening of Extreme Ultraviolet Emission Lines
    near the Solar Limb
Authors: Mariska, J. T.; Feldman, U.; Doschek, G. A.
Bibcode: 1978BAAS...10..432M
Altcode:
  No abstract at ADS

Title: The Dynamical Properties of the Solar Corona from Intensities
    and Line Widths of EUV Forbidden Lines of Si VIII, Fe XI, and Fe XII.
Authors: Cheng, C. C.; Doschek, G. A.; Feldman, U.
Bibcode: 1978BAAS...10Q.439C
Altcode:
  No abstract at ADS

Title: Electron densities in solar flare and active region plasmas
    from a density-sensitive line ratio of Fe IX.
Authors: Feldman, U.; Doschek, G. A.; Widing, K. G.
Bibcode: 1978ApJ...219..304F
Altcode:
  We demonstrate that the intensity ratio of the two lines of Fe IX
  at 241.739 and 244.911 A (3p53d 3P2 2p6 `So and 3p53d 3P, 2p6 `So)
  is sensitive to electron density above about 1010 . We calculate the
  intensity ratio as a function of density, and apply the result to two
  spectroheliograms of flares and surrounding plage regions recorded by
  the Naval Research Laboratory spectroheliograph on Skylab. We find that
  the densities at coronal temperatures of 106K vary considerably from
  region to region and can be at least as high as 2 x 10" cm 3. Subject
  headings: Sun: flares - Sun: spectroheliograms - ultraviolet: spectra

Title: High-resolution spectra of the solar Mg II h and k lines
    from Skylab.
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1977ApJS...35..471D
Altcode:
  Spectra of the Mg II h and k lines emitted by different regions in the
  solar atmosphere have been recorded by the NRL slit spectrograph on
  Skylab. The spectral resolution is 0.12 A, and the spatial resolution
  is 2 by 60 arcsec. Several examples are presented, including spectra
  of a chromospheric supergranulation cell boundary and interior and of
  a quiet-sun region above the limb, as well as selected active-region
  spectra on the disk and above the limb. Obvious differences among
  these spectra are noted and qualitatively discussed.

Title: The solar spectrum in the vicinity of the Si IV lines at 1122
    and 1128 Å.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977A&A....61..295F
Altcode:
  Summary. The extreme ultraviolet solar spectrum in the vicinity of
  the Si iv lines at 1122 and 1128 A is presented with a wavelength
  resolution of 0.06 A. The Si iv line at 1122.486 A is blended with
  an unresolved line of Fe "I at 1122.526 A. The Siiv line at 1128.340A
  is near two faint Fe iii lines. However, these lines will contribute
  little to the intensity of the Si iv line, even when the intensity is
  recorded with a wide spectrograph slit. Key words: extreme ultraviolet
  solar spectrum solar transition zone

Title: A search for a turbulent-free region in the solar transition
    zone.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977ApJ...216L.119F
Altcode:
  A search for a turbulence-free transition-zone region was conducted. The
  data used were spectra recorded by a slit spectrograph on Skylab. It
  was found that the nonthermal turbulent motions are smallest in
  certain active regions and quiescent prominences. The spectra of one
  such region, a quiescent prominence, are discussed. The nonthermal
  turbulence in the region is between about 2 and 7 km/s. Therefore,
  the widths of lines emitted by transition-zone ions are determined
  primarily by the ion temperature. To within the experimental error,
  temperatures derived from the line widths are equal to the temperatures
  of maximum emitting efficiency obtained using the ionization equilibrium
  calculations of Jordan (1969).

Title: Electron densities in solar flares from line ratios of Ca XVII.
Authors: Doschek, G. A.; Feldman, U.; Dere, K. P.
Bibcode: 1977A&A....60L..11D
Altcode:
  Summary. We show that the intensity ratios of certain extreme
  ultraviolet spectral lines of Ca XVII are sensitive to electron density
  in solar flares. Calculations of the line ratios as functions of
  density are presented. These calculations are based on published atomic
  data for Ca XVII and for other ions of the beryllium isoelectronic
  sequence. For a flare that occurred on 9 August 1973, we derive a
  density of about 5 x 101 from the Ca XVII line ratios. Key words:
  solar flares - Be I sequence

Title: XUV spectra of the 1973 June 15 solar flare observed from
    Skylab. I. Allowed transitions in chromospheric and transition
    zone ions.
Authors: Doschek, G. A.; Feldman, U.; Rosenberg, F. D.
Bibcode: 1977ApJ...215..329D
Altcode:
  Spectra between 1100 and 1940 A of the 1973 June 15 solar flare are
  discussed. The spectra were recorded by the NRL normal-incidence slit
  spectrograph on Skylab. In this paper we discuss allowed transitions in
  ions formed in the chromosphere and transition zone. We give the power
  (ergs s-1) in the emission lines produced by the plasma viewed by the
  instrument, and we give the widths and shapes of the line profiles as
  a function of time during the flare. We calculate emission measures
  and volumes of the flare plasma for lines of Si iv, C iv, and N V. The
  characteristic lengths (= V113) are quite small, ranging between 0'
  1 to 1'.'0. The smaller values are the more reliable. The flare can be
  qualitatively divided into two distinct phases. An eruptive phase occurs
  near the beginning of the flare and lasts for about 2 minutes. Plasma
  is observed moving toward the observer at velocities as high as km 1
  during this phase. A continuous energy input is necessary to account
  for the lifetime of the moving plasma. A much longer lived quiescent
  phase follows the eruptive phase and lasts for about 23 minutes. Subject
  headings: Sun: chromosphere - Sun: flares - Sun: spectra - ultraviolet:
  spectra

Title: XUV spectra of the 1973 June 15 solar flares observed from
    Skylab. II. Intersystem and forbidden transitions in transition zone
    and coronal ions.
Authors: Feldman, U.; Doschek, G. A.; Rosenberg, F. D.
Bibcode: 1977ApJ...215..652F
Altcode:
  An analysis is given of the intersystem lines of transition zone ions
  and high-temperature forbidden lines for the 1973 June 15 flare. The
  electron density in the erupting part of the plasma is at least 1013
  at temperatures of 1.3 x l0 K. The density of the stationary component
  of the flare plasma at similar temperatures varies between 1.5 x 1011
  and 1012 . A density decrease observed in the stationary component
  occurs nearly simultaneously with an intensity enhancement of forbidden
  coronal lines such as Fe xii. These lines are believed to originate in
  arch-type structures. The electron density in the temperature regions
  1.5 x 106K is between 2 x 1010 cm-3 and 2 x 1011 cm-3. These regions
  appear to be stationary. Their motion relative to the observer is less
  than 4 km 1 A continuous energy input is necessary to account for the
  transition zone emission. The transition zone emission arises in small
  regions, perhaps filaments. Subject headings: plasmas - Sun: flares -
  Sun: spectra - ultraviolet: spectra

Title: On the problem of density diagnostics for the EUV spectrum
    of the solar transition zone.
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1977A&A....58L..13D
Altcode:
  Spectral-line ratios that may be used to determine the electron
  temperature and density in the solar transition zone and corona are
  identified. The problem of interpreting the intensity ratios of C
  III lines observed in Skylab EUV limb spectra is considered. It is
  shown that the intensity distribution with height above the solar
  limb of the 1176-A C III lines is different from that of the 1909-A
  C III lines in the Skylab spectra, suggesting that model atmospheres
  must be folded into the C III calculations for proper interpretation
  of the data. Possible reasons for the differences in the intensity
  distributions and widths of the 1176-A and 1909-A lines are discussed
  along with an application to the analogous lines of Si III.

Title: The 3s-3p and 3p-3d lines of Mg II observed above the solar
    limb from Skylab.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977ApJ...212L.147F
Altcode:
  No abstract at ADS

Title: The emission spectrum of the hydrogen Balmer series observed
    above the solar limb from Skylab. I. A quiet Sun and a polar
    coronal hole.
Authors: Rosenberg, F. D.; Feldman, U.; Doschek, G. A.
Bibcode: 1977ApJ...212..905R
Altcode:
  The hydrogen Balmer emission-line spectrum (H9 [3835 A] to the series
  limit at 3646 A) above the limb of the quiet Sun and above the north
  polar coronal hole is discussed. The data were obtained by the NRL XUV
  spectrograph aboard Skylab, with the slit tangent to the limb at 2"
  (1450 km) and at 4" (2900 km) above the limb. Electron densities of 2 x
  1011 cm - , 2" above the limb of both the quiet Sun and coronal hole,
  are calculated from the Stark broadening of the higher series member
  lines, and the related merging of the higher member lines. The widths
  of the lines with principal quantum number m &lt; 15 are broadened
  by opacity, and the opacities are estimated from the line widths. The
  widths of lines of m 15 are not appreciably affected by either opacity
  or Stark broadening. The combined ion temperature and nonthermal mass
  motion determined from the widths of these lines are consistent with
  previously determined values. The intensities of the lines indicate that
  the upper levels (&gt;9) are populated in statistical equilibrium with
  each other. Absolute intensities are given, as well as the decrease of
  the intensity of the lines as a function of height above the limb. The
  Balmer emission-line spectrum above the limb over three active regions
  is discussed in the following paper. Subject headings: Sun: corona -
  Sun: spectra

Title: The Emission Spectrum of the Hydrogen Balmer Series Observed
    above the Solar Limb from SKYLAB. II. Active Regions . . . .
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977ApJ...212..913F
Altcode:
  Electron densities are determined from the Stark broadening of Balmer
  hydrogen lines at 2" above the limb over three active regions. The
  spectra were recorded by the NRL slit spectrograph on Skylab. The
  density was found to be the same for all three regions and is 2 x 1011
  with an error of less than 15% in fitting the theoretical curves to the
  data. The intensity falloff of the hydrogen lines above the limb over
  the active regions is compared with previous results obtained over a
  quiet Sun region and a polar coronal hole. The falloff is also compared
  with the intensity falloff of optically thin lines of Si II, Mg II,
  C II, singly ionized metals, and the neutral element, O I, recorded
  over a quiet Sun region. From this comparison, the temperature of the
  hydrogen plasma in all of the quiet and active regions that we observed
  is no more than about 8000 K. The intensity decrease of the hydrogen
  lines is the same as the intensity falloff of intersystem lines of
  01. Nonthermal velocities of the hydrogen lines over the active regions
  are also derived. At 2" above the limb, these range from 0 km 1 to
  about 15 km s - . The lines of high members of the Balmer series are
  in Boltzmann equilibrium. The hydrogen observations are combined with
  our previous observations of singly ionized elements and are compared
  with observations of spicule s. Subject headings: Sun: chromosphere -
  Sun: corona - Sun: spectra

Title: The coronal temperature and nonthermal motions in a coronal
    hole compared with other solar regions.
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1977ApJ...212L.143D
Altcode:
  The coronal lines Si VIII (1446 A), Fe X (1463 A), Fe XI (1467 A), and
  Fe XII (1242 A and 1349 A) were observed above the limb over a quiet
  region, a coronal hole, and two active regions. The lines emitted at
  temperatures greater than 1 million K; i.e., the iron lines, are not
  observed in the coronal-hole spectra, so the indication is that in
  the coronal hole most of the plasma is at a temperature of less than
  1 million K. The emission measures and column densities of the lines
  are derived from available atomic cross-section data, and the results
  are discussed. The nonthermal velocities in the coronal hole and quiet
  region are about 20 km/s. The velocities in the active regions are
  substantially less.

Title: Observations of a Radiatively Cooling Subflare.
Authors: Antiochos, S. K.; Underwood, J. H.; Feldman, U.
Bibcode: 1977BAAS....9..329A
Altcode:
  No abstract at ADS

Title: Chromospheric limb spectra from Skylab: 2000 to 3200 Å-.
Authors: Doschek, G. A.; Feldman, U.; Cohen, L.
Bibcode: 1977ApJS...33..101D
Altcode:
  Chromospheric limb spectra of a quiet-sun region between 2000 and
  3200 A recorded by the normal-incidence spectrograph on Skylab are
  discussed. The spectral resolution is 0.12 A, and the projected slit
  area on the sun is 2 by 60 arcsec. A list of lines with wavelengths,
  identifications, and absolute intensities is given for the spectrum
  recorded at +4 arcsec outside the white-light limb. The intensity
  behavior outside the limb is shown for lines of the ions C II, Si
  II, Cr II, Mn II, Fe II, Fe III, Co II, and Ni II. The widths of the
  intersystem lines of Si II and C II increase monotonically with height
  above the limb. The full width at half-maximum of the Si II lines
  increases from 0.034 A at the limb to 0.27 A at +12 arcsec above the
  limb. The widths of the C II lines increase from 0.17 A at +2 arcsec
  to 0.31 A at +12 arcsec.

Title: EUV Spectroscopy of Solar Transition-Zone Plasmas.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977uxsa.coll...11F
Altcode: 1977IAUCo..43...11F
  No abstract at ADS

Title: Plasma diagnostics using high-resolution spectroscopic
    techniques.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1977JOSA...67..726F
Altcode: 1977OSAJ...67..726F
  No abstract at ADS

Title: Recent High Spectral and Spatial Resolution Spectroscopy of
    Laser-Produced Plasmas and Electron-Ion Beam Plasmas.
Authors: Doschek, G. A.; Feldman, U.; Johnson, D. J.; Nagel, D. J.
Bibcode: 1977uxsa.coll...18D
Altcode: 1977IAUCo..43...18D
  No abstract at ADS

Title: The emission-line spectrum of a sunspot in the far-ultraviolet.
Authors: Cheng, C. -C.; Doschek, G. A.; Feldman, U.
Bibcode: 1976ApJ...210..836C
Altcode:
  The emission-line spectrum between 1200 and 1817 A from a sunspot in
  McMath region 12510 near the solar center is discussed. The spectrum
  was obtained by the normal-incidence spectrograph on Skylab. The
  principal results are: (1) the widths of emission lines originating
  in the chromosphere and lower transition region over the sunspot are
  much narrower than those previously reported for a polar coronal hole
  observed above the limb and a quiet chromospheric network observed
  near the solar center, indicating that the mass motions in the sunspot
  are less than in these other regions; (2) the sunspot spectrum, aside
  from the narrow widths of emission lines, is similar to spectra from
  the chromospheric network boundary. The intensities of lines in the
  sunspot are much enhanced relative to the network interior. From the
  full-width at half-maximum of the 1207-A Si III line, an optical depth
  at line center of 3.6 is deduced. Comparison with Parker's (1974) theory
  of sunspots shows that, if the enhancement of emission lines is due
  to enhanced transport of hydromagnetic waves generated in the sunspot
  convective zone, the mode of the waves is predominately Alfvenic.

Title: The quiet sun chromospheric network observed from Skylab.
Authors: Feldman, U.; Doschek, G. A.; Patterson, N. P.
Bibcode: 1976ApJ...209..270F
Altcode:
  The paper analyzes spectra of a supergranulation cell interior and cell
  boundary obtained near the solar center at wavelengths between 1200
  and 1560 A with a normal-incidence spectrograph aboard Skylab. Absolute
  intensities, relative intensities, and profiles are given for selected
  optically thin and optically thick lines over the cell interior, the
  boundary, and intermediate positions; the results are compared with
  spectra obtained at the limb. Characteristic lengths along the line of
  sight are derived for the Si III emitting region, and these are compared
  with the predictions of Gabriel's (1975) model. It is concluded that
  the present data are representative of a fairly typical cell interior
  and boundary, that nonthermal motions are isotropic and the same for
  the interior and boundary, and that the electron-density ratio between
  the interior and the boundary is about a factor of two or less.

Title: EUV Spectra of the 15 June 1973 Solar Flare Observed from
    Skylab.
Authors: Doschek, G. A.; Feldman, U.; Rosenberg, F.
Bibcode: 1976BAAS....8..555D
Altcode:
  No abstract at ADS

Title: The Solar Mg II h and k Lines Observed from Skylab.
Authors: Feldman, U.; Doschek, G. A.
Bibcode: 1976BAAS....8..523F
Altcode:
  No abstract at ADS

Title: Exploring plasmas: in the Sun and in the laboratory.
Authors: Doschek, G. A.; Feldman, U.
Bibcode: 1976AsAer..14...24D
Altcode: 1976AsAau..14...24D
  In recent years, high-resolution spectroscopy in the X-ray,
  extreme-ultraviolet, ultraviolet, and visible spectral regions has found
  increasing application for the study of conditions in solar plasmas. The
  use of spectroscopic techniques in the X-ray and extreme-ultraviolet
  spectral regions to determine such physical quantities as electron and
  ion temperature, electron and ion density, turbulence or anisotropic
  motions, and the departure of the ionic species from kinetic equilibrium
  in solar and laboratory plasmas is discussed. Solar-flare spectra are
  compared to the spectra of active solar regions.

Title: XUV spectrum of CI observed from Skylab during a solar flare.
Authors: Feldman, U.; Brown, C. M.; Doschek, G. A.; Moore, C. E.;
   Rosenberg, F. D.
Bibcode: 1976JOSA...66..853F
Altcode: 1976OSAJ...66..853F
  A list of 193 neutral carbon lines observed in the XUV spectrum
  of a solar flare between 100 and 2000 A using the normal incidence
  spectrograph flown on Skylab is presented. Of these, 69 are newly
  identified lines arising from transitions from upper levels of
  high quantum number where the quantum number is not less than
  six. The new lines have allowed the determination of 63 new energy
  levels. Wavelengths for an additional 109 transitions were calculated
  by polynomial fitting using reference wavelengths of unblended neutral
  carbon, Si, N, and S lines emitted in the same atmospheric regions of
  the flare. The calculated lines falling between 1102 and 1140 A were not
  observed due to low instrumental efficiency at these wavelengths. The
  calculated wavelengths are in excellent agreement with those of
  Johansson (1965). It appears that in solar spectra recombination
  processes are dominant, enhancing the populations of the high quantum
  levels relative to the populations of levels with small quantum numbers.

Title: The emission-line spectrum above the limb of a solar coronal
hole: 1175 - 1940 Å.
Authors: Feldman, U.; Doschek, G. A.; Vanhoosier, M. E.; Purcell, J. D.
Bibcode: 1976ApJS...31..445F
Altcode:
  Emission-line spectra of a coronal hole that coincided with the
  north pole of the sun are discussed which were obtained with a slit
  spectrograph aboard Skylab at positions within and above the solar
  white-light limb in the wavelength range from 1175 to 1940 A. Relative
  line intensities, line profiles, and full widths at half-maximum
  are presented for selected chromospheric and transition-zone lines
  observed above the present polar coronal hole. Average mass motions
  in the transition zone are determined as a function of electron
  temperature from the widths of the optically thin lines by assuming
  ionization equilibrium. The line intensities and profiles are compared
  with corresponding results deduced from spectra obtained above a quiet
  solar region. The coronal-hole spectra are found to imply an angular
  dependence for the source function as well as a radial dependence
  such that the source function is the smallest at the south pole and
  increases with decreasing solar latitude.

Title: The emission-line spectrum above the limb of the quiet sun:
    1175 - 1940 Å.
Authors: Doschek, G. A.; Feldman, U.; Vanhoosier, M. E.; Bartoe,
   J. -D. F.
Bibcode: 1976ApJS...31..417D
Altcode:
  Spectra of a quiet solar region obtained at positions within and above
  the solar white-light limb in the wavelength region from 1175 to 1940
  A are discussed. The spectra were obtained by the slit spectrograph
  (SO82-B) on Skylab. The spectral resolution is 0.06 A, and the projected
  slit area on the sun was 2 x 60 arcsec (1450 x 43500 km). Relative line
  intensities are presented for lines formed in the temperature region of
  the solar atmosphere from about 8000 to 220,000 K. Representative line
  profiles of both optically thin and optically thick lines are shown
  as a function of height above the limb. Random mass-motion velocities
  are deduced from the optically thin lines, and the relative intensities
  and profiles of the lines are discussed in terms of current theoretical
  models. A wavelength list with identifications is given for the spectrum
  obtained at +4 arcsec above the white-light limb.

Title: Spectroscopy from Laser-produced Plasmas at Flare Temperatures
Authors: Feldman, U.
Bibcode: 1976Ap&SS..41..155F
Altcode:
  A discussion of laboratory spectra similar in temperatures and ion
  abundances to solar flare spectra is given. The laboratory spectra were
  obtained from high temperature plasmas produced by high power lasers and
  low inductance vacuum sparks. The current state of knowledge regarding
  line identifications in laboratory spectra is reviewed, and some of the
  results are used to identify lines in the high temperature solar flare
  spectrum in the 100 Å region and in the 1000 Å region. In addition,
  the physical dimensions and temperatures of the hot regions in the
  plasmas produced by the low inductance spark were recently measured,
  and a short summary of the results is given.

Title: Doppler wavelength shifts of transition zone lines measured
    in Skylab solar spectra.
Authors: Doschek, G. A.; Feldman, U.; Bohlin, J. D.
Bibcode: 1976ApJ...205L.177D
Altcode:
  Wavelengths of lines of the transition-zone ions Si IV, C IV, O IV,
  N V, and O V are observed to be redshifted relative to the wavelengths
  of chromospheric lines in XUV spectra obtained from the normal-incidence
  spectrograph on Skylab. The spectra cover the wavelength range from 1200
  to 1565 A and were obtained with the slit positioned over chromospheric
  network and cell regions, on coronal holes, and above the limb. The
  network-area and coronal-hole spectra were obtained near the disk
  center. Only some of the spectra show redshifted transition-zone
  lines. The observed shifts are between 0.03 and 0.08 A, implying
  velocities of 15 km/s or less. The amount of wavelength shift does not
  always appear to be the same for lines of different ions. The shifts
  imply that descending plasma in the solar atmosphere produces more
  emission than ascending plasma at temperatures between approximately
  70,000 and 200,000 K.

Title: Densities in the Solar Chromosphere above the Quiet sun and
    a Coronal Hole Derived from the Hydrogen Balmer Lines
Authors: Rosenberg, F. D.; Feldman, U.; Doschek, G. A.
Bibcode: 1976BAAS....8..338R
Altcode:
  No abstract at ADS

Title: The solar spectrum: wavelengths and identifications from 160
    to 770 Ångstroms.
Authors: Behring, W. E.; Cohen, L.; Feldman, U.; Doschek, G. A.
Bibcode: 1976ApJ...203..521B
Altcode:
  The full-Sun solar spectrum from 160 to 770 A was photographed
  under quiet solar conditions by a rocket-borne spectrograph flown
  in 1973 September. The spectral resolution is 0.06 A or better. We
  present a composite list of spectral lines, including wavelengths,
  identifications, and approximate intensities that were obtained from
  the present flight and from a previous flight in 1969 May. This line
  list contains the most accurate solar wavelengths yet obtained in this
  spectral region. One result is improved energy levels which are given
  for the two lowest energy configurations of Fe ix through Fe xvi. No
  detectable relative mass motions of more than 4 km s ' exist between
  transition zone and coronal regions averaged over the visible disk
  of the Sun. The wavelengths of emission lines in this spectrum were
  determined with indicated accuracies ranging between 2 and 20 mA. The
  spectrograph employed a 3 m radius, 600 grooves mm ' gold grating used
  at grazing incidence. Subject headings: line identifications - Sun:
  corona - Sun: spectra - ultraviolet: spectra

Title: Limb-brightening curves of XUV transition zone lines in the
    quiet sun and in a polar coronal hole observed from Skylab.
Authors: Doschek, G. A.; Feldman, U.; Tousey, R.
Bibcode: 1975ApJ...202L.151D
Altcode:
  Solar limb-brightening curves are discussed for XUV spectral lines
  formed in the upper chromosphere and transition zone of a quiet region
  and a polar coronal hole. The spectra were recorded with a slit
  spectrograph on Skylab. The lines considered are emitted from ions
  formed within the temperature range from 10,000 to 220,000 K. The
  limb-brightening curves cover a region from -4 sec within the limb
  to +20 sec above it. The data from 0 sec to +20 sec are compared with
  predictions based on both homogeneous and inhomogeneous models of the
  transition zone. The limb-brightening curve of the O I line at 1355.6 A
  indicates that O I is formed in spicules. The limb brightening of the
  He II line at 1640.4 A is consistent with a temperature of formation
  between about 40,000 and 90,000 K for He II.

Title: The intensities and profiles of XUV transition zone lines in
    a quiet sun region compared to a polar coronal hole.
Authors: Feldman, U.; Doschek, G. A.; Tousey, R.
Bibcode: 1975ApJ...202L.147F
Altcode:
  The intensities of XUV transition-zone lines from limb spectra of a
  quiet-sun region and a polar coronal hole are compared. The spectra
  were obtained with a slit spectrograph on Skylab and cover a region
  from -12 sec within the limb to 20 sec above it. The lines selected for
  comparison are formed at temperatures that range from 36,000 to 220,000
  K. Lines of the higher-temperature ions, e.g. O v, are significantly
  less intense in the coronal hole, and lines of lower-temperature ions
  show little change. Profiles of selected optically thin transition-zone
  lines from the quiet-sun and coronal-hole spectra are also shown. The
  lines are broader than expected in ionization equilibrium, and
  bulk-motion velocities are deduced from the widths of the lines. There
  appears to be little, if any, statistically significant difference in
  the velocities obtained from the quiet-sun region and the coronal hole.

Title: The spatial and temperature structure of vacuum spark plasmas.
Authors: Feldman, U.; Goldsmith, S.; Schwob, J. L.; Doschek, G. A.
Bibcode: 1975ApJ...201..225F
Altcode:
  The spatial and temperature structures of the X-ray emitting components
  of low-inductance vacuum-spark plasmas are investigated. The plasmas
  produced by low-inductance vacuum sparks show striking resemblances
  to solar-flare plasmas. High-resolution photographs show that the
  spark plasmas are composed of hot (about 30 million K) compact sources
  (less than 20 microns) and cooler (about 10 million K) larger sources
  (of the order of 100 microns). Both types of sources may be produced by
  the same plasma at different times. The differences between the solar
  flare iron-line spectrum near 1.9 A and the spark iron-line spectrum
  are discussed and interpreted.

Title: Density sensitive lines of highly ionized iron
Authors: Doschek, G. A.; Feldman, U.; Davis, J.; Cowan, R. D.
Bibcode: 1975PhRvA..12..980D
Altcode:
  Spectral lines from ions in the nitrogen
  isoelectronic sequence due to transitions of the type,
  2s2p<SUP>4</SUP><SUP>2</SUP>D<SUB>32,52</SUB>-2p<SUP>5</SUP><SUP>2</SUP>P<SUB>32</SUB>,
  and
  2s2p<SUP>4</SUP><SUP>2</SUP>D<SUB>32</SUB>-2p<SUP>5</SUP><SUP>2</SUP>P<SUB>12</SUB>,
  are identified in the 100-Å region in laser-produced plasma
  spectra of titanium (Ti xvi) through cobalt (Co xxi). It is
  proposed that the intensities of these lines relative to the
  intensities of lines of the same ions due to transitions of the
  type 2s<SUP>2</SUP>2p<SUP>3</SUP>-2s2p<SUP>4</SUP> are sensitive
  to electron density in the range from ~ 10<SUP>18</SUP>
  to ~ 10<SUP>20</SUP> cm<SUP>-3</SUP>. Calculations
  are performed for Fe xx, and a similar calculation
  is performed for a density-sensitive line ratio of Fe xix, i.e.,
  (2s2p<SUP>5</SUP><SUP>1</SUP>P<SUB>1</SUB>-2p<SUP>6</SUP><SUP>1</SUP>S<SUB>0</SUB>)(2s<SUP>2</SUP>2p<SUP>4</SUP><SUP>1</SUP>S<SUB>0</SUB>-2s2p<SUP>5</SUP><SUP>1</SUP>P<SUB>1</SUB>).
  This line ratio is also sensitive to electron density between
  about 10<SUP>18</SUP> and 10<SUP>20</SUP> cm<SUP>-3</SUP>. The
  2s2p<SUP>5</SUP><SUP>1</SUP>P<SUB>1</SUB>-2p<SUP>6</SUP><SUP>1</SUP>S<SUB>0</SUB>
  line is newly indentified in Cr xvii, Co xx, and Ni xxi.

Title: The 1640.4 Å Halpha line of He II observed from Skylab.
Authors: Feldman, U.; Doschek, G. A.; Vanhoosier, M. E.; Tousey, R.
Bibcode: 1975ApJ...199L..67F
Altcode:
  Profiles obtained from NRL Skylab solar spectra of the 1640.4 A feature
  identified as the H-alpha line of He II are discussed and compared with
  theoretical profiles derived assuming (1) collisional excitation and (2)
  radiative recombination as the dominant excitation mechanism. Relative
  intensities of this line as a function of altitude above and below
  the solar white-light limb are also given for a representative quiet
  sun region and for a polar coronal hole.

Title: Forbidden lines of highly ionized iron in solar flare spectra.
Authors: Doschek, G. A.; Feldman, U.; Dere, K. P.; Sandlin, G. D.;
   Vanhoosier, M. E.; Brueckner, G. E.; Purcell, J. D.; Tousey, R.
Bibcode: 1975ApJ...196L..83D
Altcode:
  No abstract at ADS

Title: Transitions 2s'2pk -2s2p"I of the N i and C i Isoelectronic
    Sequences
Authors: Feldman, U.; Doschek, G. A.; Cowan, R. D.; Cohen, Leonard
Bibcode: 1975ApJ...196..613F
Altcode:
  Transitions of the type +1 have been identified for the elements
  from titanium through iron for ions of the nitrogen isoelectronic
  sequence and for the elements titanium through nickel for ions of
  the carbon isoelectronic sequence. Wavelengths, intensity estimates
  and energies are given. The lines were identified from EUV spectra
  obtained from laser-produced plasmas. The energy differences of levels
  of the ground configuration for the C I isoelectronic sequence are
  compared with extrapolations based on semiempirical equations derived
  by Edlen. Wavelengths of forbidden Fe XXI lines that can be seen in
  low-density plasmas such as solar flare plasmas are predicted. The
  laser plasma spectrum is briefly compared with available solar flare
  spectra. Subject headings: flares, solar - line identifications -
  spectra, laboratory - spectra, ultraviolet

Title: Transitions 2s<SUP>2</SUP>2p-2s2p<SUP>2</SUP> in the B I
    isoelectronic sequence.
Authors: Doschek, G. A.; Feldman, U.; Cohen, L.
Bibcode: 1975JOSA...65..463D
Altcode: 1975OSAJ...65..463D
  No abstract at ADS

Title: Meteorological Conditions near the Wise Observatory, Israel
Authors: Vidal, N. V.; Feldman, U.
Bibcode: 1974QJRAS..15..462V
Altcode:
  No abstract at ADS

Title: Satellite Line Spectra from Laser-Produced Plasmas
Authors: Feldman, U.; Doschek, G. A.; Nagel, D. J.; Cowan, R. D.;
   Whitlock, R. R.
Bibcode: 1974ApJ...192..213F
Altcode:
  We have obtained X-ray spectra of high-temperature plasmas produced by
  the 100 GW glass laser at the Naval Research Laboratory. In this paper,
  we discuss the satellite lines of hydrogen-like and helium-like ions,
  observed in the 2-12 A region for elements ranging from sodium through
  titanium. The satellite lines are due to transitions of the type,
  lsnl-2pnl, ls2nl-ls2pnl, n = 2, 3; and ls22l-ls2l3p. Physical conditions
  in the plasma are discussed in terms of relative line-intensity ratios
  and line profiles. Subject headings: plasmas - spectra, laboratory -
  spectra, X-ray

Title: The Widths of the Solar he i and he II Lines at 584, 537,
    and 304 Å
Authors: Doschek, G. A.; Behring, W. E.; Feldman, U.
Bibcode: 1974ApJ...190L.141D
Altcode:
  In this Letter we report direct measurements from a rocket spectrograph
  of the widths of the solar He I lines, 152 1s2p and 1s2-1s3p, at 584 and
  537 A. We also report the width of the solar resonance line of He II at
  304 A. The deduced full widths at hall-maximum intensity are 0.14,0.12,
  and 0.10 A for the 584, 537, and 304 A lines, respectively. These
  widths represent averages over the entire Sun. Line profiles corrected
  for the nonlinear film response are presented for the 584 and 304 A
  lines. Subject headings: line profiles - spectra, solar

Title: Solar Coronal Line Profiles in the Extreme-Ultraviolet
Authors: Feldman, U.; Behring, W. E.
Bibcode: 1974ApJ...189L..45F
Altcode:
  We report here the first direct measurements of the widths of the lines
  emitted by the solar corona from 170 to 370 A. The transitions 1s-2p and
  in He ii are wider than 0.1 A, perhaps showing the effect of optical
  depth. The lines of highly ionized 0, Mg, Si, S, and Fe have widths
  which may be ascribed to a mean random turbulent velocity of about 30
  km Sri in addition to thermal Doppler broadening. Subject headings:
  corona, solar - line profiles - ultraviolet

Title: Solar Flare Emission Lines of Highly-Ionized Iron and Nickel
Authors: Doschek, G. A.; Feldman, U.; Cowan, R. D.; Cohen, Leonard
Bibcode: 1974BAAS....6T.286D
Altcode:
  No abstract at ADS

Title: Transitions 2S22pk -2s2 pk+, of the F i, 0 I, and N i
    Isoelectronic Sequences
Authors: Doschek, G. A.; Feldman, U.; Cowan, R. D.; Cohen, Leonard
Bibcode: 1974ApJ...188..417D
Altcode:
  Transitions of the type, 2s +1, have been identified for the
  elements from titanium through nickel for ions of the fluorine,
  oxygen, and nitrogen isoelectronic sequences. Wavelengths, visual
  intensity estimates, and energies are given. The energy differences
  of levels of the ground configuration are compared with predictions
  based on semiempirical equations derived by Edlen. Some of the lines
  of these isoelectronic sequences should be strong lines in solar-flare
  spectra. Subject headings: line identifications - spectra, laboratory -
  spectra, ultraviolet

Title: The Width of the Solar 584 Å Line of Neutral Helium
Authors: Behring, W. E.; Doschek, G. A.; Feldman, U.; Cohen, Leonard;
   Houston, James
Bibcode: 1974BAAS....6R.284B
Altcode:
  No abstract at ADS

Title: X-ray Satellite Lines of Hydrogenlike and Heliumlike Ions
Authors: Feldman, U.; Doschek, G. A.; Nagel, D. J.; Cowan, R. D.;
   Whitlock, R. R.
Bibcode: 1974BAAS....6R.286F
Altcode:
  No abstract at ADS

Title: Laser-Plasma Spectra of Highly Ionized Fluorine
Authors: Feldman, U.; Doschek, G. A.; Nagel, J.; Behring, W. E.;
   Cowan, R. D.
Bibcode: 1974ApJ...187..417F
Altcode:
  Lines between 11.3 A and 17.2 A of lithium-like, helium-like, and
  hydrogen-like fluorine have been observed in spectra of laser-produced
  plasmas. These lines include nine members of the Lyman series of F IX;
  eight members of the principal series of F VIII; and satellite lines
  arising from doubly excited configurations of F VII and F VIII. Similar
  satellite lines of the abundant solar elements have been identified in
  soft X-ray spectra of solar flares. A wavelength list of fluorine lines
  is given, and physical conditions in the plasma are discussed. Subject
  headings: flares, solar - line identifications - plasmas - spectra,
  laboratory - spectra, X-ray

Title: Transitions of Fe XVIII and Fe XIX Observed in Laser-Produced
    Plasmas
Authors: Feldman, U.; Doschek, G. A.; Nagel, D. J.; Behring, W. E.;
   Cohen, Leonard
Bibcode: 1973ApJ...183L..43F
Altcode:
  Lines of Fe xvm and Fe XIX near 100 A have been ohserved in spectra
  from plasmas produced by 5-joule laser pulses of 0.9 ns duration. These
  lines produced by transitions of the type 2s2 +1 Transitions of the
  type -131 are prominent in the spectra below 20 A observed during solar
  flares. The splittings of the ground levels are obtained and compared
  with isoelectronic extrapolations. The corresponding forbidden lines
  as well as the allowed lines near 100 A inay be observable in flare
  spectra with some of the instruments to be flown on Skylab. Subject
  headings: flares, solar - spectra, ultraviolet - spectra, X-ray

Title: Fluorine isoelectronic sequence.
Authors: Feldman, U.; Doschek, G. A.; Cowan, R. D.; Cohen, L.
Bibcode: 1973JOSA...63.1445F
Altcode:
  No abstract at ADS

Title: High-resolution rocket EUV solar spectrograph.
Authors: Behring, W. E.; Ugiansky, R. J.; Feldman, U.
Bibcode: 1973JOSA...63R.484B
Altcode:
  No abstract at ADS

Title: High resolution rocket EUV solar spectrograph.
Authors: Behring, W. E.; Ugiansky, R. J.; Feldman, U.
Bibcode: 1973ApOpt..12..528B
Altcode:
  No abstract at ADS

Title: On I isoelectronic sequence: transitions
    2p<SUP>4</SUP>-2p<SUP>3</SUP>3s.
Authors: Doschek, G. A.; Feldman, U.; Cohen, L.
Bibcode: 1973JOSA...63.1463D
Altcode:
  No abstract at ADS

Title: Statistical Analysis of Multiple Absorption Spectra in QSO
Authors: Shaviv, Giora; Feldman, Uri; Koslovsky, Ben-Zion
Bibcode: 1972Ap&SS..19..159S
Altcode:
  A detailed statistical analysis was carried out for several quasars
  with multiple red-shifts systems. The most important results are (a) The
  statistical test of the reliability of az-system is very sensitive toz,
  the total number of absorption lines, the selected set of reference
  lines and the number of identified lines (b) The standard deviation
  σ from μ, the average number of randomz-systems per random spectra
  is larger than μ. Consequently, the reliability of any system depends
  predominately on σ and not on μ.

Title: Energy levels and spectra of the Li  i and Be  i isoelectronic
    sequences in the fourth row
Authors: Goldsmith, S.; Feldman, U.; Oren, L.; Cohen, L.
Bibcode: 1972SSRv...13..560G
Altcode: 1972IAUCo..14..560G
  No abstract at ADS

Title: Wavelengths of solar lines in the 50 380Å region and their
    identifications
Authors: Feldman, U.; Behring, W.; Cohen, L.
Bibcode: 1972SSRv...13..608F
Altcode: 1972IAUCo..14..608F
  No abstract at ADS

Title: Erratum: the Lithium-Like Spectra of K XVII Through MN XXIII
    in the Extreme-Ultraviolet Region
Authors: Goldsmith, S.; Feldman, U.; Oren, L.; Cohen, L.
Bibcode: 1972ApJ...175..589G
Altcode:
  No abstract at ADS

Title: The Solar Spectrum: Wavelengths and Identifications from 60
    TO 385 Angstroms
Authors: Behring, W. E.; Cohen, Leonard; Feldman, Uri
Bibcode: 1972ApJ...175..493B
Altcode:
  The solar spectrum from 60 to 158 A and 163 to 385 - was photographed
  at a resolution of 004 A or better on glass plates The wavelengths
  of emission lines in these records were determined with a typical
  accuracy of 0.008 A above 100 A and 0.004 A below 100 A. The
  spectrograph employed a 3-meter radius, 1200 grooves gold grating at
  graxing incidence The design considerations and limitations of this
  instrument are presented along with a description of the Aerobee 130
  flight mission on 1969 May t6. The wavelengths for the 370 observed
  lines are listed together with intensity estimates. Of these, the 180
  identified lines are due to ions of lle, 0, Ne, Mg, Si, S, Ar, Ca,
  Fe, and Ni. These identified lines are also tabulated separately foi
  each isoelectronic sequence from Li I to K I. The solar lines are well
  enough resolved that wavelength determinations to t 0.004 A can be made
  whenever better laboratory wavelengths become available. The reliability
  of the solar line "Mentifications" could then be much improved.

Title: Improved Wavelengths and Identifications in the Solar Spectrum
    from 60-385 Å
Authors: Behring, W. E.; Cohen, Leonard; Feldman, Uri
Bibcode: 1972BAAS....4U.377B
Altcode:
  No abstract at ADS

Title: The Lithium-Like Spectra of K XVII Through MN XXIII in the
    Extremeultraviolet Region
Authors: Goldsmith, S.; Feldman, U.; Oren, L.; Cohen, L.
Bibcode: 1972ApJ...174..209G
Altcode:
  Identifications and classifications of spectral lines in the
  lithium-like spectra of the elements K through n is presented for
  the first time. The extrapolation procedures used to calculate these
  spectra are presented in detail. The excellent agreement between the
  predicted and measured lines establish the longrange extrapolation.

Title: Carbon-like spectra of Sc XVI, Ti XVII, and V XVIII in the
    range 16 - 22 Å.
Authors: Goldsmith, S.; Feldman, U.; Crooker, A.; Cohen, L.
Bibcode: 1972JOSA...62..260G
Altcode:
  No abstract at ADS

Title: Extreme-ultraviolet spectra of Sc XIV, Ti XV, and V XVI.
Authors: Goldsmith, S.; Feldman, U.; Cohen, L.
Bibcode: 1971JOSA...61..615G
Altcode:
  No abstract at ADS

Title: Boron-like spectra: Mg VIII, Al IX, and Si X.
Authors: Hoory, S.; Goldsmith, S.; Feldman, U.; Behring, W.; Cohen, L.
Bibcode: 1971JOSA...61..504H
Altcode:
  No abstract at ADS

Title: Spectra of Fe, Co, Ni, and Cu isoelectronic with Na I and Mg I.
Authors: Feldman, U.; Katz, L.; Behring, W.; Cohen, L.
Bibcode: 1971JOSA...61...91F
Altcode:
  No abstract at ADS

Title: On the Rich Absorption Spectra of Three Quasi-Stellar Objects
Authors: Bahcall, John N.; Feldman, Uri
Bibcode: 1970ApJ...161..389B
Altcode:
  The absorption spectra of PHL 938, TON 1530, and PKS 0237-23 have
  been searched in a systematic way for redshifts that may include lines
  arising from metastable states, interstellar lines, and Balmer lines. A
  search for blueshifts was also carried out for the first time. The
  statistical significance of the redshift system I = 0.6128 in PIlL
  938 was established by analyzing random-number spectra. It is shown
  that the electron density is less than 50 T4112 in the vicinity of
  this absorption system and that the minimum separation between PHL 938
  and the absorption system is about 100 pc. A critical test of the idea
  that normal galaxies produce the absorption lines is described. Nine
  interstellar lines observed in the spectra of stars in the galaxy might
  appear in the.observationally accessible region between 4956 and 6400
  A for the redshift system I = 0.6128 of PHL 938.

Title: Identification and Classification of the 3p^{6}3d-3p^{5}3d4s;
    Transitions in CO ix, NI x, and CU XI
Authors: Hoory, S.; Goldsmith, S.; Fraenkel, B. S.; Feldman, U.
Bibcode: 1970ApJ...160..781H
Altcode:
  In this work the identification and classification of the 3p63d-3p53d4s
  transitions are extended from Fe viii to Cu xi.

Title: A Line List for an Iron-Spark Spectrum (10-18 Å)
Authors: Cohen, Leonard; Feldman, Uri
Bibcode: 1970ApJ...160L.105C
Altcode:
  A low-inductance 17-19 kV vacuum spark was used to generate spark
  spectra of iron electrodes. Wavelengths and visually estimated
  intensities are given for the region A.

Title: Lithium-like spectra in Mg, Al, and Si.
Authors: Feldman, U.; Cohen, L.; Behring, W.
Bibcode: 1970JOSA...60..891F
Altcode:
  No abstract at ADS

Title: C V Spectra Near the 1s-2p Line of C VI
Authors: Feldman, Uri; Cohen, Leonard
Bibcode: 1969ApJ...158L.169F
Altcode:
  We have measured seven lines of C v near the ls-2p line of C
  vi. The lines were first reported by Edlén and Tyr~n. Six of them
  are identified as belonging to transitions of the types ls2s-2s2p,
  ls2p-2p2, and ls3s-2p3s

Title: Round-the-Clock Photoheliography
Authors: Zirin, Harold; Bohlin, J. David; Weart, Spencer; Feldman, Uri
Bibcode: 1969BAAS....1..297Z
Altcode:
  No abstract at ADS

Title: Observations of the Sun and Laboratory Sources with a
    Three-Meter xuv Spectrograph
Authors: Behring, W. E.; Cohen, L.; Saffer, K.; Feldman, U.
Bibcode: 1969BAAS....1S.272B
Altcode:
  No abstract at ADS

Title: An Iron Spark Line List in the 10-18 Å Range and its
    Comparison with Flare Spectra
Authors: Feldman, U.; Cohen, L.
Bibcode: 1968ApJ...151L..55F
Altcode:
  No abstract at ADS

Title: Spectra of Solar Physics Interest Produced by a Vacuum
    Spark Source
Authors: Feldman, U.; Cohen, L.; Underwood, J. H.
Bibcode: 1968AJS....73Q..60F
Altcode:
  No abstract at ADS

Title: Newly Identified Lines in the NE i Isoelectronic Sequences
Authors: Feldman, U.; Cohen, L.
Bibcode: 1967ApJ...149..265F
Altcode:
  Using a graxing-incidence spectrometer and a low inductance, 14- F,
  12-17 kV spark source, the authors have observed spectra of Sc xu,
  Ti xiii, and V xiv. The lines have been identified as arising from
  transitions between the ground level 2s2 2p6 iS0 and the following
  electronic configurations: 2s 2p6 3p, and 2s2 2p5 4s, 4d, 5d. The
  transitions of the type 2s2 2p8-2s2 2p5 4d have been observed also in
  Co xviii, Ni xix, and Cu xx.

Title: Newly Identified Resonance Lines of NI XIX, CU xx, and zn XXI
Authors: Feldman, U.; Cohen, L.; Swartz, M.
Bibcode: 1967ApJ...148..585F
Altcode:
  By using a grazing-incidence spectrometer and a lowAnductance
  condensed-spark source, the authors have observed spectra of Ni xix, Cu
  xx, and Zn xxi By extrapolating the known data of the Ne i isoelectronic
  sequence, the new lines have been identified as belonging to transition
  arrays between the ground level 2s22p6 15o and the following electronic
  configurations: 2s22p53s, 2s22p53d, and 2s2p63p Some of these lines
  may be emitted from the solar corona.

Title: Unclassified 3p<SUP>6</SUP>3d-3p<SUP>5</SUP>3d4s Transition
    Lines of Fe VIII, Mn VII, and Cr VI
Authors: Feldman, U.; Fraenkel, B. S.
Bibcode: 1966ApJ...145..959F
Altcode:
  No abstract at ADS

Title: Identification of Solar Ultraviolet Lines Resulting from a
    Study of the AR i and K i Isolelctronic Sequences.
Authors: Feldman, U.; Fraenkel, B. S.; Hoory, S.
Bibcode: 1965ApJ...142..719F
Altcode:
  The classification of the 3p5 3d level in Ar I isoelectronic spectra
  and the interaction between configurations 3p6 and 3p5 are discussed
  Solar lines of transitions 3p6-3p5nl, 3p6 3d-3p6nl and 3p6 3d-3p5 3d3
  are identified.

Title: 3p<SUP>6</SUP>-3p<SUP>5</SUP>3d Transitions of Fe IX and Ni
    XI in the Solar Spectrum
Authors: Alexander, E.; Feldman, U.; Fraenkel, B. S.; Hoory, S.
Bibcode: 1965Natur.206..176A
Altcode:
  USING rocket spectroscopy, Hinteregger et al.<SUP>1</SUP> obtained
  interesting new solar lines, the majority of which could not
  be classified up to now. Among these lines, two strong lines
  at 171.1 Å and at 148.5 Å have been seen. We have been able,
  using the technique of differentiation between different degrees
  of ionization<SUP>2,3</SUP>, to classify these two lines as
  the 3p<SUP>6</SUP> <SUP>1</SUP>S<SUB>0</SUB> - 3p<SUP>5</SUP>3d
  <SUP>1</SUP>P<SUB>1</SUB> transition of Fe IX and Ni XI. This line
  was found to be very prominent in the isoelectronic sequence of A I
  (Table 1). The foregoing classification is based on the assumption of
  LS coupling.

