Author name code: beckers
ADS astronomy entries on 2022-09-14
author:"Beckers, Jacques Maurice"
------------------------------------------------------------------------  

Title: Charge of clustered microparticles measured in spatial plasma
    afterglows follows the smallest enclosing sphere model
Authors: van Minderhout, B.; van Huijstee, J. C. A.; Rompelberg,
   R. M. H.; Post, A.; Peijnenburg, A. T. A.; Blom, P.; Beckers, J.
Bibcode: 2021NatCo..12.4692V
Altcode:
  The plasma-induced charge of non-spherical microparticles is a
  crucial parameter in complex plasma physics, aerosol science and
  astrophysics. Yet, the literature describes this charge by two
  competing models, neither of which has been experimentally verified
  or refuted. Here we offer experimental proof that the charge on
  a two-particle cluster (doublet) in the spatial afterglow of a
  low-pressure plasma equals the charge that would be obtained by the
  smallest enclosing sphere and that it should therefore not be based
  on its geometrical capacitance but rather on the capacitance of its
  smallest enclosing sphere. To support this conclusion, the size, mass
  and charge of single particles (singlets) and doublets are measured with
  high precision. The measured ratio between the plasma-afterglow-induced
  charges on doublets and singlets is compared to both models and shows
  perfect agreement with the predicted ratio using the capacitance of
  the smallest enclosing sphere, while being significantly dissimilar
  to the predicted ratio based on the particle's geometrical capacitance.

Title: Continuation of the X-ray monitoring of Sgr A*: the increase
    in bright flaring rate confirmed
Authors: Mossoux, E.; Finociety, B.; Beckers, J. -M.; Vincent, F. H.
Bibcode: 2020A&A...636A..25M
Altcode: 2020arXiv200306191M
  Context. The supermassive black hole Sagittarius A* (Sgr A*) is
  located at the dynamical center of the Milky Way. In a recent study
  of the X-ray flaring activity from Sgr A* using Chandra, XMM-Newton,
  and Swift observations from 1999 to 2015, it has been argued that the
  bright flaring rate has increased from 2014 August 31 while the faint
  flaring rate decreased from around 2013 August. <BR /> Aims: We tested
  the persistence of these changes in the flaring rates with new X-ray
  observations of Sgr A* performed from 2016 to 2018 (total exposure
  of 1.4 Ms). <BR /> Methods: We reprocessed the Chandra, XMM-Newton,
  and Swift observations from 2016 to 2018. We detected 9 flares in the
  Chandra data and 5 flares in the Swift data that we added to the set of
  107 previously detected flares. We computed the intrinsic distribution
  of flare fluxes and durations corrected for the sensitivity bias using
  a new method that allowed us to take the error on the flare fluxes and
  durations into account. From this intrinsic distribution, we determined
  the average flare detection efficiency for each Chandra, XMM-Newton,
  and Swift observation. After correcting each observational exposure
  for this efficiency, we applied the Bayesian blocks algorithm on the
  concatenated flare arrival times. As in the above-mentioned study,
  we also searched for a flux and fluence threshold that might lead to a
  change in flaring rate. We improved the previous method by computing
  the average flare detection efficiencies for each flux and fluence
  range. <BR /> Results: The Bayesian block algorithm did not detect
  any significant change in flaring rate of the 121 flares. However,
  we detected an increase by a factor of about three in the flaring
  rate of the most luminous and most energetic flares that have occurred
  since 2014 August 30. <BR /> Conclusions: The X-ray activity of Sgr A*
  has increased for more than four years. Additional studies about the
  overall near-infrared and radio behavior of Sgr A* are required to
  draw strong results on the multiwavelength activity of the black hole.

Title: Tropospheric seeing effects on site selection and the use of
    adaptive optics for solar telescopes
Authors: Beckers, Jacques M.
Bibcode: 2018SPIE10703E..6YB
Altcode:
  Because of the very small size of the isoplanatic patch resulting from
  high altitude, tropopause seeing, the use of the Solar Differential
  Image Motion Monitor (S-DIMM) for solar seeing observations at large
  zenith distances is significantly compromised. I examine the resulting
  limitations and attempt to correct for these in its use for the Advanced
  Technology Solar Telescope (ATST/DKIST) site survey. Suggestions are
  given about how one might correct for this altitude seeing by Dual
  Conjugate and Multi-Conjugate Adaptive Optics (DCAO/MCAO). I also
  comment on adaptive optics for corona observations with the use of
  Laser Guide Star aided wavefront sensing.

Title: The Effect of Tropopause Seeing on Solar Telescope Site Testing
Authors: Beckers, Jacques M.
Bibcode: 2017SPD....4811002B
Altcode:
  The site testing for and seeing correction planning of the 4-m solar
  telescopes has failed to take into account the significant amount of
  seeing at tropopause levels (10-20 km altitude).The worst aspect of
  that seeing layer is its small isoplanatic patch size which at low solar
  elevations can be significantly less than 1 arcsec. The CLEAR/ATST/DKIST
  SDIMM seeing monitor is insensitive to this type of seeing. A correction
  for this missed seeing significantly decreases the measured seeing
  qualities for the sites tested especially in the early morning and late
  afternoon. It clearly shows the lake site to be superior with mid-day
  observations much to be preferred. The small tropopause isoplanatic
  patch size values also complicate the implementation of the solar
  MCAO systems aimed at large field-of-view sun imaging. Currently
  planned systems only correct for lower-layer seeing for which the
  isoplanatic patch size is about one arc minute. To fully achieve the
  diffraction limit of the 4-meter class (0.025 arcsec at 500 nm), over
  a large enough field-of-view to be of scientific interest, complicated
  Multi-Conjugate Adaptive Optics systems will be needed.

Title: Isoplanatic patch considerations for solar telescope
    multi-conjugate adaptive optics
Authors: Beckers, Jacques M.
Bibcode: 2014SPIE.9148E..60B
Altcode:
  I compare recent site surveys for the future large 4-meter solar and
  30-meter nighttime telescopes at the nearby Haleakala and Mauna Kea
  sites respectively. They show that the outstanding early morning image
  quality at the solar site corresponds indeed to that observed at the
  late night one at the nighttime site. That confirms the notion that
  daytime solar site heating only shows itself later in the morning. The
  nighttime survey includes observations of the refractive index
  structure function C<SUB>n</SUB> <SUP>2</SUP>(h) to high altitudes
  from which the radius of the isoplanatic patch (Ɵ<SUB>0</SUB>)
  can be determined. At zenith (ζ = 0<SUP>0</SUP>) it equals 2.5
  arcsec at 500 nm wavelength. For the early morning (best) seeing at
  the solar site, which occurs at ζ<SUB>sun</SUB> = 75<SUP>0</SUP>
  and the cos<SUP>1.6</SUP>(ζ) dependence of Θ<SUB>0</SUB>,that
  means an extremely small Ɵ<SUB>0</SUB> (0.26 arcsec). Such small
  values compromise Adaptive Optics (AO) solar correlation wavefront
  sensing for which areas are needed equal to about 8"× 8" I suggest
  options for measuring C<SUB>n</SUB><SUP>2</SUP>(h), and therefore
  Ɵ<SUB>0</SUB>, during the day. These make use of the solar image as
  well as of daytime images of bright stars and planets. Some use the
  MASS technique on stars; some use the SHABAR technique using very large
  detector baselines on the Sun and shorter baselines on planets. It
  is suggested that these C<SUB>n</SUB><SUP>2</SUP>(h) measurements are
  made also during regular solar observations. In that way optimal solar
  observations can be planned using real-time Ɵ<SUB>0</SUB> observations
  by image selection and optimization of the MCAO configuration.

Title: Adaptive Optics for the 8 meter Chinese Giant Solar Telescope
Authors: Beckers, Jacques; Liu, Zhong; Deng, Yuanyong; Ji, Haisheng
Bibcode: 2013aoel.confE...5B
Altcode:
  Solar ELTs enable diffraction limited imaging of the basic structure of
  the solar atmosphere. Magneto-hydrodynamic considerations limit their
  size to about 0.03 arcsec. To observe them in the near-infrared 8-meter
  class telescopes are needed. The Chinese Giant Solar Telescope, or CGST,
  is such a NIR solar ELT. It is a Ring Telescope with 8-meter outer
  diameter and a central clear aperture of about 6-meter diameter. At
  present various options for such a Gregorian type telescope are
  under study like a continuous ring made of segments or a multiple
  aperture ring made of 7 off-axis telescopes. The advantages of such a
  ring telescope is that its MTF covers all spatial frequencies out to
  those corresponding to its outer diameter, that its circular symmetry
  makes it polarization neutral, and that its large central hole helps
  thermal control and provides ample space for MCAO and Gregorian
  instrumentation. We present the current status of the design of the
  CGST. Our thinking is guided by the outstanding performance of the
  1-meter vacuum solar telescope of the Yunnan Solar Observatory which
  like the CGST uses both AO and image reconstruction. Using it with
  a ring-shape aperture mask the imaging techniques for the CGST are
  being explored. The CGST will have Multi-Conjugate Adaptive Optics
  (MCAO). The peculiarities of Atmospheric Wavefront Tomography for Ring
  Telescopes are aided by the ample availability of guide stars on the
  Sun. IR MCAO-aided diffraction limited imaging offers the advantage of
  a large FOV, and high solar magnetic field sensitivity. Site testing
  is proceeding in western China, (e.g. northern Yunnan Province and
  Tibet). The CGST is a Chinese solar community project originated
  by the Yunnan Astronomical Observatory, the National Astronomical
  Observatories, the Purple Mountain Observatory, the Nanjing University,
  the Nanjing Institute of Astronomical Optics &amp; Technology and the
  Beijing Normal University.

Title: The History of the Fourier Tachometer
Authors: Beckers, J. M.; Brown, T. M.
Bibcode: 2013ASPC..478...93B
Altcode:
  Following a suggestion by one of us (T. Brown) we developed in 1978
  at the Sacramento Peak Observatory the first version of what we
  called a Fourier Tachometer which measured the phase of a single
  frequency component of the Fourier transform of the solar spectrum
  associated with a specific solar spectrum line (Beckers &amp; Brown
  1978). This phase is a direct measure of the wavelength of that
  Line, its Doppler shift and by using polarization optics, its Zeeman
  splitting. This first version based on a Michelson interferometer
  (FT I) was later (Evans 1081) greatly improved by J.W. Evans by using
  a Solid Polarizing Interferometer (version FT II). The latest version
  stands out by its ability to: (i) get wavelength measurements over a
  large 2D field-of-view without the cumbersome use of a high-resolution
  spectrograph, (ii) have a wide angular field-of-view and étendue, (iii)
  be mechanically stable and use much real-time digital processing. The
  FT II was selected for use in Global Oscillation Network Group (GONG)
  in about 1985 and has since then also been used in the space based
  helioseismometers — Micheson Doppler Imager (MDI) onboard Solar
  and Heliospheric Observatory (Scherrer et al. 1995) and Helioseismic
  Magnetic Imager (HMI) onboard Solar Dynamics Observatory (Scherrer et
  al. 2012). The FT II performance has increased over the years with the
  current HMI version having 4096 × 4096 pixels, or 0.5 × 0.5 arcsec
  for the HMI full disk facility, and a cadence of 45 seconds. However,
  except for some early observations at the Sacramento Peak, the Fourier
  Tachometer has not appeared to have been applied to non-helioseismology
  ground-based observations. In ground-based telescopes science full
  precise line profiles are generally desired making the FT II undesirable
  since it only measures something close to their center-of-gravity. For
  future very large diameter (1.5 - 8 m) ground-based solar telescopes
  that will also be the case. But complimentary FT II observations,
  for example from the spectrograph reflecting slit-jaws, would
  provide valuable, high time and spatial resolution complimentary
  observations. The HMI version would have pixel sizes of about 0.03
  × 0.03 arcsec, closely matching the telescope resolution over a 2
  × 2 arcmin field-of-view provided by its Multi-Conjugate Adaptive
  Optics system.

Title: Planning the 8-meter Chinese Giant Solar Telescope
Authors: Beckers, Jacques M.; Liu, Z.; Deng, Y.; Ji, H.
Bibcode: 2013SPD....4440104B
Altcode:
  The Chinese Giant Solar Telescope (CGST) will be a diffraction limited
  solar telescope optimized for the near-infrared (NIR) spectral region
  (0.8 - 2.5 microns). Its diffraction limit will be reached by the
  incorporation of Multi-Conjugate Adaptive Optics (MCAO) enhanced by
  image restoration techniques to achieve uniform (u.v) plane coverage
  over the angular spatial frequency region allowed by its 8-meter
  aperture. Thus it will complement the imaging capabilities of 4-meter
  telescopes being planned elsewhere which are optimized for the visible
  (VIS) spectral region (300 - 1000 nm) In the NIR spectral regions the
  CGST will have access to unique spectral features which will improve
  the diagnostics of the solar atmosphere. These include the CaII lines
  near 860 nm , the HeI lines near 1083 nm, the 1074 nm FeXIII coronal
  lines, the large Zeeman-split FeI line at 1548 nm, and (v) the H-
  continuum absorption minimum at 1.6 micron. Especially in sunspot
  umbrae the simultaneous observation of continua and lines across the
  NIR spectral range will cover a substantial depth range in the solar
  atmosphere. Of course the mid- and far- infrared regions are also
  available for unequalled high-angular resolution solar observations,
  for example, in the Hydrogen Bracket lines, CO molecular bands, and
  the MgI emission line at 12.3 microns. The CGST is a so-called ring
  telescope in which the light is captured by a 1 meter wide segmented
  ring or by a ring of 7 smaller off-axis aperture telescopes. The open
  central area of the telescope is large. The advantages of such a ring
  configuration is that (a) it covers all the spatial frequencies out to
  those corresponding to its outer diameter, (b) its circular symmetry
  makes it polarization neutral, (c) its large central hole helps
  thermal control, and (d) it provides ample space for the MCAO system
  and instrumentation in the Gregorian focus. Even though optimized for
  the NIR, we expect to use the CGST also at visible wavelengths in the
  so-called “Partial Adaptive Optics” (PAO) mode (Applied Optics
  31,424,1992) to obtain angular resolution twice that of a 4-meter
  telescope if their observations indicate that higher resolution is
  desirable. The CGST is a Chinese solar community project.

Title: Daytime Observations with ELTs in the Thermal Infrared Using
    Laser Guide Star Adaptive Optics
Authors: Beckers, J. M.
Bibcode: 2011aoel.confP..38B
Altcode:
  Using Magneto-Optical Filters (MOFs; also called FADOFs = Faraday
  Anomalous Dispersion Optical Filters) it is possible to clearly see
  Sodium Laser Guide Stars in the daytime sky. This makes it possible to
  use ELT Adaptive Optics systems for diffraction limited observations 24
  hours/day. Because of the bright daytime sky this LGS AO application is
  only of astronomical interest in the mid-infrared wavelength region
  (4 - 25 microns wavelengths) where the thermal radiation of the
  atmosphere-telescope system dominates the scattering of sunlight thus
  making the day- and night- sky background comparable. Incorporating
  MOFs in the LGS wavefront sensor thus would more than double
  the ELT observing time for mid-infrared astronomy and would make
  sources in almost the entire sky available for observation at any
  time of the year. Even though the AO would increase the brightness
  of point-sources, it would not compete with the James Webb Space
  Telescope in terms of detectability. The gain with respect to the
  JWST lies in the 5 to 6 times better linear angular resolution. The
  contrast gain in brightness at near-IR wavelengths is sufficient to
  give sufficient natural guide stars there for tip-tilt control. MOFs
  have been shown to function with Na lasers in LIDAR applications (see
  Beckers and Cacciani, Experimental Astronomy 11, 133, 2001). The main
  complication associated with incorporating MOFs in ELT AO system is
  likely the requirement to make the telescope and its enclosure robust
  in the daytime environment. I refer to SPIE Proceedings 6986 (2008)
  for a recent reference on this topic.

Title: Satellite Calibration And Validation Experiments Over Arctic
    Sea Ice In The Vicinity Of Svalbard
Authors: Gerland, S.; Brandt, O.; Hansen, E.; Rnner, A. H. H.;
   Granskog, M.; Forsstrom, S.; Eltoft, T.; Fors Schwenke, A.; Moen,
   M. -A.; Doulgeris, A.; Haas, C.; Beckers, J.; Hughes, N.
Bibcode: 2011ESASP.693E..22G
Altcode:
  In late summer 2010, in situ observations on Arctic sea ice were
  performed at the end of the melting season north of Svalbard,
  and in the Fram Strait. High resolution Radarsat-2 SAR images were
  obtained. Simultaneously, data about sea ice and snow thickness, ice
  topography, and melt ponds was collected. A helicopter performed ice
  thickness surveys using an electromagnetic (EM) device, accompanied
  with automatic photography and laser altimetry. The EM method is also
  used for the calibration and validation of data from the new CryoSat-2
  radar altimetry satellite. Data on snow and ice properties have been
  collected over several years for satellite altimetry calibration. These
  are necessary for estimating the sea ice thickness from measured
  freeboard. Preliminary results indicate the improved possibilities for
  ice type classification from SAR satellite imagery. Data collected for
  CryoSat- 2 calibration and validation will contribute to improve data
  quality of CryoSat-2 products.

Title: Enhanced ocean temperature forecast skills through 3-D
    super-ensemble multi-model fusion
Authors: Lenartz, F.; Mourre, B.; Barth, A.; Beckers, J. -M.;
   Vandenbulcke, L.; Rixen, M.
Bibcode: 2010GeoRL..3719606L
Altcode:
  An innovative multi-model fusion technique is proposed to improve
  short-term ocean temperature forecasts: the three-dimensional
  super-ensemble. In this method, a Kalman Filter is used to adjust
  three-dimensional model weights over a past learning period, allowing
  to give more importance to recent observations, and take into account
  spatially varying model skills. The predictive performance is evaluated
  against SST analyses, CTD casts and gliders tracks collected during
  the Ligurian Sea Cal/Val 2008 experiment. Statistical results not
  only show a very significant bias reduction of this multi-model
  forecast in comparison with the individual models, their ensemble
  mean and a single-weight-per-model version of the super-ensemble,
  but also the improvement of other pattern-related skills. In a 48-h
  forecast experiment, and with respect to the ensemble mean, surface and
  subsurface root-mean-square differences with observations are reduced
  by 57% and 35% respectively, making this new technique a suitable
  non-intrusive post-processing method for multi-model operational
  forecasting systems.

Title: Optical Turbulence in High Angular Resolution Techniques
    in Astronomy
Authors: Beckers, Jacques M.
Bibcode: 2009otam.conf....1B
Altcode:
  All astronomical observations are done best from space where the
  absorption by and turbulence in the Earth atmosphere are absent. One has
  access to the entire electromagnetic radiation spectrum and the absence
  of seeing allows unlimited angular resolution. However, the cost of
  facilities in space and their operation is 3 orders of magnitude of
  similar sized facilities on Earth. Experimental astrophysicists have
  therefore in the past decades pursued the development of techniques
  to overcome the seeing limitations by the atmosphere. So far they
  have been very successful at this and much more is almost certain
  to come. Adaptive Optics (AO) will make very large (8 - 10-meters
  diameter) and extremely large (30 - 42 meters diameter) telescopes
  diffraction limited first at infrared wavelengths and eventually at
  visible wavelengths. The development of fast optical turbulence/seeing
  wavefront sensing techniques using artificial sources (Laser Beacons)
  will enable doing that over the entire sky. Atmospheric Tomography (AT)
  needed for Multi-Conjugate Adaptive Optics (MCAO) will give 3D maps
  of the rapidly variable atmospheric turbulence. Large interferometers
  with baselines of hundreds of meters will further enhance the angular
  resolution using fringe tracking for both co-phasing and coherent
  operation. Ground-based astronomy is therefore entering a new era
  in which milli-arcsecond observations and better are foreseen even
  of objects at the edge of the universe. The astronomical techniques
  will result in information of atmospheric optical turbulence which is
  likely to be of interest for meteorologists.

Title: Pupil Slicing Adaptive Optics:. Making Extremely Large
    Telescopes Diffraction Limited at Short Wavelengths
Authors: Beckers, Jacques M.
Bibcode: 2009otam.conf..307B
Altcode:
  Extremely Large Telescopes (ELTs) will have aperture diameters up to
  42 meters. Adaptive Optics (AO) at short wavelengths (&lt; 1 micron)
  will be very hard to implement at these wavelengths because of the
  limited number of actuators on state-of-the-art deformable mirrors and
  because of the limited brightness of Laser Guide Stars (LGSs). For
  1 arcsec seeing at 500 nm wavelength deformable mirrors (DMs) with
  about 150000 actuators will be needed and LGSs of a brightness of V =
  8 to 9. That exceeds our present capabilities by a factor of about 100
  and 2 magnitudes respectively. One might expect both to improve with
  time. We propose to combine the techniques of "pupil slicing" and AO to
  sharpen the telescope images at short wavelengths to the size of Airy
  disk of the pupil slices. I refer to this technique as "Pupil Slicing
  Adaptive Optics" or PSAO. At 500 nm wavelength that would correspond
  to the Airy disk of an approximately 5 meter diameter aperture, or a
  FWHM of 0.02 arcsec. As DMs increase in their number of actuators,
  the size of the pupil slices increases thus improving the angular
  resolution. Ultimately the full angular resolution of, for example, a 42
  meter aperture would be reached (0.0024 arcsec at 500 nm). Of course,
  this does not resolve the issue of the limited brightness of LGSs. For
  it one has to wait for more powerful lasers and the development of
  perspective elongation correction techniques. Alternatively one would
  accept limited sky coverage (0.1%) when using natural guide stars
  (NGSs). Particularly interesting is the PSAO technique for high
  resolution spectroscopy where the smaller image sizes even for many
  slices results in a significant decrease in spectrograph dimensions. <P
  />Note from Publisher: This article contains the abstract only.

Title: Using the Scintillation of Extended Objects to Probe the
    Lower Atmosphere
Authors: Beckers, Jacques M.
Bibcode: 2009otam.conf...23B
Altcode:
  The scintillation of point-like objects is primarily caused by thermal
  fluctuations in the upper atmosphere. For it the scintillation index
  (σ<SUB>I</SUB><SUP>2</SUP>) is proportional to the height integral of
  C<SUB>n</SUB><SUP>2</SUP>(h) weighted by a height dependent function
  F(h) = h<SUP>α</SUP> where α = +5/3. For extended objects like the Sun
  or the Moon the height contribution to the (much smaller) scintillation
  is quite different. Because of their size the effects of the optical
  turbulence is averaged over an ever increasing area as the distance to
  the detector increases. Assuming vertical viewing, the area diameter
  increases like h*Ω where Ω is the angular diameter of the Sun or
  Moon. For Kolmogorov turbulence the function F(h) then still has the
  same shape, but with α = -1/3 so that the lower layers contribute
  more to scintillation. This makes it a good tool for the probing of
  the lower atmospheric layers. Unlike the σ<SUB>I</SUB><SUP>2</SUP> for
  stellar scintillation, the σ<SUB>I</SUB><SUP>2</SUP> for the Sun and
  the Moon is wavelength independent. Using an array of scintillometers
  one can probe the C<SUB>n</SUB><SUP>2</SUP>(h) distribution of
  those lower layers in a technique called SHABAR. SHABARs have been
  used in site testing for lower atmosphere probing for solar and
  nighttime telescopes. The aim is to establish the height to place
  telescopes, like the Advanced Technology Solar Telescope (ATST),
  to minimize boundary layer seeing effects. SHABAR site tests using
  the Moon are planned both for Arctic sites (Hickson's contribution
  to this meeting) and Antarctic sites (Storey's contribution to this
  meeting) where boundary layer heights are very site dependant reaching
  sometimes very small values. In my contribution I described some of
  the solar results related to the ATST site testing. The scintillation
  of planets have an F(h) function different in shape from that of the
  Sun or Moon. For low heights, where their beams still are narrow,
  F(h) has an α of +5/3 (as for stars); for large heights it is -1/3
  (as for the Sun &amp; Moon). For Mars the height contributions F(h)
  for seeing and scintillation are similar.

Title: Laser guide stars for daytime thermal IR observations
Authors: Beckers, Jacques M.
Bibcode: 2008SPIE.6986E..0GB
Altcode: 2008SPIE.6986E..16B
  In connection with the planning for Extremely Large Telescopes,
  I revisit a 2001 paper in which Cacciani and I describe the use
  of Sodium Laser Guide Stars (LGSs) for diffraction limited daytime
  astronomical observations. The enabling technology for seeing LGSs in
  broad daylight is the availability of very narrow band magneto-optical
  filters. Considering the dominance of the atmospheric scattering of
  sunlight at wavelengths below 3.5 μm, daytime use is only indicated for
  mid- and thermal IR observations. The launch of the 6.5 meter aperture
  James Web Space Telescope (JWST) appears to be assured and planned for
  2013, preceding the most optimistic projections for the completion date
  of the first ELT. The projected thermal background of the JWST is very
  much less than that of ground-based telescopes so that any competing
  ground-based observations are limited to those parameters not covered
  by the JWST: angular resolution (requiring apertures &gt; 6.5 meter)
  and spectral resolution (R&gt;3000). I compare the benefits of daytime
  observations with Na-LGS equipped telescopes and interferometers at
  moderate latitudes and in the Antarctic (specifically Dome C). In both
  cases daytime observations extend the amount of observing time available
  for TIR observations. Antarctic observations have the advantage of
  having very good seeing during the daytime, significantly better than
  nighttime seeing. In contrast the seeing at moderate latitude sites
  significantly deteriorates during daytime resulting in lower quality
  observations than during nighttime. In addition Antarctic sites are
  less hostile to maintenance and operations during daytime (summer)
  observations as compared to nighttime (winter) observations.

Title: Introduction to the Discussion on: How to Mitigate the
    Ground-Layer Seeing Effects at Dome C?
Authors: Beckers, J.; Travouillon, T.
Bibcode: 2008EAS....33..221B
Altcode:
  At Dome C most of the seeing is located in the lower atmosphere,
  below 50 meters height. In this introduction we describe ways in
  which one might mitigate those ground layer seeing effects and thus
  be limited solely by the ~0.25 arcsec seeing of the so-called “free
  atmosphere”.

Title: On the Daytime Use of Dome C for Astronomy
Authors: Beckers, J. M.
Bibcode: 2008EAS....33..307B
Altcode:
  I describe aspects of the non-solar astronomy use of Dome C telescopes
  under daytime/summer conditions. In the thermal IR (TIR) wavelength
  region, where scattered sunlight is dwarfed by sky and facility
  radiation, astronomy benefits from the better seeing, continuous sky
  coverage, a more than doubling of the observing time and the improved
  site accessibility and logistics. Na-Laser Guide Stars (LGSs) can be
  used for wavefront sensing in daytime using very narrow band filters to
  suppress the sky background at visible wavelengths. It enables the use
  of Adaptive Optics for diffraction limited imaging in the TIR during
  daytime at Dome C.

Title: Towards the Interferometric Imaging of Red Supergiants
Authors: Ludwig, Hans-Günter; Beckers, Jacques
Bibcode: 2008poii.conf..485L
Altcode: 2008poio.conf..485L
  No abstract at ADS

Title: 1988 1993: The Final Definition of the Very Large Telescope
    Interferometer, its Site and Configuration
Authors: Beckers, Jacques M.
Bibcode: 2008poii.conf...23B
Altcode: 2008poio.conf...23B
  This paper focuses on the period during which the VLTI evolved from its
  conceptual phase to the way it is largely implemented now. That phase
  did not include the VLTI instrumentation, which was defined later and
  which did not make use of the homothetic beamcombining system that
  was part of the 1988 - 199 design.

Title: Can variable meridional flows lead to false exoplanet
    detections?
Authors: Beckers, J. M.
Bibcode: 2007AN....328.1084B
Altcode:
  The search for habitable exoplanets centers on planets with Earth-like
  conditions around late type stars. Radial velocity searches for these
  planets require precisions of 1 m/s and better. That is now being
  achieved. At these precisions stellar surface motions might lead to
  false detections. Of particular interest are variable meridional
  flows on stellar surfaces. I review the available observations of
  solar surface meridional flows using both Doppler shift and local
  helioseismology techniques. Interpretation in terms of Doppler shifts
  in integrated starlight leads to estimates of the likelihood of false
  detections. It is unlikely that these false detections occur in the
  habitability zones of exoplanets.

Title: Very high-resolution spectroscopy for extremely large
    telescopes using pupil slicing and adaptive optics
Authors: Beckers, Jacques M.; Andersen, Torben E.; Owner-Petersen,
   Mette
Bibcode: 2007OExpr..15.1983B
Altcode:
  Under seeing limited conditions very high resolution spectroscopy
  becomes very difficult for extremely large telescopes (ELTs). Using
  adaptive optics (AO) the stellar image size decreases proportional with
  the telescope diameter. This makes the spectrograph optics and hence
  its resolution independent of the telescope diameter. However AO for
  use with ELTs at visible wavelengths require deformable mirrors with
  many elements. Those are not likely to be available for quite some
  time. We propose to use the pupil slicing technique to create a number
  of sub-pupils each of which having its own deformable mirror. The
  images from all sub-pupils are combined incoherently with a diameter
  corresponding to the diffraction limit of the sub-pupil. The technique
  is referred to as “Pupil Slicing Adaptive Optics” or PSAO.

Title: Effects of Foreshortening on Shallow Sub-surface Flows Observed
    with Local Helioseismology
Authors: Beckers, Jacques M.
Bibcode: 2007SoPh..240....3B
Altcode:
  From the results given in a recent paper by Zaatri et al. (2006,
  Solar Phys.236, 227) it is clear that foreshortening effects play a
  major role in estimating the magnitude and direction of meridional
  and other flows in the shallow solar sub-surface layers using local
  helioseismology. Using a different algorithm to account for these
  effects I arrive at a significantly different estimate for the
  meridional flows.

Title: From Euro50 toward a European ELT
Authors: Ardeberg, Arne; Andersen, Torben; Beckers, Jacques; Browne,
   Michael; Enmark, Anita; Knutsson, Per; Owner-Petersen, Mette
Bibcode: 2006SPIE.6267E..25A
Altcode: 2006SPIE.6267E..68A
  With Euro50 as a convenient telescope laboratory, the Euro50 team has
  continued development aiming at a European extremely large telescope
  (ELT). Here, we give a progress report. The needs of science
  and instrumentation are briefly discussed as is the importance
  of photometric stability and precision. Results are reported
  from work on integrated modelling. Details are given concerning
  point-spread functions (PSFs) obtained with and without adaptive optics
  (AO). Our results are rather encouraging concerning AO photometry and
  compensation of edge sensor noise as well as regarding seeing-limited
  ELT operation. The current status of our development of large deformable
  mirrors is shown. Low-cost actuators and deflection sensors have been
  developed as have hierarchic control algorithms. Fabrication of large
  thin mirror blanks as well as polishing and handling of thin mirrors
  has been studied experimentally. Regarding adaptive optics, we discuss
  differential refraction and the limitations imposed by dispersive
  optical path differences (OPDs) and dispersive anisoplanatism. We report
  on progress in laser guide star (LGS) performance and a real-time
  online experiment in multi-conjugate AO (MCAO). We discuss ELTs,
  high-resolution spectroscopy and pupil slicing with and without use
  of AO. Finally, we present some recent studies of ELT enclosure options.

Title: High Resolution Spectroscopy with Extremely Large Telescopes
    Using Pupil Slicing Adaptive Optics
Authors: Beckers, Jacques M.; Andersen, T.; Owner-Petersen, M.
Bibcode: 2006AAS...208.5504B
Altcode: 2006BAAS...38R.135B
  Under seeing limited imaging conditions, high resolution spectroscopy
  (R ≥ 100,000 at visible wavelengths) on large aperture telescopes
  requires huge instruments. This will cause major problems in future
  Extremely Large Telescopes (ELTs; diameters D = 20 - 60 meters). With
  diffraction limited imaging using adaptive optics the size of the
  spectrograph will become independent of the telescope diameter since
  the image size shrinks at the same rate as the telescope diameter
  increases. However the complexity of adaptive optics at visible
  wavelengths will be very high, requiring a large number of deformable
  mirrors elements (50000 to 100000 for D = 50 meters). It is not likely
  that devices of that complexity will be available soon.In this paper
  we propose an intermediate step in that direction using so-called
  Pupil-Slicing Adaptive Optics (PSAO). In it the telescope aperture (its
  "pupil") will be divided into N equal sub-pupils. Each sub-pupil will
  have its own adaptive optics to give a diffraction limited image size
  corresponding to its diameter. The N resulting images are then combined
  on the entrance of a multi-mode fiber which feeds the high resolution
  spectrograph. The fiber scrambles the light and avoids variations of
  the position of the spectrum due to variations of the spectrograph
  slit illumination.As an example, we present a strawman design for a
  PSAO spectrograph for the Euro50, D = 50 meter telescope. It uses N =
  18 and 4000 element MEMS deformable mirrors. Such mirrors are currently
  under development and are likely to be available at the time of the
  commissioning of the first ELT. A spectral resolution of around R =
  200000 seems feasible for spectrographs less than 2 meters in size.

Title: Site testing for the Advanced Technology Solar Telescope
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.;
   Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
   T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn,
   M.; Radick, R.; Rimmele, T.; Socas-Navarro, H.; Streander, K.
Bibcode: 2006SPIE.6267E..1TH
Altcode: 2006SPIE.6267E..59H
  The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope
  being designed for high spatial, spectral and temporal resolution,
  as well as IR and low-scattered light observations. The overall
  limit of performance of the telescope is strongly influenced by the
  qualities of the site at which it is located. Six sites were tested
  with a seeing monitor and a sky brightness instrument for 1.5 to 2
  years. The sites were Big Bear (California), Haleakala (Hawaii), La
  Palma (Canary Islands, Spain), Panguitch Lake (Utah), Sacramento Peak
  (New Mexico), and San Pedro Martir (Baja California, Mexico). In this
  paper we will describe the methods and results of the site survey,
  which chose Haleakala as the location of the ATST.

Title: Solar Site Survey for the Advanced Technology Solar
    Telescope. I. Analysis of the Seeing Data
Authors: Socas-Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.;
   Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer,
   S.; Hill, F.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.;
   Oncley, S.; Penn, M.; Rimmele, T.; Streander, K.
Bibcode: 2005PASP..117.1296S
Altcode: 2005astro.ph..8690S
  The site survey for the Advanced Technology Solar Telescope concluded
  recently after more than 2 years of data gathering and analysis. Six
  locations, including lake, island, and continental sites, were
  thoroughly probed for image quality and sky brightness. The present
  paper describes the analysis methodology employed to determine the
  height stratification of the atmospheric turbulence. This information
  is crucial, because daytime seeing is often very different between the
  actual telescope aperture (~30 m) and the ground. Two independent
  inversion codes have been developed to simultaneously analyze
  data from a scintillometer array and a solar differential image
  monitor. We show here the results of applying them to a sample subset
  of data from 2003 May that was used for testing. Both codes retrieve a
  similar seeing stratification through the height range of interest. A
  quantitative comparison between our analysis procedure and actual in
  situ measurements confirms the validity of the inversions. The sample
  data presented in this paper reveal a qualitatively different behavior
  for the lake sites (dominated by high-altitude seeing) and the rest
  (dominated by near-ground turbulence).

Title: The Western Mediterranean Deep Water: A proxy for climate
    change
Authors: Rixen, M.; Beckers, J. -M.; Levitus, S.; Antonov, J.; Boyer,
   T.; Maillard, C.; Fichaut, M.; Balopoulos, E.; Iona, S.; Dooley, H.;
   Garcia, M. -J.; Manca, B.; Giorgetti, A.; Manzella, G.; Mikhailov,
   N.; Pinardi, N.; Zavatarelli, M.
Bibcode: 2005GeoRL..3212608R
Altcode:
  Reconstructions of Mediterranean ocean temperature fields back to 1950
  show a proxy relationship between heat content changes in the North
  Atlantic and the Western Mediterranean Deep Water (WMDW) formed in
  the Gulf of Lions in winter, because of consistent air-sea heat fluxes
  over these areas, strongly correlated to the North Atlantic Oscillation
  (NAO).

Title: The ATST Site Survey
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J. W.; Brown, T.;
   Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
   T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.;
   Radick, R.; Rimmele, T.; Socas-Navarro, H.; Soltau, D.; Streander, K.
Bibcode: 2005AGUSMSP34A..04H
Altcode:
  The Advanced Technology Solar Telescope (ATST) will be the world's
  largest aperture solar telescope, and is being designed for high
  resolution, IR, and coronal research. It must be located at a site that
  maximizes the scientific return of this substantial investment. We
  present the instrumentation, analysis and results of the ATST site
  survey. Two instrumentation sets were deployed at each of six sites to
  measure seeing as a function of height, and sky brightness as a function
  of wavelength and off-limb position. Analysis software was developed
  to estimate the structure function Cn2 as a function of height near
  the ground, and the results were verified by comparison with in-situ
  measurements. Additional software was developed to estimate the sky
  brightness. The statistics of the conditions at the sites were corrected
  for observing habits and the annualized hours of specific observing
  conditions were estimated. These results were used to identify three
  excellent sites suitable to host the ATST: Haleakala, Big Bear and La
  Palma. Among them, Haleakala is proposed as the optimal location of
  the ATST, La Palma and Big Bear being viable alternative sites.

Title: The Effect of Stellar Meridional Motions on Extrasolar Planet
    Detection
Authors: Beckers, J. M.
Bibcode: 2005AAS...206.2306B
Altcode: 2005BAAS...37..464B
  Most Extrasolar Planet detections use periodic Doppler velocity
  variations of the parent star to infer the presence of a
  planet. Refinements of this technique have reached precisions of 1
  m/sec and better. At these precisions periodic flows on the stellar
  surface may well lead to false detections. The most likely flows of
  concern are meridional motions. <P />Solar surface meridional motions
  have unambiguously been observed. They move towards the pole and have
  an approximate shape of the second Legendre Polynomial of order m=1
  reaching a maximum surface velocity of about 30 m/sec. Depending on the
  inclination of the rotation axis to the line of sight this would cause a
  red shift in the spectrum of integrated sunlight of 8 m/sec when viewed
  perpendicular to this axis [sin(i)=1] and a blue shift of 15 m/sec when
  viewed along this axis [sin(i)=0]. The Sun is a relatively slow rotator
  among G and earlier type stars, so that many of the stellar effects
  are likely to be larger. <P />Of interest is, of course, the temporal
  variation of this motion. Observations of solar surface meridional
  flows go back to 1967. They appear to show variations but my search
  for periodic meridional motion changes is so far inconclusive. This
  search is complicated by possible changing instrumental effects and
  latitudinal change in convective blue shift ("limb effect"). The latter
  is also of interest for false Extrasolar Planet detection techniques. It
  can be evaluated by observing the Doppler shifts for different line
  strengths and excitation potential. The former requires a long time
  sequence of solar observations of surface meridional flows using the
  same, unchanging instrument. The GONG and SOHO/MDI helioseismology
  observatories, now in operation for about one solar cycle, might
  provide the necessary data.

Title: Sunspots, gravitational redshift and exo-solar planet detection
Authors: Beckers, Jacques M.
Bibcode: 2005dsr..conf..285B
Altcode:
  No abstract at ADS

Title: Sunspots, gravitational redshift and exo-solar planet detection
Authors: Beckers, Jacques M.
Bibcode: 2005AcHA...25..285B
Altcode:
  I revisit a paper that I published over 25 years ago (Beckers 1977)
  which has recently attracted renewed attention in connection with
  searches for exo-solar planets using the periodic Doppler motions
  of the star resulting from the center of gravity in these planetary
  systems being offset from the center of that star. The original
  goal of the research reported in the paper was concerned with the
  accurate determination of absolute motions of and in sunspots. I
  used the wavelengths of Iodine absorption lines introduced by an
  Iodine absorption tube as the wavelength reference. The experiment
  resulted in addition to the intended measurement of sunspot motions
  in the affirmation of the interpretation of the solar limb effect and
  in the measurement of the gravitational redshift of the solar disk
  radiation. Only recently did I become aware that it was this use of the
  Iodine absorption spectrum as a stable and precise wavelength reference
  that led to many of the current programs aimed at the detection of
  exo-solar planets.

Title: Solar site testing for the Advanced Technology Solar Telescope
Authors: Hill, Frank; Beckers, Jacques; Brandt, Peter; Briggs, John;
   Brown, Timothy; Brown, W.; Collados, Manuel; Denker, Carsten; Fletcher,
   Steven; Hegwer, Steven; Horst, T.; Komsa, Mark; Kuhn, Jeff; Lecinski,
   Alice; Lin, Haosheng; Oncley, Steve; Penn, Matthew; Rimmele, Thomas
   R.; Socas-Navarro, Hector; Streander, Kim
Bibcode: 2004SPIE.5489..122H
Altcode:
  The location of the Advanced Technology Solar Telescope (ATST) is a
  critical factor in the overall performance of the telescope. We have
  developed a set of instrumentation to measure daytime seeing, sky
  brightness, cloud cover, water vapor, dust levels, and weather. The
  instruments have been located at six sites for periods of one to two
  years. Here we describe the sites and instrumentation, discuss the
  data reduction, and present some preliminary results. We demonstrate
  that it is possible to estimate seeing as a function of height near the
  ground with an array of scintillometers, and that there is a distinct
  qualitative difference in daytime seeing between sites with or without
  a nearby lake.

Title: Euro50
Authors: Andersen, Torben E.; Ardeberg, Arne L.; Beckers, Jacques M.;
   Goncharov, Alexander V.; Owner-Petersen, Mette; Riewaldt, Holger
Bibcode: 2004SPIE.5382..169A
Altcode:
  The Euro50 is a telescope for optical and infrared wavelengths. It
  has an aspherical primary mirror with a size of 50 meters and 618
  segments. The optical configuration is of Gregorian type and the
  secondary mirror is deformable for adaptive optics. Observations can
  take place in prime focus, Gregorian foci, and Nasmyth foci using
  additional relay mirrors. The telescope provides seeing limited
  observations, partial adaptive optics with ground layer correction,
  single conjugate adaptive optics and dual-conjugate adaptive
  optics. For prime focus observations, a clam-shell corrector with a
  doublet lens is used. The primary mirror segments can be polished using
  the precessions polishing technique. "Live Optics" denotes the joint
  segment alignment system, secondary mirror control system, adaptive
  optics and main axes servos. An overview is given of the live optics
  architecture, including feedback from wavefront sensors for natural
  and laser guide stars, and from primary mirror segment edge sensors. A
  straw man concept of the laser guide star system using sum-frequency
  YAG lasers is presented together with a solution to the laser guide
  star perspective elongation problem. The structural design involves a
  large steel structure and a tripod of carbon fiber reinforced polymer
  to support the secondary mirror. Integrated models have been set up
  to simulate telescope performance. Results show that an enclosure is
  needed to protect the telescope against wind during observations. The
  enclosure is very large box-shaped steel structure.

Title: Sodium beacon wavefront sensing for the Euro50 telescope in
    the presence of perspective elongation
Authors: Beckers, Jacques M.; Owner-Petersen, Mette; Andersen,
   Torben E.
Bibcode: 2004SPIE.5382..510B
Altcode:
  To obtain full sky coverage, astronomical adaptive optics systems
  require Na Sodium Beacons (SBs) (also referred to as Laser Guide Stars
  or LGSs) located at heights extending from 85 to 100 km. When viewed at
  the edge of large telescopes these SBs appear elongated. For the Euro50
  50 meter aperture telecopes this elongation amounts to 6 to 9 arcseconds
  when the laser is launched from a point on the telescope axis. This is
  substantially larger than the -0.6 arcsec FWHM SB when viewed near the
  telescope center. This so-called "perspective elongation" substantially
  decreases the sensitivity of SB aided adaptive optics. We describe a
  way of removing this elongation when using pulsed lasers. It uses rapid
  (microsecond) refocusing of the telescope with the aid of birefringent
  lenses and polarization modulators. We present an outline of the SB
  wavefront sensor for the Euro50.

Title: Latest Results from the ATST Site Survey
Authors: Hill, F.; Collados, M.; Navarro, H.; Beckers, J.; Brandt,
   P.; Briggs, J.; Brown, T.; Denker, C.; Hegwer, S.; Horst, T.; Komsa,
   M.; Kuhn, J.; Lin, H.; Oncley, S.; Penn, M.; Rimmele, T.; Soltau,
   D.; Streander, K.
Bibcode: 2004AAS...204.6909H
Altcode: 2004BAAS...36..795H
  We present the latest results and current status of the site survey
  portion of the Advanced Technology Solar Telescope (ATST) project. The
  ATST will provide high resolution solar data in the visible and IR. The
  site is a major factor determining the performance of the telescope. The
  most critical site characteristics are the statistics of daytime seeing
  quality and sky clarity. These conditions are being measured by a suite
  of instruments at three sites (Big Bear, Haleakala, La Palma). These
  sites were chosen from a set of six that have been tested starting in
  November 2001. The instrumentation includes a solar differential image
  motion monitor, an array of scintillometers, a miniature coronagraph,
  a dust monitor, and a weather station. The analysis of the data provides
  an estimate of the seeing as a function of height near the ground. We
  will present the latest results of the analysis of the survey data set.

Title: Development of SCIDAR for solar observations
Authors: Beckers, Jacques M.; Rimmele, Thomas R.
Bibcode: 2004SPIE.5171..195B
Altcode:
  In nighttime astronomy Vernin and co-workers have proposed and
  subsequently developed the so-called SCIDAR (SCIntillation Detection
  And Ranging) technique to probe C<SUB>n</SUB><SUP>2</SUP>(h). It makes
  use of the double shadow band (or scintillation) pattern formed on
  a telescope aperture by the two components of a binary star. We are
  developing a variant of this technique for solar astronomy. It uses
  pairs of small apertures on the solar image with diameters smaller
  than the isoplanatic patch ("artificial double stars"). Within
  the isoplanatic patch the complex amplitude (intensity and phase)
  of the atmospheric wavefront disturbances is constant. Solar SCIDAR
  (or S-SCIDAR) makes use of this. We will present the results of the
  first (inconclusive) experiments of this S-SCIDAR technique as used on
  the 76 cm aperture Dunn Solar Telescope (DST) and the 152 cm aperture
  McMath-Pierce facility (McM-P) of the US National Solar Observatory. It
  uses a 45 x 45 lenslet array placed in the solar image. The size of
  the lenslets corresponds to 2.25 x 2.25 arcsec at the DST and 1.67 x
  1.67 arcsec at the McM-P; the separation of lenslet pairs on the DST
  (and hence of the separations of the artificial double stars) ranges
  from 2.25 arcsec to 140 arcsec. The lenslet array forms an array of
  pupil images on a CCD detector.

Title: Interferometric Imaging in Astronomy: A Personal Retrospective
    (With 17 Figures)
Authors: Beckers, Jacques M.
Bibcode: 2004RvMA...17..239B
Altcode:
  No abstract at ADS

Title: Study of the impact of satellite data assimilation into
    a hydrodynamic model of the Ligurian Sea. Comparison between SST
    fields and SST satellite-based predicted fields
Authors: Alvera-Azcarate, A.; Barth, A.; Rixen, M.; Beckers, J. -M.
Bibcode: 2004cosp...35.2968A
Altcode: 2004cosp.meet.2968A
  The verification of a 3D hydrodynamic model of the Ligurian Sea is
  presented. Two assimilation experiments have been carried out with
  this model: the assimilation of real SST, and the assimilation of
  SST forecasted by a statistical predictor. The aim of the study is
  to establish the skill of the model in these two configurations. The
  assimilation of predicted SST can help to increase the model skill
  when observations are not available, and preliminary results show
  that both approaches obtained similar results. The verification is
  done in a multi-scale approach, by decomposing the model results
  and the observations into several spatial scales, using 2D discrete
  wavelet transforms. At each scale the error between the model and the
  observations is calculated, and the scales where the biggest errors
  occur can be identified. The variability distribution of the model and
  the observations is also examined at each scale, to study the impact of
  the assimilation on the model variability. This methodology provides
  a scale-dependent insight in the study of the assimilation of SST and
  predicted SST. The differences between both assimilated data and how
  these differences affect the model results are examined.

Title: Recovering missing data in satellite images. An application
    to Adriatic SST and comparison with in situ data
Authors: Alvera-Azcarate, A.; Barth, A.; Rixen, M.; Beckers, J. -M.
Bibcode: 2004cosp...35.2980A
Altcode: 2004cosp.meet.2980A
  Satellite images are very useful for many applications in oceanography
  and other environmental sciences. They offer a great coverage both
  in time and space, not attained by in situ measurements. Clouds
  are responsible for missing data on images provided by receptors
  working in the visible and IR range receptors. In some seasons
  the cloud coverage can reach an important percentage. Many data
  analysis techniques do not need a total coverage, although it is
  always desirable. Some applications, such as Empirical Orthogonal
  Function (EOF) analysis, or wavelet decomposition need a complete
  set of data, and a technique for recovering these missing data is
  indispensable. In this work we present DINEOF (Data INterpolating
  Empirical Orthogonal Functions), a method for the reconstruction of
  satellite data, based on an EOF decomposition. DINEOF reconstructs
  the missing data from an optimal set of EOFs. The optimal number of
  EOFs is determined by cross-validation. This method has shown to
  obtain robust results. DINEOF has been applied to a series of 105
  AVHRR SST images of the Adriatic Sea, in a period ranging from May to
  October 1995. The mean cloud coverage of this data set is 52%. The
  error obtained by the cross-validation is of 0.6°C, and a total of
  10 EOFs were necessary to reconstruct the data. A comparison with in
  situ data obtained form the MEDAR/Medatlas database is made. A total
  of 452 stations are examined. The RMS error between MEDAR/Medatlas and
  the reconstructed data is of 0.95°C. The error between MEDAR/Medatlas
  data and the points that are not missing in the Adriatic data set is
  of 0.67°C, which can be considered as the inherent error between the
  in situ and remote sensed data sets.

Title: Assimilation of Sea Surface Temperature predicted by a
    satellite-based forecasting system in a doubly nested primitive
    equation model of the Ligurian Sea
Authors: Barth, A.; Alvera-Azcárate, A.; Alvarez, A.; Beckers, J. -M.
Bibcode: 2004cosp...35.2744B
Altcode: 2004cosp.meet.2744B
  Data assimilation is traditionally used to combine model dynamics and
  observations in a statistical optimal way. Assimilation of observations
  improves therefore hindcasts and nowcasts of the ocean state than
  otherwise obtained by the model alone. The observational constraints
  are necessary to reduce uncertainties and imperfections of the ocean
  model. Due to the obvious lack of future observations, the model
  forecast cannot be controlled by observations and the predictive
  skill degrades as the forecast time lag increases. The error grow
  is not only caused by the chaotic nature of the system but also by
  the biases and drifts of the model. The later part can be reduced
  by considering different models with different imperfections. Data
  assimilation provides the statistical frame for merging the different
  model results. A primitive equation model of the Mediterranean Sea
  (1/4° resolution) has been implemented with two successive grid
  refinements of the Liguro-Provençal Basin (1/20°) and the Ligurian
  Sea (1/60°) respectively (Barth et al, 2003). The dependence of the
  ``parent'' model and the embedded ``child'' model is bi-directional;
  it involves the exchange of boundary conditions and feedback between
  the models. Alvarez el al. (2004) developed a statistical predictor for
  forecasting the SST of the Ligurian Sea with a time lag of 7 days based
  on the previous remote sensed SST. The degrees of freedom of the SST are
  reduced by an Empirical Orthogonal Function (EOF) analysis. A genetic
  algorithm trained by the historical SST evolution in the Ligurian Sea
  is used to predict the EOF amplitudes. Observed and forecasted SST
  are assimilated in the hydrodynamic model and the results of this two
  experiments are compared to the model run without assimilation. The
  assimilation of the forecasted SST reduces the error of the model by an
  amount comparable to the assimilation of real SST, showing the potential
  of skill improvement of combining statistical and hydrodynamic models.

Title: Rapid refocusing system for the Euro50 telescope aimed at
    removing the perspective elongation of laser beacons
Authors: Beckers, Jacques M.; Owner-Petersen, Mette; Andersen, Torben
Bibcode: 2003SPIE.5169..123B
Altcode:
  To obtain full sky coverage, astronomical adaptive optics systems
  require Na Sodium Beacons (SBs) (also referred to as Laser Guide Stars
  or LGSs) located at heights extending from 85 to 100 km. When viewed
  at the edge of large telescopes these SBs appear elongated. For the
  Euro50 50 meter aperture telescopes this elongation amounts to 6 to 9
  arcseconds when the laser is launched from a point on the telescope
  axis. This is substantially larger than the ~0.6 arcsec FWHM SB
  when viewed near the telescope center. This so-called "perspective
  elongation" substantially decreases the sensitivity of SB aided adaptive
  optics. We describe a way of removing this elongation when using pulsed
  lasers. It uses rapid (microsecond) refocusing of the telescope with
  the aid of birefringent lenses and polarization modulators. We present
  an outline of the SB wavefront sensor for the Euro50.

Title: Sunspots, Gravitational Redshift and Exo-solar Planet Detection
Authors: Beckers, Jacques M.
Bibcode: 2003ANS...324Q..95B
Altcode: 2003ANS...324..K10B
  No abstract at ADS

Title: Along or across front ocean survey strategy? The estimation
    of quasi-geostrophic vertical velocities and temperature fluxes
Authors: Rixen, M.; Allen, J. T.; Pollard, R. T.; Beckers, J. -M.
Bibcode: 2003GeoRL..30.1264R
Altcode: 2003GeoRL..30e..68R
  In a companion paper we have shown that at the mesoscale, the unusual
  across front sampling strategy (AL) is more accurate than the usual
  across front sampling strategy (AC) on hydrographic and bio-chemical
  properties when the front is sufficiently developed. The cruise design
  based on the optimal reconstruction of the density fields does however
  not imply that derived variables like quasi-geostrophic (QG) vertical
  velocities and temperature fluxes also exhibit minimal associated
  errors. Here we present results of optimized sampling strategies for
  diagnostic QG vertical velocities (w<SUB>QG</SUB>) and temperature
  fluxes (θ<SUB>QG</SUB>) derived from the omega equation. Results
  are illustrated in the same framework, for the Iceland-Faroes
  oceanic frontal area and for a control model and reveal that at
  these spatio-temporal scales, the unusual AL may also provide better
  estimations of vertical velocities and temperature fluxes compared to
  the classic AC, especially when the front is sufficiently developed.

Title: ATST seeing monitor: February 2002 observations at Fuxian Lake
Authors: Beckers, Jacques M.; Liu, Zhong; Jin, Zhenyu
Bibcode: 2003SPIE.4853..273B
Altcode:
  We describe a solar seeing monitor used for the site testing for
  the 4 meter US Advanced Technology Solar Telescope and the 1 meter
  Yunnan Observatory Solar Telescope. It has two parts: a solar
  Differential Image Motion Monitor (S-DIMM) and a linear array of
  6 solar scintillometers (SHABAR= SHAdow BAnd Ranger). The results
  obtained by both methods are compared on the basis of observations
  obtained in February 2002 at the Yunnan Observatory Fuxian Lake solar
  station. Analysis showed that these two ways of measuring the Fried
  parameter give consistent results. We confirm earlier observations
  that showed that the boundary layer seeing over lakes is strongly
  suppressed. The amount of this boundary layer seeing depends on the
  temperature difference between lake and air and on the wind velocity. We
  have also carried out seeing observation along a 9.15 km horizontal
  path across the lake. The C<SUB>n</SUB><SUP>2</SUP> values derived
  from these is consistent with the solar observations. They confirm the
  dependence of C<SUB>n</SUB><SUP>2</SUP> on the lake-to-air temperature
  difference. From the SHABAR we find a typical scale height for the
  boundary layer seeing of 20 meters and from inter-comparison of the
  S-DIMM and SHABAR observations we derive an outer scale of turbulence
  of about 50 meters.

Title: Adaptive optics for the Euro50: design and performance
Authors: Goncharov, Alexander V.; Owner-Petersen, Mette; Andersen,
   Torben; Beckers, Jacques M.; Devaney, Nicholas
Bibcode: 2003SPIE.4840...36G
Altcode:
  The optical design for the proposed Euro50 extremely large telescope
  with integrated adaptive optics (AO) is presented. For atmospheric
  turbulence correction, we propose using single and dual-conjugate AO
  systems working with natural and laser guide stars. The corrective shape
  of the deformable mirrors (DMs) is derived from an analytical algorithm
  based on minimization of the sum of the residual power spectra of the
  phase fluctuations seen by guide stars after correction. Predictions for
  performance of the Euro50 ELT with Dual-conjugate AO are given for the
  K band using a seven layer atmospheric model for the atmosphere at the
  Observatorio del Roque de los Muchachos (ORM) on La Palma. The average
  Strehl ratio is used to quantify the system performance for different
  values of actuator pitch and DM conjugation altitudes. The influence
  of the outer scale and telescope pointing on the RMS stroke of the
  DMs is presented. It is concluded that construction of such a system
  is feasible and that there is a need for development of a simulation
  tool to verify the analytical calculations. Precise knowledge of the
  outer scale of the atmosphere at the ORM is needed to establish the
  dynamical range of the mirrors.

Title: The Euro50 Extremely Large Telescope
Authors: Andersen, Torben; Ardeberg, Arne L.; Beckers, Jacques;
   Goncharov, Alexander; Owner-Petersen, Mette; Riewaldt, Holger; Snel,
   Ralph; Walker, David
Bibcode: 2003SPIE.4840..214A
Altcode:
  Euro50 is a proposed optical telescope with an equivalent primary
  mirror diameter of 50 m. Partners of the collaboration are institutes
  in Sweden, Spain, Ireland, Finland, and the UK. The telescope will have
  a segmented primary mirror and an aplanatic Gregorian configuration
  with two elliptical mirrors. For a 50 m telescope there would be no
  economical advantage in going to a spherical primary. The size of
  the primary mirror segments (2 m) has been selected on the basis of
  a minimization of cost. An adaptive optics system will be integrated
  into the telescope. The telescope will have three operational modes:
  Seeing limited observations, single conjugate adaptive observations
  in the K-band, and dual conjugate observations also in the K-band. An
  upgrade to adaptive optics also in the visible down to 500 nm is
  foreseen. There will be an enclosure to protect the telescope against
  adverse weather and wind disturbances. Integrated simulation models
  are under development. The project time will be 10 years and the cost
  some 591 MEuros.

Title: Future giant telescopes: astronomy's Holy Grail or Pandora's
    Box?
Authors: Beckers, Jacques M.
Bibcode: 2003SPIE.4840..378B
Altcode:
  In this paper I review and reflect on the contributions given at this
  conference and place them in a broader context. Emboldened by the
  recent successes of 8 to 10-meter class telescopes and by the success
  of adaptive optics in making these telescopes diffraction limited,
  astronomers and engineers are now embarking on the quest for giant
  telescopes. Are these plans realistic? Are we overreaching ourselves?

Title: Along or across front survey strategy? An operational example
    at an unstable front
Authors: Rixen, M.; Allen, J. T.; Alderson, S.; Cornell, V.; Crisp,
   N.; Fielding, S.; Mustard, A. T.; Pollard, R. T.; Popova, E. E.;
   Smeed, D. A.; Srokosz, M. A.; Barth, A.; Beckers, J. -M.
Bibcode: 2003GeoRL..30.1017R
Altcode: 2003GeoRL..30a..17R
  We present results of the optimization of near-real time on-board
  sampling strategy in the Iceland-Faroes oceanic frontal area, based on
  the outputs of a mesoscale 3D operational data assimilation forecasting
  experiment. By minimizing a root mean square error cost function, we
  show that in this example an along-front sampling strategy, i.e. with
  transects parallel to the front, produces smaller errors in temperature,
  salinity, nitrate, phytoplankton, and zooplankton fields, as a result of
  a combination of the direction of the sampling of the front and errors
  associated with the asynopticy of observations (Doppler effect). This
  is contrary to the classic across-front sampling strategies that are
  used in most field experiments reported in the literature, i.e. where
  transects are perpendicular to the front. A control model shows that
  at these spatio-temporal scales, the along front sampling strategy is
  optimal when the frontal instability has sufficiently developed.

Title: Control strategy for the adaptive optics of the Euro50
Authors: Owner-Petersen, Mette; Andersen, Torben; Goncharov, Alexander
   V.; Beckers, Jacques M.
Bibcode: 2003SPIE.4840..427O
Altcode:
  The scheme presently envisaged for the EURO50 adaptive optics is
  presented. The Euro50 adaptive optics will primarily work with laser
  guide stars (LGSs) and control of either one or two deformable mirrors
  (SCAO and DCAO respectively), but operation using a natural guide
  star (NGS) is also foreseen. The point spread function (PSF) for SCAO
  operation using a single NGS is evaluated. An algorithm for optimal
  control of the deformable mirrors (DMs) using LGSs and Shack-Hartman
  wavefront sensors is presented and commented upon. It is an extension
  of a recently developed algorithm for optimal control using NGSs and
  working in the spatial Fourier domain. In addition the concept of a
  virtual wavefront sensor is introduced to overcome the difficulty in
  transmitting a large number (37) of LGSs to the final DCAO focus with
  both adequate field and adequate aberrations. The expected performance
  is estimated in form of maps of the Strehl ratio versus field angle
  using a standard seven layer atmospheric model for the Observatorio del
  Roque de los Muchachos (ORM) site on la Palma for the case of the outer
  scale being either 20 m (nominal for ORM) or infinity (Kolmogorov -
  most pessimistic case).

Title: Adaptive optics schemes for future extremely large telescopes
Authors: Goncharov, Alexander V.; Owner-Petersen, Mette; Andersen,
   Torben; Beckers, Jacques M.
Bibcode: 2002OptEn..41.1065G
Altcode:
  The adaptive optics for any telescope in the 25- to 100-m class will
  be complex. It is believed that adaptive optics should, to the maximum
  extent, be designed as an integrated part of a telescope. The proposed
  Swedish 50-m Extremely Large Telescope is considered here to illustrate
  the principle of integrated adaptive optics. Two alternative designs
  both using the Ritchey-Chretien telescope system and laser guide star
  (LGS) reference sources are presented. The first design employs trombone
  optics, which bring the laser guide star images back to the normal
  Ritchey-Chretien focal surface (referred to as the RC-focus) from the
  LGS focal surface (referred to as the LRC-focus), and a layer-oriented
  wavefront sensor system optically performing the averaging `shift and
  add' in the final focus. According to this procedure, sensed wavefronts
  are overlapped with a certain mutual shift and added for estimation
  of wavefront average slope values, resulting in actuator commands for
  driving the shape of the deformable mirrors. The second design employs a
  numerical `shift and add' procedure and has two wavefront sensors. The
  first one performs LGS sensing in an intermediate focus (LRC-focus),
  giving the input data for an analytical algorithm for deriving the
  mirror deformations to correct for atmospheric turbulence. By using
  an artificial laser source at the intermediate focus, the shape of the
  second deformable mirror is controlled by a second wavefront sensor in
  the final focus. The capability of the analytical algorithm to derive
  the mirror corrections from the measured wavefronts ensures proper
  functioning of the adaptive optics system. This system has a simpler
  optical design compared to the first design.

Title: Solar Seeing Measurements at the Fuxian Lake Observatory
Authors: Beckers, J. M.; Liu, Zhong
Bibcode: 2002AAS...200.5603B
Altcode: 2002BAAS...34Q.735B
  A collaborative effort between the Yunnan Observatory (YO) of the
  Chinese Academy of Science and the National Solar Observatory (NSO) has
  led to the development of the seeing monitor now being used by the NSO
  for the site testing for the 4 meter Advanced Technology Solar Telescope
  (ATST). The ATST seeing monitor contains a solar differential image
  motion monitor (S-DIMM) modeled after the one used by the YO for the
  site testing at Fuxian Lake. The S-DIMM results in a determination of
  the Fried Parameter r0. NSO added a linear array of 6 scintillometers
  which measure cloud cover, the scintillation index and the spatial
  co-variance of the solar shadow bands. This array is called the SHABAR =
  SHAdow BAnd Ranger because of its ability to give the height structure
  of the atmospheric seeing (see the attached web page). In February
  this year we combined the ATST SHABAR with the S-DIMM at the Fuxian
  Lake site. We describe the results of 5 days of observations in the
  February 9 to 14 period. In summary they are: (a) the average seeing
  was 1.6 arcsec in the solar direction, 1.2 arcsec for zenith direction,
  (b) for half of the time the boundary layer seeing contribution was
  negligible (&lt;10%), (c) at the times when it was significant the scale
  height of the refractive index structure constant Cn2 was determined to
  be 20 meters, (d) at those times the r0 derived from the SHABAR agreed
  well with that observed with the S-DIMM, and (e) the r0 derived from
  the SHABAR at times when it is small exceeds that of the S-DIMM. This
  is almost certainly due to the outer scale of turbulence being around
  10 - 30 meters in the free atmosphere at heights 1 km and above.

Title: Correlation tracking algorithms for low-contrast extended
    object
Authors: Rao, Changhui; Jiang, Wenhan; Ning, Ling; Beckers, Jacques M.
Bibcode: 2002SPIE.4494..245R
Altcode:
  Based on the principle of correlation tracking algorithm, the
  effectiveness of Cross Correlation coefficient and Absolute Difference
  algorithms for the low contrast extended objects such as solar
  granulation and the sunspot is studied. The tilt signals computed by
  computer post- processing are presented for the successively acquired
  solar granulation images. Moreover, the contrasts of the long exposure
  images of the solar granulation and sunspot without and with tilt
  removal are compared.

Title: Multi-conjugate Adaptive Optics: Experiment in Atmospheric
    Tomography
Authors: Beckers, J.
Bibcode: 2002ASPC..266..562B
Altcode: 2002asev.conf..562B
  No abstract at ADS

Title: Tracking algorithms for low-contrast extended objects
Authors: Rao, Chang-hui; Jiang, Wen-han; Ling, Ning; Beckers,
   Jacques M.
Bibcode: 2002ChA&A..26..115R
Altcode:
  We studied the effectiveness of two algorithms, of cross-correlation
  coefficient and of absolute difference in the case of extended,
  low-contrast objects, such as solar granulation and sunspots. Wave-front
  overall tilt signals, acquired via post-processing of sampled
  solar granulation and sunspot images, are presented. Furthermore,
  long-exposure images of solar granulation before and after the tilt
  elimination are compared as regards rms contrast.

Title: Daytime seeing measurements for the advanced technology
    Sslar telescope
Authors: Beckers, J.
Bibcode: 2002ASPC..266..350B
Altcode: 2002asev.conf..350B
  No abstract at ADS

Title: The daytime use of Adaptive Optics for solar and stellar
    Extremely Large Telescopes
Authors: Beckers, Jacques
Bibcode: 2002ESOC...58...83B
Altcode: 2002bcao.conf...83B
  Now Single Conjugate Adaptive Optics (SCAO) has been successfully
  implemented on both nighttime and solar telescopes, there is a
  rapidly growing interest in developing, what will be the next step
  in astronomical adaptive optics, Multi-Conjugate Adaptive Optics
  (MCAO). MCAO aims at breaking the small field-of-view barrier inherent
  in SCAO. MCAO is considered an essential component for both future
  solar and nighttime extremely large telescopes (4<SUP>m</SUP> and
  30<SUP>m</SUP> telescope apertures respectively). I will compare
  the application of MCAO to both types of telescope. Specifically
  my talk will focus on the following topics: (i) the advantages and
  disadvantages in of MCAO for solar telescopes, (ii) the status of a
  program for developing Atmospheric Wavefront Tomography using a large
  area solar Shack-Hartmann wavefront sensors, (iii) the daytime use of
  Sodium Laser Guide Stars in solar ELTs for observing the solar corona
  and prominences, (iv) the opportunities that this daytime use of Na
  LGS open up for nighttime ELTs. The latter of course requires the
  engineering of the nighttime ELTs to take into account their exposure
  to the daytime thermal and radiation environment. The resulting
  pay-off in extending the observing time beyond the common nighttime
  interval is scientifically significant especially when observations
  of objects in the thermal infrared and of time variable objects at all
  wavelengths are considered, and (v) the development of the solar SHAdow
  BAnd Ranging (SHABAR) device which is the solar equivalent of SCIDAR
  both of which aim at measuring in real time the height distribution of
  C<SUB>n</SUB><SUP>2</SUP>, information important for the implementation
  of MCAO systems.

Title: An analysis of the observed contrast of solar surface
    granulation
Authors: Rao, Chang-hui; Jiang, Wen-han; Ling, Ning; Beckers,
   Jacques M.
Bibcode: 2001ChA&A..25..439R
Altcode:
  The contrast of the solar surface granulation detected in the focal
  plane of the observing system as well as its relations with the aperture
  of the observing system, the coherent length of atmospheric turbulence
  and the sensitivity of the detecting system are analyzed. The results
  of numerical calculation of the granulation contrast as functions of
  aperture, coherent length of atmospheric turbulence and sensitivity of
  the detecting system are presented. Results of a related observation
  are also given.

Title: Tracking algorithm for low contrast extended object
Authors: Rao, C. H.; Jiang, W. H.; Ling, N.; Beckers, Jacques M.
Bibcode: 2001AcASn..42..329R
Altcode:
  No abstract at ADS

Title: Analysis of the observed r.m.s contrast in solar granulation
Authors: Rao, C. H.; Jiang, W. H.; Ling, N.; Beckers, J. M.
Bibcode: 2001AcASn..42..134R
Altcode:
  On the focal plane of the telescope and the detector, the relationships
  between the r.m.s. contrast in the solar granulation and the diameter
  of the telescope, the atmospheric coherent length and the detecting
  sensitivity of the system are analyzed respectively. The numerical
  results of the r.m.s. contrast in the solar granulation as functions
  of the diameter, the atmospheric coherent length and the detecting
  sensitivity of the system are presented. Furthermore, the related
  experimental results are given.

Title: Solar Seeing Seven Ways From Sunday
Authors: Hill, F.; Balasubramaniam, K. S.; Beckers, J. M.; Briggs,
   J. W.; Hegwer, S.; Radick, R. R.; Rimmele, T. R.; Richards, K.;
   Denker, C.
Bibcode: 2001AGUSM..SP21B03H
Altcode:
  The Advanced Technology Solar Telescope (ATST) site survey will be
  carried out with a Solar Differential Image Motion Monitor (S-DIMM)
  and a six-scintillometer SHAdow BAnd Ranging (SHABAR) array. This
  device will provide estimates of the Fried parameter, R<SUB>0</SUB>,
  derived from the differential motion measurements of two images of the
  same cut across the solar limb formed by two 45 mm diameter telescope
  apertures 225 mm apart, and an estimate of the height dependence of the
  index of refraction structure parameter, C<SUB>n<SUP>2</SUP></SUB>, from
  the co-variance of the signals from an array of 6 scintillometers with
  15 baseline separations. It will also provide a cloud cover measurement
  and RMS scintillation signal. In preparation for the survey, we compare
  estimates of daytime solar seeing obtained simultaneously from seven
  different instruments. The observations were made at NSO/Sacramento
  Peak during the period January 26 - February 5, 2001 under a variety of
  seeing and transparency conditions ranging from poor to excellent. The
  seven instruments were: 1. a S-DIMM/SHABAR mounted at the top of
  the Dunn Solar Tower (DST) 2. an identical S-DIMM/SHABAR mounted at
  ground level 3. the NSO/SP Adaptive Optics wavefront sensor providing
  subaperature image motion measurements 4. a Dalsa camera providing
  bursts of high-speed images for spectral ratio seeing estimates 5. a
  Xedar camera obtaining granulation images for contrast and differential
  stretching measurements 6. a Seykora scintillometer mounted in the
  DST 7. a video camera recording a movie of the visual quality of the
  image The analysis of this data set will provide the first direct
  comparison of this many simultaneous solar seeing measurements, test
  the ATST site survey system, and verify the SHABAR measurement of the
  seeing height profile.

Title: Using Laser Beacons for Daytime Adaptive Optics
Authors: Beckers, Jacques M.; Cacciani, Alessandro
Bibcode: 2001ExA....11..133B
Altcode:
  This article examines the use of Laser Beacons for daytime astronomical
  observations. There are two potential applications: the diffraction
  limited observation of (1) the structure in the solar corona at all
  wavelengths, and (2) non-solar astronomical objects in the thermal
  infrared part of the spectrum. We examine the brightness of the Laser
  Beacon required as well as the limitations imposed by the daytime
  sky brightness and sky/telescope thermal emission on the observable
  magnitude limits. For both applications the use of Laser Beacon adaptive
  optics in daytime results in important research opportunities.

Title: A Seeing Monitor for Solar and Other Extended Object
    Observations
Authors: Beckers, Jacques M.
Bibcode: 2001ExA....12....1B
Altcode:
  In this article I describe a site survey facility, which measures
  the signals of the solar equivalent of a Differential Image
  Motion Monitor (S-DIMM) and of a six element linear array of
  solar scintillometers. Combining the S-DIMM r_o and scintillometer
  σ_I observations allows the determination of the fractions of the
  seeing in the free atmosphere and in the ground/lake layer. From the
  scintillometer array observations C_n^2(h) is determined for heights
  corresponding to the first ~500 m along the line-of-sight. With minor
  changes this seeing monitor can also be used for other extended objects
  like the Moon and planets.

Title: Comparative Solar Seeing and Scintillation Studies at the
    Fuxian Lake Solar Station
Authors: Liu, Zhong; Beckers, Jacques M.
Bibcode: 2001SoPh..198..197L
Altcode: 2001SoPh..198..197Z
  Starting November 1999 we are carrying out simultaneous seeing
  observations with the Solar Differential Image Motion Monitor
  (S-DIMM) at the Fuxian Lake station of the Yunnan Observatory and
  a solar scintillometer of the type used in the recent site survey
  by one of us (Beckers et al., 1997). The purpose was to compare the
  two methods of assessing the daytime atmospheric seeing for a lake
  site. We report here the first results of this comparison. We find that
  the relation between the seeing as measured by the S-DIMM (the Fried
  parameter r_0) and the scintillation in the solar irradiance (σ_I)
  differs greatly from the relation found by Seykora (1993) for NSO/Sac
  Peak. We conclude that the σ_I measurements give a good indication
  for the amount of near-Earth seeing but that they are a poor proxy
  for the total atmospheric seeing. We interpret the simultaneous (r_0,
  σ_I) observations in terms of an atmospheric seeing model and find
  good quantitative agreement with a model in which a fraction (α) of
  the seeing originated near the Earth (ground or water) and the rest
  (1-α) originates at higher layers. For lake sites α is small all
  day and the seeing is determined primarily by the refractive index
  variations at higher atmospheric layers. For land sites α is small
  in the early morning but rapidly increases as the day progresses,
  near-Earth seeing dominating there most of the time.

Title: Chromosphere: Spicules
Authors: Beckers, J.
Bibcode: 2000eaa..bookE2019B
Altcode:
  As early as 1877 Father Secchi described the jet like, elongated
  structures in the solar chromospheres which were named spicules
  by Walter Orr Roberts in 1945. They are observed in the optical
  chromospheric emission lines of hydrogen (especially the 656 nm Hα
  line), ionized calcium (especially the 393 nm and 397 nm H and K lines)
  and helium lines (especially the 588 nm and 1083 nm neutral helium ...

Title: Multiconjugate adaptive optics: experiments in atmospheric
    tomography
Authors: Beckers, Jacques M.
Bibcode: 2000SPIE.4007.1056B
Altcode:
  In 1987 I described a technique call Multi-Conjugate Adaptive Optics
  (MCAO) as a way of increasing the size of the area on the sky over which
  Adaptive Optics corrects for atmospheric wavefront distortions. An
  essential component of MCAO is the estimation of this wavefront
  distortion at different heights in the atmosphere. The technique
  proposed to do so was called 'Atmospheric Tomography,' or AT, since
  it uses tomographic techniques using the wavefront distortions at the
  telescope entrance pupil of objects observed in a number of different
  directions in the sky to infer the 3-D wavefront behavior. This
  paper describes a program to do so using the small scale structure
  on the solar surface (sunspots, pores and granulation). The Sun has
  the advantage of being an extended object on which the wavefront
  can be observed in a large number of directions using correlation
  Hartmann-Shack wavefront sensing. The AT experiment described in this
  paper uses the 76 cm Dunn Solar Telescope at NSO, 69 sub-apertures,
  a 2 X 2 arcmin<SUP>2</SUP> field-of-view and a wavelength of 411
  nm. The MCAO-AT system is being developed for the future 4 meter
  aperture Advanced Solar Telescope.

Title: The proposed 50 m Swedish Extremely Large Telescope
Authors: Andersen, T.; Ardeberg, A.; Beckers, J. M.; Flicker, R.;
   Jessen, N. C.; Gontcharov, A.; Mannery, E.; Owner-Petersen, M.;
   Riewaldt, H.
Bibcode: 2000ESOC...57...72A
Altcode: 2000elt..conf...72A
  No abstract at ADS

Title: Extremely large multiple mirror telescopes
Authors: Beckers, J. M.
Bibcode: 2000ESOC...57...83B
Altcode: 2000elt..conf...83B
  No abstract at ADS

Title: The Determination of Seeing, Isoplanatic Patch Size and
    Coherence Time by Solar Shadow Band Ranging
Authors: Beckers, J. M.
Bibcode: 1999ASPC..184..309B
Altcode:
  Using an array of solar scintillometers (Seykora 1993; Beckers and
  Mason 1998), I characterize the shadow band patterns as seen from the
  un-eclipsed sun. The spatial and temporal structure of these patterns
  provide a measure of the optical turbulence in the earth' atmosphere
  from which the r_0 (Fried Parameter), Θ_0 (isoplanatic patch diameter)
  and τ_0 (coherence time) can be estimated.

Title: The Advanced Solar Telescope: II. Technical Aspects
Authors: Beckers, J.
Bibcode: 1999ASPC..183..177B
Altcode: 1999hrsp.conf..177B
  No abstract at ADS

Title: Adaptive optics in solar astronomy
Authors: Beckers, J.
Bibcode: 1999aoa..book..235B
Altcode:
  No abstract at ADS

Title: Site tests for CLEAR by solar scintillometry
Authors: Beckers, Jacques M.; Rutten, Robert J.
Bibcode: 1998NewAR..42..489B
Altcode:
  We briefly describe the ongoing site survey for the NSO CLEAR project
  which aims to put a large-aperture solar telescope at a superior
  location. The initial results indicate that lake sites are far better
  than mountain sites, at least in the US.

Title: Site survey for a large solar telescope
Authors: Beckers, Jacques M.; Mason, James
Bibcode: 1998SPIE.3352..858B
Altcode:
  In 1996 we started a seeing survey of a number of existing and potential
  solar observing sites using solar scintillometry. This paper reports
  the result of the first year of that survey. It confirms earlier reports
  about the superior observing conditions of lake sites. I also describe
  the first results of atmospheric structure constant (C(subscript
  n)(superscript 2)) probing using a solar scintillometer array.

Title: Design of a large low-scattered light telescope for solar
    observations
Authors: Beckers, Jacques M.
Bibcode: 1998SPIE.3352..588B
Altcode:
  This paper is an interim report of a feasibility study which is in
  progress for a large 400 cm aperture solar telescope (`CLEAR'). Unlike
  other large solar telescopes constructed in the last three decades,
  CLEAR does not use the concept of evacuated telescopes to eliminate
  internal seeing. The requirement for full access to the far infrared
  spectral region (&gt; 2.5 micrometers ), and for low scattered light,
  eliminates the use of the entrance window which evacuated telescopes
  require. Instead, CLEAR avoids internal seeing by carefully controlling
  the internal thermal environment of the telescope by a number of means:
  (1) thermal control of the primary mirror; (2) flow of ambient air
  over the primary mirror surface and in the telescope; (3) locating the
  primary focus outside the telescope beam and enclosure where the heating
  resulting in concentrated sunlight can be managed better (this requires
  the use of an off-axis primary mirror); and (4) the use of a prime focus
  heat stop/absorber. In addition to controlling the internal seeing,
  such a configuration produces a telescope with very low scattered light
  characteristics, allowing quality observation of regions outside the
  solar limb and of sunspots. By eliminating the need for a large entrance
  window, the CLEAR concept therefore opens up the possibility of larger
  aperture solar telescopes. Notwithstanding its off-axis configuration,
  the Gregorian telescope produces excellent images (&lt; 0.1 arcsec) over
  a 5 arcminute diameter field-of-view at the f/130 Gregorian focus. In
  addition to the four instrumentation stations near the Gregorian focus
  (i.e., direct Gregorian, Nasmyth, two `folded Gregorian'), the design
  provides for extensive instrumentation locations in a coude area. By
  means of a 3- level rotating coude platform, large instruments can be
  located at respectively f/30, f/45 and f/60 foci.

Title: Effect of telecentric use of narrow-band filters on
    diffraction-limited imaging
Authors: Beckers, Jacques M.
Bibcode: 1998SPIE.3355..955B
Altcode:
  Sometimes Fabry-Perot, and other narrow-band filters, are used
  for astronomical imaging in the so-called telecentric mode. In it
  the pupil is collimated through the filter, resulting in different
  incidence angles on the filter for rays coming from different parts of
  the objective. This results in variations of the central transmission
  wavelength, which broaden the effective filter bandpath. In addition
  each wavelength within this filter bandpath sees a different illumiatnon
  of the pupil when viewed from behind the fitler. This causes the
  diffraction limited point-spread-function to vary with wavelength. With
  the advent of diffraction limited imaging using adaptive optics, this
  can cause complications. In this paper, which elaborates further on
  research published elsewhere, I examine the magnitude of this effect.

Title: On the effect of narrow-band filters on the diffraction
    limited resolution of astronomical telescopes
Authors: Beckers, J. M.
Bibcode: 1998A&AS..129..191B
Altcode:
  Sometimes Fabry-Perot and other narrow-band filters are used for
  astronomical imaging in the so-called telecentric mode. In it the
  pupil is collimated through the filter, resulting in different
  incidence angles on the filter for rays coming from different
  parts of the objective. This results in variations of the central
  transmission wavelength, which broaden the effective filter band
  path. In addition each wavelength within this filter band path sees
  a different illumination of the pupil when viewed from behind the
  filter. This causes the diffraction limited point-spread-function to
  vary with wavelength. With the advent of diffraction limited imaging
  using adaptive optics, this can cause complications. In this note I
  examine the magnitude of this effect.

Title: Results of Site Testing for a Large Visible/Infrared Telescope
Authors: Beckers, Jacques M.
Bibcode: 1998ASPC..155..255B
Altcode: 1998sasp.conf..255B
  No abstract at ADS

Title: Solar Scintillometry: Calibration of Signals and its Use for
    Seeing Measurements
Authors: Beckers, Jacques M.; Leon, Ed; Mason, Jim; Wilkins, Larry
Bibcode: 1997SoPh..176...23B
Altcode:
  Since 1993 it is known that there is a good correlation between the
  scintillation in the solar irradiance and solar image quality (Seykora,
  1993). This effect is now being used in a number of experiments to
  evaluate solar image quality and to measure site seeing. In this
  paper we explore further the calibration of this scintillation
  (<SUB>σI</SUB>) in terms of the Fried parameter (<SUB>r0</SUB>)
  taking into account variations in the refractive index structure
  constant C<SUB>N</SUB><SUP>2</SUP> with height (h), zenith distance
  (ζ) dependence and the effects of wind velocities. A variant in the
  scintillometer setup is proposed which decreases sharply the dependance
  on C<SUB>N</SUB><SUP>2</SUP> , ζ, and the wind velocities. It uses
  an array of scintillometers. The same array can be used to measure
  theC<SUB>N</SUB><SUP>2</SUP> profile with height. Some preliminary
  results of the calibration of current NSO site survey measurements
  are presented.

Title: High Resolution Solar Observations from the Ground
Authors: Rimmele, T.; Beckers, J.; Dunn, R.; Radick, R.; Roeser, M.
Bibcode: 1997hrsa.rept.....R
Altcode:
  We describe an ongoing effort to improve the capabilities for achieving
  spectroscopic and imaging observations at the highest spatial resolution
  at the Sacramento Peak Vacuum Tower Telescope of the National Solar
  Observatory. We report on improvements of the optical performance of the
  VTT/SP and describe results from the first solar active optics system,
  which was recently successfully tested at the VTT/SP. Our final goal is
  the implementation of solar adaptive optics at the VTT/SP. We describe
  progress and future plans of the adaptive optics program.

Title: First Results of the Site Survey for a Large Solar
    Optical/Infrared Telescope
Authors: Beckers, Jacques M.; Mason, Jim
Bibcode: 1997SPD....28.0223B
Altcode: 1997BAAS...29..897B
  We will present the first results of a seeing survey of four existing
  solar observatories : the HAO Mauna Loa Observatory, the Big Bear Solar
  Observatory, the Sacramento Peak Observatory and the solar observatory
  site on La Palma. The measurements started in September 1996. The
  survey uses observations of the scintillation of the solar irradiance
  (Seykora meters, see Solar Physics Volume 145, p.389) as a proxy for
  the atmospheric seeing. In addition to presenting the results, issues
  relating to the calibration of the measurements in terms of the Fried
  Parameter will be discussed. A modification of the Seykora meter will
  be described which is capable of measuring the atmospheric refractive
  index structure constant as a function of height.

Title: Atmospheric dispersion correction for the FORS Focal Reducers
    at the ESO VLT
Authors: Avila, Gerardo; Rupprecht, Gero; Beckers, J. M.
Bibcode: 1997SPIE.2871.1135A
Altcode:
  The need for atmospheric dispersion correction on large telescopes
  is well known. Therefore it was decided to implement atmospheric
  dispersion correctors for FORS, the focal reducer/spectrographs of
  the ESO very large telescope. The boundary conditions at the VLT
  Cassegrain foci excluded however all previously known ADC concepts
  and therefore we were forced to design a new one, the longitudinal
  atmospheric dispersion corrector (LADC) consisting of two thin prisms
  with variable distance. This design has several advantages compared to
  the 'classical concepts:' among others it avoids tilting the pupil axis
  and uses only one material (silica) which has a very high transmission
  over the operating wavelength range of FORS (330 - 1000 nm).

Title: Progress Report on a Feasibility Study of a Large
    Optical/Infrared Solar Telescope (CLEAR)
Authors: Beckers, Jacques M.; NSO Staff
Bibcode: 1997ASPC..118..340B
Altcode: 1997fasp.conf..340B
  With the end of the US participation in LEST, the question of the
  development of modern, large, ground-based facilities to satisfy the
  research needs of solar physics in the USA is open. Large telescopes
  are needed to answer many important science issues. Among these are (i)
  high angular resolution needed to resolve the scales at which most of
  the action is in solar magneto-hydrodynamics (ii) access to the infrared
  part of the solar spectrum wanted to extend the range over physical
  conditions over which the solar atmosphere is studied (iii) accurate
  polarization observations needed to measure solar magnetic fields,
  (iv) high sensitivities, essential to study variations in these and
  other solar conditions, and (v) coronagraphic capability to observe
  magnetic fields and small scale structures in the solar corona. CLEAR
  (Coronagraph and Low Emissivity Astronomical Reflector) is a concept
  that attempts to combine these qualities in one telescope, 2 to 4 meter
  in aperture, without compromising the solar science goals. This is a
  status report on the on-going feasibility study of CLEAR that addresses
  both technical and budgetary issues. A site survey is being conducted
  among existing solar sites to identify the optimum location.

Title: Techniques for high angular resolution astronomical imaging.
Authors: Beckers, J. M.
Bibcode: 1997ilt..book....1B
Altcode:
  After introducing the basics of atmospheric wavefront distortions,
  the author describes the principles of adaptive optics for large
  optical telescopes and gives an overview of the present status of its
  application. Then, he discusses the principles and the development of
  interferometric arrays of optical telescopes. As specific example,
  the author describes in some detail ESO's Very Large Telescope
  Interferometer project.

Title: Comments on the Next Generation of Ground-based Solar
    Telescopes
Authors: Beckers, Jacques M.
Bibcode: 1996SoPh..169..431B
Altcode:
  The development of telescope capabilities tends to go in spurts. These
  are triggered by the availability of new techniques in optics,
  mechanics and/or instrumentation. So has nighttime telescope technology
  developed since the construction in the nineteen-forties of the 5-m Hale
  telescope, first by the introduction in the sixties of high efficiency
  electronic detectors, followed recently by the production of large 8-
  to 10-m mirrors and now by the implementation of adaptive optics. In
  solar astronomy, major steps were the introduction of the coronagraph
  by Lyot in the nineteen-thirties and the vacuum telescope concept by
  Dunn in the sixties. In the last thirty years, telescope developments
  in solar astronomy have relied primarily on improved instrumental
  capabilities. As in nighttime astronomy, these instruments and their
  detectors are reaching their limits set by the quantum nature of
  light and the telescope diffraction. Larger telescopes are needed to
  increase sensitivity and angular resolution of the observations. In
  this paper, I will review recent efforts to increase substantially
  the telescope capabilities themselves. I will emphasize the concept
  of a large all-wavelength, coronagraphic telescope (CLEAR) which is
  presently being developed.

Title: Limitations Placed on the Time Coverage, Isoplanatic Patch
    Size and Exposure Time for Solar Observations Using Image Selection
    Procedures in the Presence of Telescope Aberrations
Authors: Beckers, J. M.; Rimmele, T. R.
Bibcode: 1996AAS...189.4209B
Altcode: 1996BAAS...28.1325B
  Image selection, adaptive optics and post-facto image restoration
  methods are all techniques being used for diffraction limited imaging
  with ground-based solar and stellar telescopes. Often these techniques
  are used in a hybrid form like e.g. the application of adaptive optics
  and/or post-facto image restoration in combination with already good
  images obtained by image selection in periods of good seeing. Fried
  (JOSA 56, 1372, 1966), Hecquet and Coupinot (J. Optics/Paris 16, 21,
  1985) and Beckers ("Solar and Stellar Granulation", Kluwer, Rutten
  &amp; Severino Eds, 55, 1988) already discussed the usefulness of
  image selection, or the "Lucky Observer" mode, for high resolution
  imaging. All assumed perfect telescope optics. In case of moderate
  telescope aberrations image selection can still lead to diffraction
  limited imaging but only when the atmospheric wavefront aberration
  happens to compensate that of the telescope. In this "Very Lucky
  Observer" mode the probability of obtaining a good image is reduced
  over the un-aberrated case, as are the size of the isoplanatic patch
  and the exposure time. We describe an analysis of these effects for
  varying telescope aberrations. These result in a strong case for the
  removal of telescope aberrations either by initial implementation or
  by the use of slow active optics.

Title: Progress Report on a Feasibility Study for a Ground-Based
    Large Solar Telescope
Authors: Beckers, J. M.
Bibcode: 1996AAS...188.6701B
Altcode: 1996BAAS...28R.933B
  Whereas optical nighttime is undergoing a revolution with the deployment
  of very large ground-based telescopes in the 6.5 to 10 meter class,
  solar telescope technology has stagnated at the meter class aperture
  level. Space and balloon borne solar telescopes are now being built
  and planned in this aperture range. Are they likely to take over most
  of the roles of these ground-based facilities? There is undoubtedly a
  need for solar telescopes with larger apertures to explore important
  solar physics issues which require the highest possible angular
  resolution, high sensitivity, full visible and infrared wavelength
  coverage and low scattered light. Using advances in astronomical
  telescope technologies at optical and X-ray wavelengths, we (NSO
  staff together with engineering and scientific working group) are
  undertaking a feasibility study of a 4-meter class solar telescope with
  these qualities. Such a powerful, special purpose telescope will find
  many applications in other areas of astronomy in which low scattered
  light coronagraphic properties are at a premium. Since the telescope
  technologies needed to achieve these are similar to those needed for low
  emissivity telescopes, the telescope concept has been labelled CLEAR =
  Coronagraphic and Low Emissivity Astronomical Reflector. CLEAR will have
  a 5 arcmin diameter field-of-view (the size of a solar active region),
  wavelength coverage of at least 0.38 to 15 microns (including all of
  the visible and infrared solar spectral lines and regions of interest),
  low and constant polarization (enabling accurate and precise magnetic
  field observations), and scattered light low enough to enable studies
  of the coronal magnetic fields and coronal fine structure. It will
  include coud, Nasmyth and Gregorian focal stations for a variety of
  instruments. Its unobstructed aperture will allow optimum imaging,
  which will be enhanced by the incorporation of adaptive optics. In
  my lecture I will review the science drivers for CLEAR, and give a
  progress report on a feasibility study now underway. The scientific
  and technical goals set for CLEAR require a number new innovative
  technological solutions. These will be described and discussed. The
  siting of CLEAR is an important aspect of the study. I will review
  our present knowledge of possible solar observatory sites for CLEAR.

Title: The Origin of Solar and Stellar Image Aureole
Authors: Beckers, J. M.; Ftaclas, C.
Bibcode: 1996AAS...188.5402B
Altcode: 1996BAAS...28..904B
  The extended wings of the telescope point-spread-function affect
  the performance of solar and stellar reflecting coronagraphs used to
  study the faint envelopes of bright objects like the sun, planets,
  and stars. We are expanding an initial examination of the origin of
  these wings (Beckers, ``Scientific and Engineering Frontiers for
  8 - 10 m Telescopes", Eds. M. Iye and T. Nishimura, 1995, 303 -
  312) in order to obtain a quantitative evaluation of the observed
  point-spread-function and to derive the technical specifications
  for solar and stellar coronagraphs. We include the following factors
  contributing to the point-spread-function wings : (i) the atmospheric
  seeing, including the effects of the finite inner scale of turbulence,
  (ii) the scattering by atmospheric aerosol particles, (iii) the
  atmospheric Rayleigh scattering, (iv) the scattering by small scale
  surface irregularities in the telescope optics (micro-ripple), (v)
  the scattering by dust in the telescope, (vi) the diffraction on the
  telescope aperture, and (vii) diffraction on objects partially obscuring
  the aperture (e.g. spiders). It is assumed that care is taken not to
  increase the point-spread-function wings by ghosting and scattering in
  the astronomical instrument and in its detector(s). Using the resulting
  algorithms, we interpret observed stellar and solar image aureolae. The
  wavelength dependence of the point-spread-function wings is evaluated
  and applied to the performance estimates and technical specification
  definition of the CLEAR facility (CLEAR = ``Coronagraphic and Low
  Emissivity Astronomical Reflector"), a 4 meter class solar/stellar
  coronagraph presently under study.

Title: CLEAR : A Concept for a "Coronagraph and Low Emissivity
    Astronomical Reflector" for Solar and Nighttime Observations
Authors: Beckers, J. M.; Kuhn, J.; Neidig, D.; Rabin, R.; Rimmele,
   T.; Smartt, R. N.
Bibcode: 1995SPD....26..722B
Altcode: 1995BAAS...27..971B
  No abstract at ADS

Title: Using Eclipse Observations to Test Scintillation Models
Authors: Georgobiani, D.; Kuhn, J. R.; Beckers, J. M.
Bibcode: 1995SoPh..156....1G
Altcode:
  Near second and third contact during a solar eclipse the spatial
  spectrum of the solar illumination changes as the relative power
  at high spatial frequencies increases strongly. Since groundlevel
  atmospheric scintillation depends on a weighted integral of the image
  power spectrum, we can expect to see a measureable time dependence
  to solar scintillation during an eclipse. This effect was observed
  during an annular solar eclipse and quantitatively compared with a
  scintillation model.

Title: CLEAR: A Concept for a Coronagraph and Low Emissivity
    Astronomical Reflector
Authors: Beckers, J. M.
Bibcode: 1995itsa.conf..145B
Altcode:
  No abstract at ADS

Title: Prospects for high spatial resolution astronomy.
Authors: Beckers, J. M.
Bibcode: 1995seft.conf..303B
Altcode:
  The author summarizes the present status in the development of
  large, 8 meter class telescopes, of adaptive optics and of imaging
  interferometers. Then he elaborates on the limitations of the
  astronomical use of adaptive optics, on stellar coronagraphy and on the
  limitations of interferometric imaging of faint astronomical sources.

Title: Estimating the effects of nitrate mining activities on the
    astronomical site quality of the Cerro Paranal Observatory
Authors: Beckers, Jacques M.
Bibcode: 1994SPIE.2199..817B
Altcode:
  The European Southern Observatory is planning to construct its Very
  Large Telescope on Cerro Paranal, a site with superb astronomical
  observing conditions located in the Atacama Desert of Northern Chile
  some 100 km south of the town of Antofagasta and 16 km from the Pacific
  Ocean. This region of Chile is know for its rich mineral resources. One
  of these, Nitrates, are mined by surface, strip mining causing extensive
  area air pollution. To estimate the effects of a Nitrate mine which may
  be started 25 km SSE from Cerro Paranal a model for this pollution,
  based on estimates of aerosols resulting from similar mines north of
  Antofagasta, was developed. These estimates are based on measurements
  of the solar aureole brightness. The expected deteriorating effects
  on atmospheric extinction, sky thermal emissivity and night-time sky
  brightness appear acceptable.

Title: Imaging with array detectors using chopping and other forms
    of differential detection
Authors: Beckers, Jacques M.
Bibcode: 1994SPIE.2198.1432B
Altcode:
  To detect faint signals in the presence of a high background,
  differential techniques are often used. In IR astronomy this has led
  to the so-called chopping and nodding techniques. The introduction
  of array detectors especially for imaging in the thermal IR region of
  the astronomical spectrum requires an adaptations of these techniques
  which also takes into account the pixel nonuniformity of the array
  detector. I describe one possible imaging algorithm and the associated
  requirements for the chopping mechanisms of an 8-m telescope.

Title: Effects of heat sources in the telescope beam on astronomical
    image quality
Authors: Beckers, Jacques M.; Melnick, Jorge
Bibcode: 1994SPIE.2199..478B
Altcode:
  Heating of the air in astronomical telescopes is known to have a
  deteriorating effect on the image quality. Main heat sources are the
  primary mirror and localized electrical components in or near the
  light beam. To evaluate the effects of these localized heat sources we
  measured the image quality deterioration at the focus of the ESO-La
  Silla 2.2 meter telescopes with variable amounts of heating of a
  dummy electronics box and of a bar simulating one of the secondary
  mirror spiders. The effects on the FWHM of the image profile turned
  out to be remarkably small. Most of the effect of the heating showed
  up in the removal of energy of the core into the far wings of the
  image profile. For a heat input of 560 Watts (resulting in an excess
  temperature of 60 K) the amount of energy removed amounted to 13%. This
  behavior can be explained by a model in which the heating destroys the
  wave-front over only a part of the aperture while leaving it unaffected
  over most of the aperture. With such a model we predict the amount of
  energy removed by a 500 Watt heat source in an 8 meter telescope to
  be only 1%.

Title: First Images with the MPE Imaging Beam Combiner Simulator COSI
Authors: Böker, T.; Cruzalèbes, P.; Hofmann, R.; Katterloher, R.;
   Eckart, A.; Genzel, R.; Drapatz, S.; Beckers, J.; von der Lühe, O.;
   Merkle, F.
Bibcode: 1994ESOC...48..161B
Altcode: 1994aao..conf..161B
  No abstract at ADS

Title: Interpretation of out-of-focus star images in terms of
    wave-front curvature.
Authors: Beckers, J. M.
Bibcode: 1994JOSAA..11..425B
Altcode: 1994JOSA...11..425B; 1994OSAJ...11..425B
  The wave-front-curvature-sensing method used by F. Roddier for the
  University of Hawaii's curvature-adaptive-optics system is derived from
  the interpretation in 1979 of the out-of-focus images obtained by use
  of the Multiple Mirror Telescope. The author summarizes those original
  Multiple Mirror Telescope observations and the simple interpretation
  given in terms of wave-front curvature by use of geometrical optics
  at that time.

Title: The VLT Interferometer [invited]
Authors: Bedding, T. R.; Beckers, J. M.; Faucherre, M.; Hubin, N.;
   Koehler, B.; von der Lühe, O.; Merkle, F.; Zhu, N.
Bibcode: 1994IAUS..158..143B
Altcode:
  No abstract at ADS

Title: Solar surface magnetism: quests for observations
Authors: Beckers, J. M.
Bibcode: 1994ASIC..433..501B
Altcode:
  No abstract at ADS

Title: Progress in High-Resolution Astronomical Imaging Including
    Active and Adaptive Optics (Invited Lecture)
Authors: Beckers, J. M.
Bibcode: 1993SPIE.1983..186B
Altcode:
  No abstract at ADS

Title: On the Relation Between Scintillation and Seeing Observations
    of Extended Objects
Authors: Beckers, Jacques M.
Bibcode: 1993SoPh..145..399B
Altcode:
  In a recent article Seykora (1993) compares measurements of
  scintillation in the solar irradiance with solar seeing measurements. In
  this article I interpret the close linear relation which he found
  in terms of the common theory of atmospheric optics in the presence
  of turbulence.

Title: Adaptive Optics for Astronomy: Principles, Performance,
    and Applications
Authors: Beckers, Jacques M.
Bibcode: 1993ARA&A..31...13B
Altcode:
  An overview of the principles, performance, and application (solar
  and nighttime) of adaptive optics for astronomical telescopes is
  presented. Attention is given to a historical background of the use
  of adaptive optics for compensating atmospheric seeing, wavefront
  distortion by the atmosphere, and assessment and correction of the
  wavefront distortion. Predicted and achieved performance, the first
  astronomical results, and limitations to the astronomical applications
  of adaptive optics systems and ways of removing them are also discussed.

Title: Summary of the splinter session on optical and UV science
Authors: Beckers, Jacques M.
Bibcode: 1992ESASP.354..157B
Altcode: 1992tsbi.rept..157B
  The goal of the splinter group was to discuss the most prominent
  astrophysical objectives for a space based interferometer in the optical
  (UV, visible, near IR) domain. The discussion was organized around
  three main themes: solar system, stellar and galactic astrophysics,
  extragalactic astrophysics and cosmology. The scientific objectives
  and specifications for a space based solar interferometer, for an
  astrometric interferometer, and for a stellar interferometer, are
  given. Tentative conclusions for the splinter session are given.

Title: Overcoming perspective elongation effects in
    laser-guide-star-aided adaptive optics
Authors: Beckers, Jacques M.
Bibcode: 1992ApOpt..31.6592B
Altcode:
  A method of compensating for the perspective elongation effect, and
  thus of separating the laser transmitter(s) from the four Very Large
  Telescope (VLT) 8-m telescopes, is presented. The method involves
  tracking the instantaneous position of the laser guide star. For the
  initial N of about 200 VLT adaptive optics system, a single laser
  transmitting station is to place all four 8-m telescopes, and a
  substantial number of auxiliary telescope stations, within the 71-m
  range of a single laser transmission system.

Title: A Fourth VLT Instrument Science Team
Authors: Beckers, J. M.
Bibcode: 1992Msngr..69....5B
Altcode:
  No abstract at ADS

Title: A Report on the Second ESO Conference on High Resolution
    Imaging by Interferometry
Authors: Beckers, J. M.; Merkle, F.
Bibcode: 1992ESOC...42..387B
Altcode: 1992ptit.conf..387B
  No abstract at ADS

Title: High Resolution Spectroscopy with the VLT - Summary of
    Experimental Aspects
Authors: Beckers, J. M.
Bibcode: 1992ESOC...40....1B
Altcode: 1992hrsw.conf....1B
  No abstract at ADS

Title: Introducing the First VLT Instrument Science Teams
Authors: Beckers, J. M.
Bibcode: 1992Msngr..68....8B
Altcode:
  No abstract at ADS

Title: ESO-VLT Program Status Report
Authors: Beckers, J. M.; Tarenghi, M.
Bibcode: 1992ESOC...42...13B
Altcode: 1992ptit.conf...13B
  No abstract at ADS

Title: Report on the Lunar Interferometry Study Team (LIST)
    activities.
Authors: Dainty, J. C.; Faucherre, M.; Greenaway, A. H.; Harris, A. I.;
   Labeyrie, A.; Noordam, J. E.; Weigelt, G. P.; Beckers, J.; Lequeux,
   J.; Fridlund, C. M.; Hawkyard, A.; Roussel, P. H.; Volonté, S.
Bibcode: 1992ESASP.344..259D
Altcode: 1992spai.rept..259D
  During the first half of 1991, the Lunar Interferometry Study Team
  (LIST) produced an Interim Report outlining a possible strategy for
  the development of a lunar interferometry programme. The formulation
  of an overall strategy for ESA towards lunar interferometry requires
  further consideration before firm recommendations can be made. However,
  it is clear at this early stage that there are three principal
  elements in that strategy. (1) ESA should commence conceptual
  studies for interferometers in readiness for their location on the
  Moon in (a) the UV/visible/IR and (b) the sub-millimetre region. (2)
  Considering the scientific benefit, technical readiness and realistic
  timescale of a lunar interferometer, ESA should plan for at least one
  "precursor" interferometer missions in space. (3) ESA should identify
  key technologies of crucial importance to space-based interferometry
  in general and lunar interferometry in particular, and support their
  development by a variety of routes.

Title: Interferometry with the Very Large Telescope.
Authors: Vonderluehe, O.; Beckers, J. M.; Faucherre, M.; Koehler,
   B.; Merkle, F.; Zhu, N.
Bibcode: 1992ESASP.344..247V
Altcode: 1992spai.rept..247V
  One of the observing modes available with the ESO Very Large Telescope
  (VLT) will be coherent combination of the light received by up to four
  8 m diameter unit telescopes and several 1.8 m diameter auxiliary
  telescopes. While the location of the main telescopes is fixed,
  auxiliary telescopes can be moved among some 30 observing stations
  designed to efficiently complement the unit telescopes as well as to
  function as an independent interferometric array. A distinct feature
  of the VLT interferometer will be its sensitivity due to the large
  diameter of the unit telescopes, and due to the adaptive optics which
  will remove instrumental and atmospheric wavefront disturbances in
  the near-infrared spectral regime. This paper presents an overview
  of the VLT interferometer, highlights some of its characteristics,
  and gives a status update.

Title: The Design of Delay Lines for the VLT Interferometer
Authors: Jorck, H.; Maurer, R.; Kase, J.; Faucherre, M.; Beckers,
   J. M.; Kuhn, G.; Hupe, H.
Bibcode: 1992ESOC...39.1157J
Altcode: 1992hrii.conf.1157J
  No abstract at ADS

Title: The Use of Differential Adaptive Optics for Astronomical
    Interferometry
Authors: Beckers, J. M.
Bibcode: 1992ESOC...39.1079B
Altcode: 1992hrii.conf.1079B
  No abstract at ADS

Title: High resolution imaging by interferometry II. Ground-based
    interferometry at visible and infrared wavelengths. Proceedings.
Authors: Beckers, J. M.; Merkle, F.
Bibcode: 1992ESOC...39.....B
Altcode: 1992hrii.conf.....B
  Contents: Part I.

Title: The Configuration of the VLT Interferometer on the Paranal Site
Authors: von der Luhe, O.; Beckers, J. M.; Braun, R.
Bibcode: 1992ESOC...39..959V
Altcode: 1992hrii.conf..959V
  No abstract at ADS

Title: A Progress Report on the Implementation of the VLT
    Interferometer
Authors: Beckers, J. M.; Faucherre, M.; Koehler, B.; von der Luhe, O.
Bibcode: 1992ESOC...39..775B
Altcode: 1992hrii.conf..775B
  No abstract at ADS

Title: Performance Comparison of VLT Using Partial Adaptive Optics
    with a Lunar Interferometer
Authors: Greenaway, A. H.; Beckers, J. M.
Bibcode: 1992ESOC...39..985G
Altcode: 1992hrii.conf..985G
  No abstract at ADS

Title: The Design of the Auxiliary Telescopes for the VLT
    Interferometer
Authors: Plathner, D.; Beckers, J. M.
Bibcode: 1992ESOC...39..939P
Altcode: 1992hrii.conf..939P
  No abstract at ADS

Title: Optimization of partial adaptive optics
Authors: Beckers, Jacques M.
Bibcode: 1992ApOpt..31..424B
Altcode:
  Partial adaptive optics employed in astronomical settings are examined
  to develop suitable wavefront control algorithms that maximize the
  fractional area of the pupil. Attention is given to the previous models
  and profiles, and the maximum-fraction and other algorithms are used to
  fit wavefront distortion profiles and develop corresponding point-spread
  functions. The algorithms are shown to maximize the fractional area
  of the pupil over which the wavefront distortion is smaller than an
  eighth of a wave.

Title: Requirements for adaptive optics in large astronomical
    telescopes.
Authors: Beckers, J. M.
Bibcode: 1992aolt.meet...56B
Altcode:
  Some of the astronomical uses of adaptive optics for large telescope
  are reviewed, and the resulting requirements discussed.

Title: On the Optimization of Partial Adaptive Optics
Authors: Beckers, J. M.
Bibcode: 1992ESOC...42..497B
Altcode: 1992ptit.conf..497B
  No abstract at ADS

Title: Removing Perspective Elongation Effects in Laser Guide Stars
    and Their Use in the ESO Very Large Telescope
Authors: Beckers, J. M.
Bibcode: 1992ESOC...42..505B
Altcode: 1992ptit.conf..505B
  No abstract at ADS

Title: A report on the second ESO Conference on High Resolution
    Imaging by Interferometry.
Authors: Beckers, J. M.; Merkle, F.
Bibcode: 1991Msngr..66....5B
Altcode:
  No abstract at ADS

Title: Differential adaptive optics for astronomical interferometry
Authors: Beckers, Jacques M.
Bibcode: 1991ApOpt..30.5010B
Altcode:
  In astronomical interferometer the interference signal is often
  detected on the pupil plane. To achieve good signal strength it is
  necessary to keep the wavefront distortions caused by the optics and
  the atmosphere small. This paper indicates that it often suffices to
  make the wavefront distortions in the pupils equal rather than zero
  to achieve good signal strength. A way to achieve this is by using a
  differential adaptive optics approach is proposed.

Title: A progress report on the VLT instrumentation plan.
Authors: D'Odorico, S.; Beckers, J.; Moorwood, A.
Bibcode: 1991Msngr..65...10D
Altcode:
  No abstract at ADS

Title: Interferometric imaging with the Very Large Telescope.
Authors: Beckers, J. M.
Bibcode: 1991JOpt...22...73B
Altcode: 1991JOp....22...73B
  The Very Large Telescope Interferometer (VLTI) is one of the operating
  modes of the VLT. In addition to consisting of an array of four
  stationary 8 m diameter telescopes, the VLTI includes a number of
  movable Auxiliary Telescopes which both complement the (u, v) plane
  coverage of the large telescopes and provide a powerful interferometric
  facility by itself (available 100% of the time). The author describes
  the current plans for the implementation of the VLTI. These plans will
  be finalized in 1991 after the choice of the VLT site.

Title: Instrumentation for the ESO Very Large Telescope.
Authors: D'Odorico, S.; Moorwood, F. M.; Beckers, J.
Bibcode: 1991JOpt...22...85D
Altcode: 1991JOp....22...85D
  The instrumentation plan for the ESO VLT has been approved in March
  1990: it includes 10 instruments, two of which are to be replicated,
  distributed among the Nasmyth, Cassegrain and coude focii of the four
  unit telescopes of the VLT and the incoherently combined focus. The
  instruments will be used for a variety of observations in the wavelength
  range from the UV atmospheric cutoff to around 20 μm. Conceptual
  designs are presented for a Medium Resolution IR Spectrometer/Imager,
  a Focal Reducer/Low Dispersion Spectrograph, an Echelle Spectrograph,
  a Multi-fibre spectrograph and an 8 - 14 μm Imager/Spectrometer. Design
  requirements and expected capabilities are given for an High Resolution
  Infrared Camera and for a Speckle Camera, planned to operate in
  combination with the telescope adaptive optics systems. The current
  design options for the high spectral resolution spectrometers for the
  UV-visual and the infrared region are also presented.

Title: Blind operation of optical astronomical interferometers
    options and predicted performance
Authors: Beckers, Jacques M.
Bibcode: 1991ExA.....2...57B
Altcode:
  Maximum sensitivity for optical interferometers is achieved only when
  the optical pathlengths between the different arms can be equalized
  without using interference fringes on the research object itself. This
  is called “blind operation” of the interferometer. In this paper I
  examine different options to achieve this, focussing on the application
  to the Very Large Telescope Interferometer (VLTI). It is proposed
  that blind operation should be done using a so-called “coherence
  autoguider”, working on an unresolved star of magnitude V=11 to
  13 within the “isoplanatic patch for coherencing”, which has a
  diameter of about 1 degree. Estimates of limiting magnitudes for the
  VLTI are also derived.

Title: Instrumental factors affecting the fringe contrast in optical
    interferometers
Authors: Beckers, Jacques M.
Bibcode: 1990Ap&SS.171..333B
Altcode:
  Interference fringes are the prime observable quantity in astronomical
  optical and radio interferometers. To maximize the signal-to-noise
  ratio it is important to keep instrumental causes of fringe contrast
  decrease to a minimum. I discuss these and derive the tolerances to be,
  placed on them.

Title: VLT Interferometer: II. Factors affecting on-axis operation
Authors: Beckers, Jacques M.
Bibcode: 1990SPIE.1236..364B
Altcode:
  The factors contributing to fringe contrast decrease for telescopes
  working near their diffraction limits are summarized. These factors
  include variations with time, such as atmospheric variations,
  vibrations, pathlength drift, and fringe tracking noise; and variations
  accross the pupil; variation with wavelength and factors relating to
  polarization effects; unequal beam intensities; detector resolution;
  and pupil transfer geometry. The effects on multispeckle images are
  also considered. The resulting error budget for the Very Large Telescope
  Interferometer (VLTI) is derived. It is concluded that the total random
  error in the fringe contrast is 4.2. The total calibratable systematic
  error amounts to 34 percent (27 percent due to the instrument, 9
  percent due to the atmosphere).

Title: VLT interferometer: IV. The utility of partial adaptive optics
Authors: Beckers, Jacques M.
Bibcode: 1990SPIE.1236..154B
Altcode:
  The application of full adaptive optics to astronomical telescopes in
  the foreseeable future is likely to be limited to infrared wavelengths
  greater than 1 micron both because of the limited number of bright
  enough wavefront sensing objects at visible wavelengths and because
  of the complexity and expense of making an adaptive optics system for
  large telescopes with the large number of elements required at visible
  wavelengths. Adaptive optics designed for infrared wavelengths do,
  however, improve the image quality at wavelengths shorter than the
  design wavelength, thus improving the sensitivity of interferometric
  imaging at those wavelengths.

Title: VLT Interferometer: III. Factors affecting wide field-of-view
    operation
Authors: Beckers, Jacques M.
Bibcode: 1990SPIE.1236..379B
Altcode:
  This paper discusses the requirements posed on the ESO Very
  Large Telescope (VLT) Interferometer by the applications
  that require a field-of-view larger than the Airy disk of the
  individual telescopes. The most essential requirement for such wide
  field-of-view use of interferometric arrays is the maintenance of
  the pupil configuration, which applies to all the details of this
  configuration. Not meeting this requirement leads to path-length
  differences among the rays of each of the telescopes composing the
  array. An error budget for the optical design parameters of the VLT
  Interferometer is derived.

Title: VLT interferometer: proposed implementation
Authors: Beckers, Jacques M.; Enard, Daniel; Faucherre, Michel; Merkle,
   Fritz; di Benedetto, G. P.; Braun, R.; Foy, R.; Genzel, R.; Koechlin,
   Laurent; Weigelt, Gerd
Bibcode: 1990SPIE.1236..108B
Altcode:
  The Very Large Telescope Interferometer (VLTI) is one of the operating
  modes of the VLT. In addition to consisting of the four stationary
  8 m diameter telescopes, it includes a number of movable Auxiliary
  Telescopes which both complement the (u, v) plane coverage of the large
  telescopes and provide a powerful interferometric facility by itself
  (available 100% of the time). The authors describe the current plans
  for the implementation of the VLTI. These plans will be finalized
  after the choice of the VLT site in 1990.

Title: Planning the VLT interferometer.
Authors: Beckers, J. M.
Bibcode: 1990Msngr..60....1B
Altcode:
  The paper deals with the implementation plan for the Very Large
  Telescope (VLT) interferometer as proposed by the European Southern
  Observatory. The philosophy followed in the plan is based on the
  opportunity provided by the presence on one site of four identical
  8-meter telescopes to do interferometric imaging. The properties of
  existing optical interferometers as well as those in the construction
  and planning stages are outlined, and the similarities and differences
  of optical and radio types of interferometry are discussed, with
  focus placed on adaptive optics. A proposed configuration of the VLT
  telescopes and the resulting plane coverage for different declinations
  and for zenith distance angles up to 60 deg are presented, along with
  some characteristics of auxiliary telescopes. Site aspects are covered,
  and attention is given to special tools developed for handling mirrors.

Title: Polarization effects in astronomical spatial interferometry.
Authors: Beckers, Jacques M.
Bibcode: 1990SPIE.1166..380B
Altcode:
  One of the operational modes of the European Very Large Telescope
  (VLT) will be the one in which the four 8.2 m diameter telescopes
  will be used together with two or more smaller telescopes with about
  2 m aperture as a spatial amplitude interferometer. One of the main
  factors affecting the performance of this interferometric array relates
  to the polarization characteristics of the optics composing the legs
  of the array. Retardation effects and reorientation of the polarization
  coordinate frame of reference by reflections are a major cause of fringe
  contrast decrease (and even disappearance). The author has analyzed
  these effects and developed a raytracing algorithm to calculate the
  polarization transfer and the resulting fringe contrast decrease.

Title: Interferometry with ESO's very large telescope.
Authors: Beckers, J. M.
Bibcode: 1990SPIE.1319..434B
Altcode:
  The Very Large Telescope, being build by the European Southern
  Observatory, has an interferoetric node in which the light of the four
  8 eter aperture telescopes, and of a number of smaller telescopes,
  will be combined coherently to give iilliarcsecond level angular
  resolution at optical wavelengths on very faint objects. This paper
  describes current plans to impleMent this mode.

Title: Adaptive Optics for Large Telescopes
Authors: Beckers, Jacques M.; Merkle, Fritz
Bibcode: 1989Ap&SS.160..345B
Altcode:
  The performance of large telescopes is determined both by their angular
  resolution and by their collection area. It is, therefore, important to
  achieve as high an angular resolution as possible by site selection,
  by avoiding image deterioration by the telescope and its environment,
  and by real time image restoration by adaptive optics. We summarize
  the principles of adaptive optics, their predicted performance and the
  current programs underway to implement adaptive optics for astronomical
  purposes.

Title: Detailed compensation of atmospheric seeing using
    multiconjugate adaptive optics.
Authors: Beckers, J. M.
Bibcode: 1989SPIE.1114..215B
Altcode:
  By the simultaneous observation of the atmospheric wavefront of a
  number of adjacent objects in the sky it appears possible to determine
  the atmospheric wavefront distortion in 3 dimensions using tomography
  techniques. Once obtained it becomes then possible to correct the
  atmospheric wavefront distortions in detail using adaptive optics at
  the conjugates of a number of atmospheric layers.

Title: Application of adaptive optics to astronomy.
Authors: Merkle, Fritz; Beckers, Jacques M.
Bibcode: 1989SPIE.1114...36M
Altcode:
  Adaptive optical systems and their applications in astronomy have
  been discussed for over a decade. Meanwhile the main components
  like deformable mirrors, wavefront sensors etc. for these real
  time correction systems of atmospheric turbulence effects, are
  commercially available. The principles of of this technology, its
  predicted performance and the current programs underway to implement
  adaptive optics for astronomical purposes are summarized.

Title: A near infrared astronomical adaptive optics system.
Authors: Goad, L.; Beckers, J.
Bibcode: 1989SPIE.1114...73G
Altcode:
  The authors describe an adaptive optics system designed to obtain
  diffraction limited imaging in the near infrared (≡2 microns) with
  the Mayall 4-meter telescope at Kitt Peak National Observatory. The
  basic system consists of a 55 element adaptive mirror, a 37 element
  Hartmann-Shack wavefront sensor, and a dedicated microprocessor for
  analysis of sensor data and active mirror control. This polychromatic
  adaptive optics system utilizes the visible radiation from a
  semi-stellar source, or nearby star, for wavefront sensing while
  imaging the near-infrared radiation on an InSb array detector. Recent
  laboratory tests of the working system are summarized.

Title: Survey of present efforts in astronomical adaptive optics
Authors: Beckers, Jacques M.; Merkle, Fritz
Bibcode: 1989SPIE.1130...10B
Altcode:
  In addition to improving the angular resolution of solar and stellar
  observations, the application of adaptive optics to astronomical
  telescopes will improve the contrast of pointlike sources against
  both sky and telescopic apparatus thermal backgrounds, enhance
  spectroscopic resolution, and increase the sensitivity of optical
  interferometry. Performance projections are made for a prospective
  8 m aperture telescope incorporating wavefront sensor-based adaptive
  mirror and digital servocontrol systems; results comparable to those
  of space-based telescopes appear obtainable, albeit at atmospherically
  transmissible wavelengths. The development status and focus of the
  various current programs in astronomical adaptive optics are noted.

Title: Workshop Impressions
Authors: Beckers, J. M.
Bibcode: 1989ASIC..263..607B
Altcode: 1989ssg..conf..607B
  No abstract at ADS

Title: Plans for high resolution imaging with the VLT.
Authors: Beckers, J. M.
Bibcode: 1989amts.conf...90B
Altcode:
  The author reviews the methods used to improve the angular resolution
  of large telescopes. He describes plans to use the VLT with adaptive
  optics and interferometric imaging techniques to improve image quality,
  and places the VLT plans in broader (past and future) perspective.

Title: Solar Image Restoration by Adaptive Optics
Authors: Beckers, J. M.
Bibcode: 1989ASIC..263...43B
Altcode: 1989ssg..conf...43B
  No abstract at ADS

Title: Cophasing Telescope Arrays
Authors: Beckers, J. M.
Bibcode: 1989ASIC..274..355B
Altcode: 1989dli..conf..355B
  No abstract at ADS

Title: Improving Solar Image Quality by Image Selection
Authors: Beckers, J. M.
Bibcode: 1989ASIC..263...55B
Altcode: 1989ssg..conf...55B
  No abstract at ADS

Title: Plan for High Resolution Imaging with the VLT.
Authors: Beckers, J. M.
Bibcode: 1989RvMA....2...90B
Altcode:
  No abstract at ADS

Title: Some Thoughts on the Combination of Beams in Interferometers
    Using Telescopes of Unequal Size
Authors: Beckers, J. M.
Bibcode: 1989ASIC..274..365B
Altcode: 1989dli..conf..365B
  No abstract at ADS

Title: Christian Perrier Recieves Award
Authors: Beckers, J.
Bibcode: 1988Msngr..54...63B
Altcode:
  Christian Perrier Receives Award

Title: Increasing the Size of the Isoplanatic Patch with
    Multiconjugate Adaptive Optics
Authors: Beckers, J. M.
Bibcode: 1988ESOC...30..693B
Altcode: 1988vlti....2..693B; 1988vltt.conf..693B
  No abstract at ADS

Title: Reducing Mirror Seeing Problems in Meniscus Mirrors
Authors: Barr, L. D.; Beckers, J. M.; Pearson, E. T.; Hobbs, T. W.;
   Spangenberg-Jolley, J.
Bibcode: 1988ESOC...30..595B
Altcode: 1988vlti....1..595B; 1988vltt.conf..595B
  It is well known that telescope seeing is worsened when temperature
  differences exist between the primary mirror and the air above the
  surface. The author describe a new mirror blank configuration that
  enables mirror blank temperature control sufficient to substantially
  eliminate mirror seeing through liquid cooling. Thermal properties
  and manufacturing feasibility have been studied.

Title: Grisms for Infrared Observations
Authors: Beckers, J. M.; Gatley, I.
Bibcode: 1988ESOC...30.1093B
Altcode: 1988vltt.conf.1093B; 1988vlti....2.1093B
  The recent availability of 2-D infrared array detectors suggests the
  application of visible light techniques to infrared astronomy. This
  paper examines grism spectroscopy and reports the first results of an
  IR grism spectrograph.

Title: Adaptive Optics Development at NOAO
Authors: Beckers, J. M.
Bibcode: 1988ESOC...30..627B
Altcode: 1988vlti....2..627B; 1988vltt.conf..627B
  The Advanced Development Program and the National Solar Observatory
  within NOAO are engaged in the development of adaptive optics for
  both solar and stellar observations and for visible and infrared
  telescopes. These different applications require different techniques
  but also share many common aspects. The author reviews these programs,
  discusses results of their analysis, discusses some of their hardware
  and project towards future plans.

Title: Diffraction-limited astronomical infrared imaging through
    the turbulent atmosphere
Authors: Christou, J. C.; Freeman, J. D.; McCarthy, D. W., Jr.;
   Roddier, F.; Beckers, J. M.
Bibcode: 1988JPhD...21S..49C
Altcode:
  No abstract at ADS

Title: Two-dimensional Infrared Diffraction-limited Imaging of
    Circumstellar Envelopes
Authors: Christou, J. C.; Ridgway, S. T.; Beckers, J. M.; Probst, R. G.
Bibcode: 1988BAAS...20.1053C
Altcode:
  No abstract at ADS

Title: Interferometry with the MMT and NNTT.
Authors: Beckers, J. M.
Bibcode: 1988ESOC...29..879B
Altcode: 1988hrii.conf..879B
  The author summarizes the experiments in interferometry done on
  the MMT and planned for the NNTT. He refers to the numerous other
  publications on this topic which are given in the references for
  detailed information.

Title: Application of the NOAO Infrared Imaging Array for 2-D Infrared
    Speckle Interferometry
Authors: Beckers, J. M.; Ridgway, S.; Christou, J. C.; Probst, R.
Bibcode: 1988BAAS...20..649B
Altcode:
  No abstract at ADS

Title: High Resolution Imaging in the Infrared Using Adaptive Optics
Authors: Beckers, Jacques M.; Goad, Larry E.
Bibcode: 1988ASSL..141..319B
Altcode: 1988uglr.work..319B
  The authors describe the principles behind the prototype of a so-called
  polychromatic adaptive optics system now being assembled at NOAO to be
  used at the 150 cm McMath and 380 cm Mayall telescopes on Kitt Peak. In
  it, the wavefront errors due to seeing and the telescope itself are
  being corrected for IR wavelengths, while the wavefront disturbances
  are being sensed at visible and near IR wavelengths.

Title: First results with the NOAO 2-D speckle camera for infrared
    wavelengths.
Authors: Beckers, J. M.; Christou, J. C.; Probst, R. G.; Ridgway,
   S. T.; von der Lühe, O.
Bibcode: 1988ESOC...29..393B
Altcode: 1988hrii.conf..393B
  The authors have constructed an infrared speckle camera using the NOAO
  SBRC 58×62 InSb array detector. The camera and detector can be used
  anywhere in the 1 to 5 μm wavelength region. The authors describe the
  first observations. These observations illustrate the performance of
  the camera for an unresolved object, for a double star (ζ Aqr) and
  for a resolved object (the "Red Rectangle"). The authors have analyzed
  the observations using shift-and-add, power spectrum/autocorrelation
  function, and Knox-Thompson methods.

Title: Some Thoughts on the Combination of Beams in Interferometers
    Using Telescopes of Unequal Size
Authors: Beckers, J. M.
Bibcode: 1988dli..conf..365B
Altcode:
  No abstract at ADS

Title: Cophasing Telescope Arrays
Authors: Beckers, J. M.
Bibcode: 1988dli..conf..355B
Altcode:
  No abstract at ADS

Title: Two-dimensional infrared astronomical speckle interferometry
Authors: Christou, Julian C.; Ridgway, Stephen T.; Probst, Ronald G.;
   Beckers, Jacques M.; Freeman, Jonathan D.
Bibcode: 1988SPIE..976..193C
Altcode:
  The infrared imager currently in use at the National Optical Astronomy
  Observatories (NOAO) has been adapted for use as a two-dinmensional
  infrared speckle camera operating at wavelengths of 1 - 5 microns. Data
  have been obtained at the Kitt Peak National Observatory (KPNO) Mayall
  telescope (effective aperture of about 3.8 m) for a number of different
  sources. Diffraction-limited images are presented for two objects, the
  'Red Rectangle' and NML Cygnus, using the Knox-Thompson algorithm to
  recover the Fourier phases. A comparison of phase-relaxation techniques
  applied to the integrated phase differences is presented using both
  the Hudgin method and successive over-relaxation.

Title: Image Reconstruction Using Adaptive Optics
Authors: Beckers, J. M.; Goad, L. E.
Bibcode: 1988igbo.conf..315B
Altcode:
  Adaptive optics is an especially powerful tool for high resolution
  imaging in the infrared beyond 2 μm, where it can cover all or a large
  fraction of the sky and where the complexity and cost is modest as
  compared with the telescope itself. The authors describe the principles
  behind the prototype of a so-called polychromatic adaptive optics system
  now being assembled at NOAO to be used at the 150 cm McMath and 380
  cm Mayall telescopes on Kitt Peak. In it, the wavefront errors due to
  seeing and the telescope itself are being corrected for IR wavelengths,
  while the wavefront disturbances are being sensed at visible and near
  IR wavelengths.

Title: Optical concepts for the Binary Star Explorer.
Authors: Traub, W. A.; Massa, D. L.; Endal, A. S.; Beckers, J. M.;
   Latham, D. W.; McAlister, H. A.; Parsons, S. B.
Bibcode: 1987SPIE..751...72T
Altcode:
  The conceptual design of a proposed first-generation optical
  interferometer in space, the Binary Star Explorer, is described. The
  scientific objectives for this interferometer are to determine the
  fundamental astrophysical quantities of distance and mass for stars
  in binary systems. In particular, the interferometer will be able
  to make accurate distance measurements to an estimated 40 Cepheid
  binary systems in the Galaxy, and 28 supergiant binary systems in
  the LMC. The interferometer comprises two fixed telescopes on a 5-m
  baseline, beam-combining optics, and a visible/ultraviolet fringe
  detecting system. The angular separation of binary systems made
  up of a cool giant star and hot dwarf companion are determined by
  measuring the shift between the optical and ultraviolet fringes. In
  combination with knowledge of the physical size of the orbit (which
  must be obtained separately from radial velocity measurements on both
  stars), the distance to the binary is obtained as the ratio of the
  physical to angular sizes.

Title: The NOAO/ADP adaptive optics program and its application to
    solar physics.
Authors: Beckers, J. M.
Bibcode: 1987LFTR...28...55B
Altcode:
  The NOAO Advanced Development Program is pursuing a program to develop
  adaptive optics for both nighttime and solar observations. Initially
  this program is directed towards image sharpening at infrared
  wavelengths (1 - 10 μm) at large stellar and solar telescopes. Although
  observing will be done in the infrared this "polychromatic" adaptive
  optics system will do the wavefront sensing at visible wavelengths.

Title: Interferometric Capabilities of the Nntt
Authors: Beckers, J. M.
Bibcode: 1987iia..conf..171B
Altcode:
  No abstract at ADS

Title: Economy figure of merit for large telescope sites.
Authors: Beckers, J. M.
Bibcode: 1987iopo.conf..138B
Altcode:
  The author attempts to combine the factors determining the quality of
  an astronomical site into a single quantity called the "Economy Figure
  of Merit," which describes a site in terms of the cost of constructing
  a facility to achieve a given performance.

Title: High angular resolution infrared imaging at NOAO (Poster)
Authors: Christou, J. C.; Beckers, J. M.; Roddier, F.; Ridgway, S.;
   Probst, R.; Freeman, J. D.; McCarthy, D. W., Jr.; Cobb, M. L.
Bibcode: 1987iawa.conf..464C
Altcode:
  The authors discuss how the SBRC 58×62 InSb infrared imaging array will
  be used for 2-D infrared speckle interferometry (IRSI) at NOAO. The
  2-D IRSI is a logical extension of the 1-D slit-scanning technique
  currently employed by a number of groups.

Title: A deep polar spectroscopic telescope "DEEPS".
Authors: Davies, R.; Seitzer, P.; Beckers, J.; Simmons, J.
Bibcode: 1987inco.conf...45D
Altcode:
  DEEPS is a concept for a fixed telescope pointing at a celestial pole
  which would perform multiple object spectroscopy on galaxies ten to
  twenty times fainter than those at the current limit of observation
  using large ground based telescopes.

Title: Telescope sites: summary and conclusions.
Authors: Beckers, J. M.
Bibcode: 1987iopo.conf..212B
Altcode:
  No abstract at ADS

Title: Two-dimensional Images of Alpha Orionis
Authors: Hebden, J. C.; Christou, J. C.; Cheng, A. Y. S.; Hege, E. K.;
   Strittmatter, P. A.; Beckers, J. M.; Murphy, H. P.
Bibcode: 1986ApJ...309..745H
Altcode:
  Between February 1981 and December 1983 a series of speckle
  interferometric observations were made of the M-type supergiant Alpha
  Orionis in an attempt to produce two-dimensional images of the star at
  the H-alpha line. Two types of data reduction techniques were used: (1)
  shift-and-add methods applied to conventional speckle interferometric
  observations, and (2) differential speckle interferometry. Data analysis
  included the application of the CLEAN algorithm to calibrate the images
  produced by the shift-and-add technique with data reduced similarly
  for a point source. The images produced are encouragingly consistent
  in suggesting asymmetric atmospheric structure; possible evolution of
  that structure over the three-year period of observations is noted.

Title: Planning the National New Technology Telescope
Authors: Beckers, J. M.
Bibcode: 1986BAAS...18..955B
Altcode:
  No abstract at ADS

Title: Differential speckle imaging with the cophased Multiple
    Mirror Telescope.
Authors: Hebden, J. C.; Hege, E. K.; Beckers, J. M.
Bibcode: 1986OptEn..25..712H
Altcode:
  Differential speckle interferometry has been applied to data obtained
  using the fully phased six-mirror aperture of te Multiple Mirror
  Telescope. Wavelength-dependent differences in the appearance of
  a stellar object are derived from simultaneous observations at two
  distinct wavebands. The supergiaint star Alpha Orionis was observed
  this way to investigate its appearance in hydrogen-alpha emission. Data
  reduction consists of a frame-by-frame weighted deconvolution. An
  inherent Wiener-type filtering must be removed in order to preserve
  high spatial frequency information. Results for Alpha Orionis are
  compared to similar results for the unresolved source Gamma Orionis.

Title: The Magnetic Field of the BY Draconis Flare Star EQ Virginis
Authors: Saar, S. H.; Linsky, J. L.; Beckers, J. M.
Bibcode: 1986ApJ...302..777S
Altcode:
  High resolution, high S/N-ratio line profiles of the BY Draconis-type
  flare star EQ Vir obtained with the MMT are presently subjected to
  a novel Zeeman analysis procedure which includes radiative transfer
  effects and compensation for blends. A mean field of 2500 + or -
  300 G covering 80 + or 15 percent of EQ Vir is determined. This
  constitutes the first positive detection of a magnetic field in a BY
  Draconis-type flare star, confirming that magnetic fields are present
  on these stars. The value of 2500 G obtained for the photospheric field
  strength is similar to the value derived by assuming equipartition of
  magnetic and thermal energy densities in the photosphere and scaling
  from the solar network fields, suggesting that equipartition may
  determine the mean field strength in the nonspotted portion of the
  flare star photosphere.

Title: IR thermography and observatory thermal pollution
Authors: Williams, J. T.; Beckers, J. M.; Salmon, D.; Kern, P.
Bibcode: 1986SPIE..628...30W
Altcode:
  A 10 micron imaging camera has been used to identify subtle and
  not-so-subtle thermal pollution of the near telescope environment at
  several large telescopes, and can also be used to monitor progress in
  eliminating such pollution. This paper reports some highlights of data
  taken at the Multiple Mirror Telescope (MMT), the Kitt Peak National
  Observatory (KPNO), and Cerro Tololo Inter-American Observatory (CTIO)
  4 meter telescopes, and Canada-France-Hawaii (CFHT) 3.6 meter telescope
  on Mauna Kea, the McDonald Observatory 2.7 and 2.1 meter telescopes
  and the 5 meter telescope at Mt. Palomar.

Title: Planning the National New Technology Telescope (NNTT). IV -
    Coalignment/cophasing system
Authors: Beckers, Jacques M.; Shu, Ker-Li; Shaklan, Stuart
Bibcode: 1986SPIE..628..102B
Altcode:
  The NNTT will be a multiple mirror telescope consisting of an array
  of four 7.5-meter telescopes to be coaligned and cophased by means of
  an internal optical metering device. As a result, the NNTT acts like
  a single telescope with a 15-meter collecting diameter and a 21-meter
  resolution diameter. This paper describes the coalignment/cophasing
  system.

Title: Field of view considerations for telescope arrays
Authors: Beckers, Jacques M.
Bibcode: 1986SPIE..628..255B
Altcode:
  The limitation of the field of view for three different types of
  interferometric imaging telescope arrays is examined, and means for its
  optimization are identified. The array types are the compact monolithic,
  thin monolithic, and nonmonolithic (individual telescopes). Attention
  is given to the optical path of two elements of the nonmonolithic
  array type for the case of an on-axis star.

Title: Use of the coherent MMT for diffraction limited imaging
Authors: Hebden, J. C.; Hege, E. K.; Beckers, J. M.
Bibcode: 1986SPIE..628...42H
Altcode:
  All six MMT telescopes can now be optically cophased simultaneously
  over a wide field of view yielding coherent coverage of the complete
  Fourier transform plane corresponding to that of a pupil-masked
  telescope of 6.86-m aperture. Open-loop phasing control compensates
  for flexure-induced path-length changes due to variable gravitational
  loading as a function of elevation. The system has been used to produce
  diffraction limited images and differential images of Alpha Orionis
  using narrow-band (1.2 A) filters centered both on Hydrogen-alpha and
  on a similar bandpass out of the absorption line. Corresponding wide
  (100 A) and narrow-band images of Gamma and Epsilon Orionis show the
  expected result for unresolved sources at the diffraction limited
  resolution of the fully-phased MMT.

Title: National Optical Astronomy Observatories (NOAO) IR adaptive
    optics program. III - Criteria for the wavefront sensor selection
Authors: Goad, L.; Roddier, F.; Beckers, J.; Eisenhardt, P.
Bibcode: 1986SPIE..628..305G
Altcode:
  The NOAO IR Adaptive Optics Program has elected to develop a system
  using the visual light from an object to sense the wavefront errors
  and generate the corrections required to give diffraction-limited
  imaging in the near-IR (2-10 microns). The performance of a variety
  of possible sensors systems has been evaluated, computing both their
  ideal performance and their expected performance with available
  detectors. A major consideration in this evaluation is the ability of
  the sensor to measure mean wavefront tilts of the visual wavefront
  over subapertures corresponding to the (larger) IR wavefront scale
  lengths. A Hartmann-Shack sensor with red-sensitive image intensifiers
  and a Reticon detector are used.

Title: The National New Technology Telescope as a phased array.
Authors: Beckers, J. M.
Bibcode: 1986JOSAA...3R...5B
Altcode: 1986OSAJ....3R...5B
  No abstract at ADS

Title: Proposal for a deep polar spectroscopic survey.
Authors: Beckers, J. M.; Davies, R. L.; Phillips, M. M.; Seitzer, P. O.
Bibcode: 1986BAAS...18Q.848B
Altcode:
  No abstract at ADS

Title: Plans for coalignment and cophasing of the optics in the 15-m
    National New Technology Telescope (NNTT).
Authors: Beckers, Jacques M.; Shu, Ker-Li; Shaklan, Stuart
Bibcode: 1986SPIE..608...18B
Altcode:
  The NNTT concept is a multiple mirror type telescope consisting of
  an array of four 7.5-meter diameter telescopes which are coaligned
  and cophased by means of an internal optical metering device. As a
  result, the NNTT acts like a single telescope with a 15-meter collecting
  diameter and a 21-meter resolution diameter. This paper describes this
  coalignment/cophasing system.

Title: National Optical Astronomy Observatories (NOAO) infrared
    adaptive optics program. I - General description
Authors: Beckers, Jacques M.; Roddier, Francois J.; Eisenhardt,
   Peter R.; Goad, Larry E.; Shu, Ker-Li
Bibcode: 1986SPIE..628..290B
Altcode:
  The authors describe the general principles behind a polychromatic
  adaptive optics program for astronomy. In this program the atmospheric
  wavefront distortions are measured at visible wavelengths (700 nm)
  using an astronomical object in the vicinity of the infrared object of
  interest. The resulting wavefront corrections are applied to an infrared
  imaging system which utilizes a two-dimensional detector array. The
  authors describe the principles of this adaptive optics system.

Title: The Coalignment and Cophasing of the National New Technology
    Telescope
Authors: Beckers, J. M.; Shu, K. L.; Shaklan, S.
Bibcode: 1985BAAS...17..900B
Altcode:
  No abstract at ADS

Title: Multiple mirror telescope as a phased array telescope
Authors: Hege, E. Keith; Beckers, Jacques Maurice; Strittmatter,
   Peter A.; McCarthy, Donald W., Jr.
Bibcode: 1985ApOpt..24.2565H
Altcode:
  Experiments are summarized which have used the multiple mirror
  telescope (MMT) subapertures as a phased array and as a coherent
  phased telescope. A simple analysis is presented of the tilted focal
  plane geometry for coherent observation. The phased operation of the
  MMT is important not only for obtaining high angular resolution but
  also for obtaining the higher detection sensitivity which results from
  the better discrimination against the sky emission background for IR
  diffraction-limited images. Full-aperture (six-beam) diffraction-limited
  results for the unresolved source Gama Orionis, the well-known close
  binary Capella, and the resolved red supergiant Betelgeuse (including
  a diffraction-limited differential speckle image of the latter) are
  presented as a preliminary demonstration of the potential capabilities
  of this configuration.

Title: Results from Optical Interferometry (Review)
Authors: Beckers, J. M.
Bibcode: 1985ASSL..117...57B
Altcode: 1985mlrg.proc...57B
  The techniques of optical speckle and Michelson interferometry have both
  contributed significant information on the diameter, the atmospheres,
  and the envelopes of red supergiant stars. In this paper, the author
  summarizes the observations obtained to date and previews future plans.

Title: Polychromatic Adaptive Optics for Infrared Telescopes
Authors: Beckers, J. M.; Eisenhardt, P.; Goad, L.; Roddier, F.
Bibcode: 1985BAAS...17R.571B
Altcode:
  No abstract at ADS

Title: Contributions by R.G. Giovanelli to Solar Instrumentation
Authors: Beckers, J. M.
Bibcode: 1985AuJPh..38..769B
Altcode:
  No abstract at ADS

Title: Differential speckle imaging with the cophased Multiple
    Mirror Telescope.
Authors: Hebden, J. C.; Hege, E. K.; Beckers, J. M.
Bibcode: 1985SPIE..556..284H
Altcode:
  A new technique known as differential speckle interferometry has been
  applied to data obtained using the fully-phased six-mirror aperture
  of the Multiple Mirror Telescope. By observing stellar objects at
  two distinct wavebands simultaneously, differences in the object
  resulting from the different wavelengths can be derived. Observations
  were made of the supergiant star Alpha Orionis in order to investigate
  the hydrogen-alpha emission from the surrounding envelope. The data
  reduction process consists of a frame-by-frame weighted deconvolution
  procedure. This process involves an inherent Wiener-type filtering
  which must be removed in order to preserve high spatial frequency
  information. Results for Alpha Orionis and for the unresolved source
  Gamma Orionis are presented.

Title: Energy Release and Energy Transport Below the Transition Zone
    in Solar Flares
Authors: Hénoux, J. C.; Chambe, G.; Heristchi, D.; Semel, M.;
   Woodgate, B.; Shine, R.; Beckers, J.
Bibcode: 1985spit.conf..758H
Altcode:
  No abstract at ADS

Title: Future techniques and instrumentation in solar-stellar physics
Authors: Beckers, J. M.
Bibcode: 1985AuJPh..38..791B
Altcode:
  A projection is made of instrumentation developments in future
  solar-stellar physics research, encompassing stellar activity and its
  cycles, stellar rotation, stellar surface motions and magnetic fields,
  stellar pulsations and oscillations, and stellar chromospheres, coronae,
  and winds. In treating each of these fields, current techniques are
  characterized and the observations integrates sunlight that couple the
  properties of the sun to those of the stars are noted. Solar-stellar
  research may be the primary driver in stellar photometric and
  spectroscopic research in the foreseeable future.

Title: Spectroscopy of 26 QSO candidates form the Jodrell Bank
    966-MHz survey.
Authors: Walsh, D.; Beckers, J. M.; Carswell, R. F.; Weymann, R. J.
Bibcode: 1984MNRAS.211..105W
Altcode:
  Twenty-six QSO candidates from the Jodrell Bank 966-MHz survey have been
  observed spectroscopically at the Multiple Mirror Telescope. Nineteen
  are emission-line QSOs and redshifts are given for these. Four have
  smooth, featureless spectra and are classified as BL Lacertae-type
  objects. The remaining three objects are galactic stars.

Title: Differential Speckle Interferometry-Using the MMT
Authors: Hebden, J.; Hege, E. K.; Beckers, J.
Bibcode: 1984BAAS...16..886H
Altcode:
  No abstract at ADS

Title: First Measurement of Magnetic Fields on a BY Draconis Flare
Star: EQ Virginis
Authors: Saar, S. H.; Linsky, J. L.; Beckers, J. M.
Bibcode: 1984BAAS...16Q.517S
Altcode: 1984BAAS...16..517S
  No abstract at ADS

Title: High Resolution Imaging of Spectroscopic Binaries
Authors: Beckers, J. M.
Bibcode: 1984BAAS...16..498B
Altcode:
  No abstract at ADS

Title: A solar Lyman alpha coronagraph.
Authors: Beckers, J. M.; Argo, H. V.
Bibcode: 1984SPIE..445..312B
Altcode:
  An all reflecting externally and internally occulting solar coronagraph
  which can be used for observations of the sun in the hydrogen
  Lyman-alpha line is described. In the particular design considered
  and tested, a multiple occulting disk assembly is integrated with a
  Gregorian telescope in such a way that (1) scattered and diffracted
  light is minimized, and (2) a large effective collecting area (16 sq cm)
  as compared to the total telescope length (95 cm) is obtained. The
  telescope is sun-centered pointed and has a large field of view
  (2.3 degrees diameter). Its image can be used to feed a multiple
  slit spectrograph, a camera using a Lyman-alpha interference filter
  or other instrumentation which can make use of the availability of a
  full coronal image.

Title: The differential speckle interferometer.
Authors: Beckers, J. M.; Hege, E. K.; Murphy, H. P.
Bibcode: 1984SPIE..445..462B
Altcode:
  The authors describe a new technique called "Differential Speckle
  Interferometry" (DSI) which uses simultaneous narrow band images of
  astronomical objects to study their structure. Simultaneous specklegrams
  of red supergiant and giant stars taken in the hydrogen lines and in
  the nearby continuum allow to reconstruct the image of the extended
  chromospheres of these stars at resolutions of 100 nanoradians and
  better. The authors describe the instrumentation, analysis techniques,
  and results related to DSI.

Title: The use of the MMT for interferometric imaging
Authors: Beckers, J. M.; Hege, E. K.
Bibcode: 1984vlti.conf..279B
Altcode: 1984IAUCo..79..279B
  The progress made in interferometric imaging using the multiple-mirror
  telescope (MMT) as a fully phased array in visible wavelengths is
  discussed. It is shown that all six MMT telescopes can now be phased
  over a wide field of view simultaneously resulting in a (u,v) plane
  coverage corresponding in size to a 686-cm telescope aperture. The
  open-loop phasing control of the MMT for gravitational changes, as well
  as a concept of an internal cophasing/coalignment system for MMT-type
  telescopes are described.

Title: The use of the Multiple Mirror Telescope as a phased array.
Authors: Beckers, J. M.; Hege, E. K.; Low, F. J.; McCarthy, D. W.;
   Strittmatter, P. A.
Bibcode: 1984SPIE..440..136B
Altcode:
  A summary is provided of the experiments which have used the Multiple
  Mirror Telescope (MMT) subapertures as a phased array in the optical,
  infrared, and submillimeter spectum regions. Those experiments exploit
  the unique, very high angular resolution of the MMT being equivalent
  to that of a conventional telescope 686 cm in diameter. The operation
  of the MMT as a phased array is not only important for obtaining
  high angular resolution but also for obtaining the higher detection
  sensitivity which results from the better discrimination against the
  sky emission background for infrared diffraction limited images. A
  description is presented of future plans to make the MMT into a phased
  telescope.

Title: Optical interferometry with the MMT.
Authors: Beckers, J. M.; Hege, E. K.; Strittmatter, P. A.
Bibcode: 1983SPIE..444...85B
Altcode: 1984SPIE..444...85B
  A phased array with a 680-cm baseline can be devised by adjusting the
  optical path lengths of the University of Arizona's six Multiple Mirror
  Telescope (MMT) elements. Attention is presently given to the procedures
  and results of experiments in spectroscopy and speckle interferometry,
  which have been conducted using either two or three of the telescopic
  elements. Adjustments of the optical configuration of the MMT are
  planned which will lead to coherent operation over a large field of
  view, with all six telescopic elements phased simultaneously.

Title: The Multiple Mirror Telescope: a progress report.
Authors: Beckers, J. M.; Ulich, B. L.; Williams, J. T.
Bibcode: 1983SPIE..444....2B
Altcode: 1984SPIE..444....2B
  Attention is given to engineering design and operational aspects of
  the Multiple Mirror Telescope (MMT). A novel detector cooling system
  for the MMT's spectrographs permits echelle spectroscopy of extremely
  faint objects to be conducted, in order to obtain data bearing on
  such questions as the chemical abundances of the early universe, the
  velocity dispersions in globular clusters and dwarf spheroidal galaxies,
  and the rotation and magnetic fields of galactic stars. The MMT's IR
  photometer has identified many optically invisible radio sources,
  and is being used to devise an improved Cepheid period-luminosity
  relationship that is not affected by interstellar absorption.

Title: Rotation among Orion IC G stars : Angular momentum loss
    considerations in pre-main-sequence stars.
Authors: Smith, M. A.; Beckers, J. M.; Barden, S. C.
Bibcode: 1983ApJ...271..237S
Altcode:
  Echelle spectra of the Na D lines or weak subordinate lines have been
  observed and analyzed for rotational velocities for 51 G type stars
  in the Orion Ic cluster. The high resolution of these MMT spectra
  permit a detection threshold V<SUB>R</SUB> sin i = 7 km s<SUP>-1</SUP>
  or better to be attained. The results indicate that the velocity
  distribution of these stars can be represented by two components, a
  quasi-Maxwellian with a low modal value, &lt;V<SUB>R</SUB><SUP>2</SUP>
  sin i&gt;<SUP>1/2</SUP> = 12 km s<SUP>-1</SUP>, and a flat distribution
  extending out to 200 km s<SUP>-1</SUP>. The D line spectra of the
  rapid rotators exhibit narrow absorption or emission features which
  are attributed to circumstellar disks close to the star. These disks
  appear to be quasi-permanent features and almost certainly are not
  remnants of the protostellar accretion phase. Several of the rapid
  rotators exhibit X-ray emission which also appears to be correlated with
  rotation. The implications of these results for the angular momentum
  problem in star formation are discussed in detail. It is suggested
  that a typical star loses some of its spin angular momentum to orbital
  momentum in a binary. This could occur by rotational synchronism during
  a protostellar fragmentation process.

Title: Conductive Heat Flux in the Chromosphere Derived from Line
    Linear Polarization Observation
Authors: Henoux, J. -C.; Chambe, G.; Heristchi, D.; Semel, M.;
   Woodgate, B.; Shine, D.; Beckers, J.
Bibcode: 1983SoPh...86..115H
Altcode:
  Linear polarization in two chromospheric lines (Hα and SI 1437 A) was
  observed in the gradual phase of solar flares. The polarized electric
  vector is directed towards disk center.

Title: Vertical Gradients of Sunspot Magnetic Fields
Authors: Hagyard, M. J.; Teuber, D.; West, E. A.; Tandberg-Hanssen,
   E.; Henze, W., Jr.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; Woodgate,
   B. E.
Bibcode: 1983SoPh...84...13H
Altcode:
  In this paper, we describe results of a Solar Maximum Mission (SMM)
  guest investigation to determine vertical gradients of sunspot
  magnetic fields for the first time from coordinated observations
  of photospheric and transition-region fields. Both the photospheric
  vector field of a sunspot, derived from observations using the NASA
  Marshall Space Flight Center vector magnetograph, and the line-of-sight
  component in the transition region, obtained from the SMM Ultraviolet
  Spectrometer and Polarimeter instrument, are described. From these
  data, vertical gradients of the line-of-sight magnetic field component
  are calculated using three methods. (1) The vertical gradient is
  derived directly from the observations assuming a height difference
  of 2000 km between the photosphere and transition region. (2) Using
  the observed transverse photospheric field, the initial gradient
  (ΔB<SUB>z</SUB>/Δz)<SUB>z = 0</SUB>, is calculated from the condition
  ▽ . B = 0. (3) Using the photospheric line-of-sight component as the
  boundary condition in a potential-field calculation, the extrapolated
  potential field at different heights is compared to the observed
  transition-region field; from these comparisons, an average height
  difference is derived and used to calculate the average vertical
  gradient (ΔB<SUB>z</SUB>/Δz). Comparisons of gradients derived
  from these three methods show consistent results for methods (2) and
  (3). Deviations of the calculated potential transverse field at z = 0
  from the observed transverse component are investigated to assess the
  validity of gradient calculations using method (3). Since the field
  is shown to be very close to a potential distribution, we conclude
  that the vertical gradient of B<SUB>z</SUB> is lower than values from
  previous studies and the transition-region field occurs at a height
  of ≈ 4000-6000 km above the photosphere.

Title: Observing White-Light Flares
Authors: Neidig, D. F.; Beckers, J. M.
Bibcode: 1983S&T....65..226N
Altcode:
  Observational techniques and instrumentation for tracking the occurrence
  of solar white light flares back to their origin are discussed. The
  rare events have been found to happen in the chromospheric and coronal
  regions over sunspots, and are thought to be the release of accumulated
  energy breaking free from the magnetic field lines and reforming into
  simpler structures. Use of an achromatic f/15 objective lens, together
  with a reimaging system for field magnification as a prelude to 35
  mm photography, at the Sacramento Peak Observatory is described. A
  Wollaston prism is also used to split the image into two beams for
  detection of intensity variations due to polarization, which has thus
  far not been observed in the white light flares. Spectroscopic data
  indicate visual emission due to negatively-charged hydrogen ions in
  the upper photosphere, and shorter wavelength neutral hydrogen Balmer
  continuum features. A white light flare can be up to 300% as brilliant
  as the surrounding region, and involve several percent of the total
  spontaneous solar output.

Title: Conductive flux in flaring solar chromospheres deduced from
    the linear polarization observations
Authors: Henoux, J. C.; Heristchi, D.; Chambe, G.; Woodgate, B.;
   Shine, R.; Beckers, J.; Machado, M.
Bibcode: 1983A&A...119..233H
Altcode:
  The linear polarization of Hα and S I 1437 Å lines produced in
  impact excitation by energetic electrons with an anisotropic velocity
  distribution function during solar flares is calculated. Selecting
  a function which represents the velocity distribution of electrons
  carrying heat flux, the relationship between conductive heat flux and
  linear line polarization has been computed. <P />The application of the
  relationship between linear polarization and heat flux to the observed
  degree of polarization leads to the determination of the conductive
  heat flux at the top of flaring chromospheric layers. This conductive
  flux is of the order of magnitude of the total radiation loss in the
  chromosphere and below, which is also of the order of magnitude of
  the conductive flux in the transition zone.

Title: Vertical Gradients of Sunspot Magnetic Fields
Authors: Hagyard, M. J.; Teuber, D.; West, E. A.; Tandberg-Hanssen,
   E.; Henze, W., Jr.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; Woodgate,
   B. E.
Bibcode: 1983BAAS...15..702H
Altcode:
  No abstract at ADS

Title: Impact linear polarization observed in a UV chromospheric
    line during a solar flare
Authors: Henoux, J. C.; Chambe, G.; Sahal, S.; Semel, M.; Woodgate,
   B.; Shine, D.; Beckers, J.; Machado, M.
Bibcode: 1983ApJ...265.1066H
Altcode:
  Linear polarization was observed in the S 11437 A line in bright
  flaring points during the soft X-ray emission from a flare on 1980
  July 15. The degree of polarization is about 25% and is detected at a
  signal-to-noise ratio of 2.9. The polarized electric vector is directed
  toward disk center to within 3°. <P />This polarization could be due
  to collisional excitation of S I by energetic electrons beamed in the
  vertical direction. Direct excitation by a highly energetic beam of
  electrons of order 10-100 keV is doubtful. We suggest that the heat flux
  in the region connecting the transition zone to the high chromosphere
  during the gradual phase of a flare could lead to an anisotropic
  excitation. Then the observed polarization would be due to vertical
  motions of the transition zone sweeping the preexisting chromosphere.

Title: Observations of Alfven waves simultaneously in H-alpha and K
Authors: Giovanelli, R. G.; Beckers, J.
Bibcode: 1983IAUS..102..407G
Altcode:
  Simultaneous spectroheliograms of a quiet region at solar disk centre
  in Hα +0.29 Å, Hα -0.29 Å, K +0.18 Å and K -0.18 Å show much
  similarity in the asymmetries in the two lines. The fibrils are
  identical geometrically. Both lines show patterns of line-of-sight
  motions propagating along the fibrils. Close to the network, the
  velocity of propagation is of the order of 12 km s<SUP>-1</SUP> towards
  or away from the network; further away the patterns propagate away from
  the network at velocities of the order of 75 km s<SUP>-1</SUP>. The
  latter are interpreted as Alfvén waves, the former as due most likely
  to variations in longitudinal velocities along the fibrils.

Title: Recent developments at the multiple mirror telescope.
Authors: Beckers, J. M.
Bibcode: 1983SPIE..365....2B
Altcode:
  Although the Multiple Mirror Telescope (MMT) is a major astronomical
  facility in virture of its large collecting area (equivalent to a 4.5-m
  diameter single mirror telescope), it serves an equally important
  function as a testbed for unconventional, potentially lower cost
  (despite superior performance) telescope designs. The unconventional
  features being refined by the MMT include the use of multiple primary
  mirrors, an altitude-over-azimuth (rather than equatorial) mount,
  a barn-like enclosure, hollow 'egg-crate' fused silica mirrors, and
  precision ball bearings. Attention is given to the coalignment hardware
  and procedures used for the six primary mirrors, the image quality and
  interferometer performance achieved, and the annual service profile
  of the MMT.

Title: Observations of the Longitudinal Magnetic Field in the
    Transition Region and Photosphere of a Sunspot
Authors: Henze, W., Jr.; Tandberg-Hanssen, E.; Hagyard, M. J.; West,
   E. A.; Woodgate, B. E.; Shine, R. A.; Beckers, J. M.; Bruner, M.;
   Hyder, C. L.; West, E. A.
Bibcode: 1982SoPh...81..231H
Altcode:
  The Ultraviolet Spectrometer and Polarimeter on the Solar Maximum
  Mission spacecraft has observed for the first time the longitudinal
  component of the magnetic field by means of the Zeeman effect in
  the transition region above a sunspot. The data presented here were
  obtained on three days in one sunspot, have spatial resolutions of
  10 arc sec and 3 arc sec, and yield maximum field strengths greater
  than 1000 G above the umbrae in the spot. The method of analysis,
  including a line-width calibration feature used during some of the
  observations, is described in some detail in an appendix; the line
  width is required for the determination of the longitudinal magnetic
  field from the observed circular polarization.

Title: Performance of the Multiple Mirror Telescope (MMT). VI -
    MMT telescope coalignment system
Authors: Beckers, J. M.; Poland, C.; Ulich, B. L.; Angel, J. R. P.;
   Low, F. J.; Wyatt, W.
Bibcode: 1982SPIE..332...42B
Altcode:
  The alignment of the Multiple Mirror Telescope (MMT) objectives so
  that the different star images coincide to within a fraction of
  the image size is conducted by the Telescope Coalignment System
  (TCS). The TCS is an autoguider which simultaneously operates on
  six telescopes, automatically coaligning them and tracking a field
  star. When such a star is not present in the small 4-arcmin field of
  view, the TCS coaligns the MMT on a nearby star and then tracks and
  maintains alignment of the six telescopes under computerized control,
  using separate flexure corrections for each.

Title: Performance of the Multiple Mirror Telescope (MMT). III Seeing
    experiments with the MMT
Authors: Beckers, J. M.; Williams, J. T.
Bibcode: 1982SPIE..332...16B
Altcode:
  Because of the Multiple Mirror Telescope's (MMT) location on an
  excellent site, the exposed construction of the telescope chamber, and
  the operator's ability to control the telescope's thermal environment,
  MMT image quality compares favorably with that of the best ground-based
  telescopes. On the nights of best seeing, image quality is determined
  by the telescope optics rather than the atmosphere, so that substantial
  improvements in image quality may be gained with further refinement of
  the MMT's multiple image integration system. MMT performance may become
  comparable to that of the Space Telescope, if its diameter/image ratio
  is taken as the figure of merit.

Title: Performance of the Multiple Mirror Telescope (MMT). I -
    MMT The first of the advanced technology telescopes
Authors: Beckers, J. M.; Ulich, B. L.; Williams, J. T.
Bibcode: 1982SPIE..332....2B
Altcode:
  The Multiple Mirror Telescope (MMT) incorporates many novel
  technological features, thereby serving as a test bed or prototype
  for future telescopes. Features of particular importance in this
  respect are the MMT altitude-over-azimuth mount, the corotating MMT
  building, lightweight honeycomb primary mirrors, multiple mirror
  optics configuration, active optical coalignment of the mirrors, and
  the ability to do interferometry using two or more of the total six
  180-cm f/2.7 Cassegrain telescopes comprising the system.

Title: First Results of Imaging of Supergiant Envelopes with the
    Differential Speckle Interferometer
Authors: Beckers, J. M.; Hege, E. K.; Murphy, H. P.; Burnette, F.
Bibcode: 1982BAAS...14R.918B
Altcode:
  No abstract at ADS

Title: The solar beacon, an experiment in solar astrometry.
Authors: Beckers, J. M.
Bibcode: 1982AcOpt..29..913B
Altcode:
  No abstract at ADS

Title: Differential speckle interferometry.
Authors: Beckers, J. M.
Bibcode: 1982AcOpt..29..361B
Altcode: 1982JMOp...29..361B
  No abstract at ADS

Title: Experiments with the Multiple Mirror Telescope.
Authors: Beckers, J. M.
Bibcode: 1982JOSA...72.1759B
Altcode: 1982OSAJ...72.1759B
  No abstract at ADS

Title: Progress report on the performance of the Multiple Mirror
    Telescope.
Authors: Beckers, J. M.; Ulich, B. L.
Bibcode: 1982ASSL...92...11B
Altcode: 1982IAUCo..67...11B; 1982ialo.coll...11B
  A discussion of the unusual features of the Multiple Mirror Telescope
  (MMT), located in Tucson, Arizona, which will probably be included
  in future advanced technology telescopes, is presented. The MMT uses
  alt-azimuth mounts, and has a special optical configuration that
  makes it possible to make the optics support structure exceedingly
  rigid. The six MMT telescopes are coaligned on field stars and the
  coalignment system relies on the extraordinary mechanical stability of
  the MMT to keep the telescopes coaligned for long periods when no field
  stars are available. Details of the image quality of the MMT and the
  use of the MMT both for IR Michelson interferometry and for optical
  speckle interferometry, as well as of the building housing the MMT,
  are provided.

Title: A rocket borne solar eclipse experiment to measure the
    temperature structure of the solar corona via Lyman-α line profile
    observations.
Authors: Argo, H. V.; Laros, J. G.; Feldman, W. C.; Beckers, J. M.;
   Bruner, E. C.
Bibcode: 1982PINSA..48...11A
Altcode:
  No abstract at ADS

Title: Impact linear polarization observed in a UV chromospheric
    line during a solar flare
Authors: Henoux, J. C.; Chambe, G.; Semel, M.; Woodgate, B.; Shine,
   R.; Beckers, J.
Bibcode: 1982AdSpR...2k.155H
Altcode: 1982AdSpR...2..155H
  Linear polarization was observed in the S I 1437Å line in bright
  flaring points during the soft X-ray emission. The degree of
  polarization is about 25% and is detected at a signal to noise ratio
  of 2.9. The polarized electric vector is directed towards disk center
  to within 3°. <P />This polarization could be due to collisional
  excitationm of S I by energetic electrons beamed in the vertical
  direction. We suggest that the heat flux in the region interconnecting
  the transition zone to the high chromosphere during the gradual phase
  of a flare could lead to an anisotropic excitation. Then the observed
  polarization would be due to vertical motions of the transition zone
  sweeping the preexisting chromosphere.

Title: Innovative research in the design and operation of large
telescopes for space: Aspects of giant telescopes in space
Authors: Angel, J. R. P.; Beckers, J. M.; Hoffmann, W. F.; McGraw,
   J. T.; Parks, R. E.; Stockman, H. S.; Woolf, N. J.
Bibcode: 1982irdo.rept.....A
Altcode:
  Eight areas of research on large space telescopes are identified and
  discussed. Telescope mirror technology in particular is addressed. Among
  the research topics described are: mirror substrates, physical optics,
  geometrical optics, optical surfaces, imagers, spacecraft guidance,
  and fiber optics.

Title: Experiments in differential speckle interferometry.
Authors: Beckers, J. M.; Hege, E. K.
Bibcode: 1982ASSL...92..199B
Altcode: 1982IAUCo..67..199B; 1982ialo.coll..199B
  A technique is proposed for achieving submillisecond of arc resolution
  on stellar objects by using the fact that the spectrum of the light
  emitted by stellar objects often changes across its surface either
  because of Doppler shifts, Zeeman splitting, abundance anomalies or
  changes in the stellar atmosphere. Differences between the positions
  of speckles in the stellar image when viewed in slightly different
  wavelengths can be obtained by using narrow band (0.5-1 A) filters. The
  difference in the position of the speckles can be determined with an
  accuracy much higher than the speckle itself using techniques which
  have already been developed for binary-star research. It is proposed
  that the technique of differential speckle interferometery be used to
  study stellar rotation, evolution of stellar systems, spectroscopic
  binaries, the mass-luminosity relation, and peculiar A stars.

Title: A Rocket Borne Solar Eclipse Experiment to measure the
    Temperature Structure of the Solar Corona via Lyman-α Line Profile
    Observations
Authors: Argo, Harold V.; Laros, John G.; Feldman, William C.; Beckers,
   Jacques M.; Bruner, Elmo C.
Bibcode: 1982tsef.conf...11A
Altcode:
  No abstract at ADS

Title: Dynamics of the solar photosphere.
Authors: Beckers, J. M.
Bibcode: 1981NASSP.450...11B
Altcode: 1981suas.nasa...11B
  Current knowledge of photospheric velocity fields is summarized. A
  model of the solar atmosphere is described along with the methods
  used in solar velocity field observations. The inferences drawn from
  integrated Sun observations, the velocity fields of the quiet Sun,
  sunspots, and other magnetic structures are discussed.

Title: Preliminary observations and results obtained with the
    ultraviolet spectrometer and polarimeter
Authors: Tandberg-Hanssen, E.; Cheng, C. C.; Athay, R. G.; Beckers,
   J. M.; Brandt, J. C.; Chapman, R. D.; Bruner, E. C.; Henze, W.; Hyder,
   C. L.; Gurman, J. B.
Bibcode: 1981ApJ...244L.127T
Altcode:
  New observation with the Ultraviolet Spectrometer and Polarimeter
  (UVSP) of a number of manifestations of solar activity obtained
  during the first three months of Solar Maximum Mission operations are
  presented. Attention is given to polarimetry in sunspots, oscillations
  above sunspots, density diagnostics of transition-zone plasmas in
  active regions, and the eruptive prominence - coronal transient link.

Title: The Solar Beacon, An Experiment in Solar Astometry
Authors: Beckers, J. M.
Bibcode: 1981BAAS...13..890B
Altcode:
  No abstract at ADS

Title: Multiple Mirror Telescope Observatory, Tucson, Arizona
    85721. Report.
Authors: Beckers, J. M.
Bibcode: 1981BAAS...13..269B
Altcode:
  No abstract at ADS

Title: Solar maximum mission experiment: Ultraviolet spectroscopy
    and polarimetry on the solar maximum mission
Authors: Tandberg-Hanssen, E.; Cheng, C. C.; Woodgate, B. E.; Brandt,
   J. C.; Chapman, R. D.; Kenney, P. J.; Michalitsianos, A. G.; Shine,
   R. A.; Athay, R. G.; Beckers, J. M.; Bruner, E. C.; Rehse, R. A.;
   Schoolman, S. A.; Gurman, J. B.; Hyder, C. L.; Henze, W.
Bibcode: 1981AdSpR...1m.275T
Altcode: 1981AdSpR...1..275T
  We describe the Ultraviolet Spectrometer and Polarimeter (UVSP) on the
  Solar Maximum Mission (SMM) spacecraft. The instrument, which operates
  in the wavelength range 1150 - 3600 Å, has a spatial resolution of 2-3
  arc sec and a spectral resolution of 0.02 Å FWHM in second order. A
  Gregorian telescope, focal length 1.8 m, feeds a 1 m Ebert-Fastie
  spectrometer. A polarimeter comprising rotating Mg F<SUB>2</SUB>
  waveplates can be inserted behind the spectrometer entrance slit and
  allows all four Stokes parameters to be determined. The observing
  modes include rasters, spectral scans, velocity measurements, and
  polarimetry. Finally, we present examples of initial observations made
  since launch.

Title: Seeing experiments with the MMT.
Authors: Beckers, J. M.
Bibcode: 1981BAAS...13..490B
Altcode:
  No abstract at ADS

Title: Thermography of the MMT.
Authors: Beckers, J. M.; Ulich, B. L.
Bibcode: 1981BAAS...13..488B
Altcode:
  No abstract at ADS

Title: The Multiple Mirror Telescope.
Authors: Beckers, J. M.; Ulich, B. L.; Shannon, R. R.; Carleton,
   N. P.; Geary, J. C.; Latham, D. W.; Roger, J.; Angel, P.; Hoffmann,
   W. F.; Low, F. J.; Weymann, R. J.; Woolf, N. J.
Bibcode: 1981tesc.book...63B
Altcode:
  The Multiple Mirror Telescope (MMT), located on top of Mount Hopkins
  (2600 m) in Arizona, consists of six main telescope systems, each of
  which is a classical Cassegrain with a 1.8 m diameter parabolic primary
  with focal ratio f/2.7, and a hyperbolic secondary producing a final
  f/31.6 for each of the individual telescopes. The most significant
  departures of the MMT from conventional optical telescope technology
  are (1) the use of light-weight 'egg-crate' mirrors, which reduced
  the telescope weight, (2) the use of an alt-azimuth mount, which
  simplifies the gravitational effects on the structure, (3) the use of
  a ball-bearing support rather than hydrostatic bearings, resulting in
  cost savings and less maintenance, (4) the use of spur gear drives
  rather than worm gears, and (5) the use of multiple coaligned light
  collectors rather than a single monolithic mirror. Early multiple
  objective telescopes are discussed, and the early history of the MMT
  project is given. The design and performance of the telescope are
  explained, and MMT instrumentation (spectrograph, optical design,
  detector, infrared photometer, SAO CCD camera) is given. Astronomical
  research with the telescope is discussed, along with plans for future
  multiple objective telescopes.

Title: Solar Maximum Mission experiment: ultraviolet spectroscopy
    and polarimetry on the Solar Maximum Mission.
Authors: Tandberg-Hanssen, E.; Woodgate, B. E.; Athay, R. G.; Beckers,
   J. M.; Brandt, J. C.; Bruner, E. C.; Chapman, R. D.; Cheng, C. -C.;
   Gurman, J. B.; Hyder, C. L.; Kenney, P. J.; Michalitsianos, A. G.;
   Rehse, R. A.; Schoolman, S. A.; Shine, R. A.; Henze, W.
Bibcode: 1981hea..conf..275T
Altcode:
  No abstract at ADS

Title: The photospheric vector magnetic field of a sunspot and its
    vertical gradient
Authors: Hagyard, M. J.; West, E. A.; Tandberg-Hanssen, E.; Smith,
   J. E.; Henze, W., Jr.; Beckers, J. M.; Bruner, E. C.; Hyder, C. L.;
   Gurman, J. B.; Shine, R. A.
Bibcode: 1981phss.conf..213H
Altcode:
  The results of direct comparisons of photospheric and transition
  region line-of-sight field observations of sunspots using the SMM UV
  spectrometer and polarimeter are reported. The analysis accompanying
  the data is concentrated on demonstrating that the sunspot concentrated
  magnetic field extends into the transition region. An observation
  of a sunspot on Oct. 23, 1980 at the S 18 E 03 location is used as
  an example. Maximum field strengths ranged from 2030-2240 gauss for
  large and small umbrae viewed and inclination of the field to the
  line-of-sight was determined for the photosphere and transition
  region. The distribution of the magnetic field over the sunspot
  and variation of the line-of-sight gradient are discussed, as are
  the magnitudes and gradients of the photospheric field across the
  penumbral-photospheric boundaries.

Title: Observations of dynamical phenomena in sunspots
Authors: Nye, A. H.; Cram, L. E.; Beckers, J. M.; Thomas, J. H.
Bibcode: 1981phss.conf..313N
Altcode:
  A preliminary report of the results of one observing run based on data
  from one spectral line, the photospheric magnetic line Fe 6303, is
  presented as part of a series of observations of dynamical phenomena
  in sunspots using photographic spectra with the SPO vacuum tower
  telescope and echelle spectrograph. The ejection of a magnetic feature
  from the outer edge of the penumbra was observed. The initial total
  field strength of the feature was about 1000 gauss, which appeared to
  decrease as the feature moved away from the sunspot. The proper motion
  was about 2 km/s, and the velocity field measured in the V profile
  showed a downflow of 400 m/s on the spot-ward side of the moving
  magnetic feature. Umbral oscillations at the photospheric level with a
  herringbone structure characteristic of horizontally propagating waves,
  suggesting some overtone mode of membrane oscillation in the umbra,
  were seen. The peak amplitude of the oscillation was about 200 m/s,
  and the mean power spectrum had several clear peaks.

Title: "Differential speckle interferometry", a new tool for double
    star research.
Authors: Beckers, J. M.
Bibcode: 1983LowOB...9..165B
Altcode: 1983IAUCo..62..165B; 1981LowOB...9..165B; 1983LowOB.167..165B
  Speckle interferometry is a powerful tool for close binary star
  research allowing angular resolutions as small as 20 milliarcsecond. A
  technique is proposed to resolve spectroscopic binaries with even
  smaller separations. It uses the fact that speckle images taken in one
  or the other of the Doppler shifted spectral lines give a different
  intensity weighting of the two components of the binary. The location
  of the speckles in the two speckle images is therefore different,
  the direction of the displacement being related to the position
  angle of the binary, the amount of the displacement being related
  to its separation. Since the location of speckles can be determined
  with a much higher precision than their diameter, this creates the
  possibility for submilliarcsecond observations. This paper describes
  an experiment being started now to use this so-called 'Differential
  Speckle Interferometry' technique for the study of binaries, stellar
  rotation, stellar chromospheres, Ap stars and other objects.

Title: Some Comments on the Limb Shift of Solar Lines - Part Three -
    Variation of Limb Shift with Solar Latitude across Plages and across
    Supergranules
Authors: Beckers, J. M.; Taylor, W. R.
Bibcode: 1980SoPh...68...41B
Altcode:
  We searched for a variation with heliographic latitude of the
  solar limb effect by comparing the relative wavelengths of weak and
  strong Fraunhofer lines. The blue shifts associated with the limb
  effect appear 9%±5% larger in the polar radius vector than in an
  equatorial radius vector at cos θ = 0.5. This should perhaps be
  interpreted as an increase with latitude of either solar convection
  or of convective overshoot. Recent observations of poleward meridional
  flows of 30m s<SUP>−1</SUP> should be corrected for this limb effect
  variation. This correction increases this flow velocity to ∼70 m
  s<SUP>−1</SUP>. A search for a similar variation in plages and in
  network boundaries had negative results, the variation being +1%±5%
  and -1%±6% respectively.

Title: SMM/UVSP Observations of Magnetic Fields in the Transition
    Region above Sunspots
Authors: Henze, W.; Beckers, J. M.; Gurman, J. B.; Hyder, C. L.;
   Schoolman, S. A.; Shine, R. A.; Tandberghanssen, E.; Woodgate, B. E.;
   Hagyard, M. J.
Bibcode: 1980BAAS...12R.896H
Altcode:
  No abstract at ADS

Title: Sunspot Observations with the Ultraviolet Spectrometer and
    Polarimeter Experiment on the Solar Maximum Mission
Authors: Gurman, J. B.; Woodgate, B. E.; Shine, R. A.; Brandt, J. C.;
   Chapman, R. D.; Michalitsianos, A. G.; Kenny, P. J.; Bruner, E. C.;
   Rehse, R.; Schoolman, S. A.; Cheng, C. C.; Tandberg-Hanssen, E. A.;
   Athay, G. R.; Beckers, J. M.; Henze, W.; Brown, Teledyne; Hyder, C. L.
Bibcode: 1980BAAS...12..535G
Altcode:
  No abstract at ADS

Title: Density Diagnostic of Solar Active Region and Flare Plasmas
    from Si IV/O IV Line Ratio as Observed from SMM
Authors: Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Brandt, J. C.;
   Chapman, R. D.; Kenny, P. J.; Michalitsianos, A. G.; Shine, R. A.;
   Woodgate, B. E.; Cheng, C. C.; Tandberg-Hanssen, E. A.; Athay, G. R.;
   Beckers, J. M.; Gurman, J.; Henze, W.; Brown, Teledyne; Hyder, C. L.
Bibcode: 1980BAAS...12R.539B
Altcode:
  No abstract at ADS

Title: Density diagnostic of solar active region and flare plasmas
    from Si IV/O IV line ratio as observed from SMM (Solar Maximum
    Mission).
Authors: Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Brandt, J. C.;
   Chapman, R. D.; Kenny, P. J.; Michalitsianos, A. G.; Shine, R. A.;
   Woodgate, B. E.; Cheng, C. -C.; Tandberg-Hanssen, E. A.; Athay, G. R.;
   Beckers, J. M.; Gurman, J. B.; Henze, W.; Hyder, C. L.
Bibcode: 1980BAAS...12..534B
Altcode:
  No abstract at ADS

Title: Solar Flare and Surge Image Sequences as Seen by the
    Ultraviolet Spectrometer and Polarimeter on SMM
Authors: Henze, W.; Brown, Teledyne; Brandt, J. C.; Chapman,
   R. D.; Kenny, P. J.; Michalitsianos, A. G.; Shine, R. A.; Woodgate,
   B. E.; Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Cheng, C. C.;
   Tandberg-Hanssen, E. A.; Athay, G. R.; Beckers, J. M.; Gurman, J.;
   Hyder, C. L.
Bibcode: 1980BAAS...12..532H
Altcode:
  No abstract at ADS

Title: The Ultraviolet Spectrometer and Polarimeter (UVSP) on the
    Solar Maximum Mission and Initial Results in Polarimetry
Authors: Tandberg-Hanssen, E.; Athay, R. G.; Bruner, E. C.; Beckers,
   J. M.; Brandt, J. C.; Chapman, R. D.; Cheng, C. C.; Gurman, J.;
   Henze, W.; Brown, Teledyne; Hyder, C. L.; Michalitsianos, A. G.;
   Shine, R. A.; Schoolman, S. A.; Woodgate, B. E.
Bibcode: 1980BAAS...12..534T
Altcode:
  No abstract at ADS

Title: The Dynamics of Solar Flares and Surges as Seen at the Solar
    Limb in the Transition Zone
Authors: Woodgate, B. E.; Brandt, J. C.; Chapman, R. D.; Kenny,
   P. J.; Michalitsianos, A. G.; Shine, R. A.; Bruner, E. C.; Rehse, R.;
   Schoolman, S. A.; Cheng, C. C.; Tandbert-Hanssen, E. A.; Athay, G. R.;
   Beckers, J. M.; Gurman, J.; Henze, W.; Brown, Teledyne; Hyder, C. L.
Bibcode: 1980BAAS...12Q.535W
Altcode:
  No abstract at ADS

Title: Active Region Morphology and Evolution Images from the
    Ultraviolet Spectrometer and Polarimeter
Authors: Shine, R. A.; Brandt, J. C.; Chapman, R. D.; Kenny, P. J.;
   Michalitsianos, A. G.; Woodgate, B. E.; Bruner, E. C.; Rehse, R.;
   Schoolman, S. A.; Cheng, C. C.; Tandberg-Hanssen, E. A.; Athay, G. R.;
   Beckers, J. M.; Gurman, J.; Henze, W.; Brown, Teledyne; Hyder, C. L.
Bibcode: 1980BAAS...12R.531S
Altcode:
  No abstract at ADS

Title: The ultraviolet spectrometer and polarimeter on the Solar
    Maximum Mission.
Authors: Woodgate, B. E.; Tandberg-Hanssen, E. A.; Bruner, E. C.;
   Beckers, J. M.; Brandt, J. C.; Henze, W.; Hyder, C. L.; Kalet, M. W.;
   Kenny, P. J.; Knox, E. D.; Michalitsianos, A. G.; Rehse, R.; Shine,
   R. A.; Tinsley, H. D.
Bibcode: 1980SoPh...65...73W
Altcode:
  The Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum
  Mission spacecraft is described, including the experiment objectives,
  system design, performance, and modes of operation. The instrument
  operates in the wavelength range 1150-3600 Å with better than 2 arc
  sec spatial resolution, raster range 256 × 256 arc sec<SUP>2</SUP>,
  and 20 mÅ spectral resolution in second order. Observations can be
  made with specific sets of 4 lines simultaneously, or with both sides
  of 2 lines simultaneously for velocity and polarization. A rotatable
  retarder can be inserted into the spectrometer beam for measurement
  of Zeeman splitting and linear polarization in the transition region
  and chromosphere.

Title: Some thoughts on the large european solar telescope
Authors: Beckers, J. M.
Bibcode: 1980fsoo.conf..279B
Altcode:
  No abstract at ADS

Title: Solar circulation measurements: consideration and plans
Authors: Beckers, J. M.; Brown, T. M.
Bibcode: 1980fsoo.conf..189B
Altcode:
  No abstract at ADS

Title: The MMT as it Exists Today
Authors: Beckers, J.; Williams, J.
Bibcode: 1980oits.conf..108B
Altcode:
  No abstract at ADS

Title: Examples of non-thermal motions as seen on the sun
Authors: Beckers, J. M.
Bibcode: 1980LNP...114...85B
Altcode: 1980IAUCo..51...85B; 1980sttu.coll...85B
  On the sun it is possible to identify many of the motions derived from
  stellar spectral analysis. A summary is given of the observed solar
  velocity phenomena. Many of these (e.g. meridional flow, giant cells,
  solar differential rotation, supergranulation) are of great interest
  in astrophysics especially for interior structure and chromospheric and
  coronal structuring but contribute virtually nothing to the velocities
  derived from a solar irradiance spectrum analysis. Others (granulation,
  very small scale motions and to a lesser extent, oscillations) do
  contribute substantially to the integrated sun velocity analysis. Some
  of the properties of these motion fields are described

Title: Spatial Variation of the Solar Limb Effect
Authors: Beckers, J. M.; Taylor, W. R.
Bibcode: 1979BAAS...11Q.658B
Altcode:
  No abstract at ADS

Title: The night sky conditions at the Sacramento Peak Observatory. II
    - Cloud cover, seeing, and precipitable water
Authors: Beckers, J. M.; Breedlove, W. O.; Devegvar, P. G. N.;
   Johansen, E. E.; Gilliam, L. B.; Mann, G. R.; Mauter, H. A.; Phillis,
   G. L.; Demastus, H. L.
Bibcode: 1979PASP...91..857B
Altcode:
  A summary is given of the following atmospheric conditions at the
  Sacramento Peak Observatory: cloud cover, seeing, and precipitable
  water. Sky brightness observations have been reported in an earlier
  paper.

Title: The night sky conditions at the Sacramento Peak
    Observatory. I. Sky brightness.
Authors: Schneeberger, T. J.; Worden, S. P.; Beckers, J. M.
Bibcode: 1979PASP...91..530S
Altcode:
  The night sky brightness at Sacramento Peak Observatory has been
  monitored over a period of nine months. The average zenith sky is 21.9
  ± 0.1 m<SUB>υ</SUB> arc sec<SUP>-2</SUP>. The night sky brightness
  shows fluctuations of up to 25% during this period. The long record
  of daytime sky-brightness observations shows a strong seasonal effect
  with brightest skies occurring in the early summer months. This seasonal
  effect is marginally present in the night sky brightness results. Light
  pollution from the closest urban areas is also detailed.

Title: Use of the solar limb effect to test photon decay and
    cosmological redshift theories
Authors: Beckers, Jacques M.; Cram, Lawrence E.
Bibcode: 1979Natur.280..255B
Altcode:
  No abstract at ADS

Title: An ultraviolet polarimeter for the Solar Maximum Mission
Authors: Calvert, J.; Griner, D.; Montenegro, J.; Nola, F.; Rutledge,
   F.; Tandberg-Hanssen, E.; Wyman, C. L.; Beckers, J. M.
Bibcode: 1979OptEn..18..287C
Altcode:
  The Solar Maximum Mission experiment contingency will include one
  instrument originally designed and built for OSO-8. The engineering
  model of the OSO-8 High Resolution Spectrometer has been rebuilt to make
  it lightworthy and to encompass several new functions, including solar
  ultraviolet polarimetry. The rebuilt package is designated as the High
  Resolution Ultraviolet Spectrometer/Polarimeter. The device that enables
  polarimetry is a dual channel rotating waveplate system. The waveplates
  are magnesium fluoride and will allow measurements to be made ranging
  from the Lyman alpha line to near visible ultraviolet. One wavelength
  channel will use the polarization characteristics of the spectrometer
  diffraction grating as the analyzer. The second channel has a built-in
  four-mirror polarizer. This paper describes the polarimeter design,
  operation, and calibration.

Title: Experiences with the Multiple Mirror Telescope.
Authors: Beckers, J. M.; Woolf, N. J.
Bibcode: 1979JOSA...69.1436B
Altcode: 1979OSAJ...69.1436B
  No abstract at ADS

Title: Some thoughts on the Large European Solar Telescope.
Authors: Beckers, J. M.
Bibcode: 1979MmArc.106..279B
Altcode:
  No abstract at ADS

Title: A broad look at solar physics adapted from the solar physics
    study of August 1975
Authors: Parker, E.; Timothy, A.; Beckers, J.; Hundhausen, A.; Kundu,
   M. R.; Leith, C. E.; Lin, R.; Linsky, J.; MacDonald, F. B.; Noyes, R.
Bibcode: 1979sswp.book....3P
Altcode: 1979sswp.book....3B
  The current status of our knowledge of the basic mechanisms involved
  in fundamental solar phenomena is reviewed. These include mechanisms
  responsible for heating the corona, the generation of the solar
  wind, the particle acceleration in flares, and the dissipation of
  magnetic energy in field reversal regions, known as current sheets. The
  discussion covers solar flares and high-energy phenomena, solar active
  regions; solar interior, convection, and activity; the structure and
  energetics of the quiet solar atmosphere; the structure of the corona;
  the solar composition; and solar terrestrial interactions. It also
  covers a program of solar research, including the special observational
  requirements for spectral and angular resolution, sensitivity, time
  resolution, and duration of the techniques employed.

Title: Solar circulation measurements: considerations and plans.
Authors: Beckers, J. M.; Brown, T. M.
Bibcode: 1979MmArc.106..189B
Altcode:
  No abstract at ADS

Title: Solar optical telescope (SOT).
Authors: Dunn, R. B.; Fisher, R.; Harvey, J.; Lemaire, P.; Milkey,
   R.; Smithson, R.; Beckers, J.; Mehltretter, J. P.; Zirin, H.
Bibcode: 1979MmArc.106..135D
Altcode:
  No abstract at ADS

Title: Solar maximum ultraviolet spectrometer and polarimeter
Authors: Tandberg-Hanssen, E.; Woodgate, B. E.; Brandt, J. C.;
   Chapman, R. D.; Hyder, C. L.; Michalitsianos, A. G.; Shine, R. A.;
   Athay, R. G.; Beckers, J. M.; Bruner, E. C.
Bibcode: 1979SPIE..184..264T
Altcode:
  The objectives of the UVSP experiment are to study solar ultraviolet
  radiations, particularly from flares and active regions, and to measure
  constituents in the terrestrial atmosphere by the extinction of sunlight
  at satellite dawn and dusk. The instrument is designed to observe the
  Sun at a variety of spectral and spatial resolutions in the range from
  1150 to 3600 A. A Gregorian telescope with effective focal length of
  1.8 m is used to feed a 1 m Ebert-Fastie spectrometer. A polarimeter
  containing rotatable magnesium fluoride waveplates is included behind
  the spectrometer entrance slit and will allow all four Stokes parameters
  to be determined. Velocities on the Sun can also be measured. The
  instrument is controlled by a computer which can interact with the data
  stream to modify the observing program. The observing modes, including
  rasters, spectral scans, velocity measurements, and polarimetry, are
  also described along with plans for mission operations, data handling,
  and analysis of the observations.

Title: Science opportunities with the SOT.
Authors: Dunn, R. B.; Fisher, R.; Harvey, J.; Lemaire, P.; Milkey,
   R.; Smithson, R.; Beckers, J.; Mehltretter, J. P.; Zirin, H.
Bibcode: 1979MmArc.106..245D
Altcode:
  No abstract at ADS

Title: Is there a solar polar vortex?
Authors: Beckers, J. M.
Bibcode: 1978ApJ...224L.143B
Altcode:
  Results are reported for a spectroscopic determination of Doppler
  velocities near the solar poles which was performed to confirm or refute
  the existence of the 'polar vortex' (an increase in angular rotation
  in the vicinity of the rotation poles) predicted by Gilman (1976). The
  measurements and the analysis are shown not to support the notion of a
  polar vortex, and it is concluded that the existence of such a vortex
  on the sun has to be definitely ruled out. The results are also found
  to provide little evidence for the existence of a supergranulation
  velocity pattern. It is noted that large-scale velocity patterns of
  an as yet unknown nature and with a scale of about 60,000 km were
  detected during this study.

Title: Spatial structure in lines in the 3398 3526 å region at the
extreme limb: Observation, identification and interpretation
Authors: Canfield, R. C.; Pasachoff, J. M.; Stencel, R. E.; Beckers,
   J. M.
Bibcode: 1978SoPh...58..263C
Altcode:
  We have obtained spectrograms of high spatial and spectral resolution
  of the extreme solar limb, using the vacuum tower telescope of
  Sacramento Peak Observatory. We have identified emission lines in
  the range 3398-3526 Å, and classified them according to intensity,
  spatial structure (intensity variation), and profile. Some lines show
  spatial intensity variation; others do not. We show that this effect
  is related to the abundance of the element responsible for the line
  and the mean lower-level excitation potential of interlocked lines. We
  explain the effect in terms of radiative interlocking with other lines,
  as well as the characteristic size of the volume contributing to the
  mean intensity.

Title: Some comments on the limb shift of solar lines. II: The effect
    of granular motions.
Authors: Beckers, J. M.; Nelson, G. D.
Bibcode: 1978SoPh...58..243B
Altcode:
  The well-known correlation between granulation intensity and velocity
  fluctuations causes a shift of the average line position called
  the `convective blue shift'. It is argued that this convective
  blue shift is most likely reponsible for the limb effect of solar
  Fraunhofer lines. To explain the center-to-limb variation of this
  limb effect it is essential that both horizontal and vertical motions
  in the granulation are considered. The effects of a variation in the
  granulation properties across the Sun on large scale velocity pattern
  observations are discussed. Abnormal granulation patterns observed
  inactive regions and at the boundaries of supergranules could be
  responsible for part or all of the `downflow' observed there.

Title: Some comments on the limb shift of solar lines. I: The effect
    of pressure shifts on iron lines in the solar atmosphere.
Authors: Beckers, J. M.; de Vegvar, P.
Bibcode: 1978SoPh...58....7B
Altcode:
  It has been suggested that pressure shifts are the sole cause for
  the systematic blue shift of solar fraunhofer lines (Hart, 1974). To
  check this we evaluate the significance of pressure shifts for Fe I
  lines. The observed wavelength shifts of a large number of lines are
  compared with the shifts calculated for the Lennard-Jones potential
  following Hindmarsh et al. (1967). The Lennard-Jones potential for the
  interatomic forces yield pressure shifts caused by neutral hydrogen,
  which explain only a small fraction of the observed blue shift. It is
  also shown that the quadratic Stark effect contributes insignificantly
  to the position of Fe I lines. Table I summarizes the average line
  shifts for iron lines at the center of the solar disk after correction
  for pressure shifts.

Title: Large Scale Flows Near the Solar Poles.
Authors: Beckers, J. M.
Bibcode: 1978BAAS...10..430B
Altcode:
  No abstract at ADS

Title: Some thoughts on the large european solar telescope
Authors: Beckers, J. M.
Bibcode: 1978fsoo.conf..279B
Altcode:
  No abstract at ADS

Title: Solar circulation measurements: consideration and plans
Authors: Beckers, J. M.; Brown, T. M.
Bibcode: 1978fsoo.conf..189B
Altcode:
  No abstract at ADS

Title: A Search for Solar Global Oscillations in the CA Ii K-Line
Authors: Beckers, Jacques M.; Ayres, Thomas R.
Bibcode: 1977ApJ...217L..69B
Altcode:
  No abstract at ADS

Title: The Solar Limb Effect.
Authors: Beckers, J. M.
Bibcode: 1977BAAS....9..616B
Altcode:
  No abstract at ADS

Title: Alfvén waves in the corona above sunspots.
Authors: Beckers, J. M.; Schneeberger, T. J.
Bibcode: 1977ApJ...215..356B
Altcode:
  From the line width in coronal arches above sunspots it is possible to
  estimate the amount of Alfven wave flux escaping from the spot into the
  solar corona. It is found to be less than 4 x 10 to the 7th ergs/sq
  cm/s in the corona just above the spot, which is less than 0.08%
  of the missing spot flux. If the Alfven-wave cooling mechanism for
  spots is to be valid, these waves have therefore to escape downward
  into the solar interior.

Title: Material motions in sunspot umbrae.
Authors: Beckers, J. M.
Bibcode: 1977ApJ...213..900B
Altcode:
  Material motions in the umbrae of a number of sunspots have been
  measured on an absolute scale by means of the g = 0 line of Ti I at 5713
  A. It is found that the rates of solar rotation as derived from sunspot
  proper motions and from spectra are identical to within 1% and that the
  vertical flow inside umbrae is small, being less than 25 m/s when the
  pressure shift is ignored. The so-called limb effect is absent in the
  umbrae leading to an upper limit to the convective energy flux of 0.5%
  of the radiative energy flux outside sunspots. The position of the line
  with respect to its laboratory wavelengths is shifted to the red by 613
  m/s, in agreement with the predicted gravitational redshift of 636 m/s.

Title: High resolution spectroscopy of the disk
    chromosphere. V. Space-time variations observed simultaneously in
    seven lines.
Authors: Cram, L. E.; Brown, D. R.; Beckers, J. M.
Bibcode: 1977A&A....57..211C
Altcode:
  Time sequence spectroscopic observations of the quiet solar
  chromosphere along a 200 Mm strip near the center of the disk were
  reduced to obtain 30 min of data. Oscillations appear in most of the
  observations in selected photospheric and chromospheric lines, but
  rarely in continuum observations. At a given point, the oscillations may
  be prominent or weak, they are never regular in time, and there is no
  unique relationship between the amplitudes at different heights. There
  are several examples of granules which apparently excite a burst of
  short period oscillations. By considering the line shift and intensity
  variations of all the lines, a working model is derived for the velocity
  field and related temperature variation.

Title: A search for auroral type motions in solar flares
Authors: Beckers, J. M.; Gilliam, L. B.; Stern, D. P.
Bibcode: 1977JGR....82.1915B
Altcode:
  The Sacramento Peak Observatory flare records of 37 double-ribbon
  solar flares observed from 1968 to 1972 were examined for evidence of
  systematic motion of the brightness along the flare ribbons. Because
  of analogies between aurorae and solar flares and because of
  well-established motion along aurorae (e.g., the so-called westward
  traveling surge) one might expect such motions. Brightness motions
  along the flare ribbon are common; we have, however, not been able to
  detect systematic motions in relation to the active region magnetic
  fields. The separation of the flare ribbons with time is well known and
  probably corresponds to the poleward motion of the aurorae during the
  auroral expansion phase. We found no counterpart in flares, however, of
  the equatorward motion of the aurorae during the auroral growth phase.

Title: Quiet Photosphere and Chromosphere
Authors: Beckers, J. M.
Bibcode: 1977ASSL...69...21B
Altcode: 1977igss.conf...21B
  Quiet Sun Atmospheric Models Oscillations Short Period Oscillations
  Limb Redshift Granulation Photospheric Network Chromospheric Network
  Supergranulation Mottle Rosette and Chain Chromospheric Grain Spicule
  Interspicular Region Macrospicule Chromospheric Bubbles or `Bulles'
  Emission Shell Flash Spectrum Spectroheliograph Birefringent Filter

Title: Fine Structure Variations in High-Spatial-Resolution Solar
    Spectra.
Authors: Pasachoff, J. M.; Canfield, R. C.; Stencel, R. E.; Beckers,
   J. M.
Bibcode: 1976BAAS....8..501P
Altcode:
  No abstract at ADS

Title: Magnetic fields in the solar atmosphere
Authors: Beckers, J. M.
Bibcode: 1976erpa.reptQ....B
Altcode:
  This paper describes the magnetic field configurations observed in
  the solar atmosphere including the corona and the solar wind. The
  techniques for observing solar magnetic fields are briefly reviewed. The
  significance of Alfven waves in transporting energy is stressed.

Title: Reliability of sunspots as tracers of solar surface rotation
Authors: Beckers, J. M.
Bibcode: 1976Natur.260..227B
Altcode:
  NEW methods of measuring solar rotation have produced
  significantly different rotation speeds to those derived from
  sunspots<SUP>1,2</SUP>. Spectroscopic measurements of Doppler
  displacements give a so-called plasma rotation velocity of 13.76°
  d<SUP>-1</SUP> (sidereal) at the solar equator<SUP>3</SUP> as
  against 14.38 ° d<SUP>-1</SUP> (sidereal) from sunspot proper
  motion velocity<SUP>4,5</SUP>. Other techniques of measuring solar
  rotation lead to differences in the differential rotation from a strong
  variation of the solar rotation with latitude for sunspots<SUP>4</SUP>
  and photospheric plasma<SUP>3</SUP> to hardly any variation at all for
  coronal holes<SUP>6</SUP>. Our understanding of these differences is
  very poor. It is therefore appropriate to obtain additional accurate
  solar rotation measurements with as many different techniques as
  possible and to check the validity of the assumption that the proper
  motion of tracers, like sunspots, correspond to the actual motion
  of matter on the solar surface. We report here the result of plasma
  rotation velocity measurements inside sunspot umbrae and their relation
  to the rotation velocities derived from spot proper motions. We find
  that plasmas inside and outside the spots rotate at similar rates,
  and conclude that sunspots make poor tracers.

Title: Solar Rotation and Gravitational Red Shift as Determined from
    Sunspot Spectra
Authors: Beckers, J. M.
Bibcode: 1976BAAS....8..308B
Altcode:
  No abstract at ADS

Title: Report on the solar physics - plasma physics workshop. held
    at Stanford University, 17 - 20 September 1974.
Authors: Sturrock, P. A.; Baum, P. J.; Beckers, J. M.; Newman, C. E.;
   Priest, E. R.; Rosenberg, H.; Smith, D. F.; Wentzel, D. G.
Bibcode: 1976SoPh...46..411S
Altcode:
  This report summarizes the proceedings of a meeting held on
  17-20 September 1974, at Stanford University. The purpose was to
  explore plasma physics problems which arise in the study of solar
  physics. Sessions were concerned with specific questions including
  the following: Is the solar plasma thermal or non-thermal? What
  spectroscopic data are required? What types of magnetic field structures
  exist? Do MHD instabilities occur? Do resistive or non-MHD instabilities
  occur? What mechanisms of particle acceleration have been proposed? What
  information do we have concerning shock waves? Very few questions were
  answered categorically but, for each question, there was discussion
  concerning the observational evidence, theoretical analyses, and
  existing or potential laboratory and numerical experiments.

Title: The flux of Alfvén waves in sunspots.
Authors: Beckers, J. M.
Bibcode: 1976ApJ...203..739B
Altcode:
  Spectrographic observations of a large sunspot are used to derive the
  flux of Alfven waves in the spot's photosphere under the assumption
  that the horizontal velocities observed in the photosphere of a sunspot
  are caused by Alfven waves. Profiles of the Ti I (5713.90 A) and Fe
  I (5691.50) absorption lines are analyzed to determine the amount
  of nonthermal motion in the spot, and it is concluded that the line
  widths are entirely consistent with the hypothesis of sunspot cooling
  by Alfven waves. The wave flux in the spot's photosphere is found to
  be equal to 20% to 50% of the missing sunspot energy flux, or two to
  three times the spot's flux of electromagnetic energy.

Title: High resolution spectral atlas of the solar irradiance from
    380 to 700 nanometers
Authors: Beckers, J. M.; Bridges, C. A.; Gilliam, L. B.
Bibcode: 1976hrsa.book.....B
Altcode:
  This report presents in graphical form the spectrum of the solar
  irradiance with high spectral resolution.

Title: A time evolution study of limb spicule spectra.
Authors: Krall, K. R.; Bessey, R. J.; Beckers, J. M.
Bibcode: 1976SoPh...46...93K
Altcode:
  Time sequences of simultaneous spectra of limb spicules, obtained
  using the Sacramento Peak Observatory's tower telescope and echelle
  spectrograph are analyzed. Intensity determinations of Hα and K, H,
  λ 8498 and λ 8542 of calcium are tabulated for three observing
  heights. Electron densities averaged over the entire visible
  lifetimes of spicules are ∼-6 × 10<SUP>10</SUP> cm<SUP>−3</SUP>
  at observing heights of 6000km, while maximum and minimum values were
  ∼-1.1 × 10<SUP>11</SUP> cm<SUP>−3</SUP> at 6000km and ∼- 2 ×
  10<SUP>10</SUP> cm<SUP>−3</SUP> at 10000km. Electron temperatures
  range between 12 000 K and 16 000 K. Profile halfwidths indicate
  turbulent velocities of 12 to 22 km s<SUP>−1</SUP>, and spectral
  tilts are interpreted as caused by differential velocity fields of ∼-3
  km s<SUP>−1</SUP> per 1000 km. No large scale spicule expansions or
  contractions are observed, although possible expulsions or accretions
  of material are observed. Spicules may be wider in the calcium K and
  H lines than in Hα.

Title: Observational evidence for unresolved motions in the solar
    atmosphere
Authors: Canfield, R. C.; Beckers, J. M.
Bibcode: 1976pmas.conf..291C
Altcode:
  No abstract at ADS

Title: Spatially resolved motions in stellar atmospheres
Authors: Beckers, J. M.; Canfield, R. C.
Bibcode: 1976pmas.conf..207B
Altcode:
  No abstract at ADS

Title: Magnetic fields in the solar atmosphere.
Authors: Beckers, J. M.
Bibcode: 1976pspe.proc...89B
Altcode: 1976pspe.conf...89B
  Observed properties of magnetic field in the solar atmosphere are
  reviewed. Among the aspects of photospheric magnetic fields which are
  considered are sunspots, plages and faculae, the motion of magnetic
  elements near sunspots, large scale magnetic field configurations,
  supergranule magnetic fields, and ephemeral regions. Methods of
  measuring solar magnetic fields are examined. Other topics include
  solar magnetic fields near the earth, the magnetic field and the mass
  and energy transport, and the extension of the solar magnetic fields
  upwards into the chromosphere and corona.

Title: Motions in the solar atmosphere
Authors: Beckers, J. M.; Canfield, R. C.
Bibcode: 1975STIN...7630135B
Altcode:
  The report presents two papers on observational evidence for large
  and small scale motions in the solar atmosphere.

Title: Observing the sun with a fully tunable Lyot-Öhman filter.
Authors: Beckers, J. M.; Dickson, L.; Joyce, R. S.
Bibcode: 1975ApOpt..14.2061B
Altcode:
  We describe the properties of the Zeiss universal birefringent filter
  and its optical and electronic interface with the Sacramento Peak
  Observatory's vacuum telescope. The instrument permits observations
  of solar intensities, velocities, and/or magnetic fields in rapid
  succession in any Fraunhofer line in the 410-700-nm wavelength region
  with high spectral (0.004-0.013 nm) and high spatial (about 1/3 sec
  of arc) resolution.

Title: The Line Response Function of Stellar Atmospheres and the
    Effective Depth of Line Formation
Authors: Beckers, J. M.; Milkey, R. W.
Bibcode: 1975SoPh...43..289B
Altcode:
  The response function defines the response of line profiles to a
  depth variation of such atmospheric parameters as velocity, magnetic
  field and turbulence. The properties of this function are derived and
  compared with the so-called contribution function.

Title: The Flux of Alfven Waves in Sunspots.
Authors: Beckers, J. M.
Bibcode: 1975BAAS....7Q.459B
Altcode:
  No abstract at ADS

Title: The compression of data resulting from photon counters.
Authors: Beckers, J. M.
Bibcode: 1975SSI.....1..153B
Altcode:
  A square-root transformation method is proposed for low-cost optimal
  compression of the counts resulting from random event detectors such
  as photon counters. As compared to the so-called floating point and
  logarithmic compression techniques proposed by Diamond et al. (1974),
  the square-root compression method permits almost doubling of the
  transmission rate for a given type of data from spacecraft with no
  significant loss of information.

Title: Is the Solar Filigree the Site of Strong Photospheric Magnetic
    Fields?
Authors: Beckers, J. M.
Bibcode: 1975BAAS....7..346B
Altcode:
  No abstract at ADS

Title: Cinematography of solar intensity, velocity, and magnetic
    fields.
Authors: Beckers, J. M.; Dickson, L.; Woodman, D.
Bibcode: 1975OptEn..14...64B
Altcode:
  Using a very narrow band (0.004-0.013 nm) Universal Birefringent Filter,
  rapidly turnable between 410 and 700 nm, and the vacuum telescope at
  the observatory, we have developed photographic and video techniques
  to observe solar magnetic and velocity fields utilizing the Zeeman and
  Doppler effects respectively. This is in addition to direct filtergrams
  which can also be obtained at any wavelength in this wavelength
  region. The video technique permits virtually real time display. Both
  techniques are used for time lapse cinematography of solar activity.

Title: A fully tunable Lyot-Ohman filter
Authors: Beckers, J. M.; Dickson, L.; Joyce, R. S.
Bibcode: 1975aifo.reptQ....B
Altcode:
  Properties of the Zeiss universal birefringent filter and its optical
  and electronic interface with the Sacramento Peak Observatory's vacuum
  telescope are described. The instrument permits observations of solar
  intensities, velocities and/or magnetic fields in rapid succession in
  any Fraunhofer line in the 410 to 700 nm wavelength region with high
  spectral (0.004 to 9.013 nm) and high spatial (approximately 1/3 arc
  second) resolution.

Title: A Comparison of Spicules in the Hα and He II (304 Å) Lines
Authors: Kjeldseth Moe, O.; Engvold, Olav Oddbjorn; Beckers, Jacques
   Maurice
Bibcode: 1975SoPh...40...65K
Altcode: 1975SoPh...40...65M
  On 1974 January 29 and 31, simultaneous satellite observations of
  spicule-like features in the 304-A L-alpha line of He(+) and ground
  observations of H-alpha spicules were obtained. It was then attempted to
  find a correlation between features of these two observations. Direct
  visual comparison failed to show a significant correspondence between
  the spicules in the He II and H-alpha spicules. Then the location and
  orientation of spicules in both images were measured and a correlation
  criterion was defined. Again no significant correspondence was found. It
  is concluded that the spicule-like structures in the He II (304) line
  are quite different from the H-alpha spicules. The possibility remains,
  though, that spicules are the same structures in both lines but that
  some spicules emit more strongly in He II (304) whereas others are
  better visible in H-alpha.

Title: A comparison of spicules in the Hα and HeII (304 Å) lines
Authors: Moe, Olav Kjeldseth; Engvold, Oddbjorn; Beckers, Jacques
   Maurice
Bibcode: 1975SoPh...40...65M
Altcode:
  No abstract at ADS

Title: A search for deuterium on the sun.
Authors: Beckers, J. M.
Bibcode: 1975ApJ...195L..43B
Altcode:
  The investigation reported is concerned with the determination of the
  D/H ratio on the sun, taking into account a study of the deuterium
  H-alpha line 1.785 A to the blue of the hydrogen H-alpha line. The
  upper limit obtained for the solar D/H ratio confirms current concepts
  regarding the creation and destruction of deuterium in the sun.

Title: The Maximum Polarization for Resonance Scattering
Authors: Beckers, J. M.
Bibcode: 1974SoPh...37..351B
Altcode:
  No abstract at ADS

Title: High Resolution Spectroscopy of the Disk Chromosphere. III:
    Upward Moving Disturbances as Observed in the Ca II K-Line Wings
Authors: Beckers, J. M.; Artzner, G.
Bibcode: 1974SoPh...37..309B
Altcode:
  We describe the properties of dark structures which are seen in the
  K-line wings and which seem to propagate inward into the K-line core,
  or upward in the solar atmosphere. These so-called dark whiskers
  appear to be related to the bright disturbances (bright whiskers)
  described by Liu (1974). Both may be related to the shocks that heat
  the chromosphere and corona.

Title: Properties of the Solar Filigree Structure
Authors: Dunn, R. B.; Zirker, J. B.; Beckers, J. M.
Bibcode: 1974IAUS...56...45D
Altcode:
  No abstract at ADS

Title: The Profile and Polarization of the Coronal Lα Line
Authors: Beckers, Jacques M.; Chipman, Eric
Bibcode: 1974SoPh...34..151B
Altcode:
  We calculate the profile and polarization of the Lα line in the solar
  corona. Coronal temperature variation, solar wind and other non-thermal
  motions have been taken into account. Because of the relatively low
  atomic weight of hydrogen the profile of the Lα line is a sensitive
  indicator of the coronal temperature. The line polarization contains
  relatively little information except for strong magnetic fields (&gt;
  70 G).

Title: Spatial and Spectral Structure of Chromospheric Lines
Authors: Pasachoff, J. M.; Harris, F. S.; Beckers, J. M.
Bibcode: 1974IAUS...56...31P
Altcode:
  No abstract at ADS

Title: Solar physics. Plasma physics workshop.
Authors: Baum, P. J.; Beckers, J. M.; Newman, C. E.; Priest, E. R.;
   Rosenberg, H.; Smith, D. F.; Sturrock, P. A.; Wentzel, D. G.
Bibcode: 1974sppp.book.....B
Altcode:
  No abstract at ADS

Title: The next decade in observational solar research.
Authors: Beckers, J. M.
Bibcode: 1974HiA.....3..149B
Altcode:
  The present status of observational solar research is examined,
  taking into account the spatial and spectral resolution which can
  be achieved with today's instrumentation, observations with the
  Harvard ATM telescope, and some experiments conducted with the
  aid of Skylab. Future objectives of observational solar research
  are considered, giving attention to the need for improved spatial
  and spectral resolution, the need for improved temporal resolution,
  and the need for novel observations and ideas. It is predicted that
  significant progress can be made in line profile calculations of two-
  and three-dimensional solar model atmospheres in which various velocity
  and magnetic field distributions are assumed.

Title: The Profile of the Coronal Lyman-α Line.
Authors: Beckers, J. M.; Chipman, E.
Bibcode: 1973BAAS....5..446B
Altcode:
  No abstract at ADS

Title: High Spatial and Temporal Resolution Observations of the
    Magnetic Field in a Sunspot.
Authors: Schultz, R. B.; White, O. R.; Beckers, J. M.
Bibcode: 1973BAAS....5..339S
Altcode:
  No abstract at ADS

Title: A Morphological Study of Solar Spicules
Authors: Lynch, D. K.; Beckers, J. M.; Dunn, R. B.
Bibcode: 1973SoPh...30...63L
Altcode:
  From improved spicule filtergrams obtained with the Sacramento Peak
  vacuum telescope we measured some spicule properties. The spicule
  diameter of 950 km was well resolved. A small decrease of diameter
  with height was observed confirming older observations. The expansion
  of the spicule was found to be at least an order of magnitude less
  than reported by Mouradian. Spicule counts are very sensitive to the
  threshold intensity of the observations. Counts, and their dependence
  on threshold intensity, height and wavelength are reported.

Title: Airborne Video Recorded Coronal Emission Line Profiles of λ
    5303 at the 10 July 1972 Total Solar Eclipse.*
Authors: Liebenberg, D. H.; Hoffman, M.; Sanders, W. M.; Beckers, J. M.
Bibcode: 1973BAAS....5T.275L
Altcode:
  No abstract at ADS

Title: The Sacramento Peak Observatory Universal Birefringent Filter
Authors: Beckers, J. M.
Bibcode: 1973BAAS....5R.269B
Altcode:
  No abstract at ADS

Title: The He<SUP>+</SUP> λ 4686 line in the low chromosphere
Authors: Worden, S. P.; Beckers, J. M.; Hirayama, T.
Bibcode: 1973SoPh...28...27W
Altcode:
  We report an unsuccessful search for the He<SUP>+</SUP> λ 4686 line
  in the low chromosphere. However, at the location of this line we
  detect a number of other chromospheric emission lines. This leads
  us to the conclusion that the He<SUP>+</SUP> λ 4686 identification
  made in the past, as well as other identifications, are probably in
  error. Additionally the region of the neutral helium λ4713 line is
  also studied.

Title: Fully tunable Lyot-Öhmann filter.
Authors: Beckers, J. M.
Bibcode: 1973JOSA...63Q.484B
Altcode:
  No abstract at ADS

Title: Solar activity (Activité solaire).
Authors: Jefferies, J. T.; Simon, P.; Beckers, J. M.; McLean, D. J.
Bibcode: 1973IAUTA..15...75J
Altcode:
  No abstract at ADS

Title: Oscillatory Motions in Sunspots
Authors: Beckers, J. M.; Schultz, R. B.
Bibcode: 1972SoPh...27...61B
Altcode:
  We observe vertical velocity oscillations in some sunspot umbrae
  with periods of about 180 s and peak to peak amplitudes up to 1 km
  s<SUP>−1</SUP>. These oscillations are not visible in either the line
  depth, line width or the continuum intensity. No correlation seems to
  exist between the occurence of these oscillations and the presence of
  the chromospheric umbral flashes (Solar Phys.7, 351, 1069). In the spot
  penumbra there is an indication of a long period oscillation, the period
  increasing from about 300 s in the inner penumbra to nearly 1000 s at
  the penumbra-photosphere boundary. An attempt has been made to interpret
  these oscillations in terms of gravity or acoustic waves, travelling
  along the magnetic field lines, taking into account the variation of
  scale height and magnetic field direction across the sunspot.

Title: High Resolution Spectroscopy of the Disk Chromosphere. II. Time
    Sequence Observations of Ca II H and K Emissions
Authors: Wilson, P. R.; Rees, D. E.; Beckers, J. M.; Brown, D. R.
Bibcode: 1972SoPh...25...86W
Altcode:
  Two independent sets of high resolution time series spectra of the
  CaII H and K emission obtained at the Solar Tower and at the Big
  Dome of the Sacramento Peak Observatory on September 11th, 1971 are
  reported. The evolutionary behaviour of the emission first reported
  by Wilson and Evans is confirmed but the detail of the evolution is
  found to be more complex. In one case, a doubly peaked feature showing
  some K<SUB>3</SUB> emission evolves into a single K<SUB>2</SUB> (red)
  peak with no K<SUB>3</SUB> emission. Coincidentally, a neighbouring
  doubly peaked feature evolves to a very strong blue peak. In an entirely
  independent sequence a doubly peaked feature evolves into a single red
  peak. The K<SUB>2</SUB> emission then fades completely although the
  continuum threads are still strong. Finally a strong K<SUB>2</SUB>
  blue peak appears. These developments are confirmed by intensity
  profiles obtained from the spectra.

Title: High Resolution Spectroscopy of the Disk
    Chromosphere. I. Observing Procedures
Authors: Beckers, J. M.; Mauter, H. A.; Mann, G. R.; Brown, D. R.
Bibcode: 1972SoPh...25...81B
Altcode:
  This paper describes the details of an extensive observing program which
  is aimed at the precise photometric observation of chromospheric fine
  structures in the λ3933, λ3968, λ8498, and λ8542 lines of ionized
  calcium, the λ6563 line of hydrogen, and the λ5890 and λ5896 lines
  of sodium.

Title: The Response of the Helium Triplet Radiation in Prominences
    to an Increase in Ultraviolet Flux resulting from Solar Flares
Authors: Beckers, J. M.
Bibcode: 1972BAAS....4T.377B
Altcode:
  No abstract at ADS

Title: Oscillatory Phenomena in Sunspots
Authors: Beckers, J. M.; Schultz, R. B.
Bibcode: 1972BAAS....4S.377B
Altcode:
  No abstract at ADS

Title: Solar Spicules
Authors: Beckers, Jacques M.
Bibcode: 1972ARA&A..10...73B
Altcode:
  No abstract at ADS

Title: The Polarization of Coronal Emission Lines (Papers presented
    at the Proceedings of the International Symposium on the 1970 Solar
    Eclipse, held in Seattle, U. S. A. , 18-21 June, 1971.)
Authors: Beckers, J. M.; Wagner, W. J.
Bibcode: 1971SoPh...21..439B
Altcode:
  By means of a photographic polarimeter, we attempted to measure both
  the amount and direction of linear polarization of all emission lines
  between 3400 and 9000 Å in the inner corona (1.034 ≤ r/r<SUB>0</SUB>
  ≤ 1.085). Only the green and red coronal lines have been analyzed
  in detail. Neither of these lines shows polarization exceeding the
  probable error of 1.0% for λ 5303 and 1.8% for λ 6374. None of the
  other 17 coronal lines observed during the 7 March, 1970 solar eclipse
  show any obvious (&gt;5%) polarization.

Title: The Measurement of Solar Magnetic Fields
Authors: Beckers, J. M.
Bibcode: 1971IAUS...43....3B
Altcode:
  No abstract at ADS

Title: Achromatic linear retarders.
Authors: Beckers, J. M.
Bibcode: 1971ApOpt..10..973B
Altcode:
  No abstract at ADS

Title: The use of colored photographic images in photographic
    subtraction.
Authors: Beckers, J. M.
Bibcode: 1971AASPB...4...13B
Altcode:
  No abstract at ADS

Title: Erratum: "The profiles of Fraunhofer lines in the presence
    of Zeeman splitting" [Sol. Phys., Vol. 9, p. 372 - 386 (1969)].
Authors: Stenflo, J. O.; Beckers, J. M.
Bibcode: 1970SoPh...15..507S
Altcode:
  No abstract at ADS

Title: The Interpretation of Velocity Filtergrams. III: Velocities
    Inside Solar Granules
Authors: Beckers, J. M.; Morrison, R. A.
Bibcode: 1970SoPh...14..280B
Altcode:
  From simultaneous filtergrams taken in opposite wings of the λ6569.2
  solar absorption line we derive the velocity profile of an average
  solar granule. We definitely established the existence of the horizontal
  outflow in a granule in addition to the vertical upflow at the granule
  center. The magnitude of this outflow is strongly dependent on the
  influence of instrumental and atmospheric smoothing and on the effective
  height in the solar atmosphere at which the velocity is measured. The
  maximum upflow (at the granule center) equals 0.4 km/sec, the maximum
  outflow (500 km from the granule center) equals 0.25 km/sec.

Title: The Flow Pattern within Solar Granules
Authors: Beckers, Jacques M.; Morrison, Roger A.
Bibcode: 1970BAAS....2R.182B
Altcode:
  No abstract at ADS

Title: Narrow band filters based on magnetooptical effects
Authors: Beckers, Jacques M.
Bibcode: 1970ApOpt...9..595B
Altcode:
  Available from <A
  href="http://www.opticsInfoBase.org/abstract.cfm?id=16268;">http://www.opticsInfoBase.org/abstract.cfm?id=16268;</A>

Title: A photographic polarimeter for solar observations.
Authors: Beckers, J. M.; Wagner, W. J.
Bibcode: 1970ApOpt...9.1933B
Altcode:
  No abstract at ADS

Title: The Profiles of Fraunhofer Lines in the Presence of Zeeman
Splitting. II: Zeeman Multiplets for Dipole and Quadrupole Radiation
Authors: Beckers, J. M.
Bibcode: 1969SoPh...10..262B
Altcode:
  The radiative transfer equations (LTE) in the four Stokes parameters
  are derived for the general case of a Zeeman multiplet for both electric
  and magnetic dipole as well as for electric quadrupole radiation.

Title: The Intensity, Velocity and Magnetic Structure of a Sunspot
Region. IV: Properties of a Unipolar Sunspot
Authors: Beckers, J. M.; Schröter, E. H.
Bibcode: 1969SoPh...10..384B
Altcode:
  From an investigation of spectra in a magnetically sensitive (λ 6173,
  g = 2.5) and insensitive line (λ 5576, g = 0), we derived the following
  properties for a symmetrical sunspot: The magnetic field strength varies
  with the distance ρ(ρ ⩽ 1) from the sunspot center like H(ρ) = H(0)
  (1 + ρ<SUP>2</SUP>)<SUP>-1</SUP>

Title: The Profiles of Fraunhofer Lines in the Presence of Zeeman
Splitting. I: The Zeeman Triplet
Authors: Beckers, J. M.
Bibcode: 1969SoPh....9..372B
Altcode:
  For the case of pure absorption lines (LTE) a method is described
  which enables the general computation of Zeeman-split line
  profiles. The magnetic field vector, the Doppler shift and the line
  absorption coefficient is permitted to vary arbitrarily with optical
  depth. Elliptical birefringence (e.g., Faraday rotation) of the solar
  atmosphere is taken into account. Some numerical examples are given
  and some interesting behaviors of the line profiles are discussed.

Title: The Interpretation of Velocity Filtergrams. II: The Velocity
    and Intensity Field of the Central Solar Disk
Authors: Beckers, J. M.; Parnell, R. L.
Bibcode: 1969SoPh....9...39B
Altcode:
  From simultaneous filtergrams obtained in the blue and red wings of a
  Fraunhofer line we analyzed the velocity and intensity field at the
  center of the solar disk. Results are as follows: Cross correlation
  between velocity and intensity is 0.6. It increases somewhat when long
  wavelengths (&gt;5000 km) are eliminated.

Title: The Interpretation of Velocity Filtergrams. I: The Effective
    Depth of Line Formation
Authors: Parnell, R. L.; Beckers, J. M.
Bibcode: 1969SoPh....9...35P
Altcode:
  The paper describes a numerical experiment in which the effect of
  an assumed velocity distribution in the solar atmosphere on the
  intensity difference between a blue- and a red-wing filter-gram is
  derived. This results in the effective optical depth at which the
  velocity is measured. It is shown that this τ<SUB>eff</SUB> strongly
  depends on the assumed velocity distribution.

Title: Chromospheric Inhomogeneities in Sunspot Umbrae
Authors: Beckers, Jacques M.; Tallant, Paul E.
Bibcode: 1969BAAS....1R.272B
Altcode:
  No abstract at ADS

Title: Chromospheric Inhomogeneities in Sunspot Umbrae
Authors: Beckers, Jacques M.; Tallant, Paul E.
Bibcode: 1969SoPh....7..351B
Altcode:
  The properties of rapidly changing inhomogeneities visible in the H
  and K lines above sunspot umbrae are described. We find as properties
  for these `Umbral Flashes': A lifetime of 50 sec. The light curve is
  asymmetrical, the increase is faster than the decrease in brightness.

Title: Analysis of Velocity Filtergrams
Authors: Parnell, R.; Beckers, J. M.
Bibcode: 1969BAAS....1Q.289P
Altcode:
  No abstract at ADS

Title: The Intensity, Velocity and Magnetic Structure of a Sunspot
Region. III: On the Origin of the Apparent π Component in Sunspot
    Umbrae
Authors: Beckers, J. M.; Schröter, E. H.
Bibcode: 1969SoPh....7...22B
Altcode:
  No abstract at ADS

Title: Solar Magnetic-Field Measurements using Babinet Compensators
Authors: Beckers, J. M.; Stenflo, J. O.
Bibcode: 1969SoPh....6..480B
Altcode:
  No abstract at ADS

Title: The microstructure of sunspots
Authors: Beckers, J. M.
Bibcode: 1969pia..conf..139B
Altcode:
  No abstract at ADS

Title: The microstructure of sunspots.
Authors: Beckers, J. M.
Bibcode: 1969misu.book.....B
Altcode:
  No abstract at ADS

Title: Photospheric Brightness Differences Associated with the
    Solar Supergranulation
Authors: Beckers, Jacques M.
Bibcode: 1968SoPh....5..309B
Altcode:
  The large scale (&gt; 5000 km) intensity structure of the photosphere
  has been examined. The power per frequency unit indicates a continuous
  increase towards smaller spatial frequency. No excess power exists at
  wavelengths near the size of the supergranulation (30000 km) or at any
  other wavelength between 5000 and 100000 km. However, direct measurement
  of the intensity distribution in 1652 supergranulation cells shows a
  very small increase of the intensity towards the cell boundary. The
  amount of this increase is larger near the solar limb. It is probably
  due to a weak continuum emission associated with the chromospheric
  network. Any temperature difference arising from the supergranulation
  convection is obscured by this emission and is probably less than 1 K.

Title: Spectral Observations of Spicules at Two Heights in the
    Solar Chromosphere
Authors: Pasachoff, Jay M.; Noyes, Robert W.; Beckers, Jacques M.
Bibcode: 1968SoPh....5..131P
Altcode:
  An observational program at the Sacramento Peak Observatory in
  1965 provided high-dispersion spectra of the solar chromosphere in
  several spectral regions simultaneously. These regions included
  various combinations of the spectral lines Hα, Hβ and Hɛ, the
  D<SUB>3</SUB>-line of HeI, the infrared triplet of OI, and the H-
  and K-lines and the infrared triplet of CaII. With the use of an image
  slicer the observations were made simultaneously at two heights in the
  solar chromosphere separated by several thousand kilometers. From these
  data we draw the following conclusions: Emission of different lines
  arises in the same chromospheric features. The intensity ratio of lines
  of different elements varies significantly from spicule to spicule. For
  the H- and K-lines of ionized calcium, this ratio remains constant,
  independent of wavelength throughout the line, overall intensity,
  and height in the chromosphere. Two rare-earth lines in the wing of
  the H-line show no spicular structure at all.

Title: Principles of operation of solar magnetographs
Authors: Beckers, J. M.
Bibcode: 1968SoPh....5...15B
Altcode:
  The principles of operation of photoelectric solar magnetographs
  are described in terms of the Poincaré sphere. The performance of
  photographic methods for measuring solar magnetic fields is compared
  with that of photoelectric magnetographs.

Title: The Intensity, Velocity and Magnetic Structure of a Sunspot
Region. II: Some Properties of Umbral Dots
Authors: Beckers, J. M.; Schröter, E. H.
Bibcode: 1968SoPh....4..303B
Altcode:
  A time sequence of high-resolution sunspot photographs, exposed
  almost simultaneously in two continuum wavelengths (4680 Å and 6400
  Å), was used to study some properties of umbral fine structures
  (`umbral dots'). The lifetime of the umbral dots is found to be 1500
  sec. Photometry of some bright dots leads to an observed intensity
  excess of 0.129 I<SUB>phot</SUB> and 0.134 I<SUB>phot</SUB> in the
  blue and red respectively. The observed mean diameter of the dots is
  found to be 420 km. These values still include the action of image
  blurring. From the color index the true intensity and diameter of the
  dots are estimated. It appears that the umbral dots are in reality
  of photospheric brightness having true diameters of 150-200 km. The
  spatial distribution of the dots in sunspot umbrae is discussed. Some
  peculiarities in recent sunspot magnetic-field observations may be
  explained by magnetic inhomogeneities associated with umbral dots.

Title: The Intensity, Velocity and Magnetic Structure of a Sunspot
Region. I: Observational Technique; Properties of Magnetic Knots
Authors: Beckers, J. M.; Schröter, E. H.
Bibcode: 1968SoPh....4..142B
Altcode:
  The observational set-up for a detailed study of the velocity,
  intensity and magnetic-field fine structure in and around a sunspot is
  described. On highly resolved spectra we detected in the vicinity of a
  sunspot a large number of points with strong magnetic fields (magnetic
  knots). The magnetic field in these knots causes a striking decrease of
  the line depth (or a `line gap' after SHEELEY, 1967). The properties
  of the magnetic knots are: (1) magnetic fields up to 1400 gauss; (2)
  diameter ≈ 1100 km; (3) coincidence with dark intergranular spaces;
  (4) generally downward material motion; (5) lifetime&gt;30min; (6)
  estimated total number around an unipolar spot ⩾ 2000; (7) combined
  magnetic flux comparable to the sunspot flux; (8) coincidence with
  Ca<SUP>+</SUP> plages.

Title: On the Relation between the Photospheric Intensity, Velocity
    and Magnetic Fields
Authors: Beckers, J. M.; Schröter, E. H.
Bibcode: 1968SoPh....4..165B
Altcode:
  No abstract at ADS

Title: Solar Spicules (Invited Review Paper)
Authors: Beckers, J. M.
Bibcode: 1968SoPh....3..367B
Altcode:
  The author of a review article is undoubtedly the one who benefits
  most from it. Only by reviewing an entire subject does it become
  clear how much is known of it and in what areas more information
  is desired. In the past 10 years, spicules have probably been the
  best studied fine structures on the sun. A substantial amount of
  observational information on spicules is available as seen in Section
  3. Some of the most important questions that remain to be answered in
  greater detail than available now are, in my opinion, the following:Do
  spicules indeed diffuse after they reach their maximum growth and
  brightness? If so, is this an expansion of the spicule magnetic field,
  a change of the properties of the gases surrounding the spicule, or
  an actual diffusion of spicular matter across the spicular magnetic
  fields? <P />Is the group behaviour of spicules as that described by
  Lippincott (1957)? If true, it would imply that the spicule mechanism
  extends over a large area of the sun (100000 km), which conflicts
  with the spicule theories as given in Section 4. <P />Is the `tilt'
  of spicule-emission lines real? If so, is it caused by spicule rotation
  and how does it differ between the various spicule-emission lines? <P
  />Is the spicule diameter different in the different spicule-emission
  lines? <P />Is it possible to measure the spicular magnetic field
  How large is it? <P />Do the physical conditions vary from spicule to
  spicule? How do they vary with height and time within one spicule? For
  this, one needs simultaneous spectra of spicules in many lines which
  have a different temperature behaviour. <P />Is it true that both the
  bright and dark elongated fine mottles seen in disk spectroheliograms
  are spicules? This requires renewed study of the solar disk. <P />After
  a definite identification of spicules with disk structure is made, what
  can one learn about spicule properties from the disk study? One can,
  for example, try to find a direct link with the solar granulation. <P
  />Are there spicules in active regions of the sun? How do they differ
  from spicules in quiescent regions? <P />Are chromospheric grains
  perhaps spicules which do not grow upwards because of a lack of
  magnetic fields? Are they perhaps related to granules? <P />What are
  the implications of a breakdown of the `statistically steady-state'
  assumption in the spicule-intensity calculations?The answers to many of
  these questions are of great importance in the precise understanding of
  a spicule, and in the derivation of a magnetohydrodynamic model for it.

Title: High-Resolution Measurements of Photosphere and Sun-Spot
    Velocity and Magnetic Fields using a Narrow-Band Birefringent Filter
Authors: Beckers, J. M.
Bibcode: 1968SoPh....3..258B
Altcode:
  Modifications to a Zeiss 1/4 Å filter are described which allow high
  spatial resolution observations of the line-of-sight velocities and
  magnetic fields in the photosphere and in sunspots. First results show:
  (1) the granular velocity field to be very strong; differences in
  upward motions in the granules and downward motions in between are
  as much as 6 km/sec; (2) the Evershed effect in sunspots to originate
  primarily in the dark regions between bright penumbral filaments.

Title: Magnetfeld und Materieströmungen in symmetrischen
    Einzelflecken
Authors: Beckers, J. M.; Schröter, E. H.
Bibcode: 1968MitAG..25..197B
Altcode:
  No abstract at ADS

Title: The Intensity, Velocity and Magnetic Structure in and around
    a Sunspot
Authors: Beckers, J. M.; Schröter, E. H.
Bibcode: 1968IAUS...35..178B
Altcode:
  No abstract at ADS

Title: Cinematography of Solar Oscillations.
Authors: Beckers, J. M.
Bibcode: 1968AJS....73Q.166B
Altcode:
  A narrow- band Lyot filter (0.25 A) can be used to study velocity
  and magnetic fields on the sun (Beckers, J. M., Solar Phys. 3,
  258,1968). Using this technique I obtained simultaneous motion pictures
  of the velocity field in the photospheric 6439 A line of Ca and in
  the chromospheric calcium K line. These motion pictures clearly show
  the 300-sec photospheric and the faster chromospheric oscillations
  in both quiescent and active regions on the sun. The reduction of
  these observations concentrates on: (a) the relation between the
  oscillations and the solar granulation and supergranulation, (b) the
  horizontal propagation of the oscillations (if any), (c) the behavior
  of the waves near and in sunspots, and (d) the relation of the waves
  and solar flares.

Title: Some Comments on the Paper, Ein neuer Magnetograph etc. by
    G. Brückner
Authors: Beckers, J. M.
Bibcode: 1968ZA.....68..406B
Altcode:
  No abstract at ADS

Title: Observational Studies of the Solar Intensity Profile in the
    Far Infrared and Millimeter Regions
Authors: Noyes, R. W.; Beckers, J. M.; Low, F. J.
Bibcode: 1968SoPh....3...36N
Altcode:
  Observations of the intensity distribution near the solar limb at 2.43
  and 22.5 μ, show the absence of limb brightening to within 1 or 2 arc
  sec of the limb. Observations at 1.2 mm indicate limb brightening at
  this wavelength. These results are compared with the Utrecht Reference
  Photosphere and with existing data on the solar flux in the millimeter
  range, and suggest that the temperature minimum is broad and extends
  above τ<SUB>5000</SUB> = 2 × 10<SUP>−3</SUP>. A sharp rise of
  temperature is required above τ<SUB>5000</SUB> = 10<SUP>−5</SUP>.

Title: Center-to-limb variations of the solar continuum in the far
    infrared and millimeter wavelength regions
Authors: Noyes, R. W.; Beckers, J. M.; Low, F. J.; Davidson, A. W.
Bibcode: 1966AJ.....71..866N
Altcode:
  No abstract at ADS

Title: A photoelectric focus and seeing monitor for solar telescopes
Authors: Beckers, J. M.
Bibcode: 1966ApOpt...5..301B
Altcode:
  Available from <A
  href="http://www.opticsInfoBase.org/abstract.cfm?id=14096;">http://www.opticsInfoBase.org/abstract.cfm?id=14096;</A>

Title: On the Relation Between Solar Granules and Spicules.
Authors: Beckers, J. M.
Bibcode: 1964ApJ...140.1339B
Altcode:
  No abstract at ADS

Title: A Study of the Fine Structures in the Solar Chromosphere
Authors: Beckers, J. M.
Bibcode: 1964PhDT........83B
Altcode:
  The study of high-resolution solar disk spectroheliograms, or
  filtergrams, gives one an insight into the horizontal distribution
  of chromospheric fine structures which is hard to obtain from limb
  observations. The main part of this paper is concerned with such
  a study in the light of the Hydrogen Hα line (6562.8A) and of the
  Calcium K line (3933.7A). <P />Section 2 gives a description of the
  instrumentation used to secure the observations as well as some notes
  on observational techniques and experiences. It especially gives in
  detail some of the properties of the Sydney 1/8 A Hα birefringent
  filter. <P />Section 3 gives a description of the high-resolution Hα
  filtergrams obtained with this instrument and compares this description
  with those given by other authors. Details are given especially on (a)
  the morphology of the elongated fine mottles, which are the components
  of coarse mottles, (b) the spatial autocorrelation function and power
  spectrum for Hα +/- 0.5A filtergrams, and (c) the sytematic inflow
  of chromospheric matter into a sunspot (Evershed effect). <P />In
  Section 4 the elongated fine mottles are studied in more detail. The
  resulting properties are compared with those for spicules as studied
  on the limb. The following properties are found for fine mottling:
  (a) The width is 1.2 sec of arc, and the average length is 4.1 sec of
  arc. (b) The average orientation in space is vertical to the solar
  surface. The average angle to the vertical is 21O. (c) The average
  lifetime is 15 minutes. (d) The mottles are at first most visible at
  Hα - 0.5A, later at Hα + 0.5A, indicating a rising and falling. (e)
  The total number on the sun is 4 x 10^5, (f) Within the coarse mottle,
  the birth rate is equal to that of the solar granulation. All these
  properties agree with those for spicules, as far as known, except
  for the one under (d). There can be little doubt however that the
  elongated fine mottles are spicules. <P />Section 5 describes an
  attempt to measure the spectrum of such a spicule on the disk. Disk
  observations have the advantage of giving the source function and
  optical depth separately. Typical values for the optical depth and
  Doppler width are 1.5 and 0.5A while the source function is always
  lower than the intensity at the Hα - line center. <P />In Section
  6, I computed the hydrogen spectrum of spicules under non-local
  thermodynamic equilibrium conditions for the Lyman α, β and γ
  lines, the Balmer α and β lines and the Paschen α line. At electron
  temperatures between 7500OK and 30,000OK, the Balmer-line emissions
  for limb spicules are nearly independent of electron temperature. The
  intensity observations give therefore a direct determination of
  the electron density. The Lyman-line intensities of the solar disk
  indicate the spicule temperature to be less than 9000OK. <P />Section
  7 describes the appearance of K spectroheliograms. Spicules in K,
  as in Hα, are dark when seen on the solar disk. The Hα3 flocculi,
  the Hα1 grains, and the Hα3 vortex are recognized on these calcium
  images. <P />In Section 8, attention is drawn to the equality in birth
  rates for granules and spicules within the K flocculi, which indicates
  a physical relationship. Table 23 and Figure 47 summarize the terms
  used by the author in describing the chromospheric structures.

Title: Inhomogeneities in the Evershed flow
Authors: Beckers, J. M.
Bibcode: 1964susp.conf..186B
Altcode:
  No abstract at ADS

Title: A study of the fine structure in the solar chromosphere
Authors: Beckers, Jacques Maurice
Bibcode: 1964PhDT.......100B
Altcode:
  No abstract at ADS

Title: Study of the Undisturbed Chromosphere from Ha-DISK Filtergrams,
    with Particular Reference to the Indentification of Spicules.
Authors: Beckers, Jacques M.
Bibcode: 1963ApJ...138..648B
Altcode:
  High-resolution Ha filtergrams, made with a -81-angstrom birefringent
  filter, are described. A detailed study is made of the dark, fine
  mottles which are visible in the line wings. At low solar latitudes
  these dark, fine mottles have the following properties: (a) They are
  frequently elongated; the average length is 4'S, and the width lies
  between 0"7 and 1'S. (b) The average lifetime is 15.5 minutes. During
  the first half of their lifetime, however, they are best visible only
  in the violent Ha wing and during the second hall in the red wing. (c)
  From orientations near the solar limb they are shown to be predominantly
  vertical to the solar surface. (d) The total number of these mottles
  on the sun is found to be 4 X 1 . (e) From the spectrum, the Doppler
  width is found as 0.50 A, the optical depth is of the order of 5, and
  the source function is about 3 X 1013 erg . Mi these properties appear
  to agree with those expected of spicules in projection on the solar
  disk. There is little doubt that the mottles actually are spicules.

Title: Appearance of Spicules on the Solar Disk.
Authors: Beckers, Jacques M.
Bibcode: 1963AJ.....68R.273B
Altcode:
  The study of the dark fine structures visible on high resolutioi~ IIoL
  spectroheliograms obtained with the Sydney 1/8 A birefringent filter led
  to the following properties: (a) They are often elongated, the average
  length is 4'S compared with a width somewhere between 0.7 and 1'.'8. (b)
  Lifetime averages 15.5 min. (c) They are first visible mainly in the
  violet H~ wing, later in the red wing. (d) Near the solar limb the
  direction of elongation is predomii~antly radial, indicating them to
  be mostly vertical to the solar surface. (e) The total number on the
  sun is found to be 3.5 X 10~. (f) The contrast is greatest 0.5 A from
  the H~-line center. From the variation of the contrast with wavelength
  the source function, optical depth and Doppler width are found to be,
  respectively, 3 X 10'~ erg sr~1 cm-3 sec-', 4 and 0.50 A. All these
  properties correspoi~d with those known for the spicules as observed
  outside the solar limb. From this their identity is concluded.

Title: Motions in the Chromosphere near Sunspots
Authors: Beckers, J. M.
Bibcode: 1962AuJPh..15..327B
Altcode:
  No abstract at ADS

Title: A search for white light flares
Authors: Beckers, J. M.
Bibcode: 1962Obs....82...66B
Altcode:
  No abstract at ADS

Title: The variation of the wings of the calcium K line across the
    solar disk
Authors: Beckers, J. M.
Bibcode: 1962BAN....16..133B
Altcode:
  No abstract at ADS

Title: Temperature variation on the Sun with heliographic latitude
Authors: Beckers, J. M.
Bibcode: 1960BAN....15...85B
Altcode:
  No abstract at ADS

