Author name code: dejager
ADS astronomy entries on 2022-09-14
=author:"De Jager, Cornelis" OR =author:"De Jager, C." 
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Title: Solar magnetic variability and climate
Authors: de Jager, Cornelis; Duhau, Silvia; Nieuwenhuizen, Adrianus
Bibcode: 2020smvc.book.....D
Altcode:
  When Kees de Jager returned to his birth ground Texel, he was asked
  by the director of Royal Institute for Sea Research, Prof. Dr. J. de
  Leeuw, to investigate the relationship between solar activity and
  climate. This research, done over a period of 15 years, generated
  about 10 papers with remarkable new insights. In 2019 Kees decided to
  compile the papers into a scientific book. This book covers: <P />The
  equatorial and poloidal magnetic fields and their relation to the
  Earth's NH temperature. <P />The notions phase diagram of the solar
  dynamo, Transition Point and Grand Episode. <P />The granular scale
  magnetic fields or 'bright spots'. <P />Telescopes for large-field
  high-resolution imaging of the sun. <P />The expectations for future
  solar activity derived from the decomposition of the solar dynamo into 8
  'modes'. This leads to prediction of the sunspot maxima till 2130. <P
  />The statistical start of the modern heating and solar variability as
  part of the modern heating curve. <P />The non-linear time difference
  between the solar magnetic variations and terrestrial warming.

Title: Pulsations, eruptions, and evolution of four yellow hypergiants
Authors: van Genderen, A. M.; Lobel, A.; Nieuwenhuijzen, H.; Henry,
   G. W.; de Jager, C.; Blown, E.; Di Scala, G.; van Ballegoij, E. J.
Bibcode: 2019A&A...631A..48V
Altcode: 2019arXiv191002460V
  <BR /> Aims: We aim to explore the variable photometric and stellar
  properties of four yellow hypergiants (YHGs), HR 8752, HR 5171A, ρ Cas,
  and HD 179821, and their pulsations of hundreds of days, and long-term
  variations (LTVs) of years. We also aim to explore light and colour
  curves for characteristics betraying evolutionary loops and eruptive
  episodes and to investigate trends of quasi-periods and the possible
  need for distance revisions. <BR /> Methods: We tackled multi-colour
  and visual photometric data sets, looked for photometric indications
  betraying eruptions or enhanced mass-loss episodes, calculated stellar
  properties mainly using a previously published temperature calibration,
  and investigated the nature of LTVs and their influence on quasi-periods
  and stellar properties. <BR /> Results: Based on driven one-zone
  stellar oscillation models, the pulsations can be characterised as
  "weakly chaotic". The BV photometry revealed a high-opacity layer in
  the atmospheres. When the temperature rises the mass loss increases
  as well, consequently, as the density of the high-opacity layer. As a
  result, the absorption in B and V grow. The absorption in B, presumably
  of the order of one to a few 0<SUB>.</SUB><SUP>m</SUP> 1, is always
  higher than in V. This difference renders redder and variable (B -
  V) colour indexes, but the absorption law is unknown. This property
  of YHGs is unpredictable and explains why spectroscopic temperatures
  (reddening independent) are always higher than photometric ones, but the
  difference decreases with the temperature. A new (weak) eruption of ρ
  Cas has been identified. We propose shorter distances for ρ Cas and
  HR 5171A than the accepted ones. Therefore, a correction to decrease
  the blue luminescence of HR 5171A by polycyclic aromatic hydrocarbon
  (PAH) molecules is necessary, and HR 5171A would no longer be a member
  of the cluster Gum48d. HR 5171A is only subject to one source of light
  variation, not by two as the literature suggests. Eruptive episodes
  (lasting one to two years), of YHGs prefer relatively cool circumstances
  when a red evolutionary loop (RL) has shifted the star to the red
  on the HR diagram. After the eruption, a blue loop evolution (BL)
  is triggered lasting one to a few decades. We claim that in addition
  to HR 8752, also the other three YHGs have shown similar cycles over
  the last 70 years. This supports the suspicion that HD 179821 might be
  a YHG (with a possible eruptive episode between 1925 and 1960). The
  range in temperature of these cyclic T<SUB>eff</SUB> variations is
  3000 K-4000 K. LTVs mainly consist of such BL and RL evolutions,
  which are responsible for a decrease and increase, respectively, of
  the quasi-periods. The reddening episode of HR 5171A between 1960 and
  1974 was most likely due to a red loop evolution, and the reddening
  after the 1975 eruption was likely due to a shell ejection, taking
  place simultaneously with a blue loop evolution. <P />Full Tables
  M.1 and M.2 are only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/631/A48">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/631/A48</A>

Title: VizieR Online Data Catalog: rho Cas differential BVRI
    photometry (van Genderen+, 2019)
Authors: van Genderen, A. M.; Lobel, A.; Nieuwenhuijzen, H.; Henry,
   G. W.; de Jager, C.; Blown, E.; di Scala, G.; van Ballegoij, E. J.
Bibcode: 2019yCat..36310048V
Altcode:
  Tablem1 contains the full T2 APT VRI photometric dataset of rho Cas,
  1986-2001. Magnitudes (mag) of variable (Var) and check (Chk) star are
  relative to the comparison star HD 223173. Tablem2 contains the full T3
  APT BV photometric dataset of rho Cas, 2003-2018. <P />(2 data files).

Title: The relation between the average northern hemisphere ground
    temperature and solar equatorial and polar magnetic activity
Authors: De Jager, Cornelis; Nieuwenhuizen, A. C. T.; Nieuwenhuizen,
   H.; Duhau, S.
Bibcode: 2018PAIJ....2..175D
Altcode: 2018PAIJ....2..175J
  No abstract at ADS

Title: A Remarkable Recent Transition in the Solar Dynamo
Authors: de Jager, C.; Akasofu, S. -I.; Duhau, S.; Livingston, W. C.;
   Nieuwenhuijzen, H.; Potgieter, M. S.
Bibcode: 2016SSRv..201..109D
Altcode: 2016SSRv..tmp...64D
  We summarize the major aspects of the remarkable, fairly long lasting
  period (∼ 2005 to ∼ 2010) of low solar activity, that we will call
  the Transition. It is the transitional stage between the Grand Maximum
  of the 20th century and a forthcoming (most probably Regular) episode
  of solar activity. The various kinds of activity in the functioning
  of the equatorial components of the solar dynamo before and during
  the Transition are summarized. While the behavior of unipolar magnetic
  regions and their rest-latitudes already gave very early indications -
  mid 20th century - of the forthcoming Transition, more such indications
  became available around 1995 and the main part of it occurred between
  2005 and 2010. Some of the inferences are discussed. We submit the
  hypothesis that the solar tachocline undergoes pulsations and we
  present some helioseismic evidences. In that scenario we find that its
  equatorial part has moved downward over a fairly small semi-amplitude
  (∼ 0.03 solar radii) during the time of the Transition. There are
  several indications, apart from this `pulsation', that the tachocline
  may even be pulsating with still smaller amplitudes in more modes. We
  speculate about the physical mechanism(s).

Title: Yellow Hypergiants: A Comparative Study of HR 5171A, Rho Cas,
    and HR 8752
Authors: Lobel, A.; de Jager, C.; Nieuwenhuijzen, H.; van Genderen,
   A. M.; Oudmaijer, R.
Bibcode: 2015EAS....71..279L
Altcode:
  We present a comparative study of the detailed spectroscopic variability
  of selected Fe i absorption lines observed between 1991 and 1995 in
  the optical spectra of the bright yellow hypergiants HR 5171A and Rho
  Cas. We also compare with the high-resolution spectrum of HR 8752. The
  three cool hypergiants reveal broad lines with very similar shapes. The
  variations with time in the line shapes and depths of HR 5171A and
  Rho Cas are very similar. The spectroscopic variability is caused by
  quasi-periodic atmospheric pulsations that strongly correlates with
  the observed radial velocity and V-brightness changes.

Title: Reply to “The influence of planetary attractions on the solar
    tachocline” by N. Scafetta, O. Humlum, J.E. Solheim, K. Stordahl
Authors: Callebaut, D.; de Jager, C.; Duhau, S.
Bibcode: 2013JASTP.102..372C
Altcode:
  There are some evidences that sunspot cycle and solar inertial force
  variability are related.It is known that differential rotation drives
  sunspot cycle.Solar inertial force is too weak to drive differential
  rotation.A mechanism able to amplify solar inertial force to its
  required strength is still missing.

Title: The Utrecht Astronomical Institute, 1632 to 2012
Authors: de Jager, C.
Bibcode: 2013ASPC..470...15D
Altcode:
  Utrecht University was founded in 1636. In 1642 the university's
  astronomical observatory was founded. It was, after that of Leyden,
  the second university observatory in the world. The observatory was
  initially located at the Smeetoren, a fortification dating from 1145. In
  1854 it moved to Sonnenborgh, a stronghold dating from 1554. In 1987
  the personnel moved again, this time to the university campus, the
  Uithof. We describe the development of research and education in Utrecht
  over the centuries, with emphasis on the period after 1920. In 2009 the
  faculty formulated a very favorable advice to the university, viz. that
  in view of its good potentials astronomical research and education
  should be strengthened in Utrecht. This decision was accentuated by a
  likely positive advice of an international visitation committee. But
  briefly after that the university decided to terminate astronomical
  education and research in Utrecht, an incomprehensible decision.

Title: The hypergiant HR 8752 evolving through the yellow evolutionary
    void
Authors: Nieuwenhuijzen, H.; De Jager, C.; Kolka, I.; Israelian, G.;
   Lobel, A.; Zsoldos, E.; Maeder, A.; Meynet, G.
Bibcode: 2012A&A...546A.105N
Altcode:
  Context. We study the time history of the yellow hypergiant HR
  8752 based on high-resolution spectra (1973-2005), the observed MK
  spectral classification data, B - V- and V-observations (1918-1996)
  and yet earlier V-observations (1840-1918). <BR /> Aims: Our local
  thermal equilibrium analysis of the spectra yields accurate values
  of the effective temperature (T<SUB>eff</SUB>), the acceleration
  of gravity (g), and the turbulent velocity (v<SUB>t</SUB>) for 26
  spectra. The standard deviations average are 82 K for T<SUB>eff</SUB>,
  0.23 for log g, and 1.1 km s<SUP>-1</SUP> for v<SUB>t</SUB>. <BR />
  Methods: A comparison of B - V observations, MK spectral types,
  and T<SUB>eff</SUB>-data yields E(B - V), "intrinsic" B - V,
  T<SUB>eff</SUB>, absorption A<SUB>V</SUB>, and the bolometric correction
  BC. With the additional information from simultaneous values of B -
  V, V, and an estimated value of R, the ratio of specific absorption
  to the interstellar absorption parameter E(B - V), the "unreddened"
  bolometric magnitude m<SUB>bol,0</SUB> can be determined. With
  Hipparcos distance measurements of HR 8752, the absolute bolometric
  magnitude M<SUB>bol,0</SUB> can be determined. <BR /> Results:
  Over the period of our study, the value of T<SUB>eff</SUB> gradually
  increased during a number of downward excursions that were observable
  over the period of sufficient time coverage. These observations,
  together with those of the effective acceleration g and the turbulent
  velocity v<SUB>t</SUB>, suggest that the star underwent a number of
  successive gas ejections. During each ejection, a pseudo photosphere
  was produced of increasingly smaller g and higher v<SUB>t</SUB>
  values. After the dispersion into space of the ejected shells and
  after the restructuring of the star's atmosphere, a hotter and more
  compact photosphere became visible. From the B - V and V observations,
  the basic stellar parameters, T<SUB>eff</SUB>, log M/M<SUB>⊙</SUB>,
  log L/L<SUB>⊙</SUB>, and log R/R<SUB>⊙</SUB> are determined for
  each of the observational points. The results show the variation in
  these basic stellar parameters over the past near-century. <BR />
  Conclusions: We show that the atmospheric instability region in the
  HR-diagram that we baptize the yellow evolutionary void actually
  consists of two parts. We claim that the present observations show
  that HR 8752 is presently climbing out of the "first" instability
  region and that it is on its way to stability, but in the course of
  its future evolution it still has to go through the second potential
  unstable region. <P />Appendix A is available in electronic form
  at <A href="http://www.aanda.org">http://www.aanda.org</A>Tables
  A.x and B.x are available in electronic form at the CDS
  via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A105">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A105</A>,
  and at the external site <A
  href="http://www.aai.ee/HR~8752">http://www.aai.ee/HR~8752</A>

Title: Solar Forcing of Climate
Authors: de Jager, C.
Bibcode: 2012SGeo...33..445D
Altcode: 2012SGeo..tmp...26D
  Solar activity is evident both in the equatorial activity centres and
  in the polar magnetic field variations. The total solar irradiance
  variation is due to the former component. During the extraordinarily
  long minimum of activity between sunspot cycles 23 and 24, the
  variations related to the equatorial field components reached their
  minimum values in the first half of 2008, while those related to the
  polar field variations had their extreme values rather at the end
  of 2009 and the first half of 2010. The explanation of this delay is
  another challenge for dynamo theories. The role of the open solar flux
  has so far been grossly underestimated in discussions of Sun-climate
  relations. The gradual increase in the average terrestrial ground
  temperature since 1610 is related both to the equatorial and polar
  field variations. The main component (0.077 K/century) is due to the
  variation of the total solar irradiance. The second component (0.040
  K/century) waits for an explanation. The smoothed residual increase,
  presumably antropogenic, obtained after subtraction of the known
  components from the total increase was 0.31 K in 1999.

Title: VizieR Online Data Catalog: HR8752 evolving through the void
    (Nieuwenhuijzen+ 2012)
Authors: Nieuwenhuijzen, H.; de Jager, C.; Kolka, I.; Israelian, G.;
   Lobel, A.; Zsoldos, E.; Maeder, A.; Meynet, G.
Bibcode: 2012yCat..35460105N
Altcode: 2012yCat..35469105N
  The main paper on the hypergiant HR8752 evolving through the void
  combines observational data from various sources: new spectral data,
  new and already published (B-V), V data. it also describes a new
  three-dimensional chebychev interpolating code, and gives information
  on the temperature calibration for hypergiants, and adds some extra
  Tables on colour excess and historical context (cf. below). <P
  />The electronic appendix contains a number of tables, too large for
  publishing in the paper. In the text and in the appendix, they are
  referred to as Table Axx, resp. Cxx. We note, however, that tables
  A1.1 to A1.6 in Section 2 of the main paper are here referred to as
  tables appena11 to appena16. <P />The observational tables appena11
  to appena16, appena2, appena3, appena4 all refer to Section 2 in the
  main paper, while tables appena5, appena6, appena7, appena8 are used
  in Section 3 of the main paper. The technical table appenc1 describes
  the three-dimensional chebychev interpolation method used in Section
  2 of the main paper. The second technical table appenc2 describes the
  (hypergiant) temperature calibration and transformation codes between
  Mk, Teff, and (B-V) data, used in Section 3 of the main paper. Table
  appena9 discusses some measured colour excesses (Section 3.3 of the
  main paper). Table appena10 discusses the possibility of historical
  context (Section 5.11 of the main paper). <P />(20 data files).

Title: Sudden transitions and grand variations in the solar dynamo,
    past and future&lt;/xref&gt;
Authors: De Jager, Cornelis; Duhau, Silvia
Bibcode: 2012JSWSC...2A..07D
Altcode:
  The solar dynamo is the exotic dance of the sun's two major magnetic
  field components, the poloidal and the toroidal, interacting in
  anti-phase. On the basis of new data on the geomagnetic aa index, we
  improve our previous forecast of the properties of the current Schwabe
  cycle #24. Its maximum will occur in 2013.5 and the maximum sunspot
  number R<SUB>max</SUB> will then be 62 ± 12, which is within the bounds
  of our earlier forecasts. The subsequent analysis, based on a phase
  diagram, which is a diagram showing the relation between maximum sunspot
  numbers and minimum geomagnetic aa index values leads to the conclusion
  that a new Grand Episode in solar activity has started in 2008. From the
  study of the natural oscillations in the sunspot number time series,
  as found by an analysis based on suitable wavelet base functions, we
  predict that this Grand Episode will be of the Regular Oscillations
  type, which is the kind of oscillations that also occurred between
  1724 and 1924. Previous expectations of a Grand (Maunder-type) Minimum
  of solar activity cannot be supported. We stress the significance
  of the Hallstatt periodicity for determining the character of the
  forthcoming Grand Episodes. No Grand Minimum is expected to occur
  during the millennium that has just started. <P />The full text of all
  quoted papers by the two authors of this paper can be consulted at <A
  href="http://www.cdejager.com/sun-earth-publications/">www.cdejager.com/sun-earth-publications/</A>.

Title: The influence of planetary attractions on the solar tachocline
Authors: Callebaut, Dirk K.; de Jager, Cornelis; Duhau, Silvia
Bibcode: 2012JASTP..80...73C
Altcode:
  We present a physical analysis of the occasionally forwarded hypothesis
  that solar variability, as shown in the various photospheric and outer
  solar layer activities, might be due to the Newtonian attraction by the
  planets. We calculate the planetary forces exerted on the tachocline
  and thereby not only include the immediate forces but we also take into
  account that these planetary or dynamo actions occur during some time,
  which demands integration. As an improvement to earlier research on this
  topic we reconsider the internal convective velocities and we examine
  several other effects, in particular those due to magnetic buoyancy
  and to the Coriolis force. The main conclusion is that in its essence:
  planetary influences are too small to be more than a small modulation
  of the solar cycle. We do not exclude the possibility that the long
  term combined action of the planets may induce small internal motions
  in the sun, which may have indirectly an effect on the solar dynamo
  after a long time.

Title: Solar Forcing of Climate
Authors: de Jager, C.
Bibcode: 2012omee.book..113D
Altcode:
  No abstract at ADS

Title: Quantifying and specifying the solar influence on terrestrial
    surface temperature
Authors: de Jager, C.; Duhau, S.; van Geel, B.
Bibcode: 2010JASTP..72..926D
Altcode:
  This investigation is a follow-up of a paper in which we showed that
  both major magnetic components of the solar dynamo, viz. the toroidal
  and the poloidal ones, are correlated with average terrestrial surface
  temperatures. Here, we quantify, improve and specify that result
  and search for their causes. We studied seven recent temperature
  files. They were smoothed in order to eliminate the Schwabe-type
  (11 years) variations. While the total temperature gradient over the
  period of investigation (1610-1970) is 0.087 °C/century; a gradient
  of 0.077 °C/century is correlated with the equatorial (toroidal)
  magnetic field component. Half of it is explained by the increase of
  the Total Solar Irradiance over the period of investigation, while
  the other half is due to feedback by evaporated water vapour. A yet
  unexplained gradient of -0.040 °C/century is correlated with the
  polar (poloidal) magnetic field. The residual temperature increase
  over that period, not correlated with solar variability, is 0.051
  °C/century. It is ascribed to climatologic forcings and internal
  modes of variation. We used these results to study present terrestrial
  surface warming. By subtracting the above-mentioned components from the
  observed temperatures we found a residual excess of 0.31° in 1999, this
  being the triangularly weighted residual over the period 1990-2008. We
  show that solar forcing of the ground temperature associated with
  significant feedback is a regularly occurring feature, by describing
  some well observed events during the Holocene.

Title: Solar Gleissberg periodicities in relation to grand episodes
Authors: Duhau, S.; de Jager, C.
Bibcode: 2009EGUGA..11.6131D
Altcode:
  The solar Gleissberg cycle is not restricted to one single periodicity,
  as was assumed by its discoverer. Later, it was shown that there are
  at least two components, each of which dominating in another period
  of time. We connect this observation to an earlier finding, viz. that
  the occurrence of the Grand Episodes is related to the behaviour of
  the solar dynamo in connection to its so-called Transition Point:
  another Grand Episode starts when the curve defined by the proxies
  of the poloidal and toroidal magnetic field components has crossed
  or passed along the Transition Point's coordinates. Here, we present
  evidence that each Grand Episode is related to one or more specific
  components of the Gleissberg cycle; each of them with its own period
  length. This finding must have implications for our understanding of
  the dynamo mechanism

Title: Forecasting the parameters of sunspot cycle 24 and beyond
Authors: de Jager, C.; Duhau, S.
Bibcode: 2009JASTP..71..239D
Altcode:
  Solar variability is controlled by the internal dynamo which is
  a non-linear system. We develop a physical-statistical method for
  forecasting solar activity that takes into account the non-linear
  character of the solar dynamo. The method is based on the generally
  accepted mechanisms of the dynamo and on recently found systematic
  properties of the long-term solar variability. The amplitude modulation
  of the Schwabe cycle in dynamo's magnetic field components can be
  decomposed in an invariant transition level and three types of
  oscillations around it. The regularities that we observe in the
  behaviour of these oscillations during the last millennium enable
  us to forecast solar activity. We find that the system is presently
  undergoing a transition from the recent Grand Maximum to another
  regime. This transition started in 2000 and it is expected to end
  around the maximum of cycle 24, foreseen for 2014, with a maximum
  sunspot number Rmax=68±17. At that time a period of lower solar
  activity will start. That period will be one of regular oscillations,
  as occurred between 1730 and 1923. The first of these oscillations may
  even turn out to be as strongly negative as around 1810, in which case
  a short Grand Minimum similar to the Dalton one might develop. This
  moderate-to-low-activity episode is expected to last for at least one
  Gleissberg cycle (60-100 years).

Title: Episodes of relative global warming
Authors: de Jager, C.; Duhau, S.
Bibcode: 2009JASTP..71..194D
Altcode:
  Solar activity is regulated by the solar dynamo. The dynamo is a
  non-linear interplay between the equatorial and polar magnetic
  field components. So far, in Sun-climate studies, only the
  equatorial component has been considered as a possible driver of
  tropospheric temperature variations. We show that, next to this,
  there is a significant contribution of the polar component. Based
  on direct observations of proxy data for the two main solar magnetic
  fields components since 1844, we derive an empirical relation between
  tropospheric temperature variation and those of the solar equatorial and
  polar activities. When applying that relation to the period 1610-1995,
  we find some quasi-regular episodes of residual temperature increases
  and decreases, with semi-amplitudes up to ~0.3 °C. The present period
  of global warming is one of them.

Title: The Solar Dynamo and Its Phase Transitions during the Last
    Millennium
Authors: Duhau, S.; de Jager, C.
Bibcode: 2008SoPh..250....1D
Altcode: 2008SoPh..tmp..112D
  We analyze the variation of the solar-dynamo magnetic-field components
  during the last millennium through a study of their proxy data. We
  introduce a phase diagram with as abscissa and ordinate the proxies of
  the values of the toroidal and poloidal magnetic field components. In
  this diagram the dynamo system appears to regularly cross a well-defined
  point, which we call the Transition Point. Such crossings occurred five
  times during the past millennium. Each of these crossings preceded
  a Grand Episode, either a Minimum or a Maximum one. In addition to
  these two types of quasiperiodic behavior, a third type consisting of
  weaker quasiregular oscillations (R) around the Transition Point's
  coordinates is identified. These periods appear to last one or two
  times the Gleissberg cycle length. Between the various types of
  episodes there are brief phase transitions. We identify two types of
  such phase transitions.

Title: A long-term relationship between solar magnetic field,
    geomagnetic field and Earth's rotation rate.
Authors: Duhau, S.; de Jager, C.
Bibcode: 2008AGUSMGP31C..06D
Altcode:
  All solar and solar terrestrial variables observables at ground
  level undergo time changes that have their origins - some of them
  only partially - in solar magnetic field variations. We have found
  that solar magnetic field amplitude cycle may be well described as the
  superposition of a attractor constant level, and oscillations around it
  that are well represented by the Gleissberg cycle - this last related
  to Grand Maxima and Grand Minima occurrence - and a decadal oscillation
  that contains the odd-even rule. In longer term scales a millennial
  oscillation must be also considered. Here we compare that signals in
  sunspot number, geomagnetic Mayaud index, sudden storm commencement
  (SI) index, length of day variation and the velocity of the westward
  drift and dipolar intensity of the geomagnetic field. Very well defined
  relationships that depend on the variable are found. In particular we
  need to divide the decadal variation in a Hale cycle and a semi-secular
  oscillation since the Hale oscillation in the Earth's rotation rate and
  in Geomagnetic field are not related and the semi secular oscillation
  is strongly amplified in these two variables. The origin of the so
  found relationship, that may help to reconstruct shorter time series
  of the related variables from other known since longer, is discussed.

Title: On the Physical Origin of the Cycles in Long-term Modulation
    of Solar Activity
Authors: Duhau, S.; de Jager, C.
Bibcode: 2007AGUSMSH23B..03D
Altcode:
  By a Morlet wavelet analysis in sub harmonics of the 11 year fundamental
  frequency of sunspot number as a proxy for the toroidal component of
  solar dynamo magnetic field the evolution for the last 400 years of
  four well defined cycles- a decadal, a semi-secular, the Gleissberg
  and the Suess ones - in the modulation of this component of the
  solar dynamo field is found. The properties of these cycles as seen
  in geomagnetic index aa and Si as proxy data for polar dynamo field
  and CME's frequency and intensity, respectively, are described . From
  this procedure and by analyzing longer proxy time series in the light
  of the known non-linear properties of solar dynamo system, the meaning
  of the four cycles and its variability are discussed.

Title: On possible drivers of Sun-induced climate changes
Authors: de Jager, Cornelis; Usoskin, Ilya
Bibcode: 2006JASTP..68.2053D
Altcode: 2006JATP...68.2053D
  We tested the validity of two current hypotheses on the dependence of
  climate change on solar activity. One of them states that variations in
  the tropospheric temperature are caused directly by changes of the solar
  radiance (total or spectral). The other suggests that cosmic ray (CR)
  fluctuations, caused by the solar/heliospheric modulation, affect the
  climate via cloud formation. Confronting these hypotheses with seven
  different sets of the global/hemispheric temperature reconstructions
  for the last 400 years, we found that the former mechanism is in
  general more prominent than the latter. Therefore, we can conclude
  that in so far as the Sun climate connection is concerned tropospheric
  temperatures are more likely affected by variations in the UV radiation
  flux rather than by those in the CR flux.

Title: Solar Forcing of Climate. 1: Solar Variability
Authors: de Jager, C.
Bibcode: 2005SSRv..120..197D
Altcode:
  We describe the properties of the Sun, those of its Active Regions
  (Centres of Activity, ARs or CAs) and the 11 and 22-year cycles
  as observed via the variable numbers of sunspots. We describe the
  variations with time of the solar irradiance and of the flux of
  ejected magnetised plasma. We discuss the probable cause of solar
  variability. Planetary influences are ruled out; the variability
  is intrinsic and is described by the solar dynamo. The dynamo is
  characterised by internal toroidal and more superficial poloidal fields,
  interchanging and alternating in a 22-year periodicity. From these two
  components in the solar magnetic fields emanate two possible scenarios
  for the Sun-climate interaction. Solar irradiance variations are
  related to those in the solar toroidal magnetic fields. The fraction
  of the solar irradiance that reaches the Earth's ground level and
  low troposphere is emitted by the solar photosphere. That fraction
  does not significantly vary since the quiet photosphere does not
  significantly vary during the cycle. The variable part of the solar
  radiation flux is mainly emitted by the chromospheric parts of the
  CAs. That radiation component does not reach the Earth's troposphere
  since it is absorbed in the higher, stratospheric terrestrial
  layers. Tropospheric solar-driven variations should therefore be
  due to stratosphere-troposphere coupling. The Group Sunspot number R
  <SUB>Gs</SUB> is a proxy for the variable irradiance component and for
  the toroidal field variations. Ejected solar plasma clouds such as the
  Coronal Mass Ejections (CMEs) and plasma ejected from Ephemeral Solar
  Regions and from the polar facular regions are related to variations in
  the poloidal magnetic fields. On the average they have their maximum
  intensity about a year after the maximum number of spots: we call
  this interval the Energetic Emissions Delay. These gas clouds fill the
  heliosphere with magnetised plasma. Thus, by emitting magnetised plasma,
  the Sun influences the Earth's atmosphere indirectly, by heliospheric
  modulation of the component of the galactic cosmic radiation (CR) that
  reaches tropospheric levels. Modulation is only important for cosmic
  ray particles with energies below about 50 GeV. Cosmic ray ionisation
  plays a minor role at ground level but it is the predominant ionising
  agent in higher atmospheric layers, already above a few kilometres. The
  amplitudes of the CR variations depend on those of the solar cycle. The
  atmospheric rate of ionisation varies with CR-intensity. A current
  hypothesis is that the variable ionisation may affect the degree
  of cloudiness. Cosmogenic radionuclides such as <SUP>10</SUP>Be are
  proxies for this influence and for the poloidal field variations. The
  R <SUB>G</SUB> and cosmogenic radionuclide proxies, although loosely
  correlated, refer to the two different aspects of the solar dynamo
  with their different terrestrial effects; they do not reach maximum
  intensity simultaneously and should therefore neither be confused
  nor be interchanged. Cases have occurred in which the one varied
  strongly while the other did hardly or not at all. The explanation
  must be intrinsic in dynamo theory. There is a significant solar
  signal in the troposphere; it depends on latitude and longitude. A
  physical investigation of the cause of the Sun-climate relationship
  based on one unique Δ T(time)-curve, assumed valid for the whole
  Earth's surface, is therefore basically incorrect. Never during the
  past 10,000 years has the Sun been as active in ejecting magnetised
  plasma as during the past few decades. Estimates suggest that the
  level of solar activity may recently have passed its maximum and that
  it may decrease in coming decades. Solar activity is variable with
  six well-determined quasi-periodicities. Attempts to theoretically
  describe the solar dynamo have so far succeeded only in explaining the
  qualitative aspects. They fail in a numerical description and notably
  in one that would permit one to forecast solar activity with acceptable
  precision. This is so because the solar dynamo is a non-linear system
  that occasionally shows phase catastrophes. It is a quasi-periodic
  engine with the properties of deterministic chaos. “The future of
  such a chaotic system is intrinsically unpredictable”.

Title: Do Planetary Motions Drive Solar Variability?
Authors: De Jager, Cornelis; Versteegh, Gerard J. M.
Bibcode: 2005SoPh..229..175D
Altcode:
  We examine the occasionally forwarded hypothesis that solar activity
  originates by planetary Newtonian attraction on the Sun. We do this
  by comparing three accelerations working on solar matter at the
  tachocline level: Those due to planetary tidal forces, to the motion
  of the Sun around the planetary system's centre of gravity, and the
  observed accelerations at that level. We find that the latter are by
  a factor of about 1000 larger than the former two and therefore cannot
  be caused by planetary attractions. We conclude that the cause of the
  dynamo is purely solar.

Title: Popularization of Astronomy in the Netherlands
Authors: de Jager, C.; Drummen, M.
Bibcode: 2004ASSL..310..233D
Altcode: 2004osa5.book..233D
  No abstract at ADS

Title: Rapid variations of narrow absorption line components in the
    spectrum of <A href="10.1016/S1384-1076(03)00018-6&amp;P Cygni">P
    Cygni</A>
Authors: de Jager, Cornelis; Israelian, Garik
Bibcode: 2003NewA....8..475D
Altcode: 2003astro.ph..4357D
  We report the detection of rapid wavelength and intensity variations
  of narrow components in absorption line profiles of the hot galactic
  supergiant P Cygni. During most of the time, in 1 week of observations,
  there were two such components present. Although the period of
  observation is too short for firm conclusions, the velocity curves
  do not contradict the photometric period of 17.3 days. These curves
  may be interpreted as a double wave, 'swinging in counterphase'. This
  observation would suggest the presence of one long wave over the stellar
  surface. The waves are possibly gravity waves with wavelengths of the
  order of half the stellar radius.

Title: High-Resolution Spectroscopy of the Yellow Hypergiant ρ
    Cassiopeiae from 1993 through the Outburst of 2000-2001
Authors: Lobel, A.; Dupree, A. K.; Stefanik, R. P.; Torres, G.;
   Israelian, G.; Morrison, N.; de Jager, C.; Nieuwenhuijzen, H.; Ilyin,
   I.; Musaev, F.
Bibcode: 2003ApJ...583..923L
Altcode: 2003astro.ph..1238L
  We present an overview of the spectral variability of the peculiar
  F-type hypergiant ρ Cas, obtained from our long-term monitoring
  campaigns over the past 8.5 yr with four spectrographs in the
  northern hemisphere. Between 2000 June and September an exceptional
  variability phase occurred when the V brightness dimmed by about a full
  magnitude. The star recovered from this deep minimum by 2001 April. It
  is the third outburst of ρ Cas on record in the last century. We
  observe TiO absorption bands in high-resolution near-IR spectra obtained
  with the Utrecht Echelle Spectrograph during the summer of 2000. TiO
  formation in the outer atmosphere occurred before the deep brightness
  minimum. Atmospheric models reveal that the effective temperature
  decreases by at least 3000 K, and the TiO shell is driven supersonically
  with M~=5.4×10<SUP>-2</SUP> M<SUB>solar</SUB> yr<SUP>-1</SUP>. Strong
  episodic mass loss and TiO have also been observed during the outbursts
  of 1945-1947 and 1985-1986. A detailed analysis of the exceptional
  outburst spectra is provided, by comparing with high-resolution optical
  spectra of the early M-type supergiants μ Cep (Ia) and Betelgeuse
  (Iab). During the outburst, central emission appears above the local
  continuum level in the split Na D lines. A prominent optical emission
  line spectrum appears in variability phases of fast wind expansion. The
  radial velocity curves of Hα and of photospheric metal absorption lines
  signal a very extended and velocity-stratified dynamic atmosphere. The
  outburst spectra indicate the formation of a low-temperature, optically
  thick circumstellar gas shell of 3×10<SUP>-2</SUP> M<SUB>solar</SUB>
  during 200 days, caused by dynamic instability of the upper atmosphere
  of this pulsating massive supergiant near the Eddington luminosity
  limit. We observe that the mass-loss rate during the outburst is of the
  same order of magnitude as has been proposed for the outbursts of η
  Carinae. We present calculations that correctly predict the outburst
  timescale, whereby the shell ejection is driven by the release of
  hydrogen ionization recombination energy.

Title: The Millennium Outburst of the Cool Hypergiant rho Cassiopeiae:
    Spectroscopy and Modeling
Authors: Lobel, A.; Dupree, A. K.; Stefanik, R. P.; Torres, G.;
   Israelian, G.; Morrison, N.; de Jager, C.; Nieuwenhuijzen, H.; Ilyin,
   I.; Musaev, F.
Bibcode: 2003IAUS..210P.F10L
Altcode: 2002astro.ph.11508L
  Between 2000 June and September an exceptional variability phase
  occurred in the peculiar F-type hypergiant Rho Cas, when the
  V-brightness dimmed by at least a full magnitude. The star recovered
  from this deep minimum by 2001 April. It is the third outburst of Rho
  Cas on record in the last century. We observe TiO absorption bands in
  high-resolution optical and near-IR spectra obtained with the Utrecht
  Echelle Spectrograph during the summer of 2000. TiO formation in the
  outer atmosphere occurred before the deep brightness minimum.Atmospheric
  models reveal that the effective temperature decreases by at least
  3000 K, and the TiO shell is driven supersonically with Mdot =~5.4
  10^-2 Msun/yr. Strong episodic mass loss and TiO have also been
  observed during the outbursts of 1945-47 and 1985-86. An analysis of
  the exceptional outburst spectra of 2000-01 is provided, by comparing
  with high-resolution optical spectra of the early M-type supergiants Mu
  Cep (Ia) and Betelgeuse (Iab). During the outburst, central emission
  appears above the local continuum level in the split Na D lines. The
  outburst spectra indicate the formation of a low- temperature, optically
  thick circumstellar gas shell of 3 10^-2 Msun during \~200 d, caused
  by dynamic instability of the upper atmosphere of this pulsating
  massive supergiant near the Eddington luminosity limit. We present
  an equation that correctly predicts the outburst time-scale, whereby
  the shell ejection is driven by the release of hydrogen recombination
  energy. We observe that the mass-loss rate during the outburst is of
  the same order of magnitude as has been proposed for the outbursts
  of Eta Carinae. The research results in this paper are described in
  further detail in Lobel et al. (2003). A spectral movie sequence of
  the outburst is available at http://cfa-www.harvard.edu/~alobel/

Title: The Millenium Outburst of the Yellow Hypergiant ρ Cassiopeiae
Authors: Lobel, A.; Dupree, A. K.; Stefanik, R. P.; Torres, G.;
   Israelian, G.; Morrison, N.; Ilyin, I.; de Jager, C.; Nieuwenhuijzen,
   H.
Bibcode: 2002AAS...201.4909L
Altcode: 2002BAAS...34.1185L
  We report the largest mass-loss rate of ~5 % of the solar mass per
  year, directly observed in any stellar object so far during the recent
  outburst of the Yellow Hypergiant ρ Cas. In the fall of 2000, the
  enigmatic cool luminous supergiant dimmed by more than a full visual
  magnitude, thereby changing its spectral type form early F- to early
  M-type. Our spectral monitoring reveals that the effective temperature
  decreased by more than 3000 K during the event, from above 7000 K
  to below 4000 K in less than ~200 days. It is the third outburst of
  ρ Cas on record in the last century. The optical spectrum becomes
  comparable to that of the red supergiant Betelgeuse, and reveals
  strongly blue-shifted molecular absorption bands of titanium-oxide
  (TiO). We determine from the newly formed TiO bands a gas mass-loss
  rate of the same order of magnitude as has been proposed for the
  giant outbursts of the Luminous Blue Variable η Carinae. The outburst
  of ρ Cas produces an outward propagating circumstellar shock wave,
  driven by recombination of hydrogen gas in its wake, resulting in a
  tremendous cooling of the entire outer atmosphere. Over the past 18
  months since the outburst we observe a very prominent inverse P Cygni
  profile in Balmer Hα . Strong emission in this line has not before
  been observed in ρ Cas over this long period of time. The optical
  spectroscopic monitoring signals an unusal strong collapse of the
  upper Hα atmosphere, which we also observed in the months before the
  outburst event. The recent observations may therefore signal that a
  new and stronger outburst of ρ Cas is imminent. This reseach has been
  supported in part by a Space Telescope Science Institute grant to the
  Smithsonian Astrophysical Observatory.

Title: Early solar space research
Authors: de Jager, C.
Bibcode: 2002css1.book..203D
Altcode:
  No abstract at ADS

Title: Spectroscopy of the Rho Cas Millennium Outburst
Authors: Lobel, A.; Dupree, A. K.; Stefanik, R. P.; Torres, G.;
   Israelian, G.; de Jager, C.; Nieuwenhuijzen, H.; Ilyin, I.
Bibcode: 2001AAS...19915802L
Altcode: 2002BAAS...34..567L
  An exceptional variability phase occurred in the peculiar F-type
  hypergiant ρ Cas (Ia+) when the V brightness dimmed by about a full
  magnitude between June and September 2000. The star recovered from
  this deep minimum by April 2001. It is the third outburst of ρ Cas
  on record in the last century. We detect the formation of TiO bands
  in high-resolution spectra obtained from our long-term monitoring
  campaigns over the past decade with the Utrecht Echelle Spectrograph
  on the William Herschel Telescope, and the Sofin spectrograph of the
  Nordic Optical Telescope (La Palma). Optical and near-IR TiO bandheads,
  i.e. from the γ -system 0-0 transition at 7050 Å, develop in the
  summer of 2000. TiO formed before the deep V minimum occurred, and a
  first analysis shows that during the descending portion of the light
  curve, the spectrum is a peculiar mixture of a F-type supergiant,
  with TiO bands that characterize the spectra of M-type stars. This
  phenomenon has also been observed during the outbursts of 1945-47
  and 1985-86. A preliminary analysis of these exceptional spectra is
  presented, by comparing them with high-resolution optical spectra of
  the early M-type supergiants μ Cep (Ia) and Betelgeuse (Iab). Central
  emission is observed above the local continuum level in the split Na D
  lines. An analysis of ρ Cas' optical emission line spectrum is provided
  in Lobel 1997, Pulsation and Atmospherical Instability of Luminous F-
  and G-type Stars, Maastricht: Shaker. We propose the formation of a
  low-temperature, optically thick, mass shell, caused by instability
  of the upper atmosphere of this pulsating massive supergiant near the
  Eddington luminosity limit (Lobel 2001, ApJ, 558, 780). A review is at
  http://xxx.lanl.gov/format/astro-ph/0108358 This research is supported
  in part by STScI grant GO-08280.02-97A to the SAO.

Title: Instability regions in the upper HR diagram
Authors: de Jager, Cornelis; Lobel, Alex; Nieuwenhuijzen, Hans;
   Stothers, Richard
Bibcode: 2001MNRAS.327..452D
Altcode:
  The following instability regions for blueward evolving-supergiants are
  outlined and compared. (1) Areas in the Hertzsprung-Russell (HR) diagram
  where stars are dynamically unstable. (2) Areas where the effective
  acceleration in the upper part of the photospheres is negative, hence
  directed outward. (3) Areas where the sonic points of the stellar
  winds (where v<SUB>wind</SUB>=v<SUB>sound</SUB>) are situated inside
  the photospheres, at a level deeper than τ<SUB>Ross</SUB>=0.01. We
  compare the results with the positions of actual stars in the HR
  diagram and we find evidence that the recent strong contraction of
  the yellow hypergiant HR 8752 was initiated in a period during which
  &lt;g<SUB>eff</SUB>&gt;&lt;0, whereupon the star became dynamically
  unstable. The instability and extreme shells around IRC+10420 are
  suggested to be related to three factors: &lt;g<SUB>eff</SUB>&gt;&lt;0
  the sonic point is situated inside the photosphere; and the star is
  dynamically unstable.

Title: The photosphere of P Cygni
Authors: de Jager, C.
Bibcode: 2001ASPC..233..215D
Altcode: 2001pcyg.conf..215D
  Investigations of P Cygni during the last few decades have yielded
  a fairly consistent set of data for the photospheric parameters. I
  use T eff = 18600; log(L/Lo) = 5.8; v<SUB>turb</SUB> = 20 km/s;
  log(M<SUB>dot</SUB>)= -4.7; X = 0.35. The resulting photospheric
  model has negative values of g<SUB>eff</SUB> in the higher parts of
  the photosphere (optical depths below 0.7). In addition, the sonic
  point is reached already at a Rosseland optical depth of 0.18. These
  properties explain the outward motions in the atmosphere and the
  observed microturbulent velocities. While the body of the star has a
  &lt;Gamma<SUB>1</SUB>&gt;-value of about 4/3, the average atmospheric
  &lt;Gamma<SUB>1</SUB>&gt; = 1.338 is just above this limit. Hence the
  star is marginally dynamically stable. The strong stellar wind is a
  consequence of the outward-directed radiation pressure. The luminosity
  variations of relative short periods (smaller than about 500 d) are
  pressure waves with wavelengths of tens of millions of kilometers. The
  brightness variations of longer periods, between 1500 and 3700 d,
  are ascribed to large-scale gravity waves (nonradial pulsations) with
  a quasi recurrence time of that order. For the evolution I suggest
  the sequence Blue supergiant - Red supergiant - Yellow hypergiant -
  S Dor star (LBV) - WR star or supernova.

Title: Will HR8752 become a P Cygni type star?
Authors: de Jager, C.; Lobel, A.; Israelian, G.; Nieuwenhuijzen, H.
Bibcode: 2001ASPC..233..191D
Altcode: 2001pcyg.conf..191D
  As long as the yellow hypergiant HR8752 has been observed
  spectroscopically it has shown erratic and significant fluctuations
  in its effective temperature. But an impressive and hitherto never
  observed rise in its temperature started around 1985. Since that time
  Teff has risen from 4600 K to 7900 K. Regular further observations
  are needed to see if and when this rise will stop, and what will
  happen thereafter. The instability is related to the fact that in
  its evolution the star has entered the Yellow Evolutionary Void,
  a region in the Hertzsprung-Russell diagram where blueward-evolving
  supergiants have unstable atmospheres and where the stars are also
  dynamically unstable. The rise in temperature started after a period of
  enhanced mass loss and at a time when the photospheric acceleration
  was directed outward. Recently (1998) the photospheric effective
  acceleration has again decreased to below zero. This star is the
  first in which dynamic instability can be studied observationally
  in great detail. We hypothesise that HR8752 will traverse the Void
  and thereafter, after a period of stability, will enter the "blue''
  region of dynamic instability, and then may become a star like P Cygni.

Title: Book Review: Plasma turbulence and energetic particles
    in astrophysics / Astronomical Observatory of the Jagiellonian
    University, 1999
Authors: De Jager, Cornelis
Bibcode: 2000SSRv...92..613D
Altcode:
  No abstract at ADS

Title: De novae van deze eeuw.
Authors: de Jager, C.
Bibcode: 2000Zenit..27..154D
Altcode:
  No abstract at ADS

Title: J. Andersen (ed.), Transactions of the International
    Astronomical Union, Volume XXIIIB
Authors: de Jager, Cornelis
Bibcode: 2000SSRv...91..718D
Altcode:
  No abstract at ADS

Title: Checking the yellow evolutionary void. Three evolutionary
critical Hypergiants: HD 33579, HR 8752 &amp; IRC +10420
Authors: Nieuwenhuijzen, H.; de Jager, C.
Bibcode: 2000A&A...353..163N
Altcode:
  We have checked the reality of the yellow evolutionary void (which
  is an area in the Hertzsprung-Russell diagram where atmospheres of
  blueward evolving super- and hypergiants are moderately unstable),
  by comparing one star inside the void: HD 33579 (= R76), and two at
  the low-temperature border of it: HR 8752 (= HD 217476, V509 Cas)
  and IRC+10420. We found that the first star has a large mass and a
  fairly stable behaviour over time. These aspects suggest, together
  with abundance determinations by others, that it is a fairly young,
  still redward-evolving supergiant. For such a star the void is not
  forbidden. The two other stars, HR 8752 resp. IRC+10420, have low masses
  which places them in the post-red blueward loop. They show indications
  of the expected bouncing effect for blueward returning red supergiants:
  when approaching the void they eject mass, resulting in a sudden
  reduction of T_eff and a decrease of the atmospheric acceleration
  to g_eff =~ zero. Thereafter T_eff and g_eff increase again. For HR
  8752 two such recent `bounces' have been identified. The photometric
  variations of HR 8752 and of HD 33579 are due to high-l gravity-wave
  pulsations. Based on observations at the La Palma Observatory and the
  ESO Observatory in Chili.

Title: Dzidek Niemirowicz 1928 - 2000
Authors: de Jager, Cornelis
Bibcode: 2000CIBu..147....2D
Altcode:
  No abstract at ADS

Title: De versnelde uitdijing van het heelal.
Authors: de Jager, C.
Bibcode: 1999Zenit..26..502D
Altcode:
  No abstract at ADS

Title: Periodieke inslagen op aarde?
Authors: de Jager, C.
Bibcode: 1999Zenit..26..427D
Altcode:
  No abstract at ADS

Title: De laatste "zonsverduistering".
Authors: de Jager, C.
Bibcode: 1999Zenit..26..340D
Altcode:
  No abstract at ADS

Title: M. Livio, S. M. Fall and P. Madau (eds.), The Hubble Deep
    Field, Space Telescope Conference Series 11
Authors: de Jager, Cornelis
Bibcode: 1999SSRv...89..693D
Altcode:
  The proceedings of a conference dealing with only one piece of
  observational activity: the deepest optical image obtained by the HST
  during a 150 orbit observational program. The main result, presented
  in several papers, is that we are now able to witness the period of
  galaxy formation. Very readable too is Allan Sandage's historical
  review, being the introductory paper to the meeting.

Title: Wat de kleintjes ons leren. Restanten van het ontstaan van
    het zonnenstelsels.
Authors: de Jager, C.
Bibcode: 1999Zenit..26..214D
Altcode:
  No abstract at ADS

Title: C. C. Petersen and J. C. Brandt, Hubble Vision, Early
    Adventures with the Hubble Space Telescope
Authors: de Jager, Cornelis
Bibcode: 1999SSRv...88..608D
Altcode:
  No abstract at ADS

Title: Stuart Ross Taylor, Destiny or Chance; our Solar System and
    its Place in the Cosmos
Authors: de Jager, Cornelis
Bibcode: 1999SSRv...88..609D
Altcode:
  No abstract at ADS

Title: Erratum: "A generalized version of the Rankine-Hugoniot
    relations including ionization, dissociation, radiation and related
    phenomena" [Astron. Astrophys., Vol. 280, No. 1, p. 195 - 200
    (Dec 1993)].
Authors: Nieuwenhuijzen, H.; de Jager, C.; Cuntz, M.; Lobel, A.;
   Achmad, L.
Bibcode: 1999A&A...343..661N
Altcode:
  No abstract at ADS

Title: Waarom kwamen de Leoniden te vroeg?
Authors: de Jager, C.; van Woerden, H.
Bibcode: 1999Zenit..26..110D
Altcode:
  No abstract at ADS

Title: De onstuimige jeugd van het heelal.
Authors: de Jager, C.
Bibcode: 1999Zenit..26...52D
Altcode:
  No abstract at ADS

Title: Onzichtbare massa is wellicht heel "gewoon".
Authors: de Jager, C.
Bibcode: 1999Zenit..26...13D
Altcode:
  No abstract at ADS

Title: Flare dynamics.
Authors: Antonucci, E.; Alexander, D.; Culhane, J. L.; de Jager, C.;
   MacNeice, P.; Somov, B. V.; Zarro, D. M.
Bibcode: 1999mfs..conf..331A
Altcode:
  The following topics were dealt with: results from soft X-ray spectra,
  chromospheric evaporation, nature of nonthermal line broadening,
  flare modelling.

Title: Announcement   Space Science Reviews Provides an Opportunity
to Debate: Challenges to Long-Standing Unsolved Space Physics Problems
    in the 20th Century
Authors: de Jager, Cornelis; Akasofu, Syun
Bibcode: 1999SSRv...87..551D
Altcode:
  No abstract at ADS

Title: G. Haskell and M. Rycroft (eds.), New Space Markets,
    Proceedings of the International Symposium held in Strasbourg,
    26-28 May, 1997
Authors: de Jager, Cornelis
Bibcode: 1999SSRv...87R.546D
Altcode:
  No abstract at ADS

Title: Drie vragen over de corona.
Authors: de Jager, C.
Bibcode: 1998Zenit..25..310D
Altcode:
  No abstract at ADS

Title: Leon Golub and Jay M. Pasachoff, The Solar Corona
Authors: de Jager, Cornelis
Bibcode: 1998SSRv...85..549D
Altcode:
  No abstract at ADS

Title: De veranderlijke zon en het klimaat.
Authors: de Jager, C.
Bibcode: 1998Zenit..25..148D
Altcode:
  No abstract at ADS

Title: Een loslopende neutronenster.
Authors: de Jager, C.
Bibcode: 1998Zenit..25..117D
Altcode:
  No abstract at ADS

Title: Toch een planetoide in Chicxulub?
Authors: de Jager, C.
Bibcode: 1998Zenit..25...82D
Altcode:
  No abstract at ADS

Title: The spectral variability of the cool hypergiant rho Cassiopeiae
Authors: Lobel, A.; Israelian, G.; de Jager, C.; Musaev, F.; Parker,
   J. Wm.; Mavrogiorgou, A.
Bibcode: 1998A&A...330..659L
Altcode:
  We checked the change of the effective temperature with the
  atmospherical pulsation of rho Cas from combined analyses of optical
  spectra of 1993-95 and IUE spectra of 1979-81. We find an upper range
  for bigtriangleup T_eff =~ 750 K over a period of 16-17 months. We
  present a thorough study of the related absorption line profile changes
  from which a velocity stratification with excitation energy could not be
  detected for the metallic lines. The distinct evolution of Hα displays
  variable distortions of filling-in by emission with the pulsation. Our
  theoretical line profile fits yield a value for vsini of 25 kms(-1)
  . We report the finding of two different causes for the splitting of
  absorption line cores in the spectra of rho Cas. For the phase near
  highest effective temperature we have analyzed the development of
  very far shortward extended line wings assuming velocities up to 150
  kms(-1) . These violet absorptions originate about 2.5 R_{*} above
  the photosphere in a cool and variable supersonic wind from which we
  determine an upper value of the mass-loss rate of 9.2 10(-5) M_⊙y(-1)
  . We also report the finding of an increase of the supersonic wind
  velocity by ~ 15 kms(-1) per electronvolt decrease, measured from the
  maximum velocities of these violet absorptions for Fei lines. A separate
  analysis of the IUE spectra reveals tremendous changes of the Balmer
  continuum flux by a factor 4 to 5 in only 26 hours, clearly distinct
  from the long-term variations of Hα . Partly based on observations
  taken at the La Palma Observatory, the Special Astrophysical Observatory
  and with the International Ultraviolet Explorer

Title: The yellow hypergiants
Authors: de Jager, Cornelis
Bibcode: 1998A&ARv...8..145D
Altcode:
  We list the main stellar data of known hypergiants and similarly
  luminous stars, and then concentrate on a review of the yellow
  hypergiants. These stars are post-red supergiants evolving along
  blueward loops in the Hertzsprung-Russell diagram. Their properties,
  their location in the Hertzsprung-Russell diagram and their occasional
  mass ejections are related to a region of atmospheric instability in the
  H-R diagram, the Yellow Void. The `bouncing against the border of the
  Void' of three objects: ρ Cas, HR8752 and IRC+10420, is described. The
  apparent atmospheric instability of yellow hypergiants is related to
  the atmospheric pulsations. There are indications that the approach to
  the Void is associated with an increased amplitude of the pulsation
  and with enhanced mass loss. The observed small-scale motion field
  is only apparently strongly supersonic; the observed large stochastic
  velocities are the quasi-stochastically varying thermal motions in the
  many hot sheets that occur in the wakes of many small shocks, while
  the real hydrodynamic velocity component is small and subsonic. This
  shock-wave field is also responsible for the observed rate of mass
  loss and for emission in the wings of Hα . Most yellow hypergiants
  have envelopes containing gas and dust, but a thick extended envelope,
  presumably dissipating and showing bipolar outflow, is only known around
  IRC+10420. At the interface of the bipolar wind and the interstellar
  medium one or more stationary shocks may develop as is observed in
  the case of IRC+10420 and suspected with ρ Cas.

Title: I knew Edith for nearly half a century
Authors: de Jager, Cornelis
Bibcode: 1998ASSL..222...21D
Altcode: 1998ream.conf...21D
  No abstract at ADS

Title: A Cold War in Space Research
Authors: de Jager, Cornelis
Bibcode: 1998fyc..conf...25D
Altcode:
  No abstract at ADS

Title: The Variable Spectrum of the Yellow Hypergiant rho Cassiopeiae
Authors: Israelian, G.; Lobel, A.; de Jager, C.; Musaev, F.
Bibcode: 1998ASPC..154.1601I
Altcode: 1998csss...10.1601I
  We have analyzed high-resolution optical spectra of the cool hypergiant
  rho Cas covering a period 2 years. The aim of this analysis is to check
  the range of the effective temperature variations with the pulsation
  of the atmosphere, in order to study variable emission components in
  Hα, to investigate the splitting of metallic absorption lines and to
  compute abundances of Na, Fe and other elements. We found an upper range
  of Delta T_eff ~= 750 K over a period 17 months, whereas the effective
  temperature change within a single pulsation period remained limited
  to 400 K. We discuss the notorious splitting of low excitation metallic
  absorption lines observed for rho Cas. The allowed emission reversals in
  the cores of these low energy lines emerge from cool and static shells
  in a bipolar stellar wind. Furthermore, variable absorption in the
  supersonic stellar wind recurrently produces far violet extended line
  wings with the atmospherical pulsations, from which we have derived the
  mass-loss rate and wind extension above the photosphere. The emission
  components of Hα suggest the presence of a thermally excited outer
  atmospherical region (a variable quasi-chromosphere). Several observed
  parameters (like the mass-loss rate) can be derived theoretically
  if we assume that the observed ``microturbulent'' line broadening is
  not caused by stochastic small-scale turbulent motions (the classical
  notion of microturbulence) but by thermal motions in stochastically
  distributed high-temperature sheets behind the many shocks.

Title: Bruine dwergen: de kleinste "sterren" in het heelal.
Authors: de Jager, C.
Bibcode: 1997Zenit..24..404D
Altcode:
  No abstract at ADS

Title: Turbulence, mass loss and Hα emission by stochastic shocks
    in the hypergiant ρ Cassiopeiae.
Authors: de Jager, C.; Lobel, A.; Israelian, G.
Bibcode: 1997A&A...325..714D
Altcode:
  The hypergiant ρ Cas is known for its variable rate of mass loss, with
  an average value of about 10^-5^M<SUB>sun</SUB>_/yr, and the supersonic
  value for the line-of-sight component of the microturbulent velocity,
  about 11km/s. Emission components in Hα suggest the presence of a
  thermally excited outer atmospheric region. Since hydrodynamical
  turbulence in a stellar atmosphere turns rapidly into a field of
  shock waves, and shock waves are known to be able to initiate a
  stellar wind and heat stellar atmospheric layers, we have tried
  to predict the rate of mass loss, the microturbulent velocity
  component and the observed Hα profile by assuming a stochastic
  field of shock waves. To that end we adopted a Kolmogoroffian
  spectrum of shock waves, characterized by only one parameter:
  the maximum Mach number in front of the shocks: M_1,max_. Behind
  every shock a thin hot region originates. Spectroscopically, the
  thermal motions in these sheetlike regions cannot be distinguished
  from the stochastic hydrodynamic (shock wave) motion component,
  and therefore these hot regions add to the line broadening and will
  also contribute to the observed 'microturbulence'. We find that it is
  indeed possible to explain the observed rate of mass loss (we derived
  log˙(M)=~-5(M<SUB>sun</SUB>_/yr)), as well as the high value for the
  quasi-microturbulence (we calculated =~12km/s). The hot sheets behind
  the shocks appear to be responsible for the observed 'microturbulence';
  this thermal contribution is much larger than that of the hydrodynamic
  (shock) motions, which is only 0.4 to 0.5km/s. Non-LTE calculations
  of the Hα line profile show that the shocks, in association with the
  observed time-dependent variation of T_eff_ can reproduce aspects of
  the variable emission in Hα. These three aspects of this star, viz. the
  observed rate of mass loss, the observed supersonic 'microturbulence',
  as well as the Hα line profile can be simulated by one parameter only:
  viz. M_1,max_=1.06 to 1.08, a value that characterizes a fairly weak
  shock-wave field.

Title: An obstacle to the late evolution of massive stars
Authors: de Jager, Cornelis; Nieuwenhuijzen, Hans
Bibcode: 1997MNRAS.290L..50D
Altcode:
  During their evolution, massive stars first swell and thus
  become red supergiants, after which they shrink again to evolve
  to the blue supergiant phase. When, during this blueward loop, the
  effective photospheric temperature T_eff has increased to values of
  about 7000 K, the main part of the photosphere becomes moderately
  unstable. Observations of the yellow hypergiant star HD 217476=HR 8752
  show that the approach to this instability region may lead to phases of
  enhanced mass loss and consequent reduced surface temperature, after
  which T_eff slowly increases until it again `bounces' against the
  atmospheric instability region. Two such bounces have been observed
  in the last 30 yr and a third seems imminent; frequent observations
  of this star are therefore useful. Other `yellow hypergiants', like
  rhoCas and IRC+10420, seem to show the same behaviour. Repeated
  observations of these stars may help us to understand how massive
  stars pass the instability region during their evolution towards the
  blue supergiant phase.

Title: Tien jaar supernova 1987A.
Authors: de Jager, C.
Bibcode: 1997Zenit..24..335D
Altcode:
  No abstract at ADS

Title: 3-D MHD Simulation of X-Type Coalescence of Two Current-Loops
Authors: Sakai, Jun-ichi; de Jager, Cornelis
Bibcode: 1997SoPh..173..347S
Altcode:
  We present simulation results of X-type coalescence of two
  current-loops, by using a 3-D resistive MHD code. The results are
  compared with the limb flare observed by Yohkoh on 2 August, 1993 at
  08:30 UT, which is a good example of partial X-type coalescence. It is
  shown that the maximum temperature enhancement near the cross-point
  of the two loops, obtained from the simulation, agrees well with the
  observations when the plasma β is 0.08.

Title: K. Madders, A New Force at a New Frontier, Europe's Development
    in the Space Field of Its Main Actors, Policies, Law and Activities
    from its Beginnings up to the Present
Authors: de Jager, C.
Bibcode: 1997SSRv...81..199D
Altcode:
  No abstract at ADS

Title: Presolaire insluitsels in meteorieten.
Authors: van Dijk, T.; de Jager, C.
Bibcode: 1997Zenit..24..290V
Altcode:
  No abstract at ADS

Title: A White and a Red Star|(Special Historical Review)
Authors: De Jager, Cornelis
Bibcode: 1996SoPh..169..443D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Shore, Steven N.; van der Kruit, P. C.; Achterberg, A.;
   Hoyng, P.; de Jager, Cornelis
Bibcode: 1996SSRv...78..557S
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Marx, G.; Jaffe, W.; Maltby, P.; Grevesse, N.; Wu, S. T.;
   Lüst, R.; Kleczek, J.; Chupp, E. L.; Bloemen, Hans; de Jager,
   Cornelis; van Teeseling, A.; Shea, M. A.; Butcher, H.; van der Kruit,
   P. C.; Nieuwenhuijzen, H.; Steeghs, Danny; Fälthammar, Carl-Günne;
   Greenberg, J. M.; Rasool, S. I.
Bibcode: 1996SSRv...77..369M
Altcode:
  No abstract at ADS

Title: Solar Flares and Collisions Between Current-Carrying Loops
    Types and Mechanisms of Solar Flares and Coronal Loop Heating
Authors: Sakai, Jun-Ichi; de Jager, Cornelis
Bibcode: 1996SSRv...77....1S
Altcode:
  This paper deals with the temporal dynamics of solar flares. It
  gives a systematic description of solar flare models and tries to
  link the observations to results of simulations. After a review
  of the development of ideas on flare structure and on theories on
  current-loop interaction in flares since the pioneering work by Gold
  and Hoyle (1960), this paper gives first a synthesis of present-days
  observationally based views on solar flares, essentially describing
  the developments since the review by de Jager (1986). We distinguish
  between confined/impulsive and eruptive/dynamic flares (briefly:
  confined and eruptive). The main difference between these two types
  is one of field-line topology: ‘closed’ or ‘open’. The
  ‘grand instability’ in a field-line system opening to space is
  basic to the relation between eruptive flares, filament instability,
  and Coronal Mass Ejections. A fair part of the paper deals with the
  developments in our understanding of the physical processes during
  collisions between current-carrying loops. After work by Tajima et
  al. (1982), who introduced the concept of current-loop coalescence
  in solar flares, using results obtained from two-dimensional particle
  simulation, it became clear that the current-loop interaction process
  includes a rich variety of physical mechanisms associated with rapid
  magnetic energy conversion through partial or complete magnetic
  reconnection, such as prompt high-energy particle acceleration,
  plasma heating, shock formation, plasma-jet formation and plasma
  radiation. This part of the paper concentrates on the developments
  since the review by Sakai and Ohsawa (1987), dealing with particle
  acceleration by magnetic reconnection and shocks during current-loop
  coalescence in solar flares. Theoretical research performed since the
  above review paper refers to magnetic reconnection, shock formation,
  particle acceleration and plasma emission during collisions between
  current-carrying loops. These theoretical developments are compared
  with observations. The Yohkoh spacecraft, launched August 30, 1991,
  observed many evidences of two-loops interaction in active regions and a
  growing number of examples of flares due to coalescence of loops. These
  observational evidences are reviewed in a systematic way (Section 6),
  by relating them to the theoretical studies described before. First we
  describe flares due to interactions of the Y-, X-, and I-types. These
  can be either confined or eruptive. A new observation is the occurrence
  of ‘ongoing partial reconnection’ in a flare. Thereafter, we discuss
  flares due to single-loop instability (these are confined flares),
  followed by the newly discovered ‘cusp-type’ flares. These are
  eruptive flares. We end with a description of a typical eruptive
  flare. In Section 7 we summarize observational and theoretical
  evidences for our earlier proposed scheme of three different phases of
  acceleration in flares. The summary in the last section compares flare
  observations with flare simulations; it deals briefly with the three
  phases of acceleration, and outlines the present status and prospects
  of simulation studies and related theoretical research.

Title: Book reviews
Authors: Humphreys, R. M.; Kemp, S.; Savonije, G.; van der Hucht,
   K. A.; van der Kruit, P. C.; Miley, G.; Bumba, V.; van Nieuwkoop,
   J.; van Hoolst, T.; Cox, A.; Rutten, R. J.; Kleczek, J.; de Jager,
   Cornelis; Jerzykiewicz, M.; Zwaan, C.; Poedts, S.; Sakai, Jun-Ichi;
   Pecker, J. -C.; Heikkila, W.; de Jong, T.; Wilson, P. R.; Müller,
   E. A.; Hoyng, P.; Icke, V.; Shore, S. N.; Achterberg, A.; Lucchin, F.;
   Butcher, H.; Ne'Eman, Y.; Heidmann, J.; Belton, M. J. S.; de Graauw,
   Th.; Waters, L. B. F. M.; Pacini, F.; Hultqvist, B.; Akasofu, S. -I.;
   Vial, J. -C.; Schatzman, E.; van der Laan, H.; Cole, K. D.; Vanbeveren,
   D.; Southwood, D.; van der Klis, M.; Katgert, Peter
Bibcode: 1996SSRv...76..339H
Altcode:
  No abstract at ADS

Title: Near-unstable stars: the yellow-white hypergiants.
Authors: de Jager, C.
Bibcode: 1996PINSA..62..461D
Altcode:
  The yellow-white hypergiants are stars of extreme
  luminosities. Atmospheric abundances and mass determinations
  suggest that the stars are evolved objects, moving blueward in their
  evolution. Three well-studied objects are described (Rho Cas, HR
  8752, and HD 33579). Methods of spectroscopic diagnosis allows for a
  determination of the various accelerations acting on the photospheric
  gas. In the Hertzsprung-Russell diagram the yellow hypergiants are
  situated at the low-temperature side of a region of atmospheric
  instability: the Yellow Evolutionary Void. This suggests a relation:
  since these stars are evolving in the HR diagram from the red supergiant
  region towards the blue, it is natural that the atmospheres become
  unstable, with a consequent increased rate of mass loss, when the star
  is nearing the Void.

Title: Atmospheric accelerations and the stability of dynamic
    supergiant atmospheres.
Authors: Nieuwenhuijzen, H.; de Jager, C.
Bibcode: 1995A&A...302..811N
Altcode:
  The goal of this paper is to study instability regions in the HR
  diagram, through a calculation of the atmospheric accelerations for
  spherically symmetric stars, in dynamic equilibrium, without using
  detailed atmospheric models. The input data are five primary data, viz.:
  the stellar luminosity L, the effective temperature T_eff_, the mass M,
  the rate of mass loss ˙(M), and the microturbulent velocity component
  ζ<SUB>mu</SUB>_, while we assume the temperature for a reference
  atmospheric layer, an assumption that appears not to be critical. An
  iterative solution of the momentum equation, simultaneous with some
  other equations, yields values for the various accelerations acting on
  a stellar atmosphere and their algebraic sum g_eff_', the predicted
  effective acceleration. In the first part of the paper we compare
  this latter quantity with the g_eff_-value derived observationally
  from spectral studies of nine program stars and we find overall fair
  agreement. This supports the method as well as the values of the five
  input data. In part 2 we determine g'_eff_ in same way for the whole
  upper part of the Hertzsprung-Russell diagram by using statistical
  primary data on the mass (based on evolutionary calculations), on
  mass-loss and on microturbulence (shock-strengths). We find as a fairly
  general rule that, as stars move along their evolutionary track, and
  for time scales longer than the dynamic time scale of the atmosphere,
  the atmosphere continuously adapts to the new (L,T_eff_)-values
  and essentially remains stable. Current practice of determining the
  stability limit of stellar atmospheres by extrapolating hydrostatic
  models to the Eddington limit is not justified by this study. There
  is one exception: we find a small area around T_eff_=8300K and
  log(L/L<SUB>sun</SUB>_)=5.7, where no solution is possible for evolved
  stars on their blueward evolutionary track; the stars in this area
  have in any case effective accelerations &lt;1mm/s^2^: the "Yellow
  Evolutionary Void". In the third part we estimate approximately
  the pulsational (in-)stability of stars in the upper part of the
  Hertzsprung-Russell diagram, by comparing the g'_eff_ values determined
  in part 2 with the average outward pulsational acceleration. We
  thus confirm the 'Yellow Evolutionary Void' for blueward evolving
  stars, and also find an instability region for blueward evolving
  stars in the area occupied by the Wolf-Rayet stars. This seems to
  agree with the observations that the low-temperature boundary of
  the Yellow Evolutionary Void appears to coincide with the region
  where the yellow hypergiants are clustering. The yellow hypergiants
  are therefore interpreted as blueward moving stars with ZAMS masses
  of about 25-40M<SUB>sun</SUB>_, and actual masses between 15 and
  25M<SUB>sun</SUB>_. For our galaxy it is found that only a few stars
  are situated within the 'Yellow Evolutionary Void', in accordance with
  our expectation.

Title: Book-Review - Isolated Pulsars
Authors: Vauclair, G.; Achterberg, A.; Narlikar, Jayant; Lub, J.;
   van der Laan, H.; Sakai, J. I.; Schrijver, C. J.; de Jager, Cornelis;
   Léna, P.; Vanbeveren, D.; Audouze, J.; van den Heuvel, E. P. J.
Bibcode: 1995SSRv...73..435V
Altcode:
  No abstract at ADS

Title: Book Review: A view of the universe / Cambridge U Press, 1993
Authors: de Jager, C.
Bibcode: 1995SSRv...73..440D
Altcode: 1995SSRv...73..440M
  No abstract at ADS

Title: Ongoing Partial Reconnection in a Limb Flare
Authors: de Jager, Cornelis; Inda-Koide, Mika; Koide, Shinji; Sakai,
   Jun-Ichi
Bibcode: 1995SoPh..158..391D
Altcode:
  The limb flare on August 2, 1993 08:30 UT, consisting of two crossed
  loops, shows evidence of partial X-type reconnection. The observations
  suggest that partial reconnection was an ongoing process during about
  10 min until flare ignition.

Title: Book reviews
Authors: Mewe, R.; de Jager, Cornelis; Kleczek, J.; Icke, Vincent;
   van Bueren, H. G.; Jones, C.; Schatzman, E.; Meynet, G.; van der Kruit,
   P. C.; van der Hucht, K. A.; Raadu, M. A.; Sterken, C.
Bibcode: 1995SSRv...72..679M
Altcode:
  No abstract at ADS

Title: Determining Stellar Masses from a Study of Atmospheric
    Accelerations
Authors: Nieuwenhuijzen, H.; de Jager, C.
Bibcode: 1995LIACo..32..239N
Altcode: 1995sews.book..239N
  No abstract at ADS

Title: Atmospheric Instability Regions in the HR-Diagram and the
    Yellow Evolutionary Void
Authors: de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1995LIACo..32..459D
Altcode: 1995sews.book..459D
  No abstract at ADS

Title: Pulsation of the yellow hypergiant ρ Cassiopeiae in 1970.
Authors: Lobel, A.; de Jager, C.; Nieuwenhuijzen, H.; Smolinski, J.;
   Gesicki, K.
Bibcode: 1994A&A...291..226L
Altcode:
  We checked the hypothesis that the yellow hypergiant ρ Cas is pulsating
  radially, by the application of an improved Baade-Wesselink test, in
  which the effective temperature during an interval of 178 days in 1970
  is determined from an analysis of five stellar spectra. We assume that
  the changing atmospherical circumstances can be represented by various
  static Kurucz models over the pulsation period. The changing effective
  temperature, combined with the radial velocity and luminosity data,
  yields that radial pulsations are only possible if the star would
  have a radius of 2000+/-200R<SUB>sun</SUB>_, while the best value is
  rather 400R<SUB>sun</SUB>_. The conclusion is supported by the study
  of allowed wave motions, which also excludes radial pulsations. An
  investigation of the evolution of splitted absorption profiles
  during this pulsation cycle combined with the radial velocity curve
  reveals that line doubling in ρ Cas is produced by a narrow emission
  line superimposed on a single broad absorption line instead of being
  produced by radially propagating shock waves. We conclude that ρ Cas
  was pulsating non-radially in 1970. Byproducts of the investigation are
  determinations of the variation of the microturbulent velocity (ranging
  between 11.1 and 13.5km/s) and of the effective acceleration of gravity.

Title: Book-Review - I.A.U. TRANS.21B - 21ST General Assembly
Authors: Bergeron, J.; de Jager, C.
Bibcode: 1994SSRv...69..209B
Altcode:
  No abstract at ADS

Title: Book Review: To a rocky moon: a geologist's history of lunar
    exploration / U Arizona Press, 1993
Authors: Williams, D. E.; de Jager, C.
Bibcode: 1994SSRv...69..213W
Altcode:
  No abstract at ADS

Title: The shock strength in super- and hypergiant atmospheres
    derived from microturbulence data
Authors: Nieuwenhuijzen, H.; de Jager, C.; Cuntz, M.
Bibcode: 1994A&A...285..595N
Altcode:
  This study is based on evidence that small-scale motions, observed
  as microturbulent line broadening, in the atmospheres of super- and
  hypergiants can possibly be interpreted as fields of shock waves moving
  outwards through the atmosphere. We derive values for the average shock
  strength M_1_ for a number of well-observed stars. We found that the
  value of M_1_ increases strongly with stellar luminosity, suggesting
  that shock wave pressure is relevant for the stability limit of most
  evolved stars (Humphreys-Davidson Limit) and for stellar evolution
  calculations. Our results however apply only to those stars in which
  photospheric shock wave patterns exist. For some stars we studied the
  dependence of M_1'_ on the Rosseland optical depths τ_R_ and we found
  that M_1'_(τ_R_) does not change very much. We compared the energy
  fluxes associated with the shocks with acoustic energy fluxes given
  by Bohn and with radiative energy losses from the chromospheres (only
  possible for cool giants and supergiants). We found that these fluxes
  are compatible for cool stars. The energy fluxes of Bohn cannot be
  used for super- and hypergiants with T_eff_ &gt; 6500 K as all these
  stars are lacking convection zones.

Title: Book reviews
Authors: Burlaga, L. F.; Kleczek, J.; Schatzman, E.; Adams, D. J.;
   Rutten, R. J.; van der Kruit, P. C.; de Jager, Cornelis; Trams, N. R.;
   Righini, Alberto; Ergma, E.; Grün, Eberhard; Icke, Vincent
Bibcode: 1994SSRv...67..223B
Altcode:
  No abstract at ADS

Title: Massive stars: setting the stage.
Authors: de Jager, C.
Bibcode: 1994ems..conf....7D
Altcode:
  The paper gives a summary of the situation mid-1993 of theory and
  observations regarding massive stars. The author describes: stellar
  mass loss and its implications, pre-main-sequence evolution, the
  main sequence, problems of atmospheric instability, Luminous Blue
  Supergiants, Yellow Hypergiants, Wolf-Rayet stars and supernovae.

Title: Current-carrying loops and their interaction in solar
    flares. Workshop summary.
Authors: de Jager, C.
Bibcode: 1994clis.conf....5D
Altcode:
  The contributions to the Workshop are placed in the context of
  present-days views on the origin, structure and development of flares,
  by discussing: flare classification; the study of gradual flares;
  the Impulsive Phase Explosion; observations of loop interactions
  and flare trigger; physics of single loops and loop reconnnection;
  the three phases of acceleration in flares. At some places one goes
  beyond the contents of the Workshop presentation in order to place
  the research in the broader context of present-days views on flares.

Title: Multiple X-type reconnection in a small solar limb flare
    observed by YOHKOH.
Authors: de Jager, C.; Inda-Koide, M.; Koide, S.; Sakai, J. -I.
Bibcode: 1994clis.conf..149D
Altcode:
  The limb flare on August 2, 1993 08:30 UT appears to be a schoolclass
  example of X-type reconnection. Its study shows that reconnection is a
  multiple process that gradually leads to flaring. The authors compared
  observations with predictions from X-type reconnection theory, while
  also including a comparison of the radiated energy with the magnetic
  energy content of the azimuthal field component.

Title: Book Review: Solar system evolution: a new perspective /
    Cambridge U Press, 1992
Authors: de Jager, C.
Bibcode: 1994SSRv...67..228D
Altcode: 1994SSRv...67..228T
  No abstract at ADS

Title: A generalized version of the Rankine-Hugoniot relations
    including ionization, dissociation and related phenomena
Authors: Nieuwenhuijzen, H.; de Jager, C.; Cuntz, M.; Lobel, A.;
   Achmad, L.
Bibcode: 1993A&A...280..195N
Altcode:
  For purposes of computing shocks in stellars atmospheres and winds we
  have developed a generalized version of the Rankine-Hugoniot relations
  including ionization, dissociation, radiation and related phenomena such
  as excitation, rotation and vibration of molecules. The new equations
  are given in analytical form. They are valid as long as the internal
  energy E, the total pressure P, and the first adiabatic coefficient
  gamma<SUB>1</SUB> can be evaluated. However, we have not treated shock
  structures. In the case of non-LTE we have to employ an approximation
  for gamma<SUB>1</SUB> because in that case no definition exists. Our new
  version of the Rankine-Hugoniot relations can easily be used for many
  purposes including ab-initio modeling. In our derivation we introduce
  a parameter gamma<SUB>H</SUB>, which is definded as the ratio of the
  enthalpy H (sometimes called heat function w) to the internal energy
  E (sometimes called U). Using this parameter we solve the equations
  for changing mu and (d(natural log P)/d(natural log rho))<SUB>ad</SUB>
  identically equal to gamma<SUB>1</SUB> on both sides of the shock. Both
  gamma<SUB>H</SUB> and gamma<SUB>1</SUB>, and also mu are functions
  of pressure P and temperature T. We present: (1) the derivation,
  (2) examples of gamma<SUB>1</SUB> (P,T) and gamma<SUB>H</SUB> (P,T)
  which include/exclude ionization and radiation, and (3) as an example
  the differences in post-shock parameters as function of the pre-shock
  temperature for the case with ionization and without radiation.

Title: A statistical study of the distribution of stars in the log
    Teff - log gN plane.
Authors: Achmad, L.; de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1993A&AS..100..465A
Altcode:
  A statistical study is made of the distribution of stars in the log
  T(eff)-log gN plane based on the photometric data set of the Geneva
  system. To that end we made an analysis of the methods for deriving the
  atmospheric parameters T(eff) and log gN (the Newtonian acceleration
  of gravity) from different sets of photometric data, corrected for
  the influence of extinction. We found, using the Geneva photometric
  system, that the Newtonian gravity can only be determined with good
  accuracy for stars with effective temperatures below 10,000 K. We
  show the relations between luminosity class and gravity for stars with
  T(eff) values of 3.75 to 3.94 and compare these with the theoretically
  predicted radiative instability line of Gustafsson and Plez (1992).

Title: Book-Review - Sky Catalogue 2000.0 - VOL.1 - Stars Magnitude
    8.0
Authors: de Jager, C.; Hirshfeld, A.; Sinnott, R. W.; Ochsenbein, F.
Bibcode: 1993SSRv...63..395D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Narlikar, J. V.; Hovenier, J. W.; Achterberg, A.; Barr, P.;
   de Jager, Cornelis; van der Hulst, J. M.
Bibcode: 1993SSRv...63..391N
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Murawski, K.; Grevesse, N.; Piteri, S.; Nieuwenhuyzen, H.;
   van der Hage, J. C. H.; Icke, Vincent; Hovenier, J. W.; Rutten, R. J.;
   De Greve, J. P.; Kaufmann, P.; Burki, G.; de Jager, Cornelis
Bibcode: 1993SSRv...65..365M
Altcode:
  No abstract at ADS

Title: Massive stars: Setting the stage
Authors: de Jager, C.
Bibcode: 1993SSRv...66....7D
Altcode:
  The paper gives a summary of the situation mid-1993 of theory and
  observations regarding massive stars. I describe: stellar mass loss
  and its implications, pre-main-sequence evolution, the main sequence,
  problems of atmospheric instability, Luminous Blue Supergiants, Yellow
  Hypergiants, Wolf-Rayet stars and supernovae.

Title: Book reviews
Authors: Rutten, R. J.; Mewe, R.; Houziaux, L.; Cheng, Chung-Chieh;
   van der Klis, M.; Sylwester, Janusz; Tajima, T.; Kresák, Ľ.; Minarik,
   S.; de Jager, Cornelis; van der Kruit, P. C.
Bibcode: 1993SSRv...65..181R
Altcode:
  No abstract at ADS

Title: Gravity waves in the atmosphere of Betelgeuse?
Authors: de Jager, C.
Bibcode: 1993Obs...113...43D
Altcode:
  No abstract at ADS

Title: Book-Review - Reports on Astronomy
Authors: McNally, D.; de Jager, C.
Bibcode: 1993SSRv...62R.211M
Altcode:
  No abstract at ADS

Title: Book Review: Men and women of space / Univelt, 1992
Authors: de Jager, C.
Bibcode: 1993SSRv...65..372D
Altcode: 1993SSRv...65..372H
  No abstract at ADS

Title: Editorial
Authors: de Jager, Cornelis; Howard, Robert F.; švestka, Zdeněk
Bibcode: 1993SoPh..143D...7D
Altcode:
  No abstract at ADS

Title: Book-Review - Mars the Red Planet
Authors: Catermole, P.; de Jager, C.
Bibcode: 1993SSRv...65..190C
Altcode:
  No abstract at ADS

Title: Book Review: The hour of our delight: cosmic evolution, order,
    and complexity / Freeman, 1991
Authors: de Jager, C.
Bibcode: 1993SSRv...62Q.210D
Altcode:
  No abstract at ADS

Title: Book Review: An introduction to astrophysical hydrodynamics /
    Academic Press, 1992
Authors: de Jager, C.
Bibcode: 1993SSRv...65..189D
Altcode: 1993SSRv...65..189S
  No abstract at ADS

Title: Book Review: The cosmic water hole / MIT Press, 1991
Authors: de Jager, C.
Bibcode: 1993SSRv...62R.210D
Altcode:
  No abstract at ADS

Title: On the instability parameters of stellar atmospheres.
Authors: Lobel, A.; Achmad, L.; de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1992A&A...264..147L
Altcode:
  We discuss the significance of the adiabatic exponents Gamma1, Gamma2,
  and Gamma3 and derive expressions for their calculation in a stellar
  atmosphere including simultaneous single-ionization of various elements
  and the presence of an equilibrium radiation field. A discussion is
  given of the relation of Gamma1 to dynamic instability. It is shown
  that some parts of some Kurucz models for extreme supergiant atmosphere
  are dynamically instable as a result of ionization and radiation in
  the deeper layers.

Title: Book Review: Infrared and radio astronomy and astrometry /
    Pergamon, 1991
Authors: de Jager, C.
Bibcode: 1992SSRv...61..428K
Altcode:
  No abstract at ADS

Title: Yellow hypergiant interferometry: a clue to understanding
    evolutionary instability.
Authors: De Jager, Cornelis; Nieuwenhuijzen, Hans
Bibcode: 1992ESASP.344..109D
Altcode: 1992spai.rept..109D
  Yellow hypergiants are stars with nearly unstable atmospheres,
  characterized by strong low-mode non-radial pulsations and intense
  mass loss. In the Hertzsprung-Russell diagram they are located at the
  cool side of a region where atmospheres are unstable. The atmospheric
  pulsations should manifest themselves as hot and cool areas on the
  disk. The strong mass loss will lead to a rather dense equatorial
  decretion disk that should be observable interferometrically. Many
  other types of stars may have similar properties.

Title: Science, para-science, pseudo-science.
Authors: de Jager, C.
Bibcode: 1992ZemVs...2...98D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Blanc, M.; van der Hucht, K. A.; Heintze, J. R. W.; Kaufmann,
   P.; Neéman, V.; Nieuwenhuijzen, H.; Stahl, O.; de Jager, Cornelis;
   van der Kruit, P. C.
Bibcode: 1992SSRv...62..205B
Altcode:
  No abstract at ADS

Title: Atmospheric model and dynamical state of the atmosphere of
    the supergiant Eta Leonis (A0 Ib).
Authors: Lobel, A.; Achmad, L.; de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1992A&A...256..159L
Altcode:
  The authors redetermined the atmospheric model parameters of η Leo
  on the basis of a set of equivalent width data of 47 Fe I and 71 Fe
  II lines, determined previously by B. Wolf (1971). The procedure
  followed is an iterative one, involving the determination of the
  depth variation of microturbulence. The authors find: T<SUB>eff</SUB>
  = 10200±370K; log g = 1.9±0.4 cm s<SUP>-1</SUP> and Δlog Z (=
  logarithmic abundances compared to the solar values) = 0.14±0.10
  for Fe. A further result is that the line of sight microturbulence
  velocity component ζ<SUB>μ</SUB> hardly varies with depth and equals
  5.4±0.7 km s<SUP>-1</SUP>, hence the motion field, which consists of
  isothermal shock waves, obeys the "limiting shockstrength regime". The
  observationally determined shock strenght is M<SUB>s</SUB><SUP>obs</SUP>
  = 2.3.

Title: Book reviews
Authors: Bhatnagar, Arvind; Achterberg, A.; de Jager, Cornelis;
   Kaufmann, P.; van Gent, R. H.; Rodríguez, L. F.
Bibcode: 1992SSRv...59..407B
Altcode:
  No abstract at ADS

Title: Areas of atmospheric instability in the Hertzsprung-Russell
    diagram
Authors: Nieuwenhuijzen, H.; de Jager, C.
Bibcode: 1992iesh.conf..171N
Altcode:
  No abstract at ADS

Title: Supergiant shock strength in relation to stellar luminosity
Authors: Nieuwenhuijzen, H.; de Jager, C.
Bibcode: 1992iesh.conf..127N
Altcode:
  No abstract at ADS

Title: Non-Spherical Envelopes and Flows (Invited Paper)
Authors: de Jager, C.
Bibcode: 1992ASPC...22..400D
Altcode: 1992nvos.work..400D
  No abstract at ADS

Title: Introduction
Authors: de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1992iesh.conf....9D
Altcode:
  No abstract at ADS

Title: Spectroscopic diagnostics of a field of shock waves
Authors: de Jager, C.
Bibcode: 1992iesh.conf..129D
Altcode:
  No abstract at ADS

Title: Dynamics and stability of supergiant atmospheres
Authors: de Jager, C.
Bibcode: 1992iesh.conf...98D
Altcode:
  No abstract at ADS

Title: Editorial
Authors: de Jager, Cornelis; Švestka, Zdeněk; Howard, Robert F.
Bibcode: 1992SoPh..137D...5D
Altcode:
  No abstract at ADS

Title: Instabilities in evolved super- and hypergiants
Authors: de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1992iesh.conf.....D
Altcode:
  No abstract at ADS

Title: The large-scale atmospheric motion field of Alpha Orionis
Authors: de Jager, C.; Eriksson, K.
Bibcode: 1992iesh.conf..117D
Altcode:
  No abstract at ADS

Title: Book-Review - Rotation and Mixing in Stellar Interiors
Authors: Goupil, M. J.; Zahn, J. P.; de Jager, C.
Bibcode: 1992SSRv...59..410G
Altcode:
  No abstract at ADS

Title: Book Review: The numerical modelling of non-linear stellar
    pulsation. Problems and prospects / Kluwer, 1990
Authors: de Jager, C.
Bibcode: 1991SSRv...58..383D
Altcode:
  No abstract at ADS

Title: The contribution function for the depth of formation of lines
    in a stellar atmosphere.
Authors: Achmad, L.; de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1991A&A...250..445A
Altcode:
  A function describing the contribution of the various layers to the
  formation of spectral lines in a stellar atmosphere is derived. The
  function is valid for absorption lines as well as for emission lines,
  and is based on the separation of the line and the continuum emergent
  radiation. In this respect, this function differs from the conventional
  contribution functions, which are based on the total radiation or on
  the line depression. It is shown that it does not appear possible
  to find a unique function using the concept of line depression, in
  contrast to the function developed in this paper.

Title: Atmospheric model parameters and shock wave field for the
    supergiant alpha Carinae (FOIb).
Authors: Achmad, L.; de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1991A&A...249..192A
Altcode:
  The depth dependence of microturbulent velocity in the atmosphere
  of alpha Carinae is examined by means of observational data from
  the 694 FeI and FeII lines. The model atmospheric parameters are
  expanded to include effective temperature, gravity, microturbulence,
  and abundance because the depth dependence is sensitive to the model
  atmosphere. The depth formation of the spectral lines is reviewed,
  and a method of linearization is applied to the analyses of both
  spectral lines and atmospheric parameters. The average microturbulent
  velocity component is 2.8 +/- 0.2 km/s, and the differences between
  the turbulent velocities are small for Fe lines that are neutral or
  singly ionized. Microturbulent velocity does not vary significantly
  with depth which suggests that the atmosphere of alpha Carinae obeys
  the limiting shock-strength regime.

Title: High-Energy Flare Explosions Driven by 3-DIMENSIONAL X-Type
    Current Loop Coalescence
Authors: Sakai, Jun-Ichi; de Jager, Cornelis
Bibcode: 1991SoPh..134..329S
Altcode:
  We present a model for high-energy solar flare explosions driven by
  3-dimensional X-type current loop coalescence. The 3-dimensional X-type
  current loop coalescence, where two crossed flux-tubes interact at
  one point, is a fundamentally new process as compared to the 1-D and
  2-D cases studied earlier. This process is studied by a first-order
  approach of the relevant variables near the point of coalescence;
  it appears to yield reliable information in a sufficiently large area
  around this point. It is shown that, following a strong plasma collapse
  due to the pinch effect, a point-like plasma explosion can be driven
  while fast magnetosonic shock waves can also be excited. We found that
  the conditions in the area producing the remarkable flare bursts of 21
  May, 1984 were indeed such that the many flare spikes could have been
  due to 3-D explosive X-type current loop coalescence. We also show,
  by studying the conditions of shock formation in a gamma ray flare,
  that the time delay of γ-rays from the impulsive phase could be the
  time needed for the shock formation in the flaring region.

Title: The luminosity of the B2 hypergiant HD 80077.
Authors: Carpay, J.; de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1991A&A...248..475C
Altcode:
  The extremely bright and relatively stable hypergiant HD 80077 is an
  enigmatic object. Since the star is assumed to have a luminosity of
  2 x 10 exp 6, considerable variability and a large mass loss rate
  would be expected. However, its mass loss rate of (5 +10/-3) x 10
  exp -6 solar mass/yr and its variability are very low with respect
  to its luminosity. The star is assumed to be a member of the cluster
  Pismis 11, and therefore to have a known distance. The above-mentioned
  luminosity has been derived using the apparent visual magnitude,
  the bolometric correction and the distance to Pismis 11. Indications
  that the star is not a member of Pismis 11, but a foreground star,
  therefore having a lower luminosity have been looked for. For this,
  no evidence has been found.

Title: Elementary Flare Bursts Explained by Explosive Coalescence
Authors: de Jager, Cornelis; Sakai, Jun-Ichi
Bibcode: 1991SoPh..133..395D
Altcode:
  The observed burst durations of Elementary Flare Bursts (5-25 s), as
  well as the related other flare characteristics, such as the temperature
  (30-50 MK), the electron density (log ne = 10 to 11) and the magnetic
  field strengths (100 G to 200 G) can be explained quantitatively by
  the mechanism of explosive coalescence.

Title: The atmospheric motion field in super- and hypergiants.
Authors: de Jager, C.; de Koter, A.; Carpay, J.; Nieuwenhuijzen, H.
Bibcode: 1991A&A...244..131D
Altcode:
  The paper presents an investigation of the motion fields in the outer
  atmospheres of a few well-studied supergiants and hypergiants for which
  good observational information is available from spectral studies. The
  following topics are examined: the existence of pressure and gravity
  waves; the dissipation of gravity-wave energy by radiative damping; the
  reduction of the radiative damping of gravity waves by layer curvature;
  the large-scale motion of two moderate supergiants (Alpha Per and 41
  Cyg); pressure waves and their transformation into shock waves; weak
  shock dissipation of wave energy; the spectrum of shock-wave energy;
  and the gravity wave and shock wave components of motion in supergiants
  and hypergiants.

Title: Hoe ontstaan zonnevlammen?
Authors: de Jager, C.
Bibcode: 1991Zenit..18...48D
Altcode:
  No abstract at ADS

Title: Book Review: Lectures on spectral-line analysis: F,G, and K
    stars / The Publisher, Ontario, Canada
Authors: de Jager, C.
Bibcode: 1990SSRv...54..451D
Altcode: 1990SSRv...54..451G
  No abstract at ADS

Title: Book Review: NGC 2000.0 : The complete new general catalogue
    and index catalogues of nebulae and star clusters. / Sky Publishing
    Corp. and CUP, 1988
Authors: Sinnnott, R. W.; de Jager, C.
Bibcode: 1990SSRv...54R.190S
Altcode:
  No abstract at ADS

Title: Book-Review - Highlights of Astronomy
Authors: McNally, D.; de Jager, C.
Bibcode: 1990SSRv...54..450M
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Haubold, Hans Joachim; Snijders, M. A. J.; van Rensbergen,
   W.; de Jager, Cornelis; van de Weygaert, R.; Achterberg, A.; Linssen,
   P. F. J.; Hoyng, P.; Kleczek, J.; Bauer, Siegfried J.; Hayakawa, S.
Bibcode: 1990SSRv...54..187H
Altcode:
  No abstract at ADS

Title: Parametrization of stellar rates of mass loss as functions
    of the fundamental stellar parameters M, L, and R.
Authors: Nieuwenhuijzen, H.; de Jager, C.
Bibcode: 1990A&A...231..134N
Altcode:
  We investigate the dependence of M<SUP>ṡ</SUP> on the three
  fundamental parameters mass M, radius R and luminosity
  L for a sample of 247 stars (number of independent
  data points with weight unity =454). "Average expected"
  mass-values are derived from evolutionary calculations. A
  simple formula, viz. <P />-M<SUP>ṡ</SUP>=9.6310<SUP>-15</SUP>
  (L/L<SUB>sun</SUB>)<SUP>1.42</SUP> (M/M<SUB>sun</SUB>)<SUP>0.16</SUP>
  (R/R<SUB>sun</SUB>)<SUP>0.81</SUP> M<SUB>sun</SUB> M<SUB>sun</SUB>
  yr<SUP>-1</SUP> <P />appears to give a good representation of observed
  rates of mass loss over the whole Hertzsprung-Russell diagram. For
  luminous stars with T<SUB>eff</SUB> &gt; 5000 K the standard deviation
  is equal to the intrinsic error (0.37) of the rate of mass loss. The
  representation is comparable to or even better than that of the
  expressions by Reimers and Lamers, which were derived for restricted
  areas of the HR-diagram.

Title: An explanation of the `granulation boundary' in the HR diagram
Authors: de Jager, Cornelis
Bibcode: 1990SoPh..126..201D
Altcode:
  The granulation boundary is a line running in the HR diagram from
  about F0V stars to G1Ib. It divides the HR diagram in two regions
  in which the `spectral line bisector' behaves differently. To the
  right (cooler stars) the Fraunhofer lines in stellar spectra show
  the characteristics typical for convective motions. For hot stars it
  indicates the presence of large velocities involving a large part of
  the line-forming region. We give evidence that the opposite behaviour
  shown by spectra of hotter stars can be explained by gravity waves.

Title: Science Fringe Science and Pseudo-Science
Authors: de Jager, C.
Bibcode: 1990QJRAS..31...31D
Altcode:
  No abstract at ADS

Title: Les étoiles les plus lumineuses.
Authors: de Jager, Cornelis
Bibcode: 1990CRASG...7....1D
Altcode:
  It is pointed out that there is an upper limit to the brightness of
  stars, beyond which no star can exist. It is shown that this limit
  coincides with the brightness limit for which the effective acceleration
  (i.e., the sum of the effects of gravitation and forces due to thermal,
  radiative, and turbulent pressure directed outward) drops to a very
  small value. In atmospheres of the most extreme stars, gravity waves can
  occur with very long wavelengths and elevated periods. It is suggested
  that it is these waves that are responsible for the instabilities of
  supergiant and hypergiant stars.

Title: Book Review: Data of the planetary system / Akademie Verlag,
    Berlin
Authors: de Jager, C.
Bibcode: 1990SSRv...53..168D
Altcode: 1990SSRv...53..168R
  No abstract at ADS

Title: Acceleration phases in high-energy solar flares
Authors: de Jager, C.
Bibcode: 1990AdSpR..10i.101D
Altcode: 1990AdSpR..10..101D
  In high-energy solar flares, defined as flares that emit an observable
  gamma-ray spectrum, there can be three subsequent phases of particle
  acceleration. Primary acceleration of electrons to ~ 10 MeV occurs
  within less than 0.1 s. It is suggested that this happens in many
  explosive coalescences between the many fluxthreads in the flare
  area. One or two seconds later ions are accelerated to ~ 100 MeV in
  an expanding shock-wave dominated electric field system; this is the
  second phase. A few minutes later ions can be further accelerated
  (to ~ GeV energies) in a field line system opening to space. This is
  the third phase.

Title: Book-Review - Planets and Perception - Telescopic Views and
    Interpretations 1609-1909
Authors: Sheehan, W.; de Jager, C.
Bibcode: 1990SSRv...53..170S
Altcode:
  No abstract at ADS

Title: Book-Review - Planets and Perception - Telescopic Views and
    Interpretations - 1609-1909
Authors: Sheehan, W.; de Jager, C.
Bibcode: 1990SSRv...53Q.170S
Altcode:
  No abstract at ADS

Title: The Solar X-Ray/Cosmic Gamma-Ray Burst Experiment Aboard the
    Ulysses Mission
Authors: Hurley, K.; Sommer, M.; Paschmann, G.; Boer, M.; de Jager,
   C.; Heise, J.; van Rooijen, J.; Niel, M.; Vedrenne, G.; Cline, T.;
   Henoux, J. -C.
Bibcode: 1990ICRC....5...74H
Altcode: 1990ICRC...21e..74H; 1989ICRC....5...74H
  No abstract at ADS

Title: Book reviews
Authors: de Graaf, W.; Doom, C.; Wesselius, P. R.; de Jager, Cornelis;
   van der Kruit, P. C.; Achterberg, A.; de Waard, H.; van Hugo, Woerden;
   Kleczek, J.; Hudson, H. S.; van der Hucht, K. A.
Bibcode: 1989SSRv...51..425D
Altcode:
  No abstract at ADS

Title: Acceleration Through X-Type Coalescence in a Small Energetic
    Flare
Authors: Sakai, Jun-Ichi; de Jager, Cornelis
Bibcode: 1989SoPh..123..389S
Altcode:
  We studied the acceleration conditions in the small but fairly energetic
  flare of May 21, 1984 at 13∶26 UT. The most pronounced aspect of
  this flare was a series of 13 microwave/X-ray spikes, each lasting
  for about 0.1 s. A previous study has shown that each of these was due
  to a series of successive sudden formations of small plasma knots of
  high-energy particles. Each of these knots lost its energy in about 50
  ms. In the present study we show that these knots can originate by the
  process of X-type (3-D) flux tube coalescence. The predicted rise time
  (30 to 50 ms) and energy are in good agreement with the observationally
  derived parameters.

Title: Coronal Explosions as a Signature of Current Loop Coalescence
    in Solar Flares
Authors: Sakai, Jun-Ichi; de Jager, Cornelis
Bibcode: 1989SoPh..123..393S
Altcode:
  The coronal explosions, discovered by De Jager and Boelee (1984),
  and interpreted by them as manifestations of plasma streaming out of
  the flare kernels, can also be interpreted as signatures of current
  loop coalescence in the flaring region.

Title: Introduction
Authors: de Jager, Cornelis
Bibcode: 1989SSRv...50..393D
Altcode:
  No abstract at ADS

Title: Space Future Forum
Authors: Sagdeev, R. Z.; Marchuk, G. I.; Raushenbakh, B. V.; de Jager,
   C.; Lown, B.; Ortner, J.; Keller, S.; Bonnet, R.; Dakov, M.; Dunaev,
   A. I.; Sagan, C.
Bibcode: 1989SSRv...50..395S
Altcode: 1989IAUCo.107..395S
  No abstract at ADS

Title: Book-Review - International Directory of Astronomical
    Associations and Societies
Authors: Heck, A.; Manfroid, J.; de Jager, C.
Bibcode: 1989SSRv...50..389H
Altcode: 1989IAUCo.107..389H
  No abstract at ADS

Title: Book reviews
Authors: Marov, M. Ya; Garmany, C. D.; Heck, André; Schadee, A.;
   McNally, D.; van der Kruit, P. C.; Pecker, J. -C.; de Jager, Cornelis;
   Somov, B. V.
Bibcode: 1989SSRv...50..385M
Altcode:
  No abstract at ADS

Title: Mass loss rate and atmospheric turbulence of the B2 hypergiant
    HD 80077.
Authors: Carpay, J.; de Jager, C.; Nieuwenhuijzen, H.; Moffat, A.
Bibcode: 1989A&A...216..143C
Altcode:
  Turbulence in the atmosphere of HD 80077, situated on the
  Humphreys-Davidson limit, has been studied in order to test whether
  turbulence plays a role in the instability of very hot stars. A
  mass loss rate of (5 +10 or -3) x 10 to the -6th solar masses/yr is
  obtained which is very low for stars along the upper luminosity limit
  in the Hertzsprung-Russell diagram. The object has a photospheric
  microturbulent velocity component of 23 + or - 2 km/s and an outwardly
  directed turbulent acceleration of 11-24 cm/sq s.

Title: Book-Review - Exploring the Universe with the IUE Satellite
Authors: Kondo, Y.; Wamsteker, W.; Boggess, A.; Grewing, M.; de Jager,
   C.; Lane, A. L.; Linksy, J. L.; Wilson, R.; Waters, R.
Bibcode: 1989SSRv...49..443K
Altcode: 1988SSRv...49..443K
  No abstract at ADS

Title: Editorial
Authors: de Jager, Cornelis; Švestka, Zdeněk; Howard, Robert F.
Bibcode: 1989SoPh..121D...9D
Altcode:
  No abstract at ADS

Title: Coordinated observations of a large impulsive flare on UV Ceti.
Authors: de Jager, C.; Heise, J.; van Genderen, A. M.; Foing, B. H.;
   Ilyin, I. V.; Kilkenny, D. S.; Marvridis, L.; Cutispoto, G.; Rodono,
   M.; Seeds, M. A.; Yuen, K. Ng.; van Driel, W.; Rabattu, X.; Zodi,
   A. M.; Vilas Boas, J. W. S.; Scalise, E.; Schaal, R. E.; Kaufmann,
   P.; Waelkens, C.
Bibcode: 1989A&A...211..157D
Altcode:
  The characteristics of the major flare observed on UV Ceti on
  Decemmber 1985 at 01:26 UT during an international observing campaign
  are described. X-ray observations were obtained with Exosat in the
  0.06-0.3 keV bands and 1-6 keV bands; optical photometry was obtained
  in 11 wavelength bands, and spectra were recorded in the wavelength
  range 3500 to 7000 A. The results of the data analysis support the
  Impulsive Explosion Model proposed for stellar flares and disclose
  some differences with the solar case.

Title: Book-Review - Reports of Astronomy
Authors: Swings, J. P.; de Jager, C.
Bibcode: 1989SSRv...51R.426S
Altcode:
  No abstract at ADS

Title: Atmospheric Dynamics of Luminous Stars
Authors: de Jager, Cornelis; Carpay, Joost; de Koter, Alex;
   Nieuwenhuijzen, Hans; Schellekens, Erik
Bibcode: 1989ASSL..157..211D
Altcode: 1989IAUCo.113..211D; 1989plbv.coll..211D
  A review is given of data and theories on the motion fields in super
  and hypergiants with special reference to LBVs. It is shown that the
  radiative momentum flux is incapable of driving the episodical bursts
  of mass loss of these stars and that there are several indications
  that the LBV-phenomenon is hydrodynamically driven. The sum of
  turbulent and radiative accelerations in the atmospheres of the most
  luminous stars compensates the gravitational acceleration for stars
  near the Humphreys-Davidson limit. This explains their atmospheric
  near-instability. The motion field in the atmosphere of a typical
  LBV consists mainly of low-order gravity waves, while acoustic waves
  are rapidly damped. These gravitation waves may be stochastic rather
  than coherently ordered. These stochastic pulsations are assumed to
  be responsible for the LBV phenomenon.

Title: Development of concepts on stellar atmospheres and envelopes.
Authors: de Jager, Cornelis
Bibcode: 1989mse..proc....3D
Altcode:
  In the years before about 1940 the physical and mathematical bases were
  laid for the quantitative analysis of stellar atmospheres, but the years
  around 1940 saw a number of research results that greatly changed the
  face of astrophysics and were the starting-points for important further
  developments. The most important of these were: the discovery of the
  sub-nuclear energy source; that the solar and cosmic abundance ratio
  H/metals was about 10000; the identification of the coronal lines;
  the elaboration of MHD. The author describes some highlights of the
  periods before and around 1940, of the period around 1950, and presents
  a brief review of current problems in the study of stellar atmospheres.

Title: Flare energetics.
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veck, N. J.
Bibcode: 1989epos.conf..377W
Altcode:
  The authors have sought to establish a comprehensive and self-consistent
  picture of the sources and transport of energy within a flare. To
  achieve this goal, they chose five flares in 1980 that were well
  observed with instruments on the Solar Maximum Mission, and with other
  space-borne and ground-based instruments. The events were chosen to
  represent various types of flares. Details of the observations available
  for them and the corresponding physical parameters derived from these
  data are presented. The flares were studied from two perspectives,
  the impulsive and gradual phases, and then the results were compared
  to obtain the overall picture of the energetics of these flares. The
  authors also discuss the role that modeling can play in estimating the
  total energy of a flare when the observationally determined parameters
  are used as the input to a numerical model. Finally, a critique of
  our current understanding of flare energetics and the methods used to
  determine various energetics terms is outlined, and possible future
  directions of research in this area are suggested.

Title: Rates of mass loss in the upper H-R diagram.
Authors: Nieuwenhuijzen, H.; de Jager, C.
Bibcode: 1989ASSL..157..305N
Altcode:
  No abstract at ADS

Title: Luminous Blue Variables Need not BE Blue
Authors: de Jager, C.; van Genderen, A. M.
Bibcode: 1989ASSL..157..127D
Altcode: 1989IAUCo.113..127D; 1989plbv.coll..127D
  No abstract at ADS

Title: Atmospheric Parameters and Accelerations in the Outer Parts
    of Luminous Hot Stars
Authors: Nieuwenhuijzen, H.; de Jager, C.
Bibcode: 1989ASSL..157..287N
Altcode: 1989plbv.coll..287N; 1989IAUCo.113..287N
  No abstract at ADS

Title: Mass Loss Rates in the Hertzprung-Russell Diagram
Authors: de Jager, C.; Nieuwenhuijden, H.; van der Hucht, K. A.
Bibcode: 1988BICDS..35..141D
Altcode:
  No abstract at ADS

Title: The relation between rotational velocity and mass-loss for
    massive stars
Authors: Nieuwenhuijzen, H.; de Jager, C.
Bibcode: 1988A&A...203..355N
Altcode:
  The dependence of stellar mass loss on rotation for nonemission-line
  stars is investigated, confirming numerically an earlier result showing
  a seemingly good correlation between the stellar mass-loss rate (MLR)
  and v(rot)sin(i) but showing that this correlation merely reflects
  the distribution of MLR and v(rot)sin(i) over the Hertzsprung-Russell
  diagram; it is physically not real. An attempt is made to disentangle
  the dependence of MLR on the three variables: Teff, L, and v(rot)sin(i)
  by empirically determining the relation over the HR diagram. It then
  appears that, for each point in the HR diagram, MLR depends only weakly
  on v(rot)sin(i), in agreement with theoretical predictions. For Be and
  shell stars the MLR for their high-latitude parts follows approximately
  the same rule as the one valid for non-Be stars, while the MLR from
  their equatorial areas is larger by a factor 100, in rough agreement
  with a theoretical prediction.

Title: The dynamical state of the atmosphere of the supergiant alpha
    Scorpii(M 1.5 Iab).
Authors: de Koter, A.; de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1988A&A...200..146D
Altcode:
  The dynamical state of the atmosphere of α Sco A (M1.5 Iab) has been
  investigated on the basis of spectra in the visual spectral range. The
  authors find the ratio between the microturbulent velocity component and
  the velocity of sound to increase from 0.4 at τ<SUB>5000</SUB> = 1 to
  0.6 at τ<SUB>5000</SUB> = 10<SUP>-3</SUP>. The turbulent acceleration
  g<SUB>t</SUB> is 0.15 cm s<SUP>-2</SUP> which should be compared
  with g<SUB>grav</SUB> = -1.0 cm s<SUP>-2</SUP>. Per scaleheight the
  fraction 0.95 of the mechanical energy flux is dissipated, a remarkably
  large value for the relatively small microturbulent velocity. The
  macroturbulent velocity component has the surprisingly large value of
  16 km s<SUP>-1</SUP>.

Title: Solar flares through electric current interaction
Authors: de Jager, Cornelis
Bibcode: 1988Ap&SS.144..311D
Altcode:
  The fundamental hypothesis by Alfvén and Carlqvist (1967) that solar
  flares are related to electrical currents in the solar chromosphere
  and low corona is investigated in the light of modern observations. We
  confirm the important role of currents in solar flares. There must
  be tens of such current loops (‘flux threads’) in any flare,
  and this explains the hierarchy of bursts in flares. We summarize
  quantitative data on energies, numbers of particles involved and
  characteristic times. A special case is the high-energy flare: this one
  may originate in the same way as less energetic ones, but it occurs
  in regions with higher magnetic field strength. Because of the high
  particle energies involved their emission seats live only very briefly;
  hence the area of emission coincides virtually with the seat of the
  instability. These flares are therefore the best examples for studying
  the primary instability leading to the flare. Finally, we compare the
  merits of the original Alfvén-Carlqvist idea (that flares originate
  by current interruption) with the one that they are due to interaction
  (reconnection) between two or more fluxthreads. We conclude that a
  final decision cannot yet be made, although the observed extremely
  short time constants of flare bursts seem to demand a reconnection-type
  instability rather than interruption of a circuit.

Title: The atmospheric structure, stellar wind and binary
    characteristics ofthe hypergiant HR 8752 (G0-5Ia+).
Authors: Piters, A.; de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1988A&A...196..115P
Altcode:
  The photospheric parameters of the hypergiant HR 8752 were determined
  on the basis of photometric and spectroscopic data. Results are T(eff)
  = 4200 K, log g(eff) = 0; the microturbulent velocity component is
  5.9 + or - 0.4 km/s, a value close to the velocity of sound. The
  turbulent pressure and its gradient could be determined by making
  use of spectral lines originating at greatly different optical
  depths. From these values the (outward) turbulent acceleration
  is derived which appears to be comparable in value to the (inward)
  gravitational acceleration. This explains the strong instability of the
  star's photosphere. The long-standing problem of the enhancement of the
  ionic lines in the star's spectrum could be solved: the major parts of
  these lines originate in the part of the wind of the hypergiant that is
  ionized by a hot (B1) companion. The radio spectrum of HR 8752 is also
  emitted by the H(+) region and can be explained quantitatively. The
  rate of mass loss is about 2 x 10 to the -5th solar mass/yr.

Title: The dynamical state of the atmosphere of the supergiant alpha
    Cygni (A2Ia).
Authors: Boer, B.; de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1988A&A...195..218B
Altcode:
  High resolution near-ultraviolet spectra of α Cygni (λ/Δλ =
  8×10<SUP>4</SUP>) were studied to investigate the dynamical state of
  the atmosphere. The microturbulent line-of-sight velocity component
  is found to be constant (10.3±0.7 km s<SUP>-1</SUP>) over a large
  range of optical depths (-4 &lt; log τ<SUB>c</SUB> &lt; -1). The
  macroturbulent velocity distribution is double-peaked at velocities,
  both positive and negative, of 14±2 km s<SUP>-1</SUP>, suggesting
  preponderantly up- and downward moving elements (convective?). These
  motions may explain the non-radial pulsations found by Lucy (1976). The
  outward turbulent acceleration in the outer layers of the atmosphere is
  7.6 cm s<SUP>-2</SUP>, yielding a gravitational acceleration of 26.0
  cm s<SUP>-2</SUP>, and a stellar mass of 18 M_sun;. The authors also
  derive a new value for v<SUB>r</SUB> sin i (8±3 km s<SUP>-1</SUP>).

Title: A differential analysis of UV photospheric lines of OBN and
    OBC stars.
Authors: Wollaert, J. P. M.; Lamers, H. J. G. L. M.; de Jager, C.
Bibcode: 1988A&A...194..197W
Altcode:
  The paper presents measurements of the equivalent widths of several
  photospheric C, N, O, He, Si and Fe lines in the ultra-violet
  spectra of 55 OBN, OBC and normal supergiants and main-sequence
  stars. Seventy-two short-wavelength, high-resolution spectrograms
  obtained with IUE were used. The differences in equivalent widths of
  OBN and OBC stars relative to normal stars are interpreted as abundance
  differences and yield upper and lower limits to respectively under-
  and overabundances of the elements C, N and O. The effects of anomalous
  strength of CNO lines appear to be less pronounced in the UV than in
  the visual. The main reason for this is the saturation of the lines
  investigated. Different scenarios to bring products of the CNO-cycle
  to the stellar surface are discussed. The OBN stars can be explained
  in terms of abundance differences due to evolutionary effects as well
  as initial differences. The OBC stars may be explained by differences
  in atmospheric structure or initial abundances.

Title: High Energy Flares
Authors: de Jager, C.
Bibcode: 1988BAAS...20..725D
Altcode:
  No abstract at ADS

Title: Experiences from the SMY/SMA Period
Authors: de Jager, C.
Bibcode: 1988BAAS...20..749D
Altcode:
  No abstract at ADS

Title: The dynamical state of the atmosphere of the supergiant Alpha
    Cygni (A2 Iae) derived from high-resolution ultraviolet spectra.
Authors: Boer, B.; de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1988JPhys..49..383B
Altcode: 1988IAUCo.102..383B
  In order to study the apparent near instability of supergiant
  atmospheres high-resolution (λ/Δλ = 8×10<SUP>4</SUP>) BUSS
  (Balloon-borne Ultraviolet Stellar Spectrometer) spectra of the
  supergiant Alpha Cyg have been investigated.

Title: Fast Variations in the Ultraviolet Resonance Lines of alpha
Camelopardalis (O9.5 Ia): Evidence for Blobs in the Wind
Authors: Lamers, Henry J. G. L. M.; Snow, Theodore P.; de Jager,
   Cornelis; Langerwerf, A.
Bibcode: 1988ApJ...325..342L
Altcode:
  The 72 IUE spectra of Alpha Cam and 19 IUE spectra of Kappa Cas,
  obtained during 72 hours of continuous IUE time in September 1978 were
  searched for variations in the profiles of the resonance lines of Si IV,
  C IV, and N V, and the results are discussed. The UV resonance lines in
  the spectra of Alpha Cam showed variations at the 2 percent level near
  -1800, -700, and +700 km/s. The first two variations can be explained
  by absorption components of outward-accelerated blobs or shells with
  an average acceleration of 1.5 cm/sq s. The characteristics of the
  blobs and shells are discussed, including the column densities and
  masses. No variations were found in the spectra of Kappa Cas.

Title: Mass loss rates in the Hertzsprung-Russell diagram.
Authors: de Jager, C.; Nieuwenhuijzen, H.; van der Hucht, K. A.
Bibcode: 1988A&AS...72..259D
Altcode:
  From the literature the authors collected values for the rate of mass
  loss for 271 stars, nearly all of population I and of spectral types
  O through M. Rates of stellar mass loss -Mdetermined according to six
  different methods were compared and appear to yield the same result per
  star within the limits of errors. The M-data can well be represented
  by one empirical interpolation formula, as a function of the effective
  temperature T<SUB>eff</SUB> and luminosity L. In addition the authors
  studied some groups of other stars: fast rotators and chemically evolved
  stars. The chemically evolved stars have rates of mass loss which are
  larger than those of "normal" stars occupying the same positions in
  the Hertzsprung-Russell diagram.

Title: Book Review: The Soviet cosmonaut team. / Unifelt Inc., 1986 ;
    GRH Publications, 1990
Authors: de Jager, C.
Bibcode: 1988SSRv...46..380D
Altcode: 1988SSRv...46..380H
  No abstract at ADS

Title: Stellar mass loss and atmospheric instability
Authors: de Jager, Cornelis; Nieuwenhuijzen, Hans
Bibcode: 1988LNP...305..101D
Altcode:
  A review is given of rate of mass-loss values M in the upper part of
  the Hertzsprung-Russell diagram. Near the luminosity limit of stellar
  existence M = -10-4 M) yr-1. Episodical mass loss in bright variable
  super- and hypergiants does not significantly increase this value. For
  Wolf-Rayet stars the rate of mass loss is larger by a factor 140 than
  for non-evolved stars with the same Teff and L; for C stars this factor
  is ten. This can be explained qualitatively. Rotation ap pears hardly
  to influence the rate of mass loss except for vrot-values close to
  the break-up velocity. This is in accordance with theory. We suggest
  the existence of a Red Supergiant Branch; along that branch mass loss
  is virtually independent of luminosity. Stellar winds along the upper
  limit of stellar existence are mainly due: to radiation pressure for hot
  supergiants ( 10 000 K) ; to turbulent pressure for cool supergiants
  (3000-10 000 K), and to dust-driven and pulsation-driven winds for
  cooler stars. The turbulent pressure may originate in large-scale
  stochastic motions as observed in Alpha Cyg. Episodical mass loss, as
  observed in P Cyg, HR 8752 and other Very Luminous Variables may be due
  to occasional violent stochastic motions, resulting in a shock-driven
  episodical mass-loss component.

Title: Energetic Phenomena in Impulsive Solar Flares
Authors: de Jager, C.
Bibcode: 1988ICRC....7...66D
Altcode: 1987ICRC....7...66D; 1988ICRC...20g..66D
  No abstract at ADS

Title: Stellar Mass Loss and Atmospheric Instability
Authors: de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1988LNP...305..102D
Altcode: 1988IAUCo.108..102D; 1988adse.conf..102D
  A review is given of rate of mass-loss values Min the upper part of
  the Hertzsprung-Russell diagram.

Title: Looking Backwards - Some Successful Programmes
Authors: de Jager, C.
Bibcode: 1988copa.conf...17D
Altcode:
  The author describes a few observational campaigns in which he
  has been involved in the past. Although these campaigns were very
  different in topic, scope and duration, some general experiences can
  be formulated which appear to have influenced the degree of success
  of these enterprises.

Title: Low Resolution Observations of a B2 Hypergiant
Authors: de Jager, C.
Bibcode: 1988iue..prop.3296D
Altcode:
  No abstract at ADS

Title: Turbulence-Driven Atmospheric Instability and Largescale
    Motions in Super Giants and Hypergiants
Authors: Boer, B.; Carpay, J.; de Koter, A.; de Jager, C.;
   Nieuwenhuijzen, H.; Piters, A.; Spaan, F.
Bibcode: 1988LNP...305..131B
Altcode: 1988adse.conf..131B; 1988IAUCo.108..131B
  Spectral studies of super- and hypergiants show that the (outward
  directed) turbulent acceleration approaches the value of the
  gravitational acceleration for the most luminous stars, which makes
  their atmospheres unstable.

Title: Book-Review - Progress in Solar Physics
Authors: de Jager, C.; Svestka, Z.
Bibcode: 1988ApL&C..26..372D
Altcode: 1988ApL....26..372D
  No abstract at ADS

Title: Sterrenwacht "Sonnenborgh": een nieuwe fase.
Authors: de Jager, C.
Bibcode: 1988Zenit..15..332D
Altcode:
  No abstract at ADS

Title: Microturbulence in the upper photosphere of alpha Persei
    (F5 Ib) derived from ultraviolet spectral observations.
Authors: Spaan, F. H. P.; de Jager, C.; Nieuwenhuijzen, H.; Kondo, Y.
Bibcode: 1987A&A...185..229S
Altcode:
  High-resolution ultraviolet spectra of the moderate supergiant α
  Per (F5 Ib) were studied to determine the dynamic state of its upper
  photosphere. It was found that the line-of-sight microturbulent velocity
  component ζ<SUB>μ</SUB> in the region of origin of the UV spectrum
  (which is 73,000 km above that of formation of the visual spectrum)
  is about 5 km s<SUP>-1</SUP>, and is slightly smaller than the value
  derived from the visual spectrum. This is ascribed to dissipation
  of mechanical energy between the higher and lower layers where,
  respectively, the ultraviolet and visual light lines originate. Between
  these two levels, which are one scale height apart, the mechanical
  energy flux decreases to about 0.3 of its photospheric value. The
  consequent value for the (outward directed) turbulent acceleration
  g<SUB>t</SUB> is 24 cm s<SUP>-2</SUP>, more than one half the
  observationally determined effective acceleration of gravity.

Title: Book Review: Transactions of the IAU, Vol. XIXB. / Reidel,
    1986.
Authors: de Jager, C.
Bibcode: 1987SSRv...45..410D
Altcode: 1987SSRv...45..410S
  No abstract at ADS

Title: The Solar Maximum Year and its Analysis Phase
Authors: De Jager, Cornelis
Bibcode: 1987SoPh..114..387D
Altcode:
  No abstract at ADS

Title: A High-Energy Solar Flare Burst Complex and the Physical
    Properties of its Source Region
Authors: de Jager, Cornelis; Kuijpers, Jan; Correia, Emilia; Kaufmann,
   Pierre
Bibcode: 1987SoPh..110..317D
Altcode:
  We discuss a solar flare microwave burst complex, which included a
  major structure consisting of some 13 spikes of 60 ms FWHM each,
  observed 21 May, 1984 at 90 GHz (3 mm). It was associated with a
  simultaneous very hard X-ray burst complex. We suggest that the
  individual spikes of both bursts were caused by the same electron
  population: the X-bursts by their bremsstrahlung, and the microwave
  bursts by their gyrosynchrotron emission. This latter conclusion
  is based on the evidence that the radio turnover frequency was ≤
  150 GHz. It follows that the emission sources were characterized
  by an electron density of about 10<SUP>11</SUP> cm<SUP>−3</SUP>,
  a temperature of 5 × 10<SUP>8</SUP> K and a magnetic field of about
  1400-2000 G. They had a size of about 350 km; if the energy release is
  caused by reconnection the sources of primary instability could have
  been smaller and in the form of thin sheets with reconnection speed at
  a fraction of the Alfvén velocity and burst-like energy injections
  of ≈ 10<SUP>27</SUP> erg during about 50 ms each. The energized
  plasma knots lost their injection energy by saturated convective flux
  (collisionless conduction) in about 30 ms.

Title: Book-Review - Progress in Solar Physics
Authors: de Jager, C.; Svestka, Z.; Jordan, C.
Bibcode: 1987Obs...107..130D
Altcode:
  No abstract at ADS

Title: A new determination of the statistical relations between
    stellar spectral and luminosity classes and stellar effective
    temperature and lumonosity.
Authors: de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1987A&A...177..217D
Altcode:
  From a set of 199 determinations of bolometric stellar luminosity
  L and 268 of stellar effective temperature T<SUB>eff</SUB> we
  derived the statistical dependances of log T<SUB>eff</SUB> and log
  (L/L<SUB>sun</SUB>) respectively on spectral type and luminosity
  class. For computer-use we introduced continuous variables s
  (for spectral type) and b (for luminosity class). The relations log
  T<SUB>eff</SUB> (s, b) and log (L/L<SUB>sun</SUB>) (s, b) are given in
  terms of Chebychev polynomials and their cross-products. A comparison
  is made with existing systems: there are small differences which we
  ascribe to the addition of new data on temperature and luminosity,
  not used in previous determinations. The 1σ values for determinations
  of unit weight of log T<SUB>eff</SUB> and log L respectively appear
  to be 0.021 and 0.164, which shows that there is a factor eight in
  their relative accuracies.

Title: Book-Review - Progress in Solar Physics
Authors: de Jager, C.; Svestka, Z.
Bibcode: 1987Sci...236R1009D
Altcode:
  No abstract at ADS

Title: Rate of mass-loss in the Hertzsprung-Russell Diagram
Authors: de Jager, C.; Nieuwenhuijzen, H.; van der Hucht, K. A.
Bibcode: 1987ilet.work..205D
Altcode:
  The authors have collected literature data on rates of mass-loss Mfor
  264 O through M-type stars and a number of stars of other types. It
  appears possible to develop log (-M) into a series of Chebychev
  polynomia of a the first kind in log T<SUB>eff</SUB> and log (L/L_sun;)
  and their cross products.

Title: The future of planetary astronomy
Authors: de Jager, Cornelis
Bibcode: 1987AdSpR...7l.161D
Altcode: 1987AdSpR...7..161D
  No abstract at ADS

Title: Stellar instabilities in the upper part of the
    Hertzsprung-Russell Diagram
Authors: de Jager, Cornelis
Bibcode: 1987ASSL..136..191D
Altcode: 1987ilet.work..191D
  A review is given of some of the main topics addressed at the present
  workshop. The main characteristics of stars in the upper part of the HR
  diagram are discussed. The properties of the most massive stars and the
  variability of blue stars are considered. Pulsations of massive stars
  and photospheric and atmospheric disturbances in luminous early-type
  stars are examined.

Title: The influence of photospheric turbulence on stellar mass loss
Authors: de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1987ilet.work..267D
Altcode:
  The authors show that the stellar rate of mass loss is positively
  correlated with the average microturbulent photospheric velocity,
  and that the energy contained in the microturbulent motions is of the
  same order of magnitude as the wind energies.

Title: Flare energetics
Authors: Wu, S. T.; De Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.;
   Bruner, M. E.; Cargill, P. J.
Bibcode: 1986epos.conf..5.1W
Altcode: 1986epos.confE...1W
  In this investigation of flare energetics, researchers sought
  to establish a comprehensive and self-consistent picture of the
  sources and transport of energy within a flare. To achieve this
  goal, they chose five flares in 1980 that were well observed with
  instruments on the Solar Maximum Mission, and with other space-borne
  and ground-based instruments. The events were chosen to represent
  various types of flares. Details of the observations available for
  them and the corresponding physical parameters derived from these
  data are presented. The flares were studied from two perspectives,
  the impulsive and gradual phases, and then the results were compared
  to obtain the overall picture of the energics of these flares. The
  role that modeling can play in estimating the total energy of a flare
  when the observationally determined parameters are used as the input
  to a numerical model is discussed. Finally, a critique of the current
  understanding of flare energetics and the methods used to determine
  various energetics terms is outlined, and possible future directions
  of research in this area are suggested.

Title: Characterization of the Total Flare Energy
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf.5.41W
Altcode: 1986epos.confE..41W
  No abstract at ADS

Title: Energetics of the Impulsive Phase
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf..5.5W
Altcode: 1986epos.confE...5W
  No abstract at ADS

Title: Energetics of the Gradual Phase
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf.5.20W
Altcode: 1986epos.confE..20W
  No abstract at ADS

Title: Review of Impulsive Phase Phenomena
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf.5.60W
Altcode: 1986epos.confE..60W
  No abstract at ADS

Title: Flares Chosen for Energetics Study
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf.5.47W
Altcode: 1986epos.confE..47W
  No abstract at ADS

Title: Relationships among the Phases
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veek, N. J.
Bibcode: 1986epos.conf.5.39W
Altcode: 1986epos.confE..39W
  No abstract at ADS

Title: A high energy solar flare burst complex and the physical
    properties of its source region
Authors: De Jager, C.; Kuijpers, J.; Correia, E.; Kaufmann, P.
Bibcode: 1986cospar........D
Altcode:
  A solar flare microwave burst complex, which exhibited a major structure
  consisting of some 13 spikes of 60 ms FWHM each, observed 21 May 1984
  at 90 GHz (3 mn) is discussed. It was associated with a simultaneous
  very hard X-ray burst complex. A possible explanation in which the
  individual spikes of both bursts were caused by the same electron
  population is developed: the X-ray bursts by their bremsstrahlung, and
  the microwave bursts by their gyro-synchrotron emission. This latter
  explanation is based on the assumption that the radio turnover frequency
  is less than 150 GHz. The emission sources were characterized by an
  electron density of about 10 to the 11th power/cu cm, a temperature
  of 5 x 10 to the 8th power K and magnetic field of about 1400 to 2000
  G. They had a size of about 350 km; if the energy release is caused
  by reconnection the sources of primary instability could have been
  smaller and in the form of thin sheets with reconnection speed at
  a fraction of the Alfven velocity and burst-like energy injections
  of 10 to the 27th power erg during about 50 ms each. The energized
  plasma knots lost their injection energy by saturated convective flux
  (collisionless conduction) in about 30 ms.

Title: Book-Review - Progress in Solar Physics
Authors: de Jager, C.; Svestka, Z.
Bibcode: 1986S&T....72R.479D
Altcode:
  No abstract at ADS

Title: New Observations of Coronal Explosions and Their Interpretation
Authors: Lemmens, Andre F. P.; de Jager, Cornelis
Bibcode: 1986SoPh..106..365L
Altcode:
  We examined five flares, observed by the Hard X-Ray Imaging
  Spectrometer aboard the Solar Maximum Mission, for the occurrence of
  coronal explosions and found that these occur only if (a) the flare
  shows distinct single impulsive hard X-ray bursts and (b) it shows
  upward (convective) motions during the initial part of the impulsive
  phase. Coronal explosions are therefore explained as a manifestation of
  plasma streaming laterally out of the flare kernel(s). There is some
  evidence that streaming occurs into a number of cylindrical fluxtubes
  which spread over a larger area, thus supporting the `spaghetti-bundle
  model' for the flaring region.

Title: Book-Review - Supernovae
Authors: Murdin, P.; Murdin, L.; de Jager, C.
Bibcode: 1986SSRv...44..186M
Altcode:
  No abstract at ADS

Title: Solar Flares and Particle Acceleration
Authors: de Jager, C.
Bibcode: 1986SSRv...44...43D
Altcode:
  Energy release in solar flares occurs during the impulsive phase,
  which is a period of a few to about ten minutes, during which
  energy is injected into the flare region in bursts with durations
  of various time scales, from a few tens of seconds down to 0.1
  s or even shorter. Non-thermal heating is observed during a short
  period, not longer than a few minutes, in the very first part of the
  impulsive phase; in average flares, with ambient particle densities not
  larger than a few times 10<SUP>10</SUP> cm<SUP>-3</SUP> it is due to
  thick-target electron beam injection, causing chromospheric ablation
  followed by convection. In flares with larger densities the heating
  is due to thermal fronts (Section 1). The average energy released in
  chromospheric regions is a few times 10<SUP>30</SUP> erg, and an average
  number of 10<SUP>38</SUP> electrons with E ≳ 15 keV is accelerated. In
  subsecond pulses these values are about 10<SUP>35</SUP> electrons
  and about 10<SUP>27</SUP> erg per subsecond pulse. The total energy
  released in flares is larger than these values (Section 2). Energization
  occurs gradually, in a series of fast non-explosive flux-thread
  interactions, on the average at levels about 10<SUP>4</SUP> km above
  the solar photosphere, a region permeated by a large number (≳ 10)
  of fluxthreads, each carrying electric currents of ≈ 10<SUP>10</SUP>
  10<SUP>11</SUP> A. The energy is fed into the flare by differential
  motions of magnetic fields driven by photospheric-chromospheric
  movements (Section 3). In contrast to these are the high-energy
  flares, characterized by the emission of gamma-radiation and/or
  very high-frequency (millimeter) radiobursts. Observations of such
  flares, of the flare neutron emission, as well as the observation of
  <SUP>3</SUP>He-rich interplanetary plasma clouds from flares all point
  to a common source, identified with shortlived (∼ 0.1 s) superhot
  (≳ 10<SUP>8</SUP> K) flare knots, situated in chromospheric levels
  (Section 4). Pre-flare phenomena and the existence of homologous flares
  prove that flare energization can occur repeatedly in the same part of
  an active region: the consequent conclusions are that only seldom the
  full energy of an active region is exhausted in one flare, or that the
  flare energy is generated anew between homologous flares; this latter
  case looks more probable (Section 5). Flare energization requires
  the formation of direct electric fields, in value comparable with,
  or somewhat smaller than the Dreicer field (Section 6). Such fields
  originate by current-thread reconnection in a regime in which the
  current sheet is thin enough to let resistive instability originate
  (Section 7). Particle acceleration occurs ‘by fast reconnection
  in magnetic fields ≳ 100 G and electric fields exceeding about
  0.3 times the Dreicer field at fairly low particle densities (≈
  10<SUP>10</SUP> cm<SUP>-3</SUP>); for larger densities plasma heating
  is expected to occur (Section 8). Transport of accelerated particles
  towards interplanetary space demands a field-line configuration open
  to space. Such a configuration originates mainly after the gradual
  gamma-ray/proton flares, and particularly after two-ribbon flares;
  these flares belong to the dynamic flares in Sturrock and Švestka's
  flare classification. Acceleration to GeV energies occurs subsequently
  in shock waves, probably by first-order Fermi acceleration (Section 9).

Title: Book reviews
Authors: Gurtovenko, E. A.; Kostik, R. I.; Tlamicha, A.; Zerull, R.;
   Schadee, Aert; Mészáros, A.; Néeman, Y.; Giese, R. H.; Sinclair,
   A. T.; Kleczek, J.; Trendelenburg, E. A.; Hillebrandt, Wolfgang;
   Sehnal, L.; de Graaff, W.; Slottje, C.; Courvisier, T.; van Beek,
   H. F.; Baud, B.; de Jager, C.; Danby, J. M. A.; Somov, B. V.;
   Cassinelli, J.; Verbunt, F.
Bibcode: 1986SSRv...44..177G
Altcode:
  No abstract at ADS

Title: Book-Review - Space Science Reviews
Authors: Akasofu, S. I. .; Beynon, W. J. G.; de Jager, C.; Rasool,
   S. I.; Krivsky, L.
Bibcode: 1986Ap&SS.122..187A
Altcode:
  No abstract at ADS

Title: La phase initiale de l'éruption solaire.
Authors: de Jager, C.
Bibcode: 1986LAstr.100..167D
Altcode:
  Characteristics of the impulsive phase of a solar flare as determined
  from SMM data are summarized. The initial phase is marked by bursts of X
  and microwave radiation. The 20-30 keV X-ray photons are 10,000 times as
  energetic as visible energy and are accompanied by electrons traveling
  at 100,000 km/sec. The bursts originate in a gas heated to 20 million
  degrees for several minutes over a solar surface area 5000 to 10,000
  km across. The two feet of a flare are sited on regions of opposite
  polarity thousands of kilometers apart. Flux tubes associated with the
  events carry currents of 10 trillion A. Gaseous clouds gathered over
  the feet of the flare arch in the first minutes of an X-ray burst are
  heated to over 50 million degrees, a temperature associated with high
  thermal conductivity and a decrease by a half within minutes. The 3-4
  km thick clouds form just above the surface and rapidly convect into
  the chromosphere where, exposed to repeated burst events, they end
  in a coronal explosion. More data is needed to identify the source of
  accompanying gamma ray photons which have energies one to two orders
  of magnitude higher than those of the X-rays.

Title: The flare kernel in the impulsive phase
Authors: De Jager, C.
Bibcode: 1986sfcp.nasa...29D
Altcode:
  The impulsive phase of a flare is characterized by impulsive bursts
  of X-ray and microwave radiation, related to impulsive footpoint
  heating up to 50 or 60 MK, by upward gas velocities (150 to 400
  km/sec) and by a gradual increase of the flare's thermal energy
  content. These phenomena, as well as non-thermal effects, are all
  related to the impulsive energy injection into the flare. The available
  observations are also quantitatively consistent with a model in which
  energy is injected into the flare by beams of energetic electrons,
  causing ablation of chromospheric gas, followed by convective rise
  of gas. Thus, a hole is burned into the chromosphere; at the end of
  impulsive phase of an average flare the lower part of that hole is
  situated about 1800 km above the photosphere. H alpha and other optical
  and UV line emission is radiated by a thin layer (approx. 20 km) at the
  bottom of the flare kernel. The upward rising and outward streaming
  gas cools down by conduction in about 45 s. The non-thermal effects
  in the initial phase are due to curtailing of the energy distribution
  function by escape of energetic electrons. The single flux tube model
  of a flare does not fit with these observations; instead we propose the
  spaghetti-bundle model. Microwave and gamma-ray observations suggest
  the occurrence of dense flare knots of approx. 800 km diameter, and of
  high temperature. Future observations should concentrate on locating
  the microwave/gamma-ray sources, and on determining the kernel's fine
  structure and the related multi-loop structure of the flaring area.

Title: Editorial
Authors: de Jager, Cornelis; Švestka, Zdeněk
Bibcode: 1986SoPh..107..200D
Altcode: 1987SoPh..107..200D
  No abstract at ADS

Title: Simultaneous optical and X-ray observations of a flare on
    BY Draconis.
Authors: de Jager, C.; Heise, J.; Avgoloupis, S.; Cutispoto, G.;
   Kieboom, K.; Herr, R. B.; Landini, M.; Langerwerf, A. F.; Mavridis,
   L. N.; Melkonian, A. S.; Molenaar, R.; Monsignori-Fossi, B. C.;
   Nations, H. L.; Pallavicini, R.; Piirola, V.; Rodono, M.; Seeds,
   M. A.; van den Oord, G. H. J.; Vilhu, O.; Waelkens, C.
Bibcode: 1986A&A...156...95D
Altcode:
  The authors present a first report on a campaign for simultaneous
  observations in the visual, radio and X-ray ranges of stellar flares
  on the binary BY Dra. During two nights of observations they observed
  one significant flare, simultaneously in soft X-rays and visible
  wavelengths, and one or two smaller bursts. The main flare impulsively
  heated an area of ⪉2×10<SUP>7</SUP>km<SUP>2</SUP> of the stellar
  photosphere to a brightness temperature ⪆25000K, during about 5
  min, and generated hot plasma, emitting soft X-rays. This emission
  reached maximum after the impulsive burst and lasted for about an
  hour; it covered a much larger area on the star than the optical
  emission. There was no significant hard X-ray component. The authors
  ascribe the optical continuous emission to the flare's impulsive phase,
  and the soft X-ray emission to the gradual phase.

Title: Stellar Atmospheric Instability in the Upper Part of the
    Hertzsprung-Russell Diagram
Authors: de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1986IAUS..116..255D
Altcode:
  The authors list evidences supporting the validity of their instability
  criterion and the consequent relations (cf. de Jager 1978, 1980, 1984).

Title: The Dependence of the Stellar Rate of Mass Loss on Effective
    Temperature and Velocity
Authors: de Jager, C.; Nieuwenhuijzen, H.; van der Hucht, K. A.
Bibcode: 1986IAUS..116..109D
Altcode:
  From the existing literature data have been collected on the stellar
  rate of mass loss for 189 stars with known or derived values of the
  effective temperature T<SUB>eff</SUB> and luminosity L. It appears
  that Mdepends only on T<SUB>eff</SUB> and L for the O- through M-type
  stars brighter that about 3×10<SUP>3</SUP>L_sun;.

Title: Acceleration in a high-energy flare.
Authors: de Jager, C.; Correia, E.; Kaufmann, P.
Bibcode: 1986AdSpR...6f.187D
Altcode: 1986AdSpR...6R.187D
  The authors describe a well-studied flare (21 May, 1984) for which
  the emission area is a plasma knot of a few hundred km diameter, with
  a temperature of 5×10<SUP>8</SUP>K and a magnetic field between 1400
  and 2000 G. The authors show that this region coincides virtually with
  the area of primary energization of the flare. The reconnection area
  has a diameter not exceeding about 50 km.

Title: The physics of solar flares. Proceedings of Symposium 5 of
    the COSPARTwenty-sixth Plenary Meeting held in Toulouse, France,
    30th June - 11th July 1986.
Authors: de Jager, C.; Svestka, Z.
Bibcode: 1986AdSpR...6f....D
Altcode: 1986AdSpR...6.....D
  Observations and theoretical models of solar-flare phenomena
  are discussed in reviews and reports presented at the
  symposium formally marking the end of the international
  Solar-Maximum-Year/Solar-Maximum-Analysis project. Topics examined
  include flare buildup, precursors, and onset; the impulsive phase;
  the gradual phase; and coronal and interplanetary phenomena.

Title: Flare energetics.
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
   Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
   M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
   Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
   G.; Serio, S.; Sylwester, J.; Veck, N. J.
Bibcode: 1986NASCP2439....5W
Altcode:
  In this investigation of flare energetics, the authors establish a
  comprehensive and self-consistent picture of the sources and transport
  of energy within a flare. They chose five flares in 1980 that were
  well observed with instruments on the SMM, and with other space-borne
  and ground-based instruments. Details of the observations available
  for them and the corresponding physical parameters derived from these
  data are presented. The flares were studied from two perspectives,
  the impulsive and gradual phases, and then the results were compared
  to obtain the overall picture of the energetics of these flares. The
  authors also discuss the role that modeling can play in estimating the
  total energy of a flare when the observationally determined parameters
  are used as the input to a numerical model.

Title: Het begin van een zonnevlam.
Authors: de Jager, C.
Bibcode: 1986Zenit..13..214D
Altcode:
  No abstract at ADS

Title: Progress in solar physics : review papers invited to celebrate
    the centennial volume of Solar physics
Authors: de Jager, Cornelis; Svestka, Zdenek
Bibcode: 1986pspr.book.....D
Altcode: 1986QB521.6.P76....
  No abstract at ADS

Title: The flare kernel in the impulsive phase.
Authors: de Jager, C.
Bibcode: 1986NASCP2421...29D
Altcode:
  The impulsive phase of a flare is characterized by impulsive bursts of
  X-ray and microwave radiation, related to impulsive footpoint heating up
  to 50 or 60 MK, by upward gas velocities (150 to 400 km s<SUP>-1</SUP>)
  and by a gradual increase of the flare's thermal energy content. A hole
  is "burned" into the chromosphere; at the end of the impulsive phase of
  an average flare the lower part of that "hole" is situated about 1800
  km above the photosphere. Hα and other optical and UV line emission
  is radiated by a thin layer (≈20 km) at the bottom of the flare
  kernel. The single flux tube model of a flare does not fit with these
  observations; instead the spaghetti-bundle model is proposed. Microwave
  and gamma-ray observations suggest the occurrence of dense flare knots
  of ≡800 km diameter, and of high temperature. Future observations
  should concentrate on locating the microwave/gamma-ray sources, and
  on determining the kernel's fine structure and the related multi-loop
  structure of the flaring area.

Title: The solar maximum year and its analysis phase
Authors: de Jager, Cornelis
Bibcode: 1986AdSpR...6f.353D
Altcode: 1986AdSpR...6..353D
  This paper concludes the Toulouse symposium on the Solar Maximum
  Analysis, and marks the end of a period which started 1973, and
  was devoted to the preparations and the observational phase of the
  Solar Maximum Year (SMY, 1979 - 1981) and the subsequent analysis
  phase (SMA). The author describes the history of SMY-SMA and briefly
  summarizes the highlight discoveries of this fascinating period during
  which the knowledge of solar flares has fundamentally changed.

Title: 21 May 1980 flare review
Authors: de Jager, C.; Svestka, Z.
Bibcode: 1985SoPh..100..435D
Altcode:
  A review is given of observations and theories relevant to the
  solar flare of 21 May, 1980, 20 ∶ 50 UT, the best studied flare
  on record. For more than 30 hr before the flare there was filament
  activation and plasma heating to above 10 MK. A flare precursor
  was present ≥6 min before the flare onset. The flare started with
  filament activation (20 ∶ 50 UT), followed by thick-target heating
  of two footpoints and subsequent ablation and convective evaporation
  involving energies of 1 to 2 × 10<SUP>31</SUP> erg. Coronal explosions
  occurred at 20 ∶ 57 UT (possibly associated with a type-II burst)
  and at 21 ∶ 04 UT (associated with an Hα spray?). Post-flare loops
  were first seen at 20 ∶ 57 UT, and their upward motion is interpreted
  as a manifestation of successive field-line reconnections. A type-IV
  radio burst which later changed into a type-I noise storm was related
  to a giant coronal arch located just below the radio noise storm
  region. Some implications and difficulties these observations present
  to current flare theories are mentioned.

Title: Book-Review - Reports on Astronomy
Authors: West, R. M.; De Jager, C.
Bibcode: 1985SSRv...41..403W
Altcode:
  No abstract at ADS

Title: Book-Review - Sky Catalogue 2000.0
Authors: Hirshfeld, A.; Sinnott, R. W.; De Jager, C.
Bibcode: 1985SSRv...41..399H
Altcode:
  No abstract at ADS

Title: Book-Review - Supernovae as Distance Indicators
Authors: Bartel, N.; De Jager, C.
Bibcode: 1985SSRv...41..404B
Altcode:
  No abstract at ADS

Title: Kernel Heating and Ablation in the Impulsive Phase of Two
    Solar Flares
Authors: de Jager, C.
Bibcode: 1985SoPh...98..267D
Altcode:
  At the very start of the impulsive phase of two solar flares the
  temperature derived from medium-energy (≈ 16 keV) X-ray countrates was
  observed to rise abruptly, by several times 10<SUP>7</SUP> K above the
  temperature derived from low-energy X-ray (≈ 7 keV) countrates. The
  difference between the two temperatures relaxed to zero thereafter,
  quasi-exponentially, with a characteristic time of ≈ 1.5 min. This
  differential temperature variation appears to mimique the differences
  between the ionic kinetic and the electron temperatures derived from
  spectral observations (Figures 1 and 2).

Title: Book-Review - Astrophysics and Space Science Reviews
Authors: Syunyaev, R. A.; De Jager, C.
Bibcode: 1985SSRv...41Q.400S
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Mészáros, Attila; Eviatar, A.; de Jager, C.; Ruttien,
   Robert J.; Hultqvist, B.; Jakimiec, J.; Paerels, F.; Storm, Richard
   G.; van der Hucht, K. A.; Riedler, W.; Nieuwstadt, F. T. M.
Bibcode: 1985SSRv...41..393M
Altcode:
  No abstract at ADS

Title: Book-Review - les Objets de Messier Reperage Observation
    Photographie
Authors: Guillaud-Saumur, B.; Rethore, O.; de Jager, C.
Bibcode: 1985SSRv...41..394G
Altcode:
  No abstract at ADS

Title: Coronal Explosions
Authors: de Jager, C.
Bibcode: 1985SoPh...96..143D
Altcode:
  We searched for a new phenomenon, called `coronal explosions', in
  three solar flares, and found them in all three. A coronal explosion
  is the propagation of a density wave through the flaring area. The wave
  emerges from one or two small areas (the `sources') which are close to,
  but not identical with the sources of hard X-ray burst emission. In
  all three cases the explosion starts at the end of the impulsive
  phase, during or after the last hard (≳ 20 keV) X-ray burst. The
  velocities of propagation range between 1800 and a few tens of km
  s<SUP>-1</SUP>, and tend to decrease with time. We suggest that the
  bursts are magneto-hydrodynamical (shock) waves moving downward into
  denser regions.

Title: The identification of massive supernova progenitors (I)
Authors: de Jager, C.
Bibcode: 1985ASSL..120..135D
Altcode: 1985bems.symp..135D
  The average observational characteristics of supernovae of types
  II and V are summarized. The ZAMS-mass of supernova progenitors is
  derived, using their rate of occurrence and theoretical considerations
  on stellar evolution (the latter only for type II supernovae). The
  preexplosion masses are derived from the lightcurves (types II and V)
  and from the absolute magnitude before the explosion (only for type
  V's). Mass ranges of 6 to 16 solar masses, average 9.5 solar masses
  (type II) and greater than 100 solar masses (type V) were found as
  well as preexplosion masses of 7 + or - 1 solar mass (type II) and
  approximately 2000 solar masses (1961v). The location of presupernovae
  in the Hertzsprung-Russell diagram is now known with a fair accuracy. It
  is suggested that Mu-Carinae was not a supernova.

Title: Solar Physics and Interplanetary Travelling Phenomena
Authors: de Jager, Cornelis; Chen, Biao
Bibcode: 1985spit.conf.....D
Altcode:
  No abstract at ADS

Title: The Impulsive Phase and Coronal Explosions in Solar X-Ray
    Flares
Authors: de Jager, C.
Bibcode: 1985spit.conf..917D
Altcode:
  No abstract at ADS

Title: Introductory Talk
Authors: de Jager, C.
Bibcode: 1985spit.conf....7D
Altcode:
  No abstract at ADS

Title: The impulsive phase of solar flares.
Authors: de Jager, C.
Bibcode: 1985BuAst..10...81D
Altcode:
  The impulsive phase of a solar flare is a period of a few minutes
  duration, characterized by impulsive release of energy, particularly
  of high energy photons. Observations made in 1980 with instrumentation
  aboard the Solar Maximum Mission have shown that the phenomena occurring
  during the impulsive phase are due to reconnection of interacting
  field line (or electrical current) systems, leading to acceleration of
  beams of energetic electrons, causing heating and subsequent ablation
  (evaporation) of localized areas of the upper chromosphere ("footpoint
  heating") followed by convective ascent of heated plasma. The upward
  and lateral spreading of this hot gas characterizes the next, the
  gradual, phase.

Title: Evidence for a supersonic turbulent velocity gradient in the
    outer photosphere of the supergiant alpha Cygni (A2Ia).
Authors: de Jager, C.; Mulder, P. S.; Kondo, Y.
Bibcode: 1984A&A...141..304D
Altcode:
  Two high-resolution near-ultraviolet spectra of the supergiant
  α Cyg have been analyzed with the aim of determining the average
  microturbulent line-of-sight velocity component which was found to
  be 15.0±0.5 km s<SUP>-1</SUP>. This value is close to the local
  sound velocity (13.7 km s<SUP>-1</SUP>). This result, together with
  previous determinations in the visual spectral region, is consistent
  with the picture that shock waves are the dominant structure in the
  outer photosphere of Deneb. The macroturbulent velocity component is
  ≈10 km s<SUP>-1</SUP>, a factor two to four smaller than earlier
  communicated values for the line of sight components of the stochastic
  macroturbulent velocities.

Title: Solar magnetohydrodynamics; Symposium review.
Authors: De Jager, C.
Bibcode: 1984ESASP.220..287D
Altcode: 1984ESPM....4..287D
  The overall structure of the Sun, solar magnetic fields, and the
  corona are reviewed. Radial variation of solar density and angular
  rotational velocity; internal mixing in the Sun; solar granulation;
  magnetic convection; umbral oscillations in sunspots; solar cycle
  variations; magnetic flux tubes; dynamo theory; coronal heating;
  coronal mass ejection; and solar activity are covered.

Title: The stability limit of hypergiant photospheres.
Authors: de Jager, C.
Bibcode: 1984A&A...138..246D
Altcode:
  The author examines the consequences of the hypothesis that the
  stability limit of the atmospheres of hypergiants is reached
  when the effective acceleration of gravity g<SUB>eff</SUB> =
  g<SUB>grav</SUB>(1 - Γ)-g<SUB>turb</SUB> ≈ 0, where g<SUB>grav</SUB>
  = GM/R<SUP>2</SUP>, g<SUB>turb</SUB> is the outward acceleration due
  to the gradient of turbulent pressure, and Γ is the Eddington ratio
  |g<SUB>rad</SUB>/g<SUB>grav</SUB>|. In stars close to the stability
  limit dissipation of mechanical energy builds up a field of supersonic
  turbulent motions in the photosphere which tends to destabilize the
  atmosphere. The larger the absolute luminosity, the deeper in the
  photosphere dissipation becomes important. This manifests itself in
  a rate of mass-loss, increasing with L. For near-unstable stars with
  T<SUB>e</SUB> ≈ 10<SUP>4</SUP>K the rate of mass-loss is predicted
  to be nearly by a factor ten larger for a star brighter by one
  magnitude. This effect greatly changes the evolutionary tracks and
  explains why brighter stars have not been detected.

Title: The Envelope of the Over-contact Binary AW UMa
Authors: de Jager, C.
Bibcode: 1984iue..prop.2017D
Altcode:
  No abstract at ADS

Title: Spatial Development of X-Ray Emission during the Impulsive
    Phase of a Solar Flare
Authors: de Jager, C.; Boelee, A.; Rust, D. M.
Bibcode: 1984SoPh...92..245D
Altcode:
  The flare of 11 November, 1980, 17∶25 UT occurred in a magnetically
  complex region. It was preceded by some ten minutes by a gradual
  flare originating over the magnetic inversion line, close to a
  small sunspot. This seems to have triggered the main flare (at 70
  000 km distance) which originated between a large sunspot and the
  inversion line. The main flare started at 17∶23∶20 UT with a slight
  enhancement of hard X-rays (E &gt; 30 keV) accompanied by the formation
  of a dark loop between two Hα bright ribbons. In 3-8 keV X-rays a
  southward expansion started at the same time, with ν ∼- 500 km s
  <SUP>−1</SUP>. At the same time a surge-like expansion started. It
  was observable slightly later in Hα, with southward velocities
  of ≳ 200 km s<SUP>−1</SUP>. The dark Hα loop dissolved at ∼
  17∶24 UT at which time several impulsive phenomena started such as a
  complex of hard X-ray bursts localized in a small area. At the end of
  the impulsive phase at 17∶25∶40 UT, a coronal explosion occurred
  directed southward with an initial expansion velocity of ∼ 1800 km
  s<SUP>−1</SUP>, decreasing in 40 s to ∼500 km s<SUP>−1</SUP>.

Title: Impulsive Phase Heating and a Coronal Explosion in a Solar
    Flare
Authors: de Jager, C.; Boelee, A.
Bibcode: 1984SoPh...92..227D
Altcode:
  The flare of 12 November 1980, 02∶50 UT, in Active Region 2779
  (NOAA classification) was studied by using X-ray images obtained
  with the Hard X-Ray Imaging Spectrometer aboard NASA's Solar Maximum
  Mission. In a ten-minute period, between about 02∶44 and 02∶54
  UT, some five short-lived impulsive bursts occurred. We found that
  the so-called `hard' bursts (≳ 15 keV) are also detectable in low
  energy images. During that 10 min period - the impulsive phase - the
  heat input into the flare and the total number of energetic electrons
  increased practically exponentially, to reach their maximum values at
  02∶54 UT. At the end of that period, when the thermal energy content
  of the flare was largest, a burst was observed, for the first time,
  to spread in a broad southern direction from an initially small area
  with a speed of about 50 km s<SUP>−1</SUP>. We have called this
  phenomenon a coronal explosion.

Title: Book reviews
Authors: van der Hucht, K. A.; Pedersen, A.; Kesák, Ľ.; Zwaan,
   C.; Fárník, F.; Kovalevsky, J.; van Beek, H. F.; Mewe, R.; Page,
   D. E.; van Genderen, A. M.; Koch-Miramond, L.; de Jager, C.; Ooms,
   G.; Pedersen, Arne; de Jager, C.; Hultqvist, Bengt; Waters, R.;
   Schrijver, J.
Bibcode: 1984SSRv...38..179V
Altcode:
  No abstract at ADS

Title: Investigating the Internal Structure and Evolution of Massive
    Stars by Space Techniques
Authors: de Jager, C.
Bibcode: 1984srps.conf...47D
Altcode:
  All massive stars (⪆15 M_sun;) are variable in luminosity (Δm ≈
  10<SUP>-2</SUP>mag) and radial velocity (Δv ≈ 1 km s<SUP>-1</SUP>),
  and have a large rate of mass loss. A precise determination of the
  spectrum of the v<SUB>R</SUB>- and m-variations with noise levels of
  ca. 10<SUP>-3</SUP>km s<SUP>-1</SUP> and 10<SUP>-5</SUP>mag would
  allow for a direct determination of the internal structure and
  (hence) evolutionary status of stars with M ⪆ 5 M_sun;. If the
  above accuracy can be reached in one hour integration time, then a
  four-years observational period would yield the following results:
  a precise spectrum of pulsations for some 20 stars, allowing for an
  accurate determination of the internal structure and evolutionary
  phase; general information on the internal structure of about 400
  stars. A lifetime of the Observatory of 12 years is suggested, which
  would yield detailed information on 60 and general data on 1200 stars.

Title: The brightest stars.
Authors: de Jager, C.
Bibcode: 1984brst.book.....D
Altcode:
  No abstract at ADS

Title: Book-Review - Astrophotography - Techniques for the Amateur
Authors: Martinez, P.; de Jager, C.
Bibcode: 1984SSRv...38..184M
Altcode:
  No abstract at ADS

Title: The Accuracy Limit of Groundbased Stellar Photometry
Authors: Heintze, J. R. W.; de Jager, C.; van der Veen, W.
Bibcode: 1984srps.conf..157H
Altcode:
  The ultimate accuracy that can be reached in ground-based stellar
  photometry depends primarily on the fluctuations of the atmosphere
  causing scintillations and variations of transparency, and besides on
  the instrumental stability and available integration time. Fluctuations
  in instrumental stability can be made negligibly small by basing the
  optical system and observational methods strictly on differential
  techniques. The integration time constitutes, together with variations
  in the atmosphere, the real limiting factor. Considerations based on
  available atmospheric and photometric observational data, yield that
  the present-days practical limiting accuracy of ground-based photometry
  is of the order of (3 - 7)×10<SUP>-4</SUP>mag for the observation of
  a 7th mag star by a one-meter telescope at an altitude of 4000 m and
  an integration time of 10<SUP>3</SUP>s.

Title: Shock-driven mass loss of stars.
Authors: de Jager, C.; van den Oord, G. H. J.
Bibcode: 1984mlao.conf...59D
Altcode:
  The authors suggest that shocks, fed by multi-mode pulsational motion
  of the photospheres of supergiants are the basic mechanism for the
  mass loss of cool and medium type supergiants. They review the present
  theoretical situation, and describe the implementations of the observed
  transient mass loss component of the pulsating Beta Cephei stars BW
  Vul and σ Sco.

Title: Energy input in solar flares and coronal explosions
Authors: de Jager, C.
Bibcode: 1984AdSpR...4g.303D
Altcode: 1984AdSpR...4..303D
  A coronal explosion is a density wave observed in X-ray images of solar
  flares. The wave occurs at the end of the impulsive phase, which is the
  time at which the flare's thermal energy content has reached its maximum
  value. It starts in a small area from where it spreads out, mainly
  into one hemisphere, with velocities that tend to rapidly decrease
  with time, and which are between ~ 10<SUP>3</SUP> and a few tens of km
  s<SUP>-1</SUP>. We interpret them as magneto-hydrodynamic waves that
  (mainly) move downward from the low corona into denser regions.

Title: Book-Review - a Field Guide to the Stars and Planets
Authors: Menzel, D. H.; Pasachoff, J. M.; de Jager, C.
Bibcode: 1984SSRv...38..185M
Altcode:
  No abstract at ADS

Title: Book-Review - 8TH International Conference on Numerical
    Methods in Fluid Dynamics
Authors: Krause, E.; de Jager, C.
Bibcode: 1983SSRv...36..429K
Altcode:
  No abstract at ADS

Title: Book-Review - Spatial Telecommunications - Part Two -
    Spatial Sector
Authors: de Jager, C.
Bibcode: 1983SSRv...36..423D
Altcode:
  No abstract at ADS

Title: Book-Review - Computational Methods for Fluid Flow
Authors: Peyret, R.; Taylor, T. D.; de Jager, C.
Bibcode: 1983SSRv...36..430P
Altcode:
  No abstract at ADS

Title: Book-Review - Landolt-Bornstein Numerical Data and Functional
    Relationship in Science and Technology
Authors: Schaifers, K.; Voigt, H. H.; de Jager, C.
Bibcode: 1983SSRv...36..420S
Altcode:
  No abstract at ADS

Title: Book-Review - I.A.U. General Assembly - 18TH - Proc.
Authors: West, R. M.; de Jager, C.
Bibcode: 1983SSRv...36..430W
Altcode:
  No abstract at ADS

Title: Enhanced X-Ray Emission above 3.5-KEV in Active Regions in
    the Absence of Flares
Authors: Schadee, A.; de Jager, C.; Svestka, Z.
Bibcode: 1983SoPh...89..287S
Altcode:
  We demonstrate that even in the absence of flares there are very
  often volumes of hot plasma in the corona above active regions with
  temperatures in excess of 10 million degrees. Characteristics of
  this hot plasma and its time variations seem to be different in
  active regions of different phase of development. These hot plasma
  regions are sources of very weak, but clearly recognizable, X-ray
  emission above 3.5 keV. Long-lived X-ray brightenings, 10<SUP>4</SUP>
  times weaker than a flare, but lasting up to 10 hr occur predominantly
  along the H<SUB>∥</SUB> = 0 line, apparently low in the corona. After
  major flares, long-lived X-ray emission is also radiated from tops of
  arches extending high into the corona. Some other long-lived sources,
  far from the H<SUB>∥</SUB> = 0 line, may be associated with newly
  emerging flux. Short-lived X-ray sources, with fluxes ranging from
  subflare levels to 10<SUP>−3</SUP> times the flare flux, last for
  2 to more than 30 min and are probably microflares. They seem to be
  most frequent in growing young active regions and appear often in
  areas with newly emerging flux.

Title: Book-Review - Spatial Telecommunications - Part Three -
    Earth Sector Systems of Telecommunications by Satellite
Authors: de Jager, C.
Bibcode: 1983SSRv...36..429D
Altcode:
  No abstract at ADS

Title: Book-Review - Numerical and Physical Aspects of Aerodynamic
    Flows
Authors: Cebeci, T.; de Jager, C.
Bibcode: 1983SSRv...36..430C
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Kleczek, J.; Nussbaumer, H.; van der Hucht, K. A.; De Greve,
   J. P.; Ooms, G.; Rutten, R. J.; van der Laan, H.; Jäger, F. W.;
   Reijnen, G. C. M.; Bijleveld, W.; Kistemaker, J.; de Jager, C.;
   Mustel, E. R.; Ne'Eman, Y.; Priest, E. R.; Stiller, H.; Seifert, W.;
   Namba, O.; Kuperus, M.; Hoekstra, Roel; Stumpers, F. L. H. M.; Frank,
   S.; Zimmerman, J. T. F.; De Loore, C.; Gendrin, R.; Schrijver, J.;
   Mulder, P. S.; Pounds, K. A.; Young, R. S.; Houziaux, L.; Engvold,
   O.; Bok, B. J.; de Graaff, W.
Bibcode: 1983SSRv...36..415K
Altcode:
  No abstract at ADS

Title: Radio, X-ray, and optical observations of the flare of June
    13, 1980, at 6<SUP>h</SUP>22<SUP>m</SUP> UT
Authors: Kattenberg, A.; Allaart, M.; de Jager, C.; Schadee, A.;
   Schrijver, J.; Shibasaki, K.; Švestka, Z.; van Tend, W.
Bibcode: 1983SoPh...88..315K
Altcode:
  A subflare of importance Sf was observed on June 13, 1980 simultaneously
  by instruments aboard the Solar Maximum Mission (SMM) and various
  ground based observatories. We describe and compare different kinds
  of observations, with emphasis on the Hard X-Ray Imaging Spectrometer
  (HXIS) images and spectra, and on the one-dimensional microwave images
  with high time and spatial resolution, obtained with the Westerbork
  Synthesis Radio Telescope (WSRT). The fast electrons causing the X-ray
  and microwave impulsive bursts had a common acceleration source, but the
  burst were produced at the opposite footpoints of the loops involved,
  with microwaves emitted near to a sunspot penumbra. The flare (of a
  `compact' type) was probably triggered by an emerging flux, and two
  possible interpretations of this process are briefly discussed.

Title: The BUSS spectrum of beta Lyrae.
Authors: Hack, M.; Sahade, J.; de Jager, C.; Kondo, Y.
Bibcode: 1983A&A...126..115H
Altcode:
  The spectrum of Beta Lyrae from about 1975 to 3010 A taken with
  the Balloon-borne ultraviolet Stellar Spectrograph experiment in
  May 1976 at phase 0.61 P is analyzed. Results show the presence
  of N II semi-forbidden emission and provide evidence for about the
  same location, in the outer envelope of the system, of the layers
  responsible for the resonance Mg II doublet emissions and for the
  "narrow" H-alpha emission. In addition, three sets of absorption lines,
  P Cygni profiles of Fe III and broad Beals Type III emissions of Mg II,
  are found to be present.

Title: Book reviews
Authors: Namba, O.; Kuijpers, Jan; De Loore, C.; Roody, R. M.;
   Marlborough, J. M.; Rasool, S. I.; Kovalesky, J.; van der Kruit, P. C.;
   Kleczek, J.; de Jager, C.; Lewis, A.; Hovenier, J. W.; Grewing, M.
Bibcode: 1983SSRv...35..293N
Altcode:
  No abstract at ADS

Title: Development of flare morphology in X-rays, and the flare
    scenario
Authors: de Jager, C.
Bibcode: 1983SoPh...86...21D
Altcode:
  We define the impulsive phase of a flare as its first phase,
  characterized by: X-ray bursts of short (seconds to tens of seconds)
  duration, a patchy X-ray morphology, and injection of energy. It
  lasts some five to ten minutes. The gradual or diffuse phase starts
  virtually at the same time as the impulsive one and is characterized by
  a gradually varying X-ray flux from a larger, diffuse, area situated
  higher than the sources of the impulsive X-ray bursts. The diffuse
  cloud is initially (during the first five minutes) hotter by a few
  million degrees than the sources of the impulsive phase bursts and
  is assumed to be caused by convective motions with upward velocities
  of a few hundred km s<SUP>−1</SUP>. It contains about the same
  number of energetic electrons as the impulsive burst patches contained
  initially. It cools gradually down by radiative and conductive losses,
  a process that may last for about an hour.

Title: The flares of April 1980. A case for flares caused by
    interacting field structures.
Authors: Machado, M. E.; Somov, B. V.; Rovira, M. G.; de Jager, C.
Bibcode: 1983SoPh...85..157M
Altcode:
  We discuss the spatial and temporal characteristics of X-ray flares
  occurring in the active region NOAA2372 from April 6 to 13, 1980. The
  flares are seen to extend in most cases across the whole active complex,
  involving several magnetic features. They originate in an intermediate
  bipole, between the two main sunspots of the active region, where high
  magnetic shear was detected. A rapid expansion is seen in some cases,
  in conjunction with the start of the impulsive hard X-ray bursts. We
  also detect, in the late phases of some of the events, a large soft
  X-ray structure overlying the whole active region, which also shows
  up as a noise storm region at metric wavelengths. These large loops
  cool by heat conduction but, in some cases, Hα condensations seem to
  appear, probably as a result of magnetic compression and a condensation
  mode of the thermal instability. The topological aspects of the field
  configuration are discussed, in the context of flare models invoking
  magnetic reconnection at the site of the primary energy release. In
  such a model, the intermediate bipole is the natural site of initial
  magnetic reconnection, particle acceleration and heating. In one
  particular case of a flare observed at the limb, we find possible
  evidence of particle acceleration in a neutral sheet at the boundary
  between two clearly defined magnetic structures.

Title: The Queen's Flare - its Structure and Development - Precursors
    Pre-Flare Brightenings and Aftermaths
Authors: de Jager, Cornelis; Machado, Marcos E.; Schadee, Aert;
   Strong, Keith T.; Švestka, Zdeněk; Woodgate, Bruce E.; van Tend, W.
Bibcode: 1983SoPh...84..205D
Altcode:
  We continue previous research on the limb flare of 30 April, 1980, 20:20
  UT, observed in X-rays by several instruments aboard the Solar Maximum
  Mission (SMM). It is shown quantitatively that the flare originated in
  an emerging magnetically confined kernel (diameter ∼ 20″) which
  existed for about ten to fifteen minutes, and from which energetic
  electrons streamed, in at least two injections, into a previously
  existing complicated magnetic loop system thus forming a less bright but
  extended and long-lived tongue. The tongue had a length of ∼ 35 000 km
  and lasted ∼ 90 min in X-rays (∼ 10 keV); at lower energies (∼ 0.7
  keV) it was larger (∼ 80 000 km) and lasted longer. The total number
  of energetic electrons (≈ 10<SUP>37</SUP>) initially present in the
  kernel is of the same order as the number present in the tongue after
  the kernel's decline. This gives evidence that the energetic electrons
  in the tongue originated mainly in the kernel. The electron number
  densities in the kernel and tongue at maximum brightness were ∼ 4.5
  × 10<SUP>11</SUP> and ∼ 1 × 10<SUP>11</SUP> cm<SUP>#X2212;3</SUP>,
  respectively. During the first eight minutes of its existence the tongue
  was hotter than the kernel, but it cooled off gradually. Its decline in
  intensity and temperature was exponential; energy was lost by radiation
  and by conduction through the footpoints of the loop system. These
  footpoints have a cross-section of only ∼ 3 × 10<SUP>6</SUP>
  km<SUP>2</SUP>. This small value, as well as photographs in a CIV UV
  emission line, suggests a highly filamentary structure of the system;
  this is further supported by the finding that the tongue had a `filling
  factor' of ∼ 10<SUP>#X2212;2</SUP>. Several faint X-ray brightenings
  (≲ 0.005 of the flare's maximum intensity) were observed at various
  locations along the solar limb for several hours before and after the
  flare. At ∼ 30 min before the flare's onset a faint (≲ 0.02) flare
  precursor occurred, coinciding in place and shape with the flare. First
  the kernel precursor was brightest but the tongue precursor increased
  continuously in brightness and was the brightest part of the precursor
  some 10-15 min after the first visibility of the kernel precursor,
  until the start of the main flare. This suggests (weak) continuous
  electron acceleration in the tongue during a period of at least 30
  min. The main flare was caused by strong emergence of magnetic field
  followed by two consecutive field line reconnections and accelerations
  in a small loop system, causing footpoint heating. Subsequently plasma
  streamed (convectively) into a pre-existing system of larger loops,
  forming the tongue.

Title: 3.5 keV X-ray Emission in Absence of Flares
Authors: Schadee, A.; de Jager, C.; Svestka, Z.
Bibcode: 1983BAAS...15R.704S
Altcode:
  No abstract at ADS

Title: Corrigendum: "The flares of April 1980. A case for flares
    caused by interacting field structures" [Sol. Phys., Vol. 85, No. 1,
    p. 157 - 184(1983)].
Authors: Machado, M. E.; Somov, B. V.; Rovira, M. G.; de Jager, C.
Bibcode: 1983SoPh...89..233M
Altcode:
  No abstract at ADS

Title: Book-Review - Astrophysics from Spacelab
Authors: Bernacca, P. L.; Ruffini, R.; de Jager, C.
Bibcode: 1983SSRv...35R.297B
Altcode:
  No abstract at ADS

Title: The ISPM solar flare X-ray and cosmic gamma-ray burst
    experiment.
Authors: Cotin, F.; de Jager, C.; Henoux, J. -C.; Heise, J.; Hilhorst,
   M.; Hurley, K.; Niel, M.; Paschmann, G.; Sommer, M.; van Rooijen,
   J.; Vedrenne, G.
Bibcode: 1983ESASP1050..209C
Altcode:
  The ISPM solar flare X-ray and cosmic gamma-ray burst instrument
  (designated the HUS experiment) consists of a pair of Cs I scintillators
  and a pair of Si surface barrier detectors for measuring X-rays in
  the ranges 15 - 150 and 5 - 15 keV, respectively. High-time-resolution
  X-ray measurements (up to 8 ms) will be used to study X- and gamma-ray
  bursts of solar and cosmic origin.

Title: Book-Review - Reports on Astronomy
Authors: Waymen, P. A.; de Jager, C.
Bibcode: 1983SSRv...35..297W
Altcode:
  No abstract at ADS

Title: Mass Loss from astronomical objects; a summary.
Authors: de Jager, C.
Bibcode: 1983HiA.....6..603D
Altcode:
  A summary of recent developments in the following research fields is
  given: (1) stellar mass loss data and possible mechanisms; (2) mass
  loss for special types of stars; (3) interaction with the interstellar
  medium; (4) mass loss from quasars.

Title: Space observations of solar flares
Authors: De Jager, C.
Bibcode: 1983ebro.conf...63D
Altcode:
  Space observations of flares are shown to help in establishing current
  theories on solar flares. The hard X-ray imaging spectrometer used
  in the Solar Maximum Mission is described. Observations with the
  instrument determine the location, morphology and energy spectra of
  high energy emissions which helps to solve the problem of flare models
  and mechanisms.

Title: Origin and development of solar flares.
Authors: de Jager, C.
Bibcode: 1983MeBel..45....1D
Altcode:
  No abstract at ADS

Title: Space observations of solar flares.
Authors: de Jager, C.
Bibcode: 1983POEM...14...63D
Altcode:
  A decision between current theories on solar flares can probably be made
  by X-ray observations of the morphology and spectrum of flares. The
  author summarizes how space observations of flares have helped to
  establish current theories on solar flares and describes the instrument
  HXIS (Hard X-ray Imaging Spectrometer) in the Solar Maximum Mission,
  launched February 14, 1980.

Title: Origin and development of solar flares
Authors: de Jager, C.
Bibcode: 1983HiA.....6...53D
Altcode:
  A review is given of knowledge on solar flares with particular
  emphasis on progress made during the international Solar Maximum Year
  (1979-1981). The pre-flare structure is described by a flux-tube
  or circuit model. The instability leading to a flare may occur by a
  disturbance of the field topology (mostly field emergence) followed by
  field-line reconnection (circuit coupling). In the first (impulsive)
  phase of a flare, this causes jets of energetic electrons originating
  near the top of the flux tube to bombard lower chromospheric regions:
  footpoint heating. In the second (gradual or diffuse) phase, heated
  gas from the footpoints ascends convectively, producing a large cloud
  of hot gas. Consequent shock-wave phenomena cause moving fronts and
  associated waves in the high parts of the corona; these show up in
  coronagraphic or radio-observations. Several hours after a large flare,
  extended loop-like structures can appear, with temperatures greater than
  6 MK, emitting a very faint X-ray flux. They are the basic structures
  of a more extended configuration, visible on metric radio waves, and
  pointing out from the area where the flare occurred. They may extend
  to distances of 10 to the 6th km or more from the solar surface.

Title: Book-Review - Revealing the Universe
Authors: Cornell, J.; Lightman, A. P.; de Jager, C.
Bibcode: 1983SSRv...35..297C
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Ne'Eman, Y.; Zahn, J. -P.; Habing, H. J.; Wittenberg, H.;
   Zwaan, C.; Murray, C. A.; de Jager, Cornelis; Kresák, L.
Bibcode: 1982SSRv...33..459N
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; Sehnal, L.; Kleczek, Josip; Vanysek, V.; Quenby,
   J. J.; van Duinen, R. J.; van Gent, R. H.; Kaastra, J. S.; Ringeard,
   G.; Mewe, R.; Stiller, H.; Wäsch, R.; Wenzel, K. -P.; Vrijer, A.;
   Ceplecha, Z.; Hellings, P.; Houziaux, L.
Bibcode: 1982SSRv...31..453D
Altcode:
  No abstract at ADS

Title: The Photospheric Velocity Field of Procyon
Authors: de Jager, C.; Neven, L.
Bibcode: 1982Ap&SS..84..297D
Altcode:
  BUSS observations of the profiles of two well observed spectral lines
  in the ultraviolet spectrum of αCMi (Procyon; F5 IV V) are analysed
  with a Fourier transform method in order to determine values of various
  parameters of the velocity field of the upper photosphere. We find a
  microturbulent line-of-sight velocity componentL <SUB>μ</SUB> = 0.9 ±
  0.4 km s<SUP>-1</SUP>, a macroturbulent velocity componentL <SUB>M</SUB>
  = 5.3 ± 0.2 km s<SUP>-1</SUP>, and a rotational velocity componentv
  <SUB>R</SUB> sini=10.0±1.2 km s<SUP>-1</SUP>. In these calculations a
  single-moded sinusoidal isotropic macroturbulent velocity function was
  assumed. The result appears to be sensitive to the assumed shape of the
  macroturbulence function: for an assumed Gaussian shape the observations
  can be described withv <SUB>R</SUB> sini=4 km s<SUP>-1</SUP> andL
  <SUB>M</SUB> = 11.6 ± 2.7 km s<SUP>-1</SUP>. A comparison is made
  with other results and theoretical predictions.

Title: Review of galactic ultraviolet astronomy.
Authors: de Jager, C.
Bibcode: 1982ESASP.176...43D
Altcode: 1982IUE3r.......43D; 1982iue..conf...43D
  Results of IUE investigations of: chromospheres, coronas and winds of
  cool stars; hot stars and supernovae; binaries and novae; mass loss
  and the late evolution of single massive stars, are summarized. Stars
  in the pre-main sequence phase; interstellar matter; and the galactic
  halo, were also studied.

Title: The pulsation of the outer layers of the BET CEP star SIG Sco.
Authors: Burger, M.; de Jager, C.; van den Oord, G. H. J.
Bibcode: 1982A&A...109..289B
Altcode:
  The pulsation of the outer layers of the Beta Cephei-type variable σ
  Sco is investigated using 17 ultraviolet spectrograms (1200-2000 A)
  obtained during seven hours of observations with the International
  Ultraviolet Explorer. A pulsational model established earlier for
  BW Vul is confirmed. According to this model, after a period of
  photospheric rest the outer layers expand suddenly. The acceleration
  for the outermost layers, investigated with the resonance lines of C
  IV and Si IV, is found to be larger than for the photosphere. During
  the phase of deceleration that follows, no falling down of the C
  IV absorbing layers is observed; their velocity component remains
  directed outward. A transient stellar wind component sets in just
  before the star has its minimum radius (phase, approximately 0.9);
  it is strongest at a phase of approximately 0.2. The observations are
  interpreted as suggesting the mechanism of pulsational driven mass loss.

Title: Stellar Atmospheric Velocity Fields - the Beta-Cephei Variables
    Gamma-Pegasi and Beta-Cephei
Authors: de Jager, C.; Sato, N.; Burger, M.; Neven, L.
Bibcode: 1982Ap&SS..83..411D
Altcode:
  The shape parameters of a number of selected ultraviolet lines in
  BUSS-spectra of the Beta Cephei stars γ Peg and β Cep have been
  analyzed to determine the principal parameters of the atmospheric
  velocity field. We find for both stars a fairly high value (∼5
  km s<SUP>-1</SUP>) for the microturbulent line-of-sight velocity
  component, which confirms an earlier result based on lower resolution
  UV spectra. Macroturbulent and rotational velocities are virtually zero
  in the atmosphere of γ Peg; for β Cep we findv <SUB>rot</SUB>sini=40
  km s<SUP>-1</SUP>.

Title: Comets
Authors: Brandt, John C.; de Jager, C.
Bibcode: 1982SSRv...31..119B
Altcode:
  No abstract at ADS

Title: The pulsation of the outer layers of the BET Cep-type variable
    BW Vul.
Authors: Burger, M.; de Jager, C.; van den Oord, G. H. J.; Sato, N.
Bibcode: 1982A&A...107..320B
Altcode:
  Eleven high-resolution ultraviolet spectrograms of BW Vul were obtained
  by means of the IUE over 1.6 periods to compare the pulsation of this
  star as observed in the strong far-UV resonance lines with observations
  of the UV lines of photospheric origin. The radial velocity curve of
  the C IV lines is different from the photospheric one, showing that
  both the photosphere and the C IV layers are accelerated upwards
  impulsively. After about one hour, the acceleration decreases to
  zero, and then the atmosphere falls with a nearly constant downward
  acceleration of 2100 cm/sq s. The varying asymmetry indicates mass loss
  due to the pulsation of the atmosphere, superimposed on the continuous
  mass loss of the star.

Title: Book Reviews
Authors: Shaviv, G.; de Jager, C.; De Loore, C.; Fricke, W.; Kleczek,
   J.; van Zolingen, R. J. C.; Vardya, M. S.; Wöhl, H.; Tauber, G.;
   de Jong, T.; de Graaff, W.
Bibcode: 1982SSRv...31..119S
Altcode:
  No abstract at ADS

Title: Space Science Comes of Age
Authors: Hanle, P.; Chamberlain, V. D.; de Jager, C.
Bibcode: 1982SSRv...31..119H
Altcode:
  No abstract at ADS

Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Hutchings, J. B.
Bibcode: 1982Natur.295..632D
Altcode:
  No abstract at ADS

Title: Book-Review - Stars and Star Clusters
Authors: Voigt, H. H.; Schaifers, K.; de Jager, C.
Bibcode: 1982SSRv...33R.461V
Altcode:
  No abstract at ADS

Title: Observations of a POST Flare Radio Burst in X-Rays
Authors: Svestka, Z.; Hoyng, P.; van Tend, W.; Boelee, A.; de Jager,
   C.; Stewart, R. T.; Acton, L. W.; Bruner, E. C.; Gabriel, A. H.;
   Rapley, C. G.; de Jager, C.; LaFleur, H.; Nelson, G.; Simnett, G. M.;
   van Beek, H. F.; Wagner, W. J.
Bibcode: 1982SoPh...75..305S
Altcode:
  More than six hours after the two-ribbon flare of 21 May 1980, the
  hard X-ray spectrometer aboard the SMM imaged an extensive arch above
  the flare region which proved to be the lowest part of a stationary
  post-flare noise storm recorded at the same time at Culgoora. The X-ray
  arch extended over 3 or more arc minutes to a projected distance of
  95 000 km, and its real altitude was most probably between 110 000
  and 180 000 km. The mean electron density in the cloud was close to
  10<SUP>9</SUP> cm<SUP>−3</SUP> and its temperature stayed for many
  hours at a fairly constant value of about 6.5 × 10<SUP>6</SUP> K. The
  bent crystal spectrometer aboard the SMM confirms that the arch emission
  was basically thermal. Variations in brightness and energy spectrum at
  one of the supposed footpoints of the arch seem to correlate in time
  with radio brightness suggesting that suprathermal particles from
  the radio noise regions dumped in variable quantities into the low
  corona and transition layer; these particles may have contributed to
  the population of the arch, after being trapped and thermalized. The
  arch extended along the H<SUB>∥</SUB> = 0 line thus apparently
  hindering any upward movement of the upper loops reconnected in the
  flare process. There is evidence from Culgoora that this obstacle may
  have been present above the flare since 15-30 min after its onset.

Title: Shock-driven Mass Loss of Stars
Authors: de Jager, C.; van den Oord, G. H. J.
Bibcode: 1982mlao.conf...59D
Altcode:
  No abstract at ADS

Title: The Brightest Stars
Authors: de Jager, C.; Vardya, M. S.
Bibcode: 1982SSRv...31..121D
Altcode:
  No abstract at ADS

Title: Looking ahead after the termination of the solar
Authors: de Jager, Cornelis
Bibcode: 1982AdSpR...2k...1D
Altcode: 1982AdSpR...2....1D
  No abstract at ADS

Title: Detection of Hydrodynamical Flow in and Around Algol Binaries
Authors: de Jager, C.
Bibcode: 1982iue..prop.1300D
Altcode:
  No abstract at ADS

Title: Book Review: Atlas of Photomicrographs of the Surface
    Structures of Lunar Regolith Particles
Authors: Rode, O.; Ivanov, A.; Nazarov, M.; Cimbálniková, A.; Jurek,
   K.; Hejl, V.; de Jager, C.
Bibcode: 1982SSRv...31..453R
Altcode:
  No abstract at ADS

Title: Book-Review - Landolt-Bornstein Numerical Data in Science
    and Technology
Authors: Schaifers, K.; Voigt, H. H.; de Jager, C.
Bibcode: 1982SSRv...32..464S
Altcode:
  No abstract at ADS

Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Marlborough, J. M.
Bibcode: 1981Obs...101..217D
Altcode:
  No abstract at ADS

Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Tutukov, A. V.
Bibcode: 1981SvA....25..750D
Altcode:
  No abstract at ADS

Title: Reflections on Solar Variability
Authors: de Jager, C.
Bibcode: 1981SoPh...74...11D
Altcode:
  The Sun is a variable star in many respects: there are secular varitions
  related to the general solar evolution, and - as discovered in recent
  years - there are many short period variations of which the 5 min
  and 160 min pulsations are the most important ones. Magnetic fields
  in the outer convective mantle play a dominant role in the 22-years
  cycle. The origin of solar magnetic variability is a key problem in
  astrophysics. The relation between solar variability and changes in
  the Earth's climate is a crucial element in climatology.

Title: Origin and Location of the Hard X-Ray Emission in a Two-Ribbon
    Flare
Authors: Hoyng, P.; Duijveman, A.; Machado, M. E.; Rust, D. M.;
   Svestka, Z.; Boelee, A.; de Jager, C.; Frost, K. T.; Lafleur, H.;
   Simnett, G. M.; van Beek, H. F.; Woodgate, B. E.
Bibcode: 1981ApJ...246L.155H
Altcode:
  No abstract at ADS

Title: The limb flare of 1980 April 30 as seen by the hard X-ray
    imaging spectrometer
Authors: van Beek, H. F.; de Jager, C.; Schadee, A.; Svestka, Z.;
   Boelee, A.; Duijveman, A.; Galama, M.; Hoekstra, R.; Hoyng, P.; Fryer,
   R.; Simnett, G. M.; Imhof, J. P.; LaFleur, H.; Maseland, H. V. A. M.;
   Mels, W. M.; Schrijver, J.; van der Laan, J. J. M.; van Rens, P.; van
   Tend, W.; Werkhoven, F.; Willmore, A. P.; Wilson, J. W. G.; Machado,
   M. E.; Zandee, W.
Bibcode: 1981ApJ...244L.157V
Altcode:
  X-ray imaging of the limb event of 1980 April 30 shows that the flaring
  involved two distinct components: a pointlike component, which was the
  source of the initial hard X-ray burst and an extensive tongue reaching
  some 30,000 km above the limb. The tongue had a higher temperature
  than the other parts of the structure and seemed to be enhanced by
  energetic electrons that derived their energy from the initial source.

Title: Multicolor linear polarimetry of Betelgeuse and Antares
Authors: Tinbergen, J.; Greenberg, J. M.; de Jager, C.
Bibcode: 1981A&A....95..215T
Altcode:
  Multicolor linear polarimetry of Alpha Ori and Sco confirms in a
  qualitative way the ideas about large-scale moving elements in these
  stellar atmospheres, as suggested by Schwarzschild (1975). For one
  well-observed scattering element, a relation between the degree
  of ionization and the fraction of silicon condensed in grains is
  deduced. Sizable residuals remain at short and long wavelengths. Time
  variations of the short-wavelength residuals suggest time variations
  in the dust formed in the stellar atmospheres.

Title: Hard X-ray imaging of two flares in active region 2372
Authors: Hoyng, P.; Duijveman, A.; Boelee, A.; de Jager, C.; Galama,
   M.; Hoekstra, R.; Imhof, J.; Lafleur, H.; Machado, M. E.; Fryer, R.
Bibcode: 1981ApJ...244L.153H
Altcode:
  Hard X-ray images of two flares observed by the Hard X-ray Imaging
  Spectrometer (HXIS) aboard SMM on 1980 April 7 and 10 are discussed. A
  comparison with H-alpha images and the photospheric magnetic field
  maps shows that the emission originates in (arcades of) loops which
  differ greatly in the hardness of the X-ray spectra. On April 7 the
  hardest X-ray emission coincided with the brightest H-alpha patch. On
  April 10 the most intense X-ray emission appeared to be concentrated
  in a looplike structure with a softer spectrum at the top and a
  harder spectrum in the legs. Temperature estimates from flux ratios
  in different energy bands tend to confirm that small, hot components
  are embedded in more extensive, cooler flaring regions.

Title: Book reviews
Authors: Page, D. E.; Pick, M.; Kresák, L.; Reijnen, G. C. M.;
   Cameron, A. G. W.; Schuurmans, Cornelius J. E.; Ya Marov, Mikhail;
   Goldberg, B.; Kaiser, T. R.; Lemaire, J.; Sehnal, L.; Elsässer,
   H.; Valniček, B.; de Graaff, W.; Pacini, Franco; Rohlfs, K.; de
   Landtsheer, A. C.; Zhongolovich, I. D.; de Jager, C.; Greve, A.;
   Ruprecht, J.; Tayler, R. J.; Kockarts, G.; Axford, W. I.; Tabor, H.;
   Bolle, H. J.; Kaldis, E.; Reijnen, Gijsbertha C. M.; De Loore, C.;
   Kleczek, J.; Murray, C. A.; Wallenquist, Åke
Bibcode: 1981SSRv...28..105P
Altcode:
  No abstract at ADS

Title: Introduction
Authors: De Jager, Cornelis; Švestka, Zdeněk
Bibcode: 1981SoPh...72D...7D
Altcode:
  No abstract at ADS

Title: Book-Review - the Brightest Stars
Authors: de Jager, C.
Bibcode: 1981Natur.289Q.733D
Altcode:
  No abstract at ADS

Title: Book Review - Transactions of the IAU V.17B
Authors: Wayman, P. A.; de Jager, C.
Bibcode: 1981SSRv...28..118W
Altcode:
  No abstract at ADS

Title: Book Review - Journal of Astrophysics and Astronomy
Authors: Ramaeshan, S.; de Jager, C.
Bibcode: 1981SSRv...28..112R
Altcode:
  No abstract at ADS

Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Smak, J.
Bibcode: 1981AcA....31..393D
Altcode:
  No abstract at ADS

Title: Book Review - Nonradial and Nonlinear Stellar Pulsations
Authors: Hill, H. A.; Dziembowski, W. A.; de Jager, C.
Bibcode: 1981SSRv...28Q.112H
Altcode:
  No abstract at ADS

Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Kriz, S.
Bibcode: 1981BAICz..32..318D
Altcode:
  No abstract at ADS

Title: Structural development of the X-ray limb flare of 30 April 1980
Authors: de Jager, C.; Hoyng, P.; Lafleur, H.; Schadee, A.; Svestka,
   Z.; van Beek, H. F.; van Tend, W.; Fryer, R.; Simnett, G. M.
Bibcode: 1981AdSpR...1m.251D
Altcode: 1981AdSpR...1..251D
  We describe the development of the limb flare of 30 April 1980, 20:20
  UT, as observed by the Hard X-ray Imaging Spectrometer (HXIS) aboard
  the Solar Maximum Mission (SMM). It consisted of a short-lived bright
  nucleus (FWHM &lt; 10,000 km), just inside the Sun's limb; a longer
  lasting tongue, extending to a height of ~ 30,000 km, and a more
  complicated feature, approximately situated at the Sun's limb. The
  tongue was a pre-existing magnetic structure that started emitting
  X-rays only a few seconds after the bright nucleus, and which had a
  slightly higher temperature than the nucleus; its X-ray emission may
  be caused by electrons escaped from the nucleus.

Title: Solar maximum mission experiment: Early results of the hard
    X-ray imaging experiment
Authors: Boelee, A.; de Jager, C.; Duijveman, A.; Galama, M.; Hoekstra,
   R.; Hoyng, P.; Imhof, J. P.; Lafleur, H.; Maseland, H. V. A. M.; Mels,
   W. A.; Schadee, A.; Schrijver, J.; Svestka, Z.; van Beek, H. F.;
   van Rens, P.; van der Laan, J. J. M.; van Tend, W.; Werkhoven, F.;
   Wiersma, G.; Zandee, W.; Simnett, G. M.; Charlton, C. P.; Fryer, R.;
   Willmore, A. P.; Wilson, J. W. G.; Machado, M. E.
Bibcode: 1981AdSpR...1m.255B
Altcode: 1981AdSpR...1R.255B
  We have selected four widely different flares from the early
  period of operations of the Hard X-Ray Imaging Spectrometer (HXIS)
  on SMM to illustrate the characteristic imaging properties of this
  experiment. For the small flare of April 4, 1980, we demonstrate the
  instrument's capability for locating a compact source. In the weak,
  but extensive, flare of April 6 we show how well the instrument can
  display spatial structure, and also the low level of the instrument
  background. In the 1B flare of April 7 we are able to locate positions
  of the X-ray emission in the soft and hard channels, and estimate
  the positional variations of the emission patches. Finally, in the IN
  flare of April 10, which produced the strongest hard X-ray burst we
  have seen so far, we repeat some of the studies made for the April 7
  event, and also demonstrate the capability of the HXIS instrument to
  study the development, with high time resolution, of individual 8''
  × 8'' elements of the flare.

Title: A relation between solar activity and winter temperatures in
    Holland between 1634 and 1975.
Authors: de Jager, C.
Bibcode: 1981PRNAA..84..457D
Altcode: 1981RNAAS..84..457D
  No abstract at ADS

Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Mihalas, D.
Bibcode: 1981S&T....61..432D
Altcode:
  No abstract at ADS

Title: Solar Maximum Mission experiment - Early results of the hard
    X-ray imaging experiment
Authors: Simnett, G. M.; Charlton, C. P.; Fryer, R.; Boelee, A.;
   de Jager, C.; Duijveman, A.; Galama, M.; Hoekstra, R.; Hoyng, P.;
   Imhof, J. P.
Bibcode: 1981AdSpR...1m.255S
Altcode: 1981AdSpR...1..255S
  Four widely different flares from the early period of operations
  of the Hard X-ray Imaging Spectrometer (HXIS) on SMM have been
  selected to illustrate the characteristic imaging properties of this
  experiment. For the small flare of April 4, 1980, the instrument's
  capability for locating a compact source is demonstrated. In the weak,
  but extensive, flare of April 6, the ability of the instrument to
  display spatial structure, and also the low level of the instrument
  background, are shown. In the 1B flare of April 7, positions of the
  X-ray emission in the soft and hard channels are capable of being
  located, and the positional variations of the emission patches can
  be estimated. Finally, in the 1N flare of April 10, which produced
  the strongest hard X-ray burst seen so far, some of the studies made
  for the April 7 event are repeated, and the capability of the HXIS
  instrument to study the development, with high time resolution, of
  individual 8 x 8 arcsec elements of the flare is also demonstrated.

Title: Two years of observation with the international ultraviolet
    explorer
Authors: de Jager, C.; Lamers, H. J. G. L. M.
Bibcode: 1981AdSpR...1m.185D
Altcode: 1981AdSpR...1..185D
  The launching of I.U.E., in January 1978, has provided the astronomical
  community with a powerful observatory-type spacecraft enabling one a
  practically continuous observation of ultra-violet spectra of celestial
  bodies. Two years of operation have led to many new developments, in
  which a large number of astronomers participated. This review summarizes
  a part of these developments. While refraining from a description of
  the results obtained in solar-system and extra-galactic research we
  discuss: early-type and Wolf-Rayet stars, medium- and late-type stars,
  planetary nebulae, novae and dwarf-novae, X-ray binaries, supernovae,
  the interstellar medium and the galactic halo.

Title: Mass Loss from Massive Stars
Authors: de Jager, C.
Bibcode: 1981mms..conf...67D
Altcode: 1982mms..conf...67D
  No abstract at ADS

Title: Book Review - Solar and Interplanetary Dynamics IAU SYMP.#91
Authors: Dryer, M.; Tandberg-Hanssen, E.; de Jager, C.
Bibcode: 1981SSRv...28..114D
Altcode:
  No abstract at ADS

Title: Observation of the Dynamical State of the Outer Atmospheres
    of Beta Cephei Stars
Authors: de Jager, C.
Bibcode: 1981iue..prop..894D
Altcode:
  No abstract at ADS

Title: Book Review - Space Art
Authors: Muller, R.; de Jager, C.
Bibcode: 1981SSRv...28..117M
Altcode:
  No abstract at ADS

Title: Book Review - Space Research V.20
Authors: Rycroft, M. J.; de Jager, C.
Bibcode: 1981SSRv...28..111R
Altcode:
  No abstract at ADS

Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Scholz, G.
Bibcode: 1981AN....302..320D
Altcode:
  No abstract at ADS

Title: The Outer Layers of the Beta-Cephei Type Variables
    Bw-Vulpeculae and Omicron-Scorpii
Authors: Burger, M.; de Jager, C.; van den Oord, G. H. J.; Groupe
   Etoiles Variables de L'Observatoire de Nice
Bibcode: 1981pbs..work..181B
Altcode:
  No abstract at ADS

Title: Book Review - Stellar Turbulence IAU Colloquium no.
Authors: Gray, D. F.; Linsky, J. L.; de Jager, C.
Bibcode: 1981SSRv...28..113G
Altcode:
  No abstract at ADS

Title: Structural development of the X-ray limb flare of 30 April
    1980.
Authors: de Jager, C.; Fryer, R.; Hoyng, P.; Lafleur, H.; Schadee,
   A.; Simnett, G. M.; Svestka, Z.; van Beek, H. F.; van Tend, W.
Bibcode: 1981hea..conf..251D
Altcode:
  No abstract at ADS

Title: Solar Maximum Mission experiment: early results of the hard
    X-ray imaging experiment.
Authors: Simnett, G. M.; Boelee, A.; Charlton, C. P.; de Jager, C.;
   Duijveman, A.; Fryer, R.; Galama, M.; Hoekstra, R.; Hoyng, P.; Imhof,
   J. P.; Lafleur, H.; Machado, M. E.; Maseland, H. V. A. M.; Mels,
   W. A.; Schadee, A.; Schrijver, J.; Svestka, Z.; van Beek, H. F.;
   van Rens, P.; van der Laan, J. J. M.; van Tend, W.; Werkhoven, F.;
   Wiersma, G.; Willmore, A. P.; Wilson, J. W. G.; Zandee, W.
Bibcode: 1981hea..conf..255S
Altcode:
  No abstract at ADS

Title: De zon een opmerkelijke ster.
Authors: de Jager, C.
Bibcode: 1981Zenit...8..242D
Altcode:
  No abstract at ADS

Title: Two years of observation with the International Ultraviolet
    Explorer.
Authors: de Jager, C.; Lamers, H. J. G. L. M.
Bibcode: 1981hea..conf..185D
Altcode:
  No abstract at ADS

Title: The ultraviolet spectrum of BET CMa stars.
Authors: Burger, M.; de Jager, C.; Kamperman, T. M.; Neven, L.
Bibcode: 1980A&A....90..170B
Altcode:
  Ultraviolet spectra of 15 beta Canis Majoris stars in wavelength bands
  of approximately 100 A around 2100, 2500, and 2800 A (resolution 1.8
  A), obtained with the Ultraviolet Stellar Spectrophotometer S 59 on
  board the ESRO TD-1A satellite are discussed. In general the spectra
  are similar to those of 'normal' stars, only the star alpha Vir has He
  I, C II, and Mg II lines slightly weaker than normal. Comparison with
  theoretical computations shows that the Fe abundance in the beta CMa
  stars is solar and that the average microturbulent velocity is about 4
  km/sec. The UV spectral lines of beta Cep do not show any significant
  variations in equivalent width with phase.

Title: Book reviews
Authors: Guest, J. E.; Malin, Michael C.; Melchior, P.; Muller, C.;
   Namba, O.; Hultqvist, B.; Stoker, P. H.; Kleczek, Josip; Balder,
   E. J.; van der Sluis, A.; van de Stadt, H.; Larsson-Leander, Gunnar;
   Fiszdon, W.; de Groot, S. R.; de Boer, W. P. H.; Tennekes, H.; de
   Jager, Cornelis; Kleczek, J.
Bibcode: 1980SSRv...26..447G
Altcode:
  No abstract at ADS

Title: The Solar Maximum Year and Related Space Experiments
Authors: Svestka, Z.; de Jager, C.
Bibcode: 1980SSRv...26..317S
Altcode:
  The Solar Maximum Year is a world-wide cooperative project to gain
  more insight in certain aspects of solar flares. It consists of three
  sub-programs: The Flare Build-up Study (FBS), the Study of Energy
  Release from Flares (SERF), and the Study of Travelling Interplanetary
  Phenomena (STIP). These programs are described. We also describe space
  observations to be performed during SMY, particularly the Solar Maximum
  Mission Satellite.

Title: Pulsation of the outer atmosphere of BW Vul.
Authors: Burger, M.; de Jager, C.
Bibcode: 1980ESASP.157...47B
Altcode: 1980IUE2n.......47B; 1980iue..conf...47B
  Observations of the far UV spectrum of the beta Cephei variable BW
  Vul show that the pulsation consists of three phases: a phase of
  photospheric rest; a sudden upward acceleration of the photosphere
  and outer atmosphere (the maximum acceleration being approximately
  equal to the gravitational value); descent of the whole atmosphere
  with downward acceleration 1/4 of the gravitational value. At the
  end of the second phase a temporal stellar wind occurs with maximum
  velocity of 500 km s(-1).

Title: Book reviews
Authors: de Groot, T.; Vesseur, H. J. A.; Heintze, J. R. W.; de Jager,
   C.; Kleczek, J.; Tuominen, Jaakko; Bogus, K.
Bibcode: 1980SSRv...25..431D
Altcode:
  No abstract at ADS

Title: Book-Review - the Sun Our Future Energy Source
Authors: McDaniels, D. K.; De Jager, C.
Bibcode: 1980SSRv...26R.453M
Altcode:
  No abstract at ADS

Title: Book-Review - Mass Loss and Evolution of O-Type Stars IAU
    SYMP.NO. 83 Vancouver-Island 1978JUN5-9
Authors: Conti, P. S.; De Loore, C. W. H.; de Jager, C.
Bibcode: 1980SSRv...25...84C
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Henrichs, H. F.; Szebehely, V.; Ponnamperuma, Cyril; de Jager,
   C.; Pfotzer, G.; Kovalevsky, J.; Habing, H. J.
Bibcode: 1980SSRv...25...83H
Altcode:
  No abstract at ADS

Title: Book-Review - New Horizons in Astronomy ed.
Authors: Brandt, J. C.; Maran, S. P.; de Jager, C.
Bibcode: 1980SSRv...25Q..85B
Altcode:
  No abstract at ADS

Title: The brightest stars
Authors: de Jager, C.
Bibcode: 1980GAM....19.....D
Altcode:
  Luminous stars of the upper part of the Hertzsprung Russell diagram are
  examined. The evolutionary relation between bright stars is discussed
  and emphasis is placed on the unity of the stars, notwithstanding the
  seeming diversity. The study deals with stars brighter than about 1000
  solar luminosity and the structure of very tenuous stellar atmospheres
  is investigated. Stellar observations with high-resolution ultraviolet
  stellar spectroscopy are reported for features of near-instable stars
  such as stellar chromospheres, coronas, and extended shells.

Title: Near-unstable supergiants.
Authors: de Jager, C.
Bibcode: 1980ESAJ....4..123D
Altcode:
  The instability of massive supergiant stars is discussed in light of the
  absence of massive luminous cool supergiants. Consideration is given
  to the Eddington limit to stellar luminosities and the dissipation of
  turbulent energy by massive stars, and it is shown that these processes
  are insufficient to explain in the absence of red supergiants larger
  than about 25 solar masses. It is suggested that in the course of
  evolution towards low temperatures, massive supergiants retrace their
  steps on the Hertzsprung-Russel diagram and move to the region of
  higher photospheric temperatures. Such stars would become unstable
  as the ratio of specific heats approaches 4/3, and would begin to
  pulsate, as is observed in all stars more than approximately 10,000
  times brighter than the sun. It is suggested that these instabilities
  would most likely originate in the convection layers just below the
  stellar surface, and would lead to the formation of stellar coronas
  as detected by ANS and the HEAO-2 satellites.

Title: Book-Review - Catalogue of the Universe
Authors: Murdin, P.; Allen, D.; Malin, D.; de Jager, C.
Bibcode: 1980SSRv...25..432M
Altcode:
  No abstract at ADS

Title: Book-Review - Nonlinear Methods of Spectral Analysis
Authors: Haykin, S.; De Jager, C.
Bibcode: 1980SSRv...26..454H
Altcode:
  No abstract at ADS

Title: Grote Europese sterrenwacht in wording.
Authors: de Jager, C.
Bibcode: 1980Zenit...7..354D
Altcode:
  No abstract at ADS

Title: Uitzonderlijke vliegtuigwaarnemingen van de zonnekorona.
Authors: de Jager, C.
Bibcode: 1980Zenit...7..226D
Altcode:
  No abstract at ADS

Title: Wringende trillingen van het zonsoppervlak.
Authors: de Jager, C.
Bibcode: 1980Zenit...7..468D
Altcode:
  No abstract at ADS

Title: On the Seats of Elementary Flare Bursts
Authors: de Jager, C.
Bibcode: 1979SoPh...64..135D
Altcode:
  We suggest to identify the elementary flare bursts with the excitation
  of the small kernels that occur in flare loops that are observed in
  soft X-ray pictures of flares. We stress the need of simultaneous
  observations of spatial structure and time variations of hard X-ray
  bursts sources in various wavelength regions.

Title: Short time changes in the terminal velocity of the stellar
    wind of alpha Cam ((O9.5 Ia).
Authors: de Jager, C.; Lamers, H. J. G. L. M.; Macchetto, F.; Snow,
   T. P.
Bibcode: 1979A&A....79L..28D
Altcode:
  The UV spectrum of the star Alpha Cam (09.5 Ia) was observed for 72
  hours continuously in September 1978, with IUE. During these three
  days the star shows gradual short-term changes of the edge velocity
  of the C IV and N V resonance lines. The change is largest for the
  lines formed at large distance from the star, and may be due to
  either UV-flux variations of the star or variations in the mass loss
  rate (puffs). Evidence is also found for erratic very-short terms
  variations of the edge velocities. These are probably correlated
  with the ionization equilibrium: the ions with the highest ionization
  potential showing the largest variations.

Title: Book-Review - Vistas in Astronomy V.22:3
Authors: Beer, A.; Beer, P.; de Jager, C.
Bibcode: 1979SSRv...24..367B
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Ooms, G.; Wittenberg, H.; de Jager, C.; Pinkau, K.; Lehr,
   A.; Rinner, K.
Bibcode: 1979SSRv...24..367O
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Gendrin, R.; Namba, O.; van Kampen, N. G.; de Jager, Cornelis;
   Forbes, E. G.; Kleczek, J.; Reijnen, G. C. M.; Genzel, R.; Smets,
   G.; Radelaar, R.
Bibcode: 1979SSRv...24..253G
Altcode:
  No abstract at ADS

Title: Balloon-borne Ultraviolet Stellar Spectrograph. II. Highlights
    of first observational results.
Authors: de Jager, C.; Kondo, Y.; Hoekstra, R.; van der Hucht, K. A.;
   Kamperman, T. M.; Lamers, H. J. G. L. M.; Modisette, J. L.; Morgan,
   T. H.
Bibcode: 1979ApJ...230..534D
Altcode:
  We describe a few of the most important features, visible in a first
  inspection of the high- resolution (0.1 A) mid-ultraviolet spectra
  ( A) of 33 stars obtained in two BUSS flights. The profiles of the
  Mg ii lines in early-type (B8-A2) supergiants show the existence of
  considerable mass flow, partly in irregular "puffs." The features in Mg
  ii in Betelgeuse are due to a cool expanding outer shell above a hotter
  chromospheric region. Emission features in the shell star Tau indicate
  infalling material, while the Be star 4) Per has a mass outflow. We have
  detected some 80 emission lines of Fe I, Fe ii, and Fe iii in spectra of
  late-type giants and supergiants. The composite spectrum of the binary
  a Sco (M1.5 lab + B2.5 V) is described, with particular reference to
  circumstellar lines. Subject headings: line identifications - stars:
  Be - stars: mass loss - stars: supergiants - ultraviolet: spectra

Title: Balloon-borne Ultraviolet Stellar
    Spectrograph. I. Instrumentation and observation.
Authors: Kondo, Y.; de Jager, C.; Hoekstra, R.; van der Hucht, K. A.;
   Kamperman, T. M.; Lamers, H. J. G. L. M.; Modisette, J. L.; Morgan,
   T. H.
Bibcode: 1979ApJ...230..526K
Altcode:
  A dual star-tracking system and a system including a telescope, an
  echelle spectrograph, and a SEC vidicon are the chief components of the
  Balloon-borne Ultraviolet Stellar Spectrograph (BUSS), which has flown
  four successful missions. The BUSS missions have yielded 81 spectra
  for 56 stars, recorded with a resolution of 0.1 A in the wavelength
  range from 2200 to 3400 A. BUSS observations include: profiles of Mg
  II lines indicating considerable mass flow in early-type supergiants;
  Mg II features suggesting a cool expanding outer shell above a hotter
  chromosphere; emission features in Zeta Tau (a shell star) indicating
  infalling material; and emission features of the Be star Phi Per
  suggesting mass outflow.

Title: Book reviews
Authors: Lequeux, J.; Reijnen, G. C. M.; Kleczek, Josip; Gray, D. F.;
   Dommanget, J.; Namba, O.; Verbunt, Frank; Savonije, Gertian; de Jager,
   Cornelis; van Bueren, H. G.; Hovenier, J. W.; Fokker, A. D.; Hoekstra,
   Roel; Hultqvist, Bengt; Kresák, L.
Bibcode: 1979SSRv...23..683L
Altcode:
  No abstract at ADS

Title: Large Turbulent Elements in Supergiant Photospheres
Authors: de Jager, C.; Vermue, J.
Bibcode: 1979Ap&SS..62..245D
Altcode:
  During the ‘cool phase’ of the super-supergiant HR 8752, which
  happened around 1973, when the star's spectral type was K2...K5
  Ia<SUP>+</SUP>, the most probable vertical extent of the main turbulent
  elements in the star's photosphere was about 6 times the density
  scale height, which is about half the stellar radius. In early-type
  photospheres (class Ia) it is about 10 times the atmospheric density
  scale height (about 0.25 of the stellar radius), while in less extreme
  (luminosity class Ib) medium-type supergiants the most probable vertical
  extent of the elements is approx. 8 times the density scale height
  (≈0.05R). Large turbulent elements are apparently a common feature
  in supergiant photospheres; the more extreme the supergiant the larger
  the relative size of the eddies.

Title: Macro- and Micro-Turbulent Filter Functions for Weak Lines
    in Stellar Atmospheres
Authors: Vermue, J.; de Jager, C.
Bibcode: 1979Ap&SS..61..129V
Altcode:
  Following a similar discussion given earlier for the solar case
  (De Jager, 1972) we compute in this paper spectral line profiles
  for the spatial wavelengths in which a stellar motion field can
  be decomposed, and thereafter the macro-and micro-turbulent filter
  functionsf <SUB>M</SUB>(θk) andf <SUB>μ</SUB>(θk), where θ is
  the optical scale height andf <SUP>2</SUP>(k) dk the fraction of
  the energy of the turbulent motions between wavenumbersk andk+dk
  of the spectrum of turbulence that contributes to either kind of
  turbulence. If micro-and macro-turbulent velocity components are known
  for a certain star, and if the spectrum of turbulence is sharp enough,
  the ratiof <SUB>M</SUB>/f <SUB>μ</SUB> would enable one to derive the
  average size of the turbulent elements in the star's atmosphere. The
  computations apply to weak lines in idealized stellar atmospheres, and
  refer to two cases: isotropic turbulence, and radial pulsations. These
  filters can be suitably used in a diagnostic method for the analysis
  of the motion field in the solar and stellar atmospheres. Some examples
  of applications to stars of very different kinds are given.

Title: K. O. Kiepenheuer, 1910 - 1975.
Authors: de Jager, C.
Bibcode: 1979ssms.conf....1D
Altcode:
  No abstract at ADS

Title: Beta CMA Stars
Authors: de Jager, C.
Bibcode: 1979iue..prop..306D
Altcode:
  No abstract at ADS

Title: Stars and their coronae.
Authors: de Jager, C.
Bibcode: 1979xrgr.conf...17D
Altcode:
  No abstract at ADS

Title: Space Research, Vol._XIX. Proceedings of the open meetings of
    the working groups on physical sciences of the twenty-first plenary
    meeting of COSPAR, Innsbruck, Austria, 29_May_- 10_June 1978.
Authors: Rycroft, M. J.; de Jager, C.
Bibcode: 1979srvp.book.....R
Altcode:
  No abstract at ADS

Title: Het ruimte-onderzoek.
Authors: de Jager, C.
Bibcode: 1979plan.book...92D
Altcode:
  No abstract at ADS

Title: Nauwelijks stabiele reuzensterren.
Authors: de Jager, C.
Bibcode: 1979PKNAW..88..120D
Altcode:
  No abstract at ADS

Title: Mass Loss from Late Supergiant B-Stars and A-Stars
Authors: Lamers, H. J. G. L. M.; Macchetto, F.; de Jager, C.
Bibcode: 1979IUE1.symp..382L
Altcode:
  No abstract at ADS

Title: Short-Time Variations in P-Cygni Profiles of Early-Type
    Supergiants
Authors: Lamers, H. J. G. L. M.; Snow, T. P.; Macchetto, F.; de
   Jager, C.
Bibcode: 1979IUE1.symp..381L
Altcode:
  No abstract at ADS

Title: Global development of space research, 1977-1978
Authors: de Jager, C.
Bibcode: 1979spre.conf....3D
Altcode: 1979spre.proc....3D
  Various aspects of space research in the 1977-1978 period are
  reviewed. Attention is given to the following fields: material
  sciences, life sciences, geophysical measurements, remote sensing of
  earth resources, weather and climate, the magnetosphere, the solar
  wind and its interactions, solar, planetary, and stellar physics,
  and high energy astrophysics.

Title: The Velocity Field in the Atmosphere of δ Cephei
Authors: de Jager, C.
Bibcode: 1978Ap&SS..59..165D
Altcode:
  Observations related to the photospheric velocity field of δ Cephei can
  be interpreted as follows: during the whole cycle of pulsations the only
  motion form in the atmosphere is a wave motion with a nearly constant
  full amplitude of approximately 15 km s<SUP>-1</SUP>, and a wavelength
  of about 10<SUP>6</SUP> km (which are quantities, about equal to the
  amplitudes of pulsational velocity and radius of the star). There are
  no significant small-scale ‘turbulent’ velocity components. The
  ‘microturbulent’ and ‘macroturbulent’ velocities, as derived
  from spectral line observations, are fully compatible with this picture.

Title: E. N. Parker first recipient of the George Ellery Hale Prize.
Authors: De Jager, Cornelis; Švestka, Zdeněk
Bibcode: 1978SoPh...60....3D
Altcode: 1978SoPh...60....3.
  No abstract at ADS

Title: Low-energy protons: Gradients in interplanetary space and
    distribution in the solar corona
Authors: Stevens, G. A.; Vanrooijen, J. J.; Svestka, Z.; De Jager, C.
Bibcode: 1978clus.nasa..234S
Altcode:
  First and second order anisotropy measurements are proposed as a tool
  for studying the coronal source function and interplanetary propagation
  of low energy protons. Optimum orbit and attitude requirements are
  suggested for a three telescope system. Some limitations with regard
  to the lower energy limit for a feasible set-up are discussed.

Title: Book reviews
Authors: Roberts, Paul H.; Scholer, Manfred; de Jager, C.; Ceplecha,
   Zdeněk; Grewing, M.; Kresák, L.; Bumba, Václav; Pottasch, S. R.;
   Sehnal, L.; Pagel, Bernard; Reijnen, G. C. M.; Ness, Norman F.;
   de Jager, Cornelis
Bibcode: 1978SSRv...22..213R
Altcode:
  No abstract at ADS

Title: Properties of elementary flare bursts.
Authors: de Jager, C.; de Jonge, G.
Bibcode: 1978SoPh...58..127D
Altcode:
  From a study of eight hard X-ray flares, all with durations of less
  than five minutes, it is found that these flares can be completely
  decomposed into short-lived bursts, called Elementary Flare Bursts
  (EFB). For each one flare the individual EFB's have approximatively the
  same Full Width at Half Maximum (FWHM); average values range between
  4 s (± 1 s) and 24 s (± 5 s) for the different flares. Yet there are
  significant differences between the FWHM's for the individual EFB's of
  a flare. The EFB's are slightly asymmetric; rise time is approx. 0.9
  of the decay time. Their half-widths decrease with increasing photon
  energy, proportional to E<SUP>-0.69±0.05</SUP>.

Title: Book reviews
Authors: de Jager, Cornelis; Takens, R. J.
Bibcode: 1978SSRv...22..115D
Altcode:
  No abstract at ADS

Title: Excited Cosmic Plasmas (Paper dedicated to Professor Hannes
    Alfvén on the occasion of his 70th birthday, 30 May 1978)
Authors: de Jager, C.
Bibcode: 1978Ap&SS..55..147D
Altcode:
  We describe some aspects of the energetic radiations of high-energy
  cosmical plasmas in stellar environments, mainly stellar chromospheres
  and coronae, and solar and stellar flare-type phenomena. As far as
  possible we discuss the morphology and physics of these plasmas,
  and we speculate on their origin. This paper is a review, partly of a
  historical character, describing particularly some contributions from
  the Astronomical Institute at Utrecht to this field of astrophysical
  research.

Title: Analysis of spectra of α CMi and α Cen A observed with
    the orbiting stellar ultraviolet spectrophotometer S59 in ESRO's
    TD1A satellite
Authors: de Jager, C.; Kamperman, T. M.; Neven, L.
Bibcode: 1978Ap&SS..54..343D
Altcode:
  Ultraviolet spectra of α CMi and α Cen A taken with moderate
  spectral resolution (approx. 1.8 Å) are used to analyse whether
  a determination of stellar chemical abundances of Fe and Cr and of
  the photospheric parameters is possible. For αCMi, for which good
  spectral data are available, we findT <SUB>eff</SUB>=7660±110 K;
  logg <SUB>eff</SUB>=3.05±0.1. Further, Δlogɛ(Fe)=-0.06±0.09; Δ log
  ɛ(Cr)=-0.01±0.09 with regard to ‘standard’ (solar) abundances. For
  α Cen A the resulting data — particularly the photospheric ones —
  are less certain, but it seems that the Fe abundance may be smaller
  than the ‘standard’ value.

Title: Book reviews
Authors: van Diggelen, J.; Ne'Eman, Yuval; Nyboer, B. R. A.; Kleczek,
   J.; Dobrzycki, Jerzy; Hartmann, G.; Swider, W.; Hempenius, S. A.;
   de Jager, C.; 't Hooft, G.; Radelaar, S.; Wisse, J. A.; de Jong, T.;
   Houtgast, J.; Bezemer, J.
Bibcode: 1978SSRv...21..703V
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Plavec, Miroslav; Hoekstra, R.; de Jager, C.; Grygar, Jiři;
   Otterman, J.; van den Dool, H. M.; Namba, O.; Gunsing, C. J. Th.;
   Pecker, Jean-Claude; Kwee, K. K.; Perek, L.; Callebaut, D.; Kuijpers,
   Jan; de Graaff, W.; Reijnen, G. C. M.; Swanenburg, B.; Grevesse,
   N.; Kleczek, J.; Piquet, P.; Fokker, A. D.; van Bueren, H. G.; Page,
   D. Edgar; van Duinen, R. J.; Pacini, Franco
Bibcode: 1978SSRv...21..469P
Altcode:
  No abstract at ADS

Title: An imaging soft X-ray telescope for Spacelab.
Authors: Catura, R. C.; Culhane, J. L.; de Jager, C.; Garmire, G. P.;
   Novick, R.
Bibcode: 1978nisa.symp..247C
Altcode: 1978nisa.conf..247C
  No abstract at ADS

Title: Editorial
Authors: De Jager, Cornelis; Švestka, Zdeněk
Bibcode: 1978SoPh...56....3D
Altcode: 1978SoPh...56....3.
  No abstract at ADS

Title: A review of space research, 1976 - 1977.
Authors: de Jager, C.
Bibcode: 1978spre.conf....3D
Altcode: 1978spre.proc....3D
  Various remote sensing projects are discussed noting the
  Fourier spectrometer and a high-resolution multispectral scanner
  camera. Projects involving the determination of crop species and
  measurements of atmospheric absorption lines are discussed. Studies
  of the upper atmosphere are considered including the ozone layer,
  the influx of energetic solar protons, and density and pressure
  profiles. Rocket sounding for ionospheric and magnetospheric
  observations is described along with determinations of the total solar
  radiation flux and X-ray emissions from solar flares. Data concerning
  the solar wind are assessed and the Viking and Luna-24 missions are
  outlined. The U.S.-Netherlands balloon-borne ultraviolet stellar
  spectrograph device and its applications are reviewed.

Title: Improved values for the solar micro- and macro-turbulent
    filter functions
Authors: de Jager, C.; Vermue, J.
Bibcode: 1977SoPh...54..313D
Altcode:
  The contributions of any arbitrary photospheric velocity field to
  (macroturbulent) line displacement, and to (microturbulent) line
  broadening can be expressed by the macro- and micro-turbulent filters
  f<SUB>M</SUB>(k) and f<SUB>t</SUB>(<SUB>k</SUB>), where <SUB>k</SUB>
  is the wavenumber of the energy spectrum in which the line-of-sight
  component of the velocity field can be decomposed. As a correction to
  a previous computation of f<SUB>M</SUB> and f<SUB>t</SUB> we give in
  this Note improved values for the filter functions for weak lines in
  LTE. An example of the way to use the filter functions is given.

Title: An imaging soft X-ray telescope for Spacelab
Authors: Catura, R. C.; Culhane, J. L.; De Jager, C.; Garmire, G. P.;
   Novick, R.
Bibcode: 1977cosp.meetR....C
Altcode:
  A grazing-incidence soft X-ray telescope (SXT) of Wolter Type I
  design is described which has been proposed for use in Spacelab
  missions. The SXT consists of a four-mirror nested array of confocal
  paraboloid-hyperboloid elements and is intended to have optimal
  response in the wavelength range from 6 to 100 A (it also covers
  the range between 100 and 1000 A). Basic elements of the SXT are
  reviewed together with a design study of two different hyperboloid
  lengths. An objective grating for studying point-source spectra is
  examined, and several focal-plane detectors are discussed, including
  an image-sensitive proportional counter, a channel electron multiplier
  array, and a gas scintillation proportional counter. SXT sensitivity
  is estimated for eight wavelength ranges between 8 and 1100 A.

Title: BUSS Observations II. Extended Atmospheres of Betelgeuse.
Authors: Kondo, Y.; Modisette, J. L.; Morgan, T. H.; de Jager, C.;
   Lamers, H. J.; van der Hucht, K. A.
Bibcode: 1977BAAS....9..365K
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Reijnen, G. C. M.; Kleczek, J.; Millman, Peter M.; Vesseur,
   H. J. A.; Bar-Nun, Akiva; de Jager, C.; van Albada, T. S.; Rawer,
   K.; Hinze, J. O.; Trümper, J.; de Jager, Cornelis; Müller, O.;
   Kovalevsky, J.; Hammerschlag, R. H.; Hoyng, Peter
Bibcode: 1977SSRv...20..235R
Altcode:
  No abstract at ADS

Title: Image Processing Techniques in Astronomy (Book Review)
Authors: de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1977ApL....18..177D
Altcode:
  No abstract at ADS

Title: The Spectroscopy and Polarimetry of Flare X-Radiation
Authors: de Jager, C.
Bibcode: 1977uxsa.collE...6D
Altcode: 1977IAUCo..43S....D
  No abstract at ADS

Title: Book reviews
Authors: Reijnen, G. C. M.; Rycroft, M. J.; de Jager, C.; Page, D. E.;
   Lyttleton, R. A.; Jongen, H. F.; Ne'Eman, Y.; Herbig, G. H.; Kleczek,
   J.; Hartmann, William K.; Delbouille, L.; Stoker, P. H.
Bibcode: 1977SSRv...20..115R
Altcode:
  No abstract at ADS

Title: High resolution stellar spectroscopy in the balloon
    ultraviolet.
Authors: de Jager, C.; Kondo, Y.; van der Hucht, K. A.; Morgan, T. H.
Bibcode: 1977spre.conf..741D
Altcode: 1977spre.proc..741D
  The JSC/SRL Balloon-borne Ultraviolet Stellar Spectrometer (BUSS)
  comprises a 40 cm telescope, an echelle spectrograph and a SEC
  Vidicon detector. Operating at an altitude of 40 km this instrument
  provides spectra of stars with 0.1 A resolution in the 2000-3400 A
  region. Observations made on 19 May 1976, are discussed.

Title: Space Research, Vol._XVII. Proceedings of open meetings
    of working groups on physical sciences of the nineteenth plenary
    meeting of COSPAR, Philadelphia, Pennsylvania, USA, 8 - 19 June 1976
    and COSPAR/IAGA symposium on minor constituents and excited species,
    Philadelphia, Pennsylvania, USA, 9 - 10 June 1976.
Authors: Rycroft, M. J.; Stickland, A. C.; de Jager, C.
Bibcode: 1977srvp.book.....R
Altcode:
  No abstract at ADS

Title: BUSS Observations. I. The Near-Ultraviolet Spectrum of α
    Sco AB.
Authors: van der Hucht, K. A.; Lamers, H. J.; de Jager, C.; Kondo,
   Y.; Morgan, T. H.; Modisette, J. L.
Bibcode: 1976BAAS....8..545V
Altcode:
  No abstract at ADS

Title: Balloon-borne High Resolution Ultraviolet Stellar
    Spectrophotometry Utilizing Echelle Spectrograph and SEC Vidicon. II.
Authors: Kondo, Y.; Modisette, J. L.; Morgan, T. H.; de Jager, C.;
   Lamers, H. J.; van der Hucht, K. A.
Bibcode: 1976BAAS....8R.548K
Altcode:
  No abstract at ADS

Title: An investigation of the ultraviolet spectra of beta Lyrae
    with the TD-1A satellite.
Authors: Hack, M.; van den Heuvel, E. P. J.; Hoekstra, R.; de Jager,
   C.; Sahade, J.
Bibcode: 1976A&A....50..335H
Altcode:
  An investigation of scans of Beta Lyrae with the S 2/68 and S 59
  experiments aboard the satellite TD-1A confirms the model accepted so
  far with the addition that the emitting regions of C IV, and probably
  of Si IV, are located in the circumstellar envelope which surrounds the
  secondary component, and that the Fe III emission originates within the
  expanding outer envelope which surrounds the whole system. The violet
  absorption borders of the Mg II doublet and of the Fe III emissions
  yield velocities which agree with those derived from the lines of
  the triplet series of He I in the optical and near infrared regions,
  and reflect the velocity of expansion of the outermost layers of the
  thin envelope in which the stars are embedded.

Title: Balloon-borne high resolution ultraviolet stellar
    spectrophotometry utilizing echelle spectrograph and SEC Vidicon.
Authors: Kondo, Y.; de Jager, C.; Morgan, T. H.; van der Hucht, K. A.;
   Modisette, J. L.
Bibcode: 1976BAAS....8..428K
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Jacchia, L. G.; de Jager, C.; van den Broek, P. Ph.; van
   Diggelen, J.; Kivelson, M. G.; Russell, C. T.
Bibcode: 1976SSRv...19..161J
Altcode:
  No abstract at ADS

Title: Solar Flares
Authors: de Jager, C.; Kuperus, M.; Rosenberg, H.
Bibcode: 1976RSPTA.281..507D
Altcode: 1976RSLPT.281..507D
  A summary is given of some recent observational data on solar
  flares. Particularly we discuss the flare build-up process and the time
  scales involved. We suggest as a possible magnetic field configuration a
  multiply kinked or supertwisted flux tube. The role of plasma turbulence
  and the Fermi mechanism in particle acceleration is discussed.

Title: Physics of the Solar Atmosphere
Authors: de Jager, C.; Kuperus, M.; Rosenberg, H.
Bibcode: 1976RSPTA.281..415D
Altcode: 1976RSLPT.281..415D
  A summary is given on recent results on the physics of the quiet solar
  atmosphere, and active regions. This includes: solar rotation, velocity
  fields and waves, magnetic field concentration, the transition region,
  coronal magnetic field structure, and prominences.

Title: Preface
Authors: de Jager, Cornelis; Obayashi, Tatsuzo; Švestka, Zdeněk
Bibcode: 1976SoPh...47....9D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; van Rensbergen, Walter; Kuperus, M.; Falthammar,
   Carl-Gunne; Mewe, R.; Reunen, G. C. M.; Bruzek, A.; Swanenburg,
   B. N.; Kleczek, J.; Millman, Peter M.; Vesseur, H. J. A.; Pacini,
   F.; Monfils, A.
Bibcode: 1976SSRv...18..541D
Altcode:
  No abstract at ADS

Title: Astronomical observations from outside the terrestrial
    atmosphere.
Authors: Code, A. D.; Bonnet, R. M.; Gorenstein, P.; Harper, D. A.;
   York, D. G.; van Duinen, R.; Wesselius, P.; de Jager, C.; Gurzadyan,
   G. A.; de Graaf, W.; Kondo, Y.
Bibcode: 1976IAUTA..16c.195C
Altcode:
  No abstract at ADS

Title: Instruments and techniques (Instruments et techniques).
Authors: Meinel, A. B.; Baranne, A.; Baum, W. A.; Dollfus, A.;
   Duchesne, M.; Godoli, G.; Hunter, A.; de Jager, C.; Livingston, W. C.;
   Mikhel'Son, N.; Sedmak, G.; Sinvhal, S. D.; Walker, M.
Bibcode: 1976IAUTA..16a..19M
Altcode:
  No abstract at ADS

Title: Het planetenstelsel. Kolleges sterrekunde voor afgestudeerden
    1976.
Authors: de Jager, C.; Reijnen, G. C. M.
Bibcode: 1976hepl.conf.....D
Altcode: 1976hpks.book.....D
  No abstract at ADS

Title: Space research XVI. Proceedings of open meetings of Working
    Groups on Physical Sciences of the eighteenth plenary meeting of
    COSPAR, Varna, Bulgaria, 29 May - 7 June 1975 and COSPAR symposium
    and workshop on results from Coordinated Upper Atmosphere Measurement
    Programs, Varna, Bulgaria, 29_-_31 May 1975.
Authors: Rycroft, M. J.; de Jager, C.
Bibcode: 1976srxp.book.....R
Altcode:
  No abstract at ADS

Title: Ultraviolet observations of beta Cephei and beta Canis Majoris.
Authors: Beeckmans, F.; Burger, M.; de Jager, C.; Kamperman, T. M.
Bibcode: 1976mpvs.conf....3B
Altcode:
  No abstract at ADS

Title: Elementary flare bursts.
Authors: van Beek, H. F.; de Feiter, L. D.; de Jager, C.
Bibcode: 1976spre.conf..819V
Altcode: 1976spre.proc..819V
  Two hard X-ray flares observed on 2 and 7 August 1972 with the hard
  X-ray detector of the Utrecht Space Research Laboratory aboard ESRO's
  TD-1A satellite are examined in detail. It is shown that both flares can
  be decomposed completely into a number of individual Elementary Flare
  Bursts (EFB's) with no residual radiation left. For one and the same
  flare all EFB's seem to have approximately the same time profile but
  these profiles are different for the two flares investigated: the full
  widths at half maximum (FWHM) of the EFB's are 5 and 15 s respectively.

Title: Non-thermal broadening of weak lines
Authors: Gurtovenko, E. A.; de Jager, C.; Lindenbergh, A.; Rutten,
   R. J.
Bibcode: 1976pmas.conf..331G
Altcode:
  No abstract at ADS

Title: Progress in Ultraviolet Stellar Spectrophotometry with S59
Authors: de Jager, C.; Lamers, H. J. G. L. M.; van der Hucht, K. A.
Bibcode: 1975Ap&SS..38..313D
Altcode: 1975IAUCo..27..313D
  A progress report is given of investigations related to observations of
  stellar spectra obtained with the ultraviolet stellar spectrophotometer
  S59 aboard the ESRO TD-1A satellite. We describe first the processing of
  the observations: intensity and wavelength calibration, identification
  of lines, classification of spectra. Thereafter some important
  groups of lines are dealt with: non-LTE computation of the Mg ii
  lines are presented: apart from the peculiar emission line and shell
  stars they compare well with the observations; intensity ratios, of
  Fe ii and Fe iii lines are an important temperature classification
  criterion. Interstellar UV lines indicate large deficiencies of some
  metals, as compared to solar values. A new ultraviolet continuous
  extinction curve is determined. We discuss the strong outstreaming
  motions observed in α Cygni, and the consequent mass loss of this star
  (&lt; 3 × 10<SUP>-10</SUP> mathfrak{M}_ odot yr<SUP>-1</SUP>and finally
  we describe the composite spectrum of the (WC8+09I) bnary γ<SUP>2</SUP>
  Velorum; the ultraviolet continuous spectrum of the WC star is about
  one magnitude brighter than any theory predicts.

Title: Image processing techniques in astronomy
Authors: de Jager, C.; Nieuwenhuijzen, H.
Bibcode: 1975ASSL...54.....D
Altcode: 1975ipta.proc.....D; 1975QB461.I48......
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; De Loore, C.; Reijnen, G. C. M.
Bibcode: 1975SSRv...18..141D
Altcode:
  No abstract at ADS

Title: Two Years of Operation of the Ultraviolet Stellar
    Spectrophotometer S59 in E.S.R.O.'s TD1A Satellite
Authors: de Jager, C.; Hoekstra, R.; van der Hucht, K. A.; Kamperman,
   T. M.; Lamers, H. J. G. L. M.
Bibcode: 1975RSPTA.279..413D
Altcode: 1975RSLPT.279..413D
  A progress report is given of the current state of the investigation of
  the ca. 3500 spectra obtained during the life time of the satellite. A
  summary is presented of the general types of investigation, namely those
  which involve a study of major parts of the observational material,
  and the more specific investigations, which refer to selected stars
  or groups of stars, or to special lines or groups of lines.

Title: The Sun in the Far Infrared and Sub-mm Region
Authors: de Jager, C.
Bibcode: 1975SSRv...17..645D
Altcode:
  A review is given of the solar radiation between wavelengths of
  approx. 5 μm. and 1 mm. After discussing the astrophysical background
  (Section 2), we review the brightness temperatures measured in the
  continuous spectrum in the disk center (Section 3), and compare them
  with model predictions. The observed limb darkening (or brightening)
  is described in Section 4, and the line spectrum in Section 5. In
  Section 6 considerations are given on the usefulness of infrared
  observations for the investigation of small structures on the Sun.

Title: Some Remarks on Supergiant Photospheres
Authors: de Jager, C.
Bibcode: 1975RSPTA.279..421D
Altcode: 1975RSLPT.279..421D
  Some characteristic aspects of near ultraviolet spectra of supergiant
  stars, observed with the Utrecht ultraviolet stellar spectrometer S59
  aboard E.S.R.O.'s TD1A satellite are described. A comparison of the
  observed maximum brightness of supergiants with theoretical computation
  shows that in the brightest early-type supergiants the outward driving
  forces due to radiation pressure and to the turbulent pressure gradient
  must be about equal.

Title: Supplementary Remarks to `On the Average Depth of Formation of
    Weak Fraunhofer Lines' by E. Gurtovenko, V. Ratnikova, and C. de Jager
Authors: Gurtovenko, E.; Ratnikova, V.; de Jager, C.
Bibcode: 1975SoPh...42...43G
Altcode:
  No abstract at ADS

Title: The Radiation Field in Photospheric Models for Extreme
    Supergiants
Authors: de Jager, C.; Neven, L.
Bibcode: 1975Ap&SS..33..295D
Altcode:
  On the basis of assumed photospheric temperature models for 36
  extreme supergiants (logg <SUB> e </SUB>-values of 1, 0.5 and 0;T
  <SUB> e </SUB>ranging from approx. 3700 33 000 K) photospheric
  fluxesS(τ<SUB>λ</SUB>) were computed for 36 wavelengths ranging
  from 100 Å to 60 000 Å. The hot models are in perfect radiative
  equilibrium; the cooler show deviations up to 10%, sometimes even
  larger. Only in the relatively deep parts of the photospheres
  (τ<SUB>5</SUB>≳1) the radiation field at each geometrical level
  can be characterized by one unique radiation temperature; for smaller
  τ<SUB>5</SUB>-values there are large deviations from local thermal
  equilibrium. The influence of deviations from local thermodynamical
  equilibrium on the fluxes is briefly examined, and appears small but
  for the shortest wavelengths. In tables and graphs we give for these
  models πF(γ)-values, integrated fluxes, effective temperatures,
  coloursU, B andV, and the Balmer discontinuityD.

Title: Hard X-rays from the sun.
Authors: van Beek, H. F.; Hoyng, P.; de Jager, C.; Stevens, G. A.
Bibcode: 1975NTNA...41..101V
Altcode:
  No abstract at ADS

Title: Dynamik von Sternatmosphären
Authors: de Jager, C.
Bibcode: 1975MitAG..36...15D
Altcode:
  The characteristics of solar convection are considered along with
  aspects of hydrodynamic turbulence, waves in the solar atmosphere,
  the mechanical energy flux of sun and stars, and questions concerning
  the occurrence of stellar chromospheres and coronas. The theory
  of convection in stellar atmospheres, which was first conceived by
  Schwarzschild (1906), has been further developed. It is pointed out
  that this theory, in principle, provides an approach to predict the
  field of motion in stellar atmospheres and to compute the mass loss
  of the stars. A realization of these possibilities requires, however,
  further advances in the theory and more observational data.

Title: Image processing techniques in astronomy; Proceedings of the
    International Conference, Utrecht, Netherlands, March 25-27, 1975
Authors: de Jager, C.; Nieuwenhuijzen, N.
Bibcode: 1975STIA...7622376D
Altcode:
  The papers deal with recent technical developments that have contributed
  to improvements in the performance of existing telescopes and in the
  design of new ones, methods for acquiring and storing astronomical
  images, image-processing hardware and software, and applications of
  these developments to astronomical problems. Topics discussed include
  photometry of extended images, trends in astronomical spectroscopy,
  photon-counting detector arrays based on microchannel array plates,
  vidicon systems, and automatic processing of star plates. Consideration
  is also given to several software techniques for image processing,
  aperture synthesis, echelle spectra image processing for the
  International Ultraviolet Explorer, an intercomparison of ground-based
  and satellite pictures of the sun, the removal of vignetting from Apollo
  low-light-level photographs, and digital image centering. Individual
  items are announced in this issue.

Title: Coronale gaten, donkere gebieden in de zonnecorona.
Authors: de Jager, C.
Bibcode: 1975Zenit...2..292D
Altcode:
  No abstract at ADS

Title: Nova Cygni 1975.
Authors: de Jager, C.; Reijmerink, F.
Bibcode: 1975Zenit...2..324D
Altcode:
  No abstract at ADS

Title: Stellar coronas.
Authors: de Jager, C.
Bibcode: 1975MSRSL...9..369D
Altcode: 1975apes.conf..369D; 1975assp.conf..369D
  The present state of knowledge about stellar coronal heating is
  reviewed, noting that such heating is due to mechanical-energy loss by
  viscous dissipation of wave energy. Wave modes in stellar photospheres
  are described along with the generation of mechanical-energy fluxes,
  early predictions of the physical parameters of stellar coronas,
  and more recent computations of expected soft X-ray fluxes from
  coronas. Results are discussed for Astronomical Netherlands Satellite
  observations of soft X radiation from the Sirius system and Capella as
  well as for UV observations of coronal lines in the spectra of several
  other stars.

Title: Ultraviolet observations of beta-Cephei and beta-Canis Majoris
Authors: Beeckmans, F.; Burger, M.; De Jager, C.; Kamperman, T. M.
Bibcode: 1975STIN...7813980B
Altcode:
  Results of ultraviolet observations obtained from onboard ESRO
  TD-1A satellite experiments S2/68 and S59 are presented. The
  Utrecht stellar spectrophotometer S59 recorded stellar fluxes in the
  spectral ranges 2060 to 2160, 2495 to 2595, and 2770 to 2870 A with a
  spectral resolution of about 1.8 A. The experiment S2/68, a combined
  experiment of British and Belgian groups, observed in the regions
  1350 to 1750, 1750 to 2150, and 2150 to 2550 A with a resolution of
  36 A. The variations of beta-Cep and beta-CMa observed are presented
  graphically. If a radiation temperature between 20,000 and 25,000 K
  is assumed, the temperature difference between minimum and maximum
  will be 600 to 1000 K for beta-Cep and 200 to 400 K for beta-CMa.

Title: Struktuur van de atmosfeer van Venus.
Authors: de Jager, C.
Bibcode: 1975Zenit...2..354D
Altcode:
  No abstract at ADS

Title: Rijpvorming op de satelliet Io.
Authors: de Jager, C.
Bibcode: 1975Zenit...2..203D
Altcode:
  No abstract at ADS

Title: Foto's van Io uit de ruimte.
Authors: de Jager, C.
Bibcode: 1975Zenit...2..349D
Altcode:
  No abstract at ADS

Title: Gasring om Jupiter in baan van Io.
Authors: de Jager, C.
Bibcode: 1975Zenit...2..362D
Altcode:
  No abstract at ADS

Title: High energy plasmas in astrophysics
Authors: de Jager, C.
Bibcode: 1975xris.conf..806D
Altcode:
  Conditions are described under which high-energy cosmic plasmas can
  originate. Some of these plasmas derive their high particle energies
  directly from the internal thermal energy of a stellar body, but most
  of them derive it from a cooler gas; hence, thermodynamic upgrading
  of energy is needed. The mechanisms by which this occurs depend on the
  (electromagnetic) configuration of the medium. Laboratory experiments
  are reviewed which were performed to examine the configurations or
  processes involved. The most relevant are the discharge-produced
  and magnetospheric types. The best studied astrophysical high-energy
  plasmas can be similarly classified. The essential characteristics and
  the upgrading processes occurring in these plasmas are reviewed. The
  analogy between solar flares and magnetospheric substorms is discussed.

Title: Space Research XV. Proceedings of open meetings of Working
    Groups on Physical Sciences of the seventeenth plenary meeting of
    COSPAR, São Paulo, Brazil - June 1974.
Authors: Rycroft, M. J.; de Jager, C.
Bibcode: 1975srxp.book.....R
Altcode:
  No abstract at ADS

Title: Phenomenology of the Subflare; A Synthesis of CINOF
Authors: de Jager, C.
Bibcode: 1975SoPh...40..133D
Altcode:
  During the CINOF Campaign, June 1972, more than a hundred small
  chromospheric brightenings were observed. The observational results
  of about ten of them were investigated in more detail. They show a
  number of regularities; these are listed in Section 7.

Title: Astronomical research in space
Authors: de Jager, C.
Bibcode: 1975STIA...7621802D
Altcode:
  The paper summarizes the experience the Dutch space research program
  has so far (1975) gathered in the area of astronomical investigations
  carried out in space, in particular, on orbiting platforms. The most
  significant accomplishments include (1) the measurement of the X-ray
  emission from the flare star YZ CMi, which was on the order of 10 to
  the 33rd erg, carried out aboard the Dutch ANS satellite; (2) solar
  X-ray burst measurements by the Dutch X-ray spectrometer aboard the
  TD-1A satellite, which are among the best as regards sensitivity,
  dynamic range, spectral range, and resolution; (3) the ANS discovery
  of permanent X-ray emission from the star Sirius, constituting the
  first discovery of a stellar corona; and (4) TD-1A spectra of the
  Wolf-Rayet component of gamma 2 Velorum. Future plans include the
  joint Dutch-Japanese project (LEINAX) for rocket measurements of
  cosmic X-ray emission, high-resolution UV measurements from a balloon
  in cooperation with the Johnson Space Center, and contributions to the
  American High Energy Astrophysical Laboratory and Solar Maximum Mission.

Title: Mercurius heeft tòch een magnetosfeer.
Authors: de Jager, C.
Bibcode: 1975Zenit...2..345D
Altcode:
  No abstract at ADS

Title: Drie wolkentypen in atmosfeer van Venus.
Authors: de Jager, C.
Bibcode: 1975Zenit...2..382D
Altcode:
  No abstract at ADS

Title: An All-Sky Camera Battery for X-Ray Astronomy
Authors: de Jager, C.
Bibcode: 1974Ap&SS..31..417D
Altcode:
  The increasing number of interesting variable X-ray sources asks
  for an instrument for continuously monitoring the brightness of
  the most important X-ray sources over the whole sky. We describe a
  system consisting of a set of identical large position-sensitive
  detectors, mounted on the sides of a polyhedral satellite. Each
  counter is illuminated through a large diaphragm, with binary shadow
  characteristics. By holographic methods the X-ray image of the observed
  part of the sky could be derived from the illumination of each detector
  by multiplex analysing methods. The satellite should have fairly coarse
  (half a degree accuracy) three-axial stabilization, and an on-board
  computersteered data accumulation system. A relation is derived
  between the number of transparent holes in the diaphragm, the total
  count rate, and the flux of the faintest observable source. It appears
  that for a diaphragm with a few hundred transparent holes (detector
  geometrical area ≈10<SUP>3</SUP> cm<SUP>2</SUP>) an integration time
  of approximately 6 min is needed in order that sources with a count
  rate of 0.01 cm<SUP>-2</SUP> s<SUP>-1</SUP> should still be observable
  with a confidence limit of 99%.

Title: On the Determination of the Photospheric Velocity Distribution
    from Profiles of Weak Fraunhofer Lines
Authors: Rutten, R. J.; Hoyng, P.; de Jager, C.
Bibcode: 1974SoPh...38..321R
Altcode:
  We derive the conditions under which the profile of a weak Fraunhofer
  line can be described as the convolution of the separate profiles
  of damping, thermal and non-thermal motions at the average depth of
  formation of the line. The average velocity distribution along the line
  of sight, rather than its customary chosen macro- and micro-turbulent
  components, is then found from the deconvolution of the observed profile
  with the known other contributions. Reversely, the observed profiles
  can be compared to predicted profiles on the basis of De Jager's (1974)
  theoretical turbulence broadening curves.

Title: On the Average Optical Depth of Formation of Weak Fraunhofer
    Lines
Authors: Gurtovenko, E.; Ratnikova, V.; De Jager, C.
Bibcode: 1974SoPh...37...43G
Altcode:
  Methods for the determination of the average optical depth of formation
  of weak Fraunhofer lines are compared, and their relative merits are
  discussed. Distinction should be made between the region of origin
  of the emergent radiation, and of the line depression. For weak or
  fairly weak lines the average optical depth of formation of the line
  depression is the relevant quantity; it should be determined by using
  a computational scheme based on the classical weighting functions
  of line formation; other methods give physically unsignificant or
  conflicting results.

Title: Book reviews
Authors: de Jager, C.
Bibcode: 1974SoPh...36..239D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; Hartle, James B.; Drawin, H. W.; Giovanelli,
   R. G.; Freudenthal, Hans; Wittenberg, H.; Tobias, Cornelius A.;
   van der Laan, H.; Smit, J. A.
Bibcode: 1974SSRv...15..741D
Altcode:
  No abstract at ADS

Title: Report from Editorial Board meeting
Authors: de Jager, C.
Bibcode: 1974SoPh...34..275D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; Bruzek, A.
Bibcode: 1974SoPh...34..507D
Altcode:
  No abstract at ADS

Title: The Influence of a Photospheric spectrum of Turbulence on
    the Profiles of Weak Fraunhofer Lines
Authors: De Jager, Cornelis
Bibcode: 1974SoPh...34...91D
Altcode:
  We assume that the motion field in the solar photosphere is described by
  a spectrum of turbulence, defined by suitably chosen parameters. For
  various values of the spectral parameters we compute average
  (i.e. averaged over a sufficiently large part of the photosphere)
  profiles of weak Fraunhofer lines. The resulting profiles which
  represent the distribution function of line-of-sight velocity components
  as modified by the transfer of radiation through the atmosphere, are
  thereupon still broadened by a function representing the influence
  of the distribution function of the granulation cell sizes. The
  resulting functions should be compared with the distribution function
  of line-of-sight velocity components as derived from observations,
  in order to arrive at an observational derivation of the parameters
  of the photospheric spectrum of turbulence.

Title: The outer layers of novae and supernovae. Joint discussion
    at the XVth general assembly of the I.A.U., Sydney 1973.
Authors: de Jager, C.
Bibcode: 1974HiA.....3..499D
Altcode:
  No abstract at ADS

Title: Time Profiles and Photon Spectra of Solar Hard X-rays
Authors: van Beek, H. F.; de Feiter, L. D.; de Jager, C.
Bibcode: 1974ASSL...42..533V
Altcode: 1974cimo.symp..533V
  With a spectrometer aboard the ESRO TD-1A satellite, time profiles
  and photon spectra of solar X-rays have been observed in the energy
  range above 24 keV. Most of the X-ray bursts studied thus far appear
  to consist of numerous short-lived spikes with rise and decay times of
  a few seconds. Such spikes, called 'Elementary Flare Bursts' (EFB's)
  cluster together in large numbers and constitute the conventional
  high energy flare. The form of the photon spectra could be determined
  very accurately and was in all cases of the power-law type. For the
  Aug. 4, 1972 flare, the photon spectra appear to be combinations of two
  power-law spectra; for the lower energies the spectral coefficient is
  smaller than for the higher energies. The transition energy is about
  60 keV.

Title: Supernova anno 1667 is door niemand gezien.
Authors: de Jager, C.
Bibcode: 1974Zenit...1R...2D
Altcode:
  No abstract at ADS

Title: The outer layers of novae and supernovae
Authors: de Jager, C.
Bibcode: 1974olns.conf.....D
Altcode:
  No abstract at ADS

Title: Sterren in wording.
Authors: de Jager, C.
Bibcode: 1974Zenit...1S...2D
Altcode:
  No abstract at ADS

Title: Observation of cosmic X-ray sources with the Netherlands
    astronomical satellite (ANS).
Authors: Brinkman, A. C.; Heise, J.; de Jager, C.
Bibcode: 1974PhiTR..34...43B
Altcode:
  No abstract at ADS

Title: Is de Gum-nevel te groot om te kunnen worden gezien?
Authors: de Jager, C.
Bibcode: 1974Zenit...1R..16D
Altcode:
  No abstract at ADS

Title: The Orbiting Stellar Ultraviolet Spectrophotometer S59 in
    ESRO's TD-1A Satellite
Authors: de Jager, C.; Hoekstra, R.; van der Hucht, K. A.; Kamperman,
   T. M.; Lamers, H. J.; Hammerschlag, A.; Werner, W.; Emming, J. G.
Bibcode: 1974Ap&SS..26..207D
Altcode:
  The ultraviolet stellar spectrophotometer S59 of the Utrecht
  Astronomical Institute uses the stabilization properties of the ESRO
  TD-1A satellite. This spacecraft scans the sky along eliptic meridians
  with an orbital precession of one degree per day, thus covering the
  whole celestial sphere in half a year. This property is combined
  with a tracking system which points the spectrophotometer during four
  minutes at stars of sufficient brightness. During this time interval
  the ultraviolet stellar spectrum is scanned with a resolution of 1.7
  Å in three bands of about 100 Å, around 2110, 2545 and 2825 Å. The
  optical, mechanical and electronic properties of the instrument and its
  tracking system are described in some detail, as well as the optical
  and technical performance in laboratory tests and in orbit. Some results
  obtained during the first half year of operation are briefly described.

Title: Satelliet kan poollicht van boven bekijken.
Authors: de Jager, C.
Bibcode: 1974Zenit...1Q...2D
Altcode:
  No abstract at ADS

Title: Apollo-experiment brengt aan het licht: toch een atmosfeer
    rondom de maan.
Authors: de Jager, C.
Bibcode: 1974Zenit...1...14D
Altcode:
  No abstract at ADS

Title: Titan [satelliet met een dampkring] geeft ons nog vele
    raadsels op.
Authors: de Jager, C.
Bibcode: 1974Zenit...1V...2D
Altcode:
  No abstract at ADS

Title: Stoten gammastraling uit het heelal.
Authors: de Jager, C.
Bibcode: 1974Zenit...1...13D
Altcode:
  No abstract at ADS

Title: Nieuwe zonnecyclus dient zich an.
Authors: de Jager, C.
Bibcode: 1974Zenit...1....6D
Altcode:
  No abstract at ADS

Title: Hard X-ray observations of elementary flare bursts, and
    their interpretation.
Authors: van Beek, H. F.; de Feiter, L. D.; de Jager, C.
Bibcode: 1974spre.conf..447V
Altcode: 1974spre.meet..447V
  Recent observations of solar hard X-ray bursts, performed with high
  time resolution aboard the ESRO TD-1A satellite, show that often these
  bursts consist of numerous short-lived spikes with rise and decay times
  of the order of a few seconds. It is argued that these spikes, which
  are called elementary flare bursts (EFB), are the essential physical
  phenomena, which, clustered together in large numbers, constitute the
  conventional high-energy flare. For some cases studied it is found that
  the rise and decay times can be as low as 1 to 2 seconds; individual
  points deviate only slightly from this average value. These times do
  not depend on the photon energy; this seems to indicate that the EFBs
  occur at a fairly low level in the chromosphere (less than or equal to
  1500 km above the photosphere). For one particular case studied this
  conclusion is corroborated by the observation of short-lived flashes
  as observed optically with an interference filter centered at 3835
  A. In this region a considerable part of the ambient electrons are
  accelerated to energies of several tens of kiloelectron volts.

Title: Book reviews
Authors: Tauber, G. E.; Ceplecha, Zdenek; Pace, Nello; Peters, Rudolph
   A.; de Graaff, W.; Vishniac, Wolf V.; Rees, M. J.; Kwee, K. K.; Rawer,
   K.; de Jager, C.; Brandt, John C.; Reeves, H.; Kleczek, J.; Fokker,
   A. D.; Seaton, M. J.; Öpik, E. J.
Bibcode: 1973SSRv...15..147T
Altcode:
  No abstract at ADS

Title: Review of Publications: Proceedings of the Fourteenth General
    Assembly Brighton, 1970
Authors: de Jager, C.; Jappel, A.
Bibcode: 1973JRASC..67...42D
Altcode:
  No abstract at ADS

Title: Solar Flares, Suprathermal Plasma Nodules, and Loop Prominences
Authors: de Feiter, L. D.; de Jager, C.
Bibcode: 1973sari.conf...93D
Altcode:
  No abstract at ADS

Title: Ontstaan en levensloop van sterren.
Authors: de Jager, C.; van den Heuvel, E. P. J.
Bibcode: 1973oelv.book.....D
Altcode:
  No abstract at ADS

Title: Space Research XIII. Proceedings of open meetings of Working
    Groups on Physical Sciences of the fifteenth plenary meeting of
    COSPAR, Madrid, Spain, 10_-_24 May, 1972. Vol._1,_2.
Authors: Rycroft, M. J.; Runcorn, S. K.; de Jager, C.
Bibcode: 1973srxp.book.....R
Altcode:
  No abstract at ADS

Title: Superthermal Plasma Nodules and Their Relation to Solar Flares
Authors: De Feiter, L. D.; De Jager, C.
Bibcode: 1973SoPh...28..183D
Altcode:
  We define superthermal plasma nodules as bright points (diameter ≲
  20″), visible on high resolution X-ray heliograms. Flares appear to
  show a strong tendency to occur at the places of these nodules. There
  are indications that (part of) the hot plasma produced by consecutive
  flares is accumulated and confined in the superthermal plasma nodules,
  and that with increasing energy content of a nodule the probability
  for a drastic change of its magnetic structure increases, thus reducing
  the possibility for more flares to occur.

Title: Ultraviolet stellar spectra obtained with the Utrecht orbiting
    stellar spectrophotometer S 59 aboard the ESRO TD-1 A satellite.
Authors: Hoekstra, R.; van der Hucht, K. A.; de Jager, C.; Kamperman,
   T.; Lamers, H. J.
Bibcode: 1973spre.conf..871H
Altcode:
  No abstract at ADS

Title: Western European Cooperation in Space Astronomy
Authors: de Jager, C.
Bibcode: 1973sari.conf..156D
Altcode:
  No abstract at ADS

Title: International Astronomical Union, Information Bulletin. No._29.
Authors: de Jager, C.
Bibcode: 1973IAUIB..29.....D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Sagan, Carl; Daniel, R. R.; de Jager, C.; Bowell, Edward L. G.
Bibcode: 1972SSRv...14..175S
Altcode:
  No abstract at ADS

Title: Review of Publications- Highlights of Astronomy, Volume 2
Authors: de Jager, C.
Bibcode: 1972JRASC..66..280D
Altcode:
  No abstract at ADS

Title: Stellar Winds and Mass Loss of a Rotating Star
Authors: de Grève, J. P.; De Loore, C.; de Jager, C.
Bibcode: 1972Ap&SS..18..128D
Altcode:
  The mass loss to be expected from the corona of a rotating
  F2-star is calculated. The rotation is supposed to be rigid up to
  a certain distances, as if it were maintained by a strong magnetic
  field. Dependent on the values of the rotational velocity the mass loss
  can increase to 26 40% forv <SUB>rot</SUB> up to 200 km s<SUP>-1</SUP>.

Title: The empirical determination of line source functions, β <SUB>
    L </SUB>-values, and the microturbulent and convective velocity
    components as functions of depth in the photosphere-chromosphere
    transition region
Authors: De Jager, C.; Neven, L.
Bibcode: 1972SoPh...25..277D
Altcode:
  An empirical method for determining line source functions, previously
  applied by us to the cores of infrared lines has now been extended to
  the whole line profile and was applied to centre-limb observations of
  sixteen lines of five infrared multiplets, mainly of high excitation
  potential (Table I). The present investigation was performed in two
  steps. In the first part of the paper approximate values are derived
  for the depth dependence of the four functions named in the title of
  this paper, where β<SUB>L</SUB> is the ratio between the actual and
  the LTE population of the lower level of the transitions involved. In
  the second part of the paper we use these empirically derived functions
  to compute the line profiles. From the remaining differences between
  observed and computed profiles, corrections are derived to the four
  functions. The main results are: (a) Convective velocities: see Table
  IV.(b)(Micro-)turbulent velocities: see Figure 8. Between τ<SUB>5</SUB>
  = 10<SUP>-4</SUP> and 10<SUP>-1</SUP>: «υ<SUB>τ</SUB>» ≈ 1.4 km
  s<SUP>-1</SUP>, which is an upper limit since an unknown contribution of
  macroscopic motions could not be separated, (c) Line source functions:
  see Figures 9, 15 and 16. The source functions are close to the
  black-body function for τ<SUB>5</SUB>≳ 10<SUP>-3</SUP>, slight
  deviations occur in higher levels. The interesting behaviour of the
  CaII source function near τ<SUB>5</SUB> = 10<SUP>-5</SUP> should be
  noted. (d) Non LTE-functions: first approximations for the functions
  log β<SUB>L</SUB> (τ<SUB>5</SUB>) were derived empirically in the
  first part, and are shown in Figure 10; the second approximation shows
  them to be too large and the real values seem to be closer to one-half
  or one-third of these functions.

Title: Editorial
Authors: De Jager, Cornelis; Švestka, Zdeněk
Bibcode: 1972SoPh...25....3D
Altcode: 1972SoPh...25....3.
  No abstract at ADS

Title: Micro- and Macroturbulent Motions and the Velocity Spectrum
    of the Solar Photosphere
Authors: De Jager, C.
Bibcode: 1972SoPh...25...71D
Altcode:
  A given motion field in a stellar atmosphere is usually observed through
  `filters' defined by line shifts and -broadenings and conventionally
  called macroturbulence and microturbulence.

Title: Book reviews
Authors: Schuiling, R. D.; Vesseur, H. J. A.; Wilhelm, Klaus; Hassan,
   H.; van Sabben, D.; de Jager, C.; van Kampen, N. G.
Bibcode: 1972SSRv...13..190S
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; Quenby, J. J.; Hutchinson, G. W.; Allan, H. R.
Bibcode: 1972SoPh...22..240D
Altcode: 1972SoPh...22..240.
  No abstract at ADS

Title: Solar Energy Sources
Authors: de Jager, C.
Bibcode: 1972ASSL...29....1D
Altcode: 1972sun..conf....1D
  No abstract at ADS

Title: On the Applicability of Goldberg and Unno's Method to the
    Determination of Microturbulent Velocities in an Atmosphere with
    Convection
Authors: De Jager, C.; Neven, L.
Bibcode: 1972SoPh...22...49D
Altcode:
  The method of Goldberg and Unno for the determination of microturbulent
  velocities in a stellar atmosphere is only applicable if there are no
  macroturbulent or convective motions.

Title: Structuur en dynamica van de zonnefotosfeer.
Authors: de Jager, C.
Bibcode: 1972KNAW...79..154D
Altcode:
  No abstract at ADS

Title: De suksesvolle lancering van ESRO's Thor-Delta 1A satelliet.
Authors: van Beek, H. F.; de Jager, C.; Lamers, H.
Bibcode: 1972HemD...70..171V
Altcode:
  No abstract at ADS

Title: Solar-terrestrial physics 1970; proceedings of the
    International Symposium on Solar-Terrestrial Physics held in
    Leningrad, U.S.S.R. 12-19 May 1970.
Authors: de Jager, C.; Dyer, E. R.
Bibcode: 1972ASSL...29.....D
Altcode: 1972sun..conf.....D
  No abstract at ADS

Title: The sun: Part I of solar-terrestrial physics/1970. Proceedings
    of the international symposium on solar-terrestrial physics held in
    Leningrad, U.S.S.R., 12 - 19 May 1970.
Authors: de Jager, C.
Bibcode: 1972sstp.conf.....D
Altcode: 1972sun..confQ....D
  No abstract at ADS

Title: International Astronomical Union, Information
    Bulletin. Nos._27,_28.
Authors: de Jager, C.
Bibcode: 1972IAUIB..27.....D
Altcode:
  No abstract at ADS

Title: Solar energy sources.
Authors: de Jager, C.
Bibcode: 1972sstp.conf....1D
Altcode:
  No abstract at ADS

Title: Editorial
Authors: De Jager, Cornelis; Švestka, Zdeněk
Bibcode: 1971SoPh...21....3D
Altcode: 1971SoPh...21....3.
  No abstract at ADS

Title: Book reviews
Authors: Chup, E. L.; Koelbloed, D.; de Jager, C.; Quenby, J. J.; van
   Kampen, N. G.; Pettengill, G. H.; Schuurmans, C. J. E.; de Graaff, W.;
   Oort, J. H.; Sagan, Carl; van der Kerk, G. J. M.; Pecker, Jean-Claude;
   Szebehely, V.; Hutchinson, G. W.; Allan, H. R.
Bibcode: 1971SSRv...12..526C
Altcode:
  No abstract at ADS

Title: The Production of Solar and Stellar Chromospheres and Coronae
Authors: de Jager, C.
Bibcode: 1971RSPTA.270..175D
Altcode:
  Knowledge of the detailed field of turbulence in the solar granulation,
  and of the consequent photospheric mechanical flux, is one of the basic
  elements for understanding the solar chromosphere and corona. The other
  element is constituted by the structure and magnetic fields of the
  supergranular network, since the coarse mottles at the supergranular
  boundaries seem to yield a mechanical flux nearly an order of magnitude
  larger than that of the supergranular cell regions. In the non-magnetic
  solar regions the upper photospheric mechanical flux is about 0.1 J
  cm<SUP>-2</SUP> s<SUP>-1</SUP>. This flux is equal to that emerging
  from the low-chromospheric vibrations; it seems not to be related to the
  observed microturbulent motions. Above such regions the chromosphere may
  be fairly thin, not exceeding 1000 or 2000 km. The precise thickness and
  detailed structure of the chromospheric layers can only be determined
  from a discussion of the interplay of the downward conductive flux with
  the dissipational losses of the up- and downward mechanical fluxes, and
  the radiative losses of the chromospheric matter. The greater apparent
  thickness of the chromosphere at the limb is due to the accumulated
  influence of the spicules seen from the side. Lack of knowledge of
  stellar photospheric inhomogeneities and fields handicaps a reliable
  prediction of stellar chromospheres and coronae. Yet a few attempts
  have been made, and predicted X-ray fluxes from coronae of some nearby
  stars are given (table 3).

Title: Editorial
Authors: de Jager, C.
Bibcode: 1971SSRv...12..135D
Altcode:
  No abstract at ADS

Title: Coronae of Cool Stars
Authors: de Jager, C.; De Loore, C.
Bibcode: 1971Ap&SS..11..284D
Altcode:
  With the hypothesis generally adopted as responsible for the heating of
  the solar corona an attempt was made to predict the coronal temperature
  for a few cool stars. Stars with effective temperatures between
  2500K and 3700K, with logg-values of 3 or 4, appear to have coronal
  temperatures only 600 to 25000K higher thanT <SUB>eff</SUB>. In order
  to determine the possibility of coronal heating caused by sound waves
  we made a comparison between the frequency of the sound waves and the
  cut-off frequencies.

Title: Book reviews
Authors: Hinze, J. O.; van Diggelen, J.; de Jager, C.; Hutchinson,
   G. W.
Bibcode: 1971SSRv...12..131H
Altcode:
  No abstract at ADS

Title: Editorial
Authors: de Jager, Cornelis; Švestka, Zdeněk
Bibcode: 1971SoPh...17..287D
Altcode: 1971SoPh...17..287.
  No abstract at ADS

Title: M. G. J. Minnaert, 1893 February 12 - 1970 October 26.
Authors: de Jager, C.
Bibcode: 1971QJRAS..12..338D
Altcode:
  No abstract at ADS

Title: Marcel Gilles Josef Minnaert
Authors: de Jager, C.
Bibcode: 1971Ap&SS..10..182D
Altcode:
  No abstract at ADS

Title: International Astronomical Union, Information Bulletin. No._26.
Authors: de Jager, C.
Bibcode: 1971IAUIB..26.....D
Altcode:
  No abstract at ADS

Title: Instrumentation for high-resolution stellar
    UV-spectrophotometry.
Authors: de Jager, C.; Hammerschlag, A.; Werner, W.
Bibcode: 1971IAUS...41..349D
Altcode:
  No abstract at ADS

Title: Joint Organization for Solar Observations. Annual report 1970.
Authors: de Jager, C.; Kiepenheuer, K. O.; Michard, R.; Maltby, P.;
   Rösch, J.; Brandt, P. N.
Bibcode: 1971joso.book.....D
Altcode:
  No abstract at ADS

Title: Solar Physics at the Utrecht Astronomical INstitute
Authors: Fokker, A. D.; Houtgast, J.; De Jager, C.
Bibcode: 1971SoPh...16..227F
Altcode:
  No abstract at ADS

Title: Atomic data of importance for ultraviolet and X-ray astronomy
Authors: de Jager, C.
Bibcode: 1971adiu.conf.....D
Altcode:
  No abstract at ADS

Title: High angular resolution astrophysical observations from space.
Authors: de Jager, C.
Bibcode: 1971EExSc...1..243D
Altcode:
  No abstract at ADS

Title: Reports on Astronomy.
Authors: de Jager, C.; Jappel, A.
Bibcode: 1971IAUTB..14.....D
Altcode:
  No abstract at ADS

Title: Highlights of Astronomy, Volume_2. presented at the XIVth
    general assembly of the I.A.U. 1970.
Authors: de Jager, C.
Bibcode: 1971havp.book.....D
Altcode:
  No abstract at ADS

Title: M. G. J. Minnaert, 1893 February 12 - 1970 October 16.
Authors: de Jager, C.
Bibcode: 1971UtrOv.160.....D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Zagar, F.; Schmidt, F. H.; Robe, H.; de Jager, C.; Kleczek, J.
Bibcode: 1970SSRv...11..453Z
Altcode:
  No abstract at ADS

Title: Book review
Authors: de Jager, C.
Bibcode: 1970SSRv...11..152D
Altcode:
  No abstract at ADS

Title: On the Ratio Between the Mechanical Fluxes in- and outside
    the Solar Chromospheric Mottles
Authors: De Jager, C.; De Loore, C.
Bibcode: 1970SoPh...13..126D
Altcode:
  Available information about the relative areas on the `quiet' and
  `active' parts of the sun covered with magnetic elements, together
  with theoretical results on the relation between the photospheric
  mechanical flux and the consequent coronal electron density, allows
  one to conclude that the mechanical flux generated in the photospheric
  magnetic elements is about seven times as large as the flux generated
  in non-magnetic regions.

Title: Book reviews
Authors: de Jager, C.; King-Hele, D. G.; Heise, John; ĹEna, P.;
   Somoza, R.; Lindblad, Per Olof; Ritchey, H. W.; de Feiter, L. D.
Bibcode: 1970SSRv...10..737D
Altcode:
  No abstract at ADS

Title: Space and Ground-Based Stellar Spectrophotometry : a Summary
Authors: de Jager, C.
Bibcode: 1970IAUS...36..355D
Altcode:
  No abstract at ADS

Title: Predicted X-Ray Fluxes of Stellar Coronas
Authors: De Loore, C.; de Jager, C.
Bibcode: 1970IAUS...37..238D
Altcode:
  No abstract at ADS

Title: High Energy Flare Radiation
Authors: de Jager, C.
Bibcode: 1970ASSL...19...25D
Altcode: 1970iso..conf...25D
  No abstract at ADS

Title: International Astronomical Union, Information Bulletin. No._25.
Authors: de Jager, C.
Bibcode: 1970IAUIB..25.....D
Altcode:
  No abstract at ADS

Title: Damping Constants for Infrared Fraunhofer Lines
Authors: De Jager, C.; Neven, L.
Bibcode: 1970SoPh...11....3D
Altcode:
  Empirical values of solar damping constants and their variation with
  optical depth were derived according to a method developed earlier by
  the authors. The damping constants refer to six infrared multiplets
  (24 lines). The average optical depths range from τ<SUB>0</SUB> =
  0.5 to 2.2. Corresponding theoretical damping constants were computed,
  mainly on the basis of Van der Waals damping, and with the help of
  detailed computations of the mean square radii of the atomic levels by
  Van Rensbergen. The empirical values are systematically larger than
  the theoretical ones, with factors ranging between 1.8 and 4.9. Some
  speculations about the source of this discrepancy are given.

Title: Editorial
Authors: De Jager, Cornelis; Švestka, Zdeněk
Bibcode: 1969SoPh...10..243D
Altcode: 1969SoPh...10..243.
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; Janssens, Paul
Bibcode: 1969SSRv...10..455D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Nicolet, M.; Müller, Edith A.; de Jager, C.; Rutten, H. S.;
   Millman, P. M.; Fielder, G.
Bibcode: 1969SSRv...10..314N
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Veldkamp, J.; Kovalevesky, J.; Plaut, L.; Bondi, H.; Mewe,
   R.; de Jager, C.
Bibcode: 1969SSRv....9..872V
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; Ollongren, A.; de Graaf, Tj.; Levin, B. J.;
   Tucker, M.
Bibcode: 1969SSRv....9..740D
Altcode:
  No abstract at ADS

Title: Editorial
Authors: Švestka, Z.; De Jager, C.
Bibcode: 1969SoPh....8....3S
Altcode: 1969SoPh....8....3.
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; di Benedetto, F.; de Groot, T.; van Diggelen,
   J.; van Diggelen, J.; Herczeg, T.; Lamers, H. J.; van Albada, G. B.
Bibcode: 1969SSRv....9..617D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Fokker, A. D.; Clark, D. D.; Kutzer, Ants; de Jager, C.
Bibcode: 1969SSRv....9..419F
Altcode:
  No abstract at ADS

Title: Solar flares; properties and problems
Authors: de Jager, C.
Bibcode: 1969sfsr.conf....1D
Altcode:
  No abstract at ADS

Title: Solar flares and space research
Authors: de Jager, C.; Svestka, Z.
Bibcode: 1969sfsr.conf.....D
Altcode: 1969sfsr.book.....D
  No abstract at ADS

Title: Sterrenkunde.
Authors: de Jager, Cornelis; van Albada, G. B.
Bibcode: 1969ster.book.....D
Altcode: 1969QB43.J34.......
  No abstract at ADS

Title: Het ruimte-onderzoek.
Authors: de Jager, C.
Bibcode: 1969HemD...67..134D
Altcode:
  No abstract at ADS

Title: Editorial
Authors: De Jager, C.; Švestka, Z.
Bibcode: 1968SoPh....5..259D
Altcode: 1968SoPh....5..259.
  No abstract at ADS

Title: Book reviews
Authors: de Graaff, W.; de Jager, C.; Emming, J. G.; van Bueren, H. G.
Bibcode: 1968SSRv....8..591D
Altcode:
  No abstract at ADS

Title: On the Occurrence of Convective Motions in the Upper
    Photosphere
Authors: De Jager, C.; Neven, L.
Bibcode: 1968SoPh....4..379D
Altcode:
  We have examined whether the motion field in the photosphere in the
  range of optical depths 0.25&lt; τ<SUB>0</SUB>&lt; 0.6 is dominated
  by thermal convection or by vibrations. The observed asymmetries
  of infrared Fraunhofer lines indicate the presence of motions, and
  the fact that the asymmetry is zero for lines of low excitation and
  increases with the excitation potential shows that these motions are
  chiefly convective in this part of the photosphere: upward moving
  elements appear to be hotter than downward moving ones.

Title: Book reviews
Authors: de Jager, C.; Kleczek, J.
Bibcode: 1968SoPh....4..375D
Altcode: 1968SoPh....4..375.
  No abstract at ADS

Title: Book reviews
Authors: de Feiter, L. D.; de Jager, C.
Bibcode: 1968SoPh....3..623D
Altcode: 1968SoPh....3..623.
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; Hinze, J. O.; Wittenberg, H.
Bibcode: 1968SSRv....8..135D
Altcode:
  No abstract at ADS

Title: Source Functions in the Cores of Infrared Fraunhofer Lines
Authors: De Jager, C.; Neven, L.
Bibcode: 1968SoPh....3..159D
Altcode:
  No abstract at ADS

Title: The Bilderberg conference on the structure of the quiet
    photosphere
Authors: De Jager, C.
Bibcode: 1968SoPh....3....4D
Altcode: 1968SoPh....3....4.
  No abstract at ADS

Title: Editorial
Authors: De Jager, C.; Švestka, Z.
Bibcode: 1968SoPh....3....3D
Altcode: 1968SoPh....3....3.
  No abstract at ADS

Title: The High-Energy Flare Plasma
Authors: de Jager, C.
Bibcode: 1968IAUS...35..480D
Altcode:
  No abstract at ADS

Title: Hard Solar X-ray Bursts
Authors: de Jager, C.
Bibcode: 1968HiA.....1..541D
Altcode:
  No abstract at ADS

Title: The Development and Structure of an Active Region
Authors: de Jager, C.
Bibcode: 1968IAUS...35..602D
Altcode:
  No abstract at ADS

Title: New Techniques in X-Ray Astronomy
Authors: de Jager, C.
Bibcode: 1968HiA.....1..108D
Altcode:
  No abstract at ADS

Title: Acceleration processes in solar flares, Introductory lecture
Authors: de Jager, C.
Bibcode: 1968mmsf.conf..171D
Altcode:
  No abstract at ADS

Title: The Coordination of Ground-Based and Space Observations:
    Summary
Authors: de Jager, C.
Bibcode: 1968HiA.....1..547D
Altcode:
  No abstract at ADS

Title: The Bilderberg Model of the Photosphere and Low Chromosphere
Authors: Gingerich, O.; De Jager, C.
Bibcode: 1968SoPh....3....5G
Altcode:
  From 17 through 21 April 1967, an international study week was held in
  the `Bilderberg' near Arnhem, Netherlands, with the aim of obtaining
  an internationally acceptable model of the solar photosphere and
  low chromosphere. It was found that such a model, based on observed
  intensities and center-to-limb observations of the solar continuous
  spectrum, could indeed be established. This model, henceforth called
  the Bilderberg Continuum Atmosphere (BCA), is shown in Table I, which
  gives the temperature, gas and electron pressures, and other data as
  functions of the continuous optical depth at 5000 Å between τ5000
  = 10<SUP>−7</SUP> and 25. The model is characterized by a flat
  temperature minimum of 4600 °K between τ5000 ≈ 10<SUP>−2</SUP>
  to 10<SUP>−4</SUP>. The model is homogeneous, and in hydrostatic
  equilibrium. A hydrogen-helium ratio of 10 has been assumed.

Title: Book reviews
Authors: van Gils, J. N.; van Diggelen, J.; de Jager, C.; Brussaard,
   P. J.
Bibcode: 1967SSRv....7..534V
Altcode:
  No abstract at ADS

Title: The Hard Solar X-Ray Burst of 18 September 1963
Authors: De Jager, C.
Bibcode: 1967SoPh....2..327D
Altcode:
  A hard solar X-ray burst was observed by J-P. Legrand on 18 September
  1963, 13:56 UT, at balloon altitude. It lasted a few minutes; a steep
  increase was followed by an exponential decay. During its declining
  phase a weak radio burst was observed on 3 and 10 cm, not on longer
  wavelengths.

Title: Note on Solar Hard X-Ray Bursts
Authors: De Jager, C.
Bibcode: 1967SoPh....2..347D
Altcode:
  Observationally solar X bursts fall into three different categories :
  soft X bursts (E &lt; 10 keV), deka-keV bursts (10-150 keV), and very
  hard X bursts or deci-MeV bursts (200-1000 keV). The first kind is
  quasi-thermal, the last kind is non-thermal. The real existence of
  the third kind of burst looks probable but has not yet been proved
  by direct observations. The difference between deci-MeV and deka-keV
  bursts may mainly be a matter of geometry of the emitting plasma.

Title: Book reviews
Authors: van Wijngaarden, L.; Zandbergen, P. J.; Slachmuylders, E.;
   de Graaff, W.; Vandenkerckhove, J.; van Herk, G.; de Jager, C.
Bibcode: 1967SSRv....7..396V
Altcode:
  No abstract at ADS

Title: Auroral and associated magnetospheric phenomena at very
    high latitudes
Authors: de Jager, C.
Bibcode: 1967SSRv....7D...3D
Altcode:
  No abstract at ADS

Title: Geodesy and satellites
Authors: de Jager, C.
Bibcode: 1967SSRv....7....3D
Altcode:
  No abstract at ADS

Title: Reviews
Authors: de Jager, C.; Hinze, J. O.; Frantzen, A. J.
Bibcode: 1967SSRv....7..135D
Altcode:
  No abstract at ADS

Title: Editorial
Authors: de Jager, C.; Švestka, Z.
Bibcode: 1967SoPh....1..303D
Altcode: 1967SoPh....1..303.
  No abstract at ADS

Title: Reviews
Authors: Jongbloed, J.; van Diggelen, J.; de Jager, C.; Busch, H.;
   Vos, J. J.
Bibcode: 1967SSRv....6..574J
Altcode:
  No abstract at ADS

Title: A Systematic Method for the Analysis of High-Resolution
    Fraunhofer Line Profiles
Authors: De Jager, C.; Neven, L.
Bibcode: 1967SoPh....1...27D
Altcode:
  A fraunhofer line profile depends on various parameters, partly
  related to the photospheric structure (T, P<SUB>g</SUB>, P<SUB>e</SUB>,
  v<SUB>conv</SUB>, v<SUB>turb</SUB>), partly to the atom or ion involved
  (such as oscillator strength, energy levels), partly also resulting
  from the interaction of the relevant kind of particles with the
  photosphere, and the photospheric radiation field. In this paper we
  shall mainly pay attention to the determination of: the macroturbulent
  (convective) velocities, v<SUB>conv</SUB> (τ); the damping constant
  γ (τ); the abundance, A<SUB>el</SUB>; the distribution function
  ϕ(v<SUB>conv</SUB>, τ) of the convective velocities at each depth
  τ; the source function, S (τ); the microturbulent velocities,
  v<SUB>turb</SUB> (τ).

Title: Editorial
Authors: de Jager, C.; Švestka, Z.
Bibcode: 1967SoPh....1....3D
Altcode: 1967SoPh....1....3.
  No abstract at ADS

Title: Observation of solar line profiles. I. The centre-to-limb
    variation of profiles of fifty lines in the near infrared solar
    spectrum
Authors: de Jager, C.; Neven, L.
Bibcode: 1967BANS....1..325D
Altcode: 1966BANS....1..325N; 1966BANS....1..325D
  No abstract at ADS

Title: Buchbesprechungen über: Solar Physics. Ed. C. DE JAGER,
    and Z. ŠVESTKA. (Ref. R. O. REDMAN)
Authors: de Jager, C.; Švestka, Z.
Bibcode: 1967ZA.....67...95D
Altcode:
  No abstract at ADS

Title: Theoretical Aspects of Solar X-Radiation
Authors: de Jager, C.
Bibcode: 1967ASSL....9..101D
Altcode: 1967ers..conf..101D
  No abstract at ADS

Title: Spectroscopic data for sixty new model photospheres
Authors: de Jager, C.; Neven, L.
Bibcode: 1967BANS....2..125D
Altcode:
  No abstract at ADS

Title: The structure of the quiet photosphere and the low chromosphere
Authors: de Jager, C.
Bibcode: 1967sqpl.conf.....D
Altcode: 1968QB528.S77......
  No abstract at ADS

Title: Observation of solar line profiles. I. The centre-to-limb
    variation of profiles of fifty lines in the near infrared solar
    spectrum (Abstract)
Authors: de Jager, C.; Neven, L.
Bibcode: 1967BAN....19..160D
Altcode:
  No abstract at ADS

Title: Spectroscopic data for sixty new model photospheres
Authors: de Jager, Cornelis; Neven, L.
Bibcode: 1967sdsn.book.....D
Altcode: 1967QB1.B94v2n4....
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.; van den Heuvel, E. P. J.; Capart, J. J.;
   Jongbloed, J.; Minnaert, M.
Bibcode: 1966SSRv....6..273D
Altcode:
  No abstract at ADS

Title: Note on the influence of the apparatus profile on spectral
    line profiles
Authors: de Jager, C.; Neven, L.
Bibcode: 1966BAN....18..306D
Altcode:
  No abstract at ADS

Title: Théorie des Atmospheres Stellaires (Theory of Stellar
    Atmospheres)
Authors: de Jager, C.
Bibcode: 1966IAUTB..12Q.334D
Altcode:
  No abstract at ADS

Title: Deviations from LTE in the Catom and the Abundance of C in
    the Solar Photosphere
Authors: de Jager, C.; Neven, L.
Bibcode: 1966IAUS...26..149D
Altcode:
  No abstract at ADS

Title: The profile of the infrared He I lines over the undisturbed
    solar disk
Authors: de Jager, C.; Namba, O.; Neven, L.
Bibcode: 1966BAN....18..128D
Altcode:
  No abstract at ADS

Title: Recommendations concerning notations to be used in transfer
    theory
Authors: de Jager, C.
Bibcode: 1966IAUTB..12R.334D
Altcode:
  No abstract at ADS

Title: Sunspots. R. J. BRAY and R. E. LOUGHEAD: Chapman and Hall,
    London, 1964. xvi + 302pp. 84 s
Authors: de Jager, C.
Bibcode: 1965P&SS...13..869D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: de Jager, C.
Bibcode: 1965SSRv....4..262D
Altcode:
  No abstract at ADS

Title: Solar X radiation
Authors: de Jager, C.
Bibcode: 1965AnAp...28..125D
Altcode:
  No abstract at ADS

Title: Editorial
Authors: de Jager, C.
Bibcode: 1965SSRv....4....3D
Altcode:
  No abstract at ADS

Title: Review paper : Solar X radiation
Authors: de Jager, C.
Bibcode: 1965IAUS...23...45D
Altcode:
  No abstract at ADS

Title: The Solar Center of Activity
Authors: de Jager, C.
Bibcode: 1965ASSL....2...55D
Altcode: 1965istr.conf...55D
  No abstract at ADS

Title: Optical Solar Flares
Authors: de Jager, C.
Bibcode: 1965ASSL....2...78D
Altcode: 1965istr.conf...78D
  No abstract at ADS

Title: Radio and X-Ray Emission Associated with Solar Flares
Authors: de Jager, C.
Bibcode: 1965ASSL....2...86D
Altcode: 1965istr.conf...86D
  No abstract at ADS

Title: The solar spectrum
Authors: de Jager, Cornelis
Bibcode: 1965ASSL....1.....D
Altcode: 1965sosp.conf.....D
  No abstract at ADS

Title: Particle Emission Associated with Solar Flares. Model of
    Flare Events
Authors: de Jager, C.
Bibcode: 1965ASSL....2...96D
Altcode: 1965istr.conf...96D
  No abstract at ADS

Title: The Solar Photosphere
Authors: de Jager, C.
Bibcode: 1965ASSL....2...13D
Altcode: 1965istr.conf...13D
  No abstract at ADS

Title: The Quiet Chromosphere and Corona
Authors: de Jager, C.
Bibcode: 1965ASSL....2...26D
Altcode: 1965istr.conf...26D
  No abstract at ADS

Title: The Computation of Spectroscopic Data for 60 New Model
    Photopheres
Authors: de Jager, C.; Neven, L.
Bibcode: 1964SAOSR.167..270D
Altcode:
  No abstract at ADS

Title: The Utrecht Reference Model of the Photosphere
Authors: Heintze, J. R. W.; Hubenet, H.; de Jager, C.
Bibcode: 1964SAOSR.167..240H
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: van Bueren, H. G.; van den Heuvel, E.; de Jager, C.;
   Kallmann-Bijl, H.
Bibcode: 1964SSRv....3..856V
Altcode:
  No abstract at ADS

Title: A reference model of the solar photosphere and low chromosphere
Authors: Heintze, J. R. W.; Hubenet, H.; de Jager, C.
Bibcode: 1964BAN....17..442H
Altcode:
  No abstract at ADS

Title: The structure of a sunspot
Authors: de Jager, C.
Bibcode: 1964susp.conf..242D
Altcode:
  No abstract at ADS

Title: Solar Ultraviolet and X-Ray Radiation
Authors: de Jager, C.
Bibcode: 1964rege....1....1D
Altcode:
  No abstract at ADS

Title: Book reviews
Authors: Jaarsma, F.; Veldkamp, J.; Underhill, Anne B.; de Jager, C.
Bibcode: 1963SSRv....2..871J
Altcode: 1963SSRv....2..871.
  No abstract at ADS

Title: Energy transport and "turbulence" in a sunspot
Authors: de Jager, C.
Bibcode: 1963BAN....17..253D
Altcode:
  No abstract at ADS

Title: Combined light-, colour- and radial-velocity measurements of
    the β Cephei-type variable 12 (DD) Lacertae
Authors: de Jager, C.
Bibcode: 1963BAN....17....1D
Altcode: 1964BAN....17....1D
  No abstract at ADS

Title: Editorial Note
Authors: de Jager, C.
Bibcode: 1963SSRv....1..619D
Altcode: 1963SSRv....1..619J
  No abstract at ADS

Title: The Sun as a Source of Interplanetary Gas
Authors: de Jager, C.
Bibcode: 1963SSRv....1..487D
Altcode: 1963SSRv....1..487J
  No abstract at ADS

Title: The temperature minimum in the upper solar photosphere
Authors: de Jager, C.
Bibcode: 1963BAN....17..209D
Altcode:
  No abstract at ADS

Title: A Note on Bursts of Radio Emission and High Energy (&gt;20 keV)
    X-Rays from Solar Flares
Authors: De Jager, C.; Kundu, M. R.
Bibcode: 1963spre.conf..836D
Altcode:
  No abstract at ADS

Title: Emission of Gas From the Sun
Authors: De Jager, C.
Bibcode: 1963spre.conf..491D
Altcode:
  No abstract at ADS

Title: Review of Publications- Space Science Reviews, vol. 1, no. 1,
    editor-in-chief
Authors: de Jager, C.
Bibcode: 1962JRASC..56..269D
Altcode:
  No abstract at ADS

Title: The abundance of lead in the Sun
Authors: de Jager, C.; Neven, L.
Bibcode: 1962BAN....16..307D
Altcode:
  No abstract at ADS

Title: Upper Atmospheric Turbulence Determined by Means of Rockets
Authors: Blamont, J. E.; de Jager, C.
Bibcode: 1962JGR....67.3113B
Altcode:
  The motion field of the upper atmosphere was studied with the aid of
  sodium trails brought to the 100-km level by means of a Véronique
  rocket. Below 102 km the trail shows globular distortions in the
  form of elements having an average diameter of 0.5 km; above that
  height the trail is completely smooth, though highly curved, showing
  no small irregularities. The turbulence state of the upper atmosphere
  was studied by investigating diffusion of the sodium atoms. Above
  102 km the broadening of the trail can be completely accounted for by
  molecular diffusion; below that height the observed rate of increase of
  the globule diameters can be explained only by assuming a combination of
  molecular and turbulent diffusion. This information and the increasing
  chemical differentiation above 102 km strongly indicate that the 100-km
  level marks the difference between the turbulent and the nonturbulent
  parts of the upper atmosphere. The absence of turbulence in the upper
  atmosphere is bound to be due to the increasing relative importance of
  the friction forces there. The Reynolds number rapidly decreases with
  increasing atmospheric height. The absence or occurrence of turbulence
  cannot be due to shear effects: the Richardson number is too great in
  the region studied by us, which shows that shear turbulence is not to be
  expected in this part of the earth's atmosphere. Since the energy fed
  into the turbulence field is rather small, turbulence cannot be fully
  developed; in fact, it is predicted that the turbulent element can only
  have diameters smaller than about 2 km, which is not in disagreement
  with the observed element diameter of 0.5 km. The smallest visible
  wavelength of the motion field is of the order 50 to 100 meters,
  in agreement with ionospheric investigations (20 to 60 meters) and
  theoretical predictions (60 meters).

Title: Introduction
Authors: de Jager, C.
Bibcode: 1962SSRv....1....5D
Altcode: 1962SSRv....1....5J
  No abstract at ADS

Title: Atmospheric turbulence near the 100 km level
Authors: Blamont, J. E.; de Jager, C.
Bibcode: 1962sose.conf...94B
Altcode:
  No abstract at ADS

Title: Tables and graphs enabling the computation of the profiles of H
    [gamma] and H [delta] in stellar spectra
Authors: de Jager, Cornelis; Neven, L.
Bibcode: 1962AnOB....9.....D
Altcode: 1962AnBel...9.....D
  No abstract at ADS

Title: The acoustic energy flux of the Sun and the formation of
    the corona
Authors: de Jager, C.; Kuperus, M.
Bibcode: 1961BAN....16...71D
Altcode:
  No abstract at ADS

Title: Satellite Photography by Means of Small Schmidt Cameras
Authors: De Jager, C.
Bibcode: 1961spre.conf...47D
Altcode:
  No abstract at ADS

Title: Space Research II
Authors: van de Hulst, H. C.; de Jager, C.; Moore, A. F.
Bibcode: 1961spre.conf.....V
Altcode:
  No abstract at ADS

Title: Non-Thermal Solar X-Rays and Radio Emission
Authors: de Jager, C.
Bibcode: 1961LIACo..10..635D
Altcode: 1961LIACo..10..631D; 1961MSRSL...4..631D
  No abstract at ADS

Title: The Ultra-Violet and X-Ray Spectra of the Stars
Authors: de Jager, C.; Neven, L.
Bibcode: 1961LIACo..10..552D
Altcode: 1961MSRSL...4..551D; 1961LIACo..10..551D
  No abstract at ADS

Title: The development of a solar centre of activity
Authors: De Jager, C.
Bibcode: 1961VA......4..143D
Altcode:
  No abstract at ADS

Title: Observations of infrared solar line profiles
Authors: Delbouille, L.; de Jager, C.; Neven, L.
Bibcode: 1960AnAp...23..949D
Altcode:
  No abstract at ADS

Title: Asymptotic widening parameters for the hydrogen lines
Authors: de Jager, C.
Bibcode: 1960AnAp...23..889D
Altcode:
  No abstract at ADS

Title: The computation of partition functions in a stellar atmosphere
Authors: de Jager, C.; Neven, L.
Bibcode: 1960BAN....15...55D
Altcode:
  No abstract at ADS

Title: A program for the computation of b<SUB>n</SUB> tables for H
    and He
Authors: de Jager, C.; Kanno, M.; Neven, L.
Bibcode: 1960AnAp...23..843D
Altcode:
  No abstract at ADS

Title: Concluding remarks
Authors: de Jager, C.
Bibcode: 1960AnAp...23..976D
Altcode:
  No abstract at ADS

Title: The X-ray radiation of the sun
Authors: De Jager, C.
Bibcode: 1960spre.conf..628D
Altcode:
  No abstract at ADS

Title: Interpretation of solar radio-observations
Authors: de Jager, C.
Bibcode: 1960raso.conf..313D
Altcode:
  No abstract at ADS

Title: Saturation effects in very faint Fraunhofer lines
Authors: de Jager, C.; Neven, L.
Bibcode: 1959Obs....79..102D
Altcode:
  No abstract at ADS

Title: Book Reviews: Discussion of Short-lived Solar Radio Transients
Authors: de Jager, C.; van't Veer, F.
Bibcode: 1959IrAJ....5..158D
Altcode:
  No abstract at ADS

Title: 36. The Influence of the Metal Abundance on the Continuous
    Stellar Spectra
Authors: De Jager, C.; Neven, L.
Bibcode: 1959LIACo...9..413D
Altcode: 1959MSRSL...3..413D
  No abstract at ADS

Title: The structure of the chromosphere and the low corona
Authors: de Jager, C.
Bibcode: 1959IAUS....9...89D
Altcode:
  No abstract at ADS

Title: Structure and Dynamics of the Solar Atmosphere.
Authors: de Jager, Cornelis
Bibcode: 1959HDP....52...80D
Altcode:
  The undisturbed photosphere and chromosphere The undisturbed photosphere
  Granulation Temperature and density inhomogeneities in the photosphere
  Micro- and macro-turbulence in the photosphere Theory of convection and
  turbulence in the solar atmosphere The chromosphere The chromosphere
  at the limb The chromosphere on the disk Structure and dynamics of the
  chromosphere; transition to - the corona The disturbed parts of the
  photosphere and chromosphere Sunspots The individual spots Group of
  spots Photospheric and chromospheric faculae The faculae proper The
  "centre of activity" Flares and associated phenomena Monochromatic
  observations Spectrographic observations Dynamical phenomena associated
  with flares Filaments and prominences The quiescent prominences Moving
  prominences The corona Optical observations The quiet minimum corona;
  photometry, ionization and excitation The structure of the quiet
  minimum corona; temperatures and - densities The active parts of the
  corona and the "maximum corona" Radio emission from the Sun The quiet
  Sun Thermal radiation from centres of activity Non-thermal radiation:
  type III and type U bursts Other non-thermal radiophenomena, often
  connected with flares Solar rotation and the solar cycle The solar
  cycle Solar rotation and the Sun's general magnetic field Solar and
  terrestrial relationship General references

Title: 27. Loss of Matter by Stars
Authors: De Jager, C.
Bibcode: 1959LIACo...9..280D
Altcode: 1959MSRSL...3..280D
  No abstract at ADS

Title: A discussion of short-lived solar radio transients at 200 Mc/s
Authors: de Jager, Cornelis; van't Veer, F.
Bibcode: 1958dsls.book.....D
Altcode: 1958QB4.U8l14p1....
  No abstract at ADS

Title: 18. The Chromospheres of G-Type Stars
Authors: De Jager, C.
Bibcode: 1958LIACo...8..172D
Altcode:
  No abstract at ADS

Title: A discussion of short-lived solar radio transients at 200 Mc/s
Authors: de Jager, C.; van't Veer, F.
Bibcode: 1958VKAWA..21....1D
Altcode:
  No abstract at ADS

Title: The helium spectrum of the chromosphere
Authors: de Jager, C.; de Groot, B. H. M.
Bibcode: 1957BAN....14...21D
Altcode:
  No abstract at ADS

Title: Temperture-variation and turbulence in the low chromosphere
Authors: de Jager, C.
Bibcode: 1957BAN....13..275D
Altcode:
  No abstract at ADS

Title: The interpretation of hydrogen spectroheliograms
Authors: de Jager, C.
Bibcode: 1957BAN....13..133D
Altcode:
  No abstract at ADS

Title: Note on the complex light- and velocity-curves of DD Lacertae
Authors: de Jager, C.
Bibcode: 1957BAN....13..149D
Altcode: 1956BAN....13..149D
  No abstract at ADS

Title: Spectroscopic data for 50 model photospherese
Authors: de Jager, Cornelis; Neven, L.
Bibcode: 1957sdfm.book.....D
Altcode: 1957QB4.U8l13p4....
  No abstract at ADS

Title: Spectroscopic data for 50 model photospheres
Authors: de Jager, Cornelis; Neven, L.
Bibcode: 1957AnOB....8.....D
Altcode: 1957AnBel...8.....D
  No abstract at ADS

Title: The Abundances of Diatomic Molecules of H, C, N, and O and
    of H2O in Stellar Atmospheres
Authors: de Jager, C.; Neven, L.
Bibcode: 1957LIACo...7..357D
Altcode:
  No abstract at ADS

Title: Some properties of solar radio-transients on fast 200
    Mc./s. records
Authors: de Jager, C.; van't Veer, F.
Bibcode: 1957IAUS....4..366D
Altcode:
  No abstract at ADS

Title: A model of the upper photosphere from eclipse photometry of
    the solar limb
Authors: Hubenet, H.; de Jager, C.
Bibcode: 1956BAN....13...43H
Altcode:
  No abstract at ADS

Title: The occurrence of technetium in the Sun
Authors: Greenstein, Jesse L.; de Jager, C.
Bibcode: 1956BAN....13...13G
Altcode:
  No abstract at ADS

Title: The molecular absorption coefficient of the A<SUB>00</SUB>
    band of O<SUB>2</SUB>
Authors: de Jager, C.
Bibcode: 1956BAN....13....9D
Altcode:
  No abstract at ADS

Title: The distribution of Lyα radiation over the solar disk
Authors: de Jager, C.
Bibcode: 1956sei..conf..174D
Altcode:
  No abstract at ADS

Title: The profile of the Brackett α line in the solar spectrum
Authors: de Jager, C.; Migeotte, M.; Neven, L.
Bibcode: 1956AnAp...19....9D
Altcode:
  No abstract at ADS

Title: Ontstaan EN levensloop van sterren EN planeten.
Authors: de Jager, Cornelis
Bibcode: 1955olvs.book.....D
Altcode: 1955QB801.J22......
  No abstract at ADS

Title: On the Influence of Temperature Inhomogeneities in the Solar
    Photosphere on the Profiles of the Hydrogen Lines; with Special
    Reference to Hα
Authors: de Jager, C.
Bibcode: 1955stat.conf..108D
Altcode: 1954stat.conf..108D
  No abstract at ADS

Title: The Capture of Zodiacal Dust by the Earth
Authors: de Jager, C.
Bibcode: 1955LIACo...6..174D
Altcode:
  No abstract at ADS

Title: High-energy Microturbulence in the Solar Photosphere
Authors: de Jager, C.
Bibcode: 1954Natur.173..680D
Altcode: 1954Natur.173..680J
  THE Balmer, Paschen and Brackett lines of hydrogen in the solar spectrum
  are much wider than they should be according to computations based on
  the classical widening mechanism of the hydrogen lines<SUP>1</SUP>-the
  statistical Stark effect of the ions surrounding the emitting atoms. The
  amount of widening is greater for the Pasohen than for the Balmer lines;
  it is greatest for the Brackett lines. It seems impossible to ascribe
  this widening to atomic processes, since Jürgens<SUP>2</SUP> has shown
  in elegant laboratory experiments that the profile of H<SUB>β</SUB>
  is explained by the statistical Stark effect of the ions. Hence,
  the abnormal widening of the hydrogen lines must be explained by a
  mechanism which is active in the solar photosphere but not in laboratory
  experiments. It is difficult to ascribe it to super-excitation since
  the wings of the hydrogen lines are formed in rather deep parts of the
  solar photosphere, where deviations from thermodynamical equilibrium
  are not very likely to occur. It can be shown that the widening is
  probably explained by the microturbulence of the solar photosphere,
  a mechanism suggested to me by Prof. A. Unsöld, of Kiel.

Title: Observational models and helium abundances of the atmospheres
    of four B-type stars
Authors: Neven, L.; de Jager, C.
Bibcode: 1954BAN....12..103N
Altcode:
  No abstract at ADS

Title: The Uranium Content of a Stone Meteorite
Authors: van Dijk, Th.; de Metter, J.; de Jager, C.
Bibcode: 1954LIACo...5..495V
Altcode: 1954MSRSL...1..495V; 1954pna..conf..495V
  No abstract at ADS

Title: A New Determination of the Abundance of Deuterium in the
    Solar Atmosphere
Authors: de Jager, C.
Bibcode: 1954LIACo...5..460D
Altcode: 1954MSRSL...1..460D; 1954pna..conf..460D
  No abstract at ADS

Title: Observations of five stars suspected to belong to the class
    of β Canis Majoris stars
Authors: de Jager, C.
Bibcode: 1953BAN....12...91D
Altcode:
  No abstract at ADS

Title: Note on the pulsation of v Eridani and 16 Lacertae
Authors: de Jager, C.
Bibcode: 1953BAN....12...88D
Altcode:
  No abstract at ADS

Title: The photo-electric star photometer of the Utrecht Observatory
Authors: de Jager, C.
Bibcode: 1953BAN....12...93D
Altcode:
  No abstract at ADS

Title: The variation of light and radial velocity of DD Lacertae
Authors: de Jager, C.
Bibcode: 1953BAN....12...81D
Altcode:
  No abstract at ADS

Title: The interpretation of the observed hydrogen lines in the
    infrared solar spectrum II.
Authors: de Jager, C.; Neven, L.
Bibcode: 1952PRNAA..55..165D
Altcode: 1952RNAAS..55..165D
  No abstract at ADS

Title: The hydrogen spectrum of the sun
Authors: de Jager, Cornelis
Bibcode: 1952hss..book.....D
Altcode: 1952QB4.U8l13p1....
  No abstract at ADS

Title: The hydrogen spectrum of the sun
Authors: de Jager, Cornelis
Bibcode: 1952RAOU....1.....D
Altcode:
  No abstract at ADS

Title: The Spectrum of Turbulence in the Earth's Upper Atmosphere
Authors: de Jager, C.
Bibcode: 1952LIACo...3..223D
Altcode:
  No abstract at ADS

Title: The Structure of the Metal Meteorites and the Problem of
    their Origin
Authors: de Jager, C.
Bibcode: 1952LIACo...4..289D
Altcode:
  No abstract at ADS

Title: The hydrogen spectrum of the sun
Authors: de Jager, Cornelis
Bibcode: 1952PhDT........29D
Altcode:
  No abstract at ADS

Title: Absence of Hydrogen Radiation of Wavelength 21 cm. in the Sun
Authors: de Jager, C.; Minnaert, M.; Muller, C. A.
Bibcode: 1951Natur.168..391D
Altcode:
  OBSERVATIONS have been made at the Kootwijk Station of the Dutch
  Organization for Radio Astronomy, in order to ascertain whether hydrogen
  radiation of 21 cm. wave-length, detected in the galaxy, would be found
  also in the sun. The 7.50metre mirror and the receiver technique were
  the same as used for the investigations of the Galaxy<SUP>*</SUP>. No
  indication of a spectral line was found. The apparatus was sufficiently
  sensitive to detect a variation of 1/260 in the continuous radio
  spectrum.

Title: The model of the solar atmosphere and the continuous absorption
    coefficient in the infrared
Authors: Neven, L.; de Jager, C.
Bibcode: 1951BAN....11..291N
Altcode:
  No abstract at ADS

Title: Interprétation des Mesures de Vitesses Radiales dans les
    Granules Solaires
Authors: de Jager, C.; Pecker, J. C.
Bibcode: 1951CRASB.232.1645D
Altcode:
  No abstract at ADS

Title: The profiles of the lines of the Paschen and Brackett series
    of hydrogen in the solar spectrum.
Authors: de Jager, C.; Neven, L.
Bibcode: 1950PRNAA..53..157D
Altcode: 1950RNAAS..53..157D
  No abstract at ADS

Title: Estimates of AZ Centauri
Authors: de Jager, C.
Bibcode: 1947BAN....10..248D
Altcode:
  No abstract at ADS

Title: Note on the distribution of light on Jupiter's bright
    satellites
Authors: de Jager, C.
Bibcode: 1946BAN....10...81D
Altcode:
  No abstract at ADS

