dejager

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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
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: The
equatorial and poloidal magnetic fields and their relation to the
Earth's NH temperature. The notions phase diagram of the solar
dynamo, Transition Point and Grand Episode. The granular scale
magnetic fields or 'bright spots'. Telescopes for large-field
high-resolution imaging of the sun. 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. The statistical start of the modern heating and solar variability as
part of the modern heating curve. The non-linear time difference
between the solar magnetic variations and terrestrial warming.

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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.
2019A&A...631A..48V Altcode: 2019arXiv191002460V
 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. 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. 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.m 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 Teff 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. 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>

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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.
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. (2 data files).

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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.
2018PAIJ....2..175D Altcode: 2018PAIJ....2..175J
No abstract at ADS

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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.
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).

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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.
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.

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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.
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.

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Title: The Utrecht Astronomical Institute, 1632 to 2012
Authors: de Jager, C.
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.

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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.
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). Aims: Our local
thermal equilibrium analysis of the spectra yields accurate values
of the effective temperature (Teff), the acceleration
of gravity (g), and the turbulent velocity (vt) for 26
spectra. The standard deviations average are 82 K for Teff,
0.23 for log g, and 1.1 km s-1 for vt. 
Methods: A comparison of B - V observations, MK spectral types,
and Teff-data yields E(B - V), "intrinsic" B - V,
Teff, absorption AV, 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 mbol,0 can be determined. With
Hipparcos distance measurements of HR 8752, the absolute bolometric
magnitude Mbol,0 can be determined. Results:
Over the period of our study, the value of Teff 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 vt, 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 vt
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, Teff, log M/M⊙,
log L/L⊙, and log R/R⊙ are determined for
each of the observational points. The results show the variation in
these basic stellar parameters over the past near-century. 
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. 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>

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Title: Solar Forcing of Climate
Authors: de Jager, C.
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.

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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.
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). 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. 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). (20 data files).

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Title: Sudden transitions and grand variations in the solar dynamo,
past and future&lt;/xref&gt;
Authors: De Jager, Cornelis; Duhau, Silvia
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 Rmax 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. 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>.

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Title: The influence of planetary attractions on the solar tachocline
Authors: Callebaut, Dirk K.; de Jager, Cornelis; Duhau, Silvia
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.

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

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Title: Quantifying and specifying the solar influence on terrestrial
surface temperature
Authors: de Jager, C.; Duhau, S.; van Geel, B.
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.

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Title: Solar Gleissberg periodicities in relation to grand episodes
Authors: Duhau, S.; de Jager, C.
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

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Title: Forecasting the parameters of sunspot cycle 24 and beyond
Authors: de Jager, C.; Duhau, S.
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).

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Title: Episodes of relative global warming
Authors: de Jager, C.; Duhau, S.
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.

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Title: The Solar Dynamo and Its Phase Transitions during the Last
Millennium
Authors: Duhau, S.; de Jager, C.
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.

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Title: A long-term relationship between solar magnetic field,
geomagnetic field and Earth's rotation rate.
Authors: Duhau, S.; de Jager, C.
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.

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Title: On the Physical Origin of the Cycles in Long-term Modulation
of Solar Activity
Authors: Duhau, S.; de Jager, C.
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.

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Title: On possible drivers of Sun-induced climate changes
Authors: de Jager, Cornelis; Usoskin, Ilya
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.

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Title: Solar Forcing of Climate. 1: Solar Variability
Authors: de Jager, C.
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
Gs 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 10Be are
proxies for this influence and for the poloidal field variations. The
R G 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.
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.
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
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.
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~=5.4×10-2 Msolar yr-1. 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 3×10-2 Msolar
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.
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.
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.
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.
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
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 vwind=vsound) are situated inside
the photospheres, at a level deeper than τRoss=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;geff&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;geff&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.
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; vturb = 20 km/s;
log(Mdot)= -4.7; X = 0.35. The resulting photospheric
model has negative values of geff 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;Gamma1&gt;-value of about 4/3, the average atmospheric
&lt;Gamma1&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.
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
2000SSRv...92..613D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: J. Andersen (ed.), Transactions of the International
Astronomical Union, Volume XXIIIB
Authors: de Jager, Cornelis
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.
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
2000CIBu..147....2D Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: De laatste "zonsverduistering".
Authors: de Jager, C.
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
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.
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
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
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.
1999A&A...343..661N Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: Onzichtbare massa is wellicht heel "gewoon".
Authors: de Jager, C.
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.
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
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
1999SSRv...87R.546D Altcode:
No abstract at ADS

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

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

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

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

---------------------------------------------------------
Title: Toch een planetoide in Chicxulub?
Authors: de Jager, C.
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.
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
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
1998ASSL..222...21D Altcode: 1998ream.conf...21D
No abstract at ADS

---------------------------------------------------------
Title: A Cold War in Space Research
Authors: de Jager, Cornelis
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.
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.
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.
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^Msun_/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(Msun_/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
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.
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
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.
1997SSRv...81..199D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: A White and a Red Star|(Special Historical Review)
Authors: De Jager, Cornelis
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
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.
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
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
1996SSRv...76..339H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Near-unstable stars: the yellow-white hypergiants.
Authors: de Jager, C.
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.
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
ζmu_, 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/Lsun_)=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 25-40Msun_, and actual masses between 15 and
25Msun_. 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.
1995SSRv...73..435V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book Review: A view of the universe / Cambridge U Press, 1993
Authors: de Jager, C.
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
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.
1995SSRv...72..679M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Determining Stellar Masses from a Study of Atmospheric
Accelerations
Authors: Nieuwenhuijzen, H.; de Jager, C.
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.
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.
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+/-200Rsun_, while the best value is
rather 400Rsun_. 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.
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.
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.
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
1994SSRv...67..223B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Massive stars: setting the stage.
Authors: de Jager, C.
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.
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.
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.
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.
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
gamma1 can be evaluated. However, we have not treated shock
structures. In the case of non-LTE we have to employ an approximation
for gamma1 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 gammaH, 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))ad
identically equal to gamma1 on both sides of the shock. Both
gammaH and gamma1, and also mu are functions
of pressure P and temperature T. We present: (1) the derivation,
(2) examples of gamma1 (P,T) and gammaH (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.
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.
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.
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
1993SSRv...65..365M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Massive stars: Setting the stage
Authors: de Jager, C.
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.
1993SSRv...65..181R Altcode:
No abstract at ADS

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

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

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

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

---------------------------------------------------------
Title: Book-Review - Mars the Red Planet
Authors: Catermole, P.; de Jager, C.
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.
1993SSRv...62Q.210D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book Review: An introduction to astrophysical hydrodynamics /
Academic Press, 1992
Authors: de Jager, C.
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.
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.
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.
1992SSRv...61..428K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Yellow hypergiant interferometry: a clue to understanding
evolutionary instability.
Authors: De Jager, Cornelis; Nieuwenhuijzen, Hans
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.
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.
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.
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: Teff
= 10200±370K; log g = 1.9±0.4 cm s-1 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 ζμ hardly varies with depth and equals
5.4±0.7 km s-1, hence the motion field, which consists of
isothermal shock waves, obeys the "limiting shockstrength regime". The
observationally determined shock strenght is Msobs
= 2.3.

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

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: The large-scale atmospheric motion field of Alpha Orionis
Authors: de Jager, C.; Eriksson, K.
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.
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.
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.
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.
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
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.
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
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.
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.
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.
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.
1990SSRv...54R.190S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Highlights of Astronomy
Authors: McNally, D.; de Jager, C.
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.
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.
1990A&A...231..134N Altcode:
We investigate the dependence of Mṡ 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. -Mṡ=9.6310-15
(L/Lsun)1.42 (M/Msun)0.16
(R/Rsun)0.81 Msun Msun
yr-1 appears to give a good representation of observed
rates of mass loss over the whole Hertzsprung-Russell diagram. For
luminous stars with Teff &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
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.
1990QJRAS..31...31D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Les étoiles les plus lumineuses.
Authors: de Jager, Cornelis
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.
1990SSRv...53..168D Altcode: 1990SSRv...53..168R
No abstract at ADS

---------------------------------------------------------
Title: Acceleration phases in high-energy solar flares
Authors: de Jager, C.
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.
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.
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.
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.
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
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
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
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.
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.
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.
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.
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.
1989SSRv...49..443K Altcode: 1988SSRv...49..443K
No abstract at ADS

---------------------------------------------------------
Title: Editorial
Authors: de Jager, Cornelis; Švestka, Zdeněk; Howard, Robert F.
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.
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.
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
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
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.
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.
1989ASSL..157..305N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Luminous Blue Variables Need not BE Blue
Authors: de Jager, C.; van Genderen, A. M.
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.
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.
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.
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.
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 τ5000 = 1 to
0.6 at τ5000 = 10-3. The turbulent acceleration
gt is 0.15 cm s-2 which should be compared
with ggrav = -1.0 cm s-2. 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-1.

---------------------------------------------------------
Title: Solar flares through electric current interaction
Authors: de Jager, Cornelis
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.
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.
1988A&A...195..218B Altcode:
High resolution near-ultraviolet spectra of α Cygni (λ/Δλ =
8×104) 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-1) over a large
range of optical depths (-4 &lt; log τc &lt; -1). The
macroturbulent velocity distribution is double-peaked at velocities,
both positive and negative, of 14±2 km s-1, 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-2, yielding a gravitational acceleration of 26.0
cm s-2, and a stellar mass of 18 M_sun;. The authors also
derive a new value for vr sin i (8±3 km s-1).

---------------------------------------------------------
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.
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.
1988BAAS...20..725D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Experiences from the SMY/SMA Period
Authors: de Jager, C.
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.
1988JPhys..49..383B Altcode: 1988IAUCo.102..383B
In order to study the apparent near instability of supergiant
atmospheres high-resolution (λ/Δλ = 8×104) 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.
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.
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 Teff 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.
1988SSRv...46..380D Altcode: 1988SSRv...46..380H
No abstract at ADS

---------------------------------------------------------
Title: Stellar mass loss and atmospheric instability
Authors: de Jager, Cornelis; Nieuwenhuijzen, Hans
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.
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.
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.
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.
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.
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.
1988ApL&C..26..372D Altcode: 1988ApL....26..372D
No abstract at ADS

---------------------------------------------------------
Title: Sterrenwacht "Sonnenborgh": een nieuwe fase.
Authors: de Jager, C.
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.
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 ζμ 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-1, 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
gt is 24 cm s-2, 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.
1987SSRv...45..410D Altcode: 1987SSRv...45..410S
No abstract at ADS

---------------------------------------------------------
Title: The Solar Maximum Year and its Analysis Phase
Authors: De Jager, Cornelis
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
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 1011 cm−3,
a temperature of 5 × 108 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 ≈ 1027 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.
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.
1987A&A...177..217D Altcode:
From a set of 199 determinations of bolometric stellar luminosity
L and 268 of stellar effective temperature Teff we
derived the statistical dependances of log Teff and log
(L/Lsun) 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
Teff (s, b) and log (L/Lsun) (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 Teff 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.
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.
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 Teff and log (L/L_sun;)
and their cross products.

---------------------------------------------------------
Title: The future of planetary astronomy
Authors: de Jager, Cornelis
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
1986SSRv...44..186M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Flares and Particle Acceleration
Authors: de Jager, C.
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 1010 cm-3 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 1030 erg, and an average
number of 1038 electrons with E ≳ 15 keV is accelerated. In
subsecond pulses these values are about 1035 electrons
and about 1027 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 104 km above
the solar photosphere, a region permeated by a large number (≳ 10)
of fluxthreads, each carrying electric currents of ≈ 1010
1011 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
3He-rich interplanetary plasma clouds from flares all point
to a common source, identified with shortlived (∼ 0.1 s) superhot
(≳ 108 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 (≈
1010 cm-3); 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.
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.
1986Ap&SS.122..187A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: La phase initiale de l'éruption solaire.
Authors: de Jager, C.
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.
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
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.
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 ⪉2×107km2 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.
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.
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 Teff and luminosity L. It appears
that Mdepends only on Teff and L for the O- through M-type
stars brighter that about 3×103L_sun;.

---------------------------------------------------------
Title: Acceleration in a high-energy flare.
Authors: de Jager, C.; Correia, E.; Kaufmann, P.
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 5×108K 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.
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.
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.
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
1986pspr.book.....D Altcode: 1986QB521.6.P76....
No abstract at ADS

---------------------------------------------------------
Title: The flare kernel in the impulsive phase.
Authors: de Jager, C.
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-1)
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
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.
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 × 1031 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.
1985SSRv...41..403W Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Book-Review - Supernovae as Distance Indicators
Authors: Bartel, N.; De Jager, C.
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.
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 107 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.
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.
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.
1985SSRv...41..394G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal Explosions
Authors: de Jager, C.
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-1, 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.
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
1985spit.conf.....D Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: The impulsive phase of solar flares.
Authors: de Jager, C.
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.
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-1. This value is close to the local
sound velocity (13.7 km s-1). 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-1, 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.
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.
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 geff =
ggrav(1 - Γ)-gturb ≈ 0, where ggrav
= GM/R2, gturb is the outward acceleration due
to the gradient of turbulent pressure, and Γ is the Eddington ratio
|grad/ggrav|. 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
Te ≈ 104K 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.
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.
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
−1. At the same time a surge-like expansion started. It
was observable slightly later in Hα, with southward velocities
of ≳ 200 km s−1. 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−1, decreasing in 40 s to ∼500 km s−1.

---------------------------------------------------------
Title: Impulsive Phase Heating and a Coronal Explosion in a Solar
Flare
Authors: de Jager, C.; Boelee, A.
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−1. 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.
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.
1984srps.conf...47D Altcode:
All massive stars (⪆15 M_sun;) are variable in luminosity (Δm ≈
10-2mag) and radial velocity (Δv ≈ 1 km s-1),
and have a large rate of mass loss. A precise determination of the
spectrum of the vR- and m-variations with noise levels of
ca. 10-3km s-1 and 10-5mag 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.
1984brst.book.....D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Astrophotography - Techniques for the Amateur
Authors: Martinez, P.; de Jager, C.
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.
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)×10-4mag for the observation of
a 7th mag star by a one-meter telescope at an altitude of 4000 m and
an integration time of 103s.

---------------------------------------------------------
Title: Shock-driven mass loss of stars.
Authors: de Jager, C.; van den Oord, G. H. J.
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.
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 ~ 103 and a few tens of km
s-1. 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.
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.
1983SSRv...36..429K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Spatial Telecommunications - Part Two -
Spatial Sector
Authors: de Jager, C.
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.
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.
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.
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.
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, 104
times weaker than a flare, but lasting up to 10 hr occur predominantly
along the H∥ = 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∥ = 0 line, may be associated with newly
emerging flux. Short-lived X-ray sources, with fluxes ranging from
subflare levels to 10−3 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.
1983SSRv...36..429D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book-Review - Numerical and Physical Aspects of Aerodynamic
Flows
Authors: Cebeci, T.; de Jager, C.
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.
1983SSRv...36..415K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radio, X-ray, and optical observations of the flare of June
13, 1980, at 6h22m UT
Authors: Kattenberg, A.; Allaart, M.; de Jager, C.; Schadee, A.;
Schrijver, J.; Shibasaki, K.; Švestka, Z.; van Tend, W.
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.
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.
1983SSRv...35..293N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Development of flare morphology in X-rays, and the flare
scenario
Authors: de Jager, C.
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−1. 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.
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.
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 (≈ 1037) 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
× 1011 and ∼ 1 × 1011 cm#X2212;3,
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 × 106
km2. 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#X2212;2. 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.
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.
1983SoPh...89..233M Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Mass Loss from astronomical objects; a summary.
Authors: de Jager, C.
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.
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.
1983MeBel..45....1D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Space observations of solar flares.
Authors: de Jager, C.
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.
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.
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.
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.
1982SSRv...31..453D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Photospheric Velocity Field of Procyon
Authors: de Jager, C.; Neven, L.
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 μ = 0.9 ±
0.4 km s-1, a macroturbulent velocity componentL M
= 5.3 ± 0.2 km s-1, and a rotational velocity componentv
R sini=10.0±1.2 km s-1. 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 R sini=4 km s-1 andL
M = 11.6 ± 2.7 km s-1. A comparison is made
with other results and theoretical predictions.

---------------------------------------------------------
Title: Review of galactic ultraviolet astronomy.
Authors: de Jager, C.
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.
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.
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-1) 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 rotsini=40
km s-1.

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

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

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

---------------------------------------------------------
Title: Book-Review - Stars and Star Clusters
Authors: Voigt, H. H.; Schaifers, K.; de Jager, C.
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.
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
109 cm−3 and its temperature stayed for many
hours at a fairly constant value of about 6.5 × 106 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∥ = 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.
1982mlao.conf...59D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Looking ahead after the termination of the solar
Authors: de Jager, Cornelis
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.
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.
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.
1982SSRv...32..464S Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: Reflections on Solar Variability
Authors: de Jager, C.
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.
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.
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.
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.
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
1981SSRv...28..105P Altcode:
No abstract at ADS

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

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

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

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

---------------------------------------------------------
Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Smak, J.
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.
1981SSRv...28Q.112H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Kriz, S.
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.
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.
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.
1981PRNAA..84..457D Altcode: 1981RNAAS..84..457D
No abstract at ADS

---------------------------------------------------------
Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Mihalas, D.
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.
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.
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.
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.
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.
1981iue..prop..894D Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: Book-Review - the Brightest Stars
Authors: de Jager, C.; Scholz, G.
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
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.
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.
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.
1981hea..conf..255S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: De zon een opmerkelijke ster.
Authors: de Jager, C.
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.
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.
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.
1980SSRv...26..447G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Solar Maximum Year and Related Space Experiments
Authors: Svestka, Z.; de Jager, C.
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.
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.
1980SSRv...25..431D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Book-Review - the Sun Our Future Energy Source
Authors: McDaniels, D. K.; De Jager, C.
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.
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.
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.
1980SSRv...25Q..85B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The brightest stars
Authors: de Jager, C.
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.
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.
1980SSRv...25..432M Altcode:
No abstract at ADS

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

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

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

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

---------------------------------------------------------
Title: On the Seats of Elementary Flare Bursts
Authors: de Jager, C.
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.
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.
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.
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.
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.
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.
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.
1979SSRv...23..683L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Large Turbulent Elements in Supergiant Photospheres
Authors: de Jager, C.; Vermue, J.
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+, 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.
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 M(θk) andf μ(θk), where θ is
the optical scale height andf 2(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 M/f μ 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.
1979ssms.conf....1D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Stars and their coronae.
Authors: de Jager, C.
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.
1979srvp.book.....R Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Nauwelijks stabiele reuzensterren.
Authors: de Jager, C.
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.
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.
1979IUE1.symp..381L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Global development of space research, 1977-1978
Authors: de Jager, C.
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.
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-1, and a wavelength
of about 106 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
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.
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
1978SSRv...22..213R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Properties of elementary flare bursts.
Authors: de Jager, C.; de Jonge, G.
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-0.69±0.05.

---------------------------------------------------------
Title: Book reviews
Authors: de Jager, Cornelis; Takens, R. J.
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.
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.
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 eff=7660±110 K;
logg eff=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.
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
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.
1978nisa.symp..247C Altcode: 1978nisa.conf..247C
No abstract at ADS

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

---------------------------------------------------------
Title: A review of space research, 1976 - 1977.
Authors: de Jager, C.
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.
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
fM(k) and ft(k), where k
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 fM and ft 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.
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.
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
1977SSRv...20..235R Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: The Spectroscopy and Polarimetry of Flare X-Radiation
Authors: de Jager, C.
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.
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.
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.
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.
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.
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.
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.
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.
1976SSRv...19..161J Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Flares
Authors: de Jager, C.; Kuperus, M.; Rosenberg, H.
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.
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
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.
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.
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.
1976IAUTA..16a..19M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Het planetenstelsel. Kolleges sterrekunde voor afgestudeerden
1976.
Authors: de Jager, C.; Reijnen, G. C. M.
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.
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.
1976mpvs.conf....3B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Elementary flare bursts.
Authors: van Beek, H. F.; de Feiter, L. D.; de Jager, C.
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.
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.
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 × 10-10 mathfrak{M}_ odot yr-1and finally
we describe the composite spectrum of the (WC8+09I) bnary γ2
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.
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.
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.
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.
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.
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.
1975SoPh...42...43G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Radiation Field in Photospheric Models for Extreme
Supergiants
Authors: de Jager, C.; Neven, L.
1975Ap&SS..33..295D Altcode:
On the basis of assumed photospheric temperature models for 36
extreme supergiants (logg e -values of 1, 0.5 and 0;T
 e ranging from approx. 3700 33 000 K) photospheric
fluxesS(τλ) 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
(τ5≳1) the radiation field at each geometrical level
can be characterized by one unique radiation temperature; for smaller
τ5-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.
1975NTNA...41..101V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dynamik von Sternatmosphären
Authors: de Jager, C.
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.
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.
1975Zenit...2..292D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Stellar coronas.
Authors: de Jager, C.
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.
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.
1975Zenit...2..354D Altcode:
No abstract at ADS

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

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

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

---------------------------------------------------------
Title: High energy plasmas in astrophysics
Authors: de Jager, C.
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.
1975srxp.book.....R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Phenomenology of the Subflare; A Synthesis of CINOF
Authors: de Jager, C.
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.
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.
1975Zenit...2..345D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: An All-Sky Camera Battery for X-Ray Astronomy
Authors: de Jager, C.
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 ≈103 cm2) an integration time
of approximately 6 min is needed in order that sources with a count
rate of 0.01 cm-2 s-1 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.
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.
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.
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.
1974SSRv...15..741D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Book reviews
Authors: de Jager, C.; Bruzek, A.
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
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.
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.
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.
1974Zenit...1R...2D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Sterren in wording.
Authors: de Jager, C.
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.
1974PhiTR..34...43B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Is de Gum-nevel te groot om te kunnen worden gezien?
Authors: de Jager, C.
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.
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.
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.
1974Zenit...1...14D Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: Nieuwe zonnecyclus dient zich an.
Authors: de Jager, C.
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.
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.
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.
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.
1973sari.conf...93D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Ontstaan en levensloop van sterren.
Authors: de Jager, C.; van den Heuvel, E. P. J.
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.
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.
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.
1973spre.conf..871H Altcode:
No abstract at ADS

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

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

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

---------------------------------------------------------
Title: Review of Publications- Highlights of Astronomy, Volume 2
Authors: de Jager, C.
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.
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 rot up to 200 km s-1.

---------------------------------------------------------
Title: The empirical determination of line source functions, β 
L -values, and the microturbulent and convective velocity
components as functions of depth in the photosphere-chromosphere
transition region
Authors: De Jager, C.; Neven, L.
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 βL 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 τ5
= 10-4 and 10-1: «υτ» ≈ 1.4 km
s-1, 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 τ5≳ 10-3, slight
deviations occur in higher levels. The interesting behaviour of the
CaII source function near τ5 = 10-5 should be
noted. (d) Non LTE-functions: first approximations for the functions
log βL (τ5) 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
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.
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.
1972SSRv...13..190S Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Solar Energy Sources
Authors: de Jager, C.
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.
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.
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.
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.
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.
1972sstp.conf.....D Altcode: 1972sun..confQ....D
No abstract at ADS

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

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

---------------------------------------------------------
Title: Editorial
Authors: De Jager, Cornelis; Švestka, Zdeněk
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.
1971SSRv...12..526C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Production of Solar and Stellar Chromospheres and Coronae
Authors: de Jager, C.
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-2 s-1. 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.
1971SSRv...12..135D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronae of Cool Stars
Authors: de Jager, C.; De Loore, C.
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 eff. 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.
1971SSRv...12..131H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Editorial
Authors: de Jager, Cornelis; Švestka, Zdeněk
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.
1971QJRAS..12..338D Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: Instrumentation for high-resolution stellar
UV-spectrophotometry.
Authors: de Jager, C.; Hammerschlag, A.; Werner, W.
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.
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.
1971SoPh...16..227F Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: Reports on Astronomy.
Authors: de Jager, C.; Jappel, A.
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.
1971havp.book.....D Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: Book review
Authors: de Jager, C.
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.
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.
1970SSRv...10..737D Altcode:
No abstract at ADS

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

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

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

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

---------------------------------------------------------
Title: Damping Constants for Infrared Fraunhofer Lines
Authors: De Jager, C.; Neven, L.
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 τ0 =
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
1969SoPh...10..243D Altcode: 1969SoPh...10..243.
No abstract at ADS

---------------------------------------------------------
Title: Book reviews
Authors: de Jager, C.; Janssens, Paul
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.
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.
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.
1969SSRv....9..740D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Editorial
Authors: Švestka, Z.; De Jager, C.
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.
1969SSRv....9..617D Altcode:
No abstract at ADS

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

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

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

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

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

---------------------------------------------------------
Title: Editorial
Authors: De Jager, C.; Švestka, Z.
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.
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.
1968SoPh....4..379D Altcode:
We have examined whether the motion field in the photosphere in the
range of optical depths 0.25&lt; τ0&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.
1968SoPh....4..375D Altcode: 1968SoPh....4..375.
No abstract at ADS

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

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

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

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: The Bilderberg Model of the Photosphere and Low Chromosphere
Authors: Gingerich, O.; De Jager, C.
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
= 10−7 and 25. The model is characterized by a flat
temperature minimum of 4600 °K between τ5000 ≈ 10−2
to 10−4. 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.
1967SSRv....7..534V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Hard Solar X-Ray Burst of 18 September 1963
Authors: De Jager, C.
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.
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.
1967SSRv....7..396V Altcode:
No abstract at ADS

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

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

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

---------------------------------------------------------
Title: Editorial
Authors: de Jager, C.; Švestka, Z.
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.
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.
1967SoPh....1...27D Altcode:
A fraunhofer line profile depends on various parameters, partly
related to the photospheric structure (T, Pg, Pe,
vconv, vturb), 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, vconv (τ); the damping constant
γ (τ); the abundance, Ael; the distribution function
ϕ(vconv, τ) of the convective velocities at each depth
τ; the source function, S (τ); the microturbulent velocities,
vturb (τ).

---------------------------------------------------------
Title: Editorial
Authors: de Jager, C.; Švestka, Z.
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.
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.
1967ZA.....67...95D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Theoretical Aspects of Solar X-Radiation
Authors: de Jager, C.
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.
1967BANS....2..125D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The structure of the quiet photosphere and the low chromosphere
Authors: de Jager, C.
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.
1967BAN....19..160D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Spectroscopic data for sixty new model photospheres
Authors: de Jager, Cornelis; Neven, L.
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.
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.
1966BAN....18..306D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Théorie des Atmospheres Stellaires (Theory of Stellar
Atmospheres)
Authors: de Jager, C.
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.
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.
1966BAN....18..128D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Recommendations concerning notations to be used in transfer
theory
Authors: de Jager, C.
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.
1965P&SS...13..869D Altcode:
No abstract at ADS

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

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

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

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

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

---------------------------------------------------------
Title: Optical Solar Flares
Authors: de Jager, C.
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.
1965ASSL....2...86D Altcode: 1965istr.conf...86D
No abstract at ADS

---------------------------------------------------------
Title: The solar spectrum
Authors: de Jager, Cornelis
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.
1965ASSL....2...96D Altcode: 1965istr.conf...96D
No abstract at ADS

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

---------------------------------------------------------
Title: The Quiet Chromosphere and Corona
Authors: de Jager, C.
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.
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.
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.
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.
1964BAN....17..442H Altcode:
No abstract at ADS

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

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

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

---------------------------------------------------------
Title: Energy transport and "turbulence" in a sunspot
Authors: de Jager, C.
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.
1963BAN....17....1D Altcode: 1964BAN....17....1D
No abstract at ADS

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

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

---------------------------------------------------------
Title: The temperature minimum in the upper solar photosphere
Authors: de Jager, C.
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.
1963spre.conf..836D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Emission of Gas From the Sun
Authors: De Jager, C.
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.
1962JRASC..56..269D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Upper Atmospheric Turbulence Determined by Means of Rockets
Authors: Blamont, J. E.; de Jager, C.
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.
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.
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.
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.
1961BAN....16...71D Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: Non-Thermal Solar X-Rays and Radio Emission
Authors: de Jager, C.
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.
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.
1961VA......4..143D Altcode:
No abstract at ADS

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

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

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

---------------------------------------------------------
Title: A program for the computation of bn tables for H
and He
Authors: de Jager, C.; Kanno, M.; Neven, L.
1960AnAp...23..843D Altcode:
No abstract at ADS

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

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

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

---------------------------------------------------------
Title: Saturation effects in very faint Fraunhofer lines
Authors: de Jager, C.; Neven, L.
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.
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.
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.
1959IAUS....9...89D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Structure and Dynamics of the Solar Atmosphere.
Authors: de Jager, Cornelis
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.
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.
1958dsls.book.....D Altcode: 1958QB4.U8l14p1....
No abstract at ADS

---------------------------------------------------------
Title: 18. The Chromospheres of G-Type Stars
Authors: De Jager, C.
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.
1958VKAWA..21....1D Altcode:
No abstract at ADS

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

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

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

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

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

---------------------------------------------------------
Title: Spectroscopic data for 50 model photospheres
Authors: de Jager, Cornelis; Neven, L.
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.
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.
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.
1956BAN....13...43H Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: The molecular absorption coefficient of the A00
band of O2
Authors: de Jager, C.
1956BAN....13....9D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The distribution of Lyα radiation over the solar disk
Authors: de Jager, C.
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.
1956AnAp...19....9D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Ontstaan EN levensloop van sterren EN planeten.
Authors: de Jager, Cornelis
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.
1955stat.conf..108D Altcode: 1954stat.conf..108D
No abstract at ADS

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

---------------------------------------------------------
Title: High-energy Microturbulence in the Solar Photosphere
Authors: de Jager, C.
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 lines1-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 Jürgens2 has shown
in elegant laboratory experiments that the profile of Hβ
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.
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.
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.
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.
1953BAN....12...91D Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: The variation of light and radial velocity of DD Lacertae
Authors: de Jager, C.
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.
1952PRNAA..55..165D Altcode: 1952RNAAS..55..165D
No abstract at ADS

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

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

---------------------------------------------------------
Title: The Spectrum of Turbulence in the Earth's Upper Atmosphere
Authors: de Jager, C.
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.
1952LIACo...4..289D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The hydrogen spectrum of the sun
Authors: de Jager, Cornelis
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.
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*. 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.
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.
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.
1950PRNAA..53..157D Altcode: 1950RNAAS..53..157D
No abstract at ADS

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

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