Author name code: holweger
ADS astronomy entries on 2022-09-14
author:"Holweger, Hartmut"
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Title: The shock-patterned solar chromosphere in the light of ALMA
Authors: Wedemeyer-Böhm, S.; Ludwig, H. -G.; Steffen, M.; Freytag,
B.; Holweger, H.
Bibcode: 2005ESASP.560.1035W
Altcode: 2005csss...13.1035W; 2005astro.ph..9747W
Recent three-dimensional radiation hydrodynamic simulations by Wedemeyer
et al. (2004) suggest that the solar chromosphere is highly structured
in space and time on scales of only 1000 km and 20-25 sec, resp.. The
resulting pattern consists of a network of hot gas and enclosed cool
regions which are due to the propagation and interaction of shock
fronts. In contrast to many other diagnostics, the radio continuum at
millimeter wavelengths is formed in LTE, and provides a rather direct
measure of the thermal structure. It thus facilitates the comparison
between numerical model and observation. While the involved time
and length scales are not accessible with todays equipment for that
wavelength range, the next generation of instruments, such as the
Atacama Large Millimeter Array (ALMA), will provide a big step towards
the required resolution. Here we present results of radiative transfer
calculations at mm and sub-mm wavelengths with emphasis on spatial
and temporal resolution which are crucial for the ongoing discussion
about the chromospheric temperature structure.
Title: Numerical simulation of the three-dimensional structure and
dynamics of the non-magnetic solar chromosphere
Authors: Wedemeyer, S.; Freytag, B.; Steffen, M.; Ludwig, H. -G.;
Holweger, H.
Bibcode: 2004A&A...414.1121W
Altcode: 2003astro.ph.11273W
Three-dimensional numerical simulations with CO5, a
new radiation hydrodynamics code, result in a dynamic, thermally
bifurcated model of the non-magnetic chromosphere of the quiet Sun. The
3D model includes the middle and low chromosphere, the photosphere,
and the top of the convection zone, where acoustic waves are excited
by convective motions. While the waves propagate upwards, they steepen
into shocks, dissipate, and deposit their mechanienergy as heat in
the chromosphere. Our numerical simulations show for the first time
a complex 3D structure of the chromospheric layers, formed by the
interaction of shock waves. Horizontal temperature cross-sections of
the model chromosphere exhibit a network of hot filaments and enclosed
cool regions. The horizontal pattern evolves on short time-scales of
the order of typically 20-25 s, and has spatial scales comparable to
those of the underlying granulation. The resulting thermal bifurcation,
i.e., the co-existence of cold and hot regions, provides temperatures
high enough to produce the observed chromospheric UV emission and -
at the same time - temperatures cold enough to allow the formation
of molecules (e.g., carbon monoxide). Our 3D model corroborates the
finding by \citet{carlsson94} that the chromospheric temperature rise
of semi-empirical models does not necessarily imply an increase in
the average gas temperature but can be explained by the presence of
substantial spatial and temporal temperature inhomogeneities.
Title: Abundance analysis of late B stars. Evidence for diffusion
and against weak stellar winds
Authors: Hempel, M.; Holweger, H.
Bibcode: 2003A&A...408.1065H
Altcode:
Based on high S/N spectra obtained at La Silla, Chile, and the Special
Astrophysical Observatory, Russia, the abundances of He, C, O, Ne, Mg,
Si, Ca, Fe, Sr, and Ba in 27 optically bright B5-B9 main-sequence
stars were determined. NLTE effects were taken into account. A
variety of abundance patterns is present in late B stars. Accurate
surface abundances of the diffusion indicators O, Mg, Ca, Sr and
Ba suggest that element stratification due to diffusion is common
in the program stars. Models of stellar atmospheres which include
meridional mixing can explain the observed anomalies. Although the
program stars represent only a volume-limited sample of the solar
neighbourhood this result is important for the cosmochemical evolution
of the Galaxy: the surface abundances of the stars investigated do
not necessarily reflect the chemical composition of the interstellar
cloud they originated from. Furthermore, five program stars show narrow
absorption lines in Ca II K which can be attributed to circumstellar
gas. Neon serves as a trace element for the occurrence of weak stellar
winds. Neon overabundances of some stars derived under the assumption
of LTE suggest that such winds have been detected. In sharp contrast,
the more realistic treatment of NLTE leads to solar neon abundances and
thus reveals that weak stellar winds are absent in the program stars. Based on observations collected at the European Southern Observatory,
La Silla, Chile and at the Special Astrophysical Observatory, Nizhnij
Arkhyz, Russia.
Title: Modelling the Chromospheric Background Pattern of the
Non-magnetic Sun
Authors: Wedemeyer, Sven; Freytag, Bernd; Steffen, Matthias; Ludwig,
Hans-Günter; Holweger, Hartmut
Bibcode: 2003ANS...324R..66W
Altcode: 2003ANS...324..I07W
No abstract at ADS
Title: Acoustic Waves in the Solar Chromosphere - Numerical
Simulations with COBOLD
Authors: Wedemeyer, S.; Freytag, B.; Steffen, M.; Ludwig, H. -G.;
Holweger, H.
Bibcode: 2003IAUS..210P..C1W
Altcode:
No abstract at ADS
Title: 3-D hydrodynamic simulations of the solar chromosphere
Authors: Wedemeyer, S.; Freytag, B.; Steffen, M.; Ludwig, H. -G.;
Holweger, H.
Bibcode: 2003AN....324..410W
Altcode:
We present first results of three-dimensional numerical simulations
of the non-magnetic solar chromosphere, computed with the radiation
hydrodynamics code CO5BOLD. Acoustic waves which are
excited at the top of the convection zone propagate upwards into the
chromosphere where the waves steepen into shocks. The interaction of
the waves leads to the formation of complex structures which evolve
on short time scales. Consequently, the model chromosphere is highly
dynamical, inhomogeneous, and thermally bifurcated.
Title: NLTE Model-Atmosphere Analysis of B Stars
Authors: Hempel, M.; Holweger, H.
Bibcode: 2003IAUS..210P.E37H
Altcode:
No abstract at ADS
Title: Granulation Abundance Corrections from Hydrodynamical
Convection Simulations
Authors: Steffen, M.; Holweger, H.
Bibcode: 2003IAUS..210P.D15S
Altcode:
No abstract at ADS
Title: Do dusty A stars exhibit accretion signatures in their
photospheres?
Authors: Kamp, I.; Hempel, M.; Holweger, H.
Bibcode: 2002A&A...388..978K
Altcode: 2002astro.ph..4449K
We determined abundances of O, Ca, Fe, Ba and Y for a sample
of dusty and dust-free A stars, taken from the list of Cheng et
al. (\cite{Cheng92}). Five of the stars have an infrared-excess due
to circumstellar dust. Ongoing accretion from their circumstellar
surroundings might have modified the abundances in the photospheres
of these stars, but our results clearly show, that there is no
difference in the photospheric composition of the dusty and dust-free
stars. Instead all of them show the typical diffusion pattern which
diminishes towards larger rotational velocities.
Title: Line formation in convective stellar
atmospheres. I. Granulation corrections for solar photospheric
abundances
Authors: Steffen, M.; Holweger, H.
Bibcode: 2002A&A...387..258S
Altcode: 2002astro.ph..3127S
In an effort to estimate the largely unknown effects of photospheric
temperature fluctuations on spectroscopic abundance determinations, we
have studied the problem of LTE line formation in the inhomogeneous
solar photosphere based on detailed 2-dimensional radiation
hydrodynamics simulations of the convective surface layers of the
Sun. By means of a strictly differential 1D/2D comparison of the
emergent equivalent widths, we have derived ``granulation abundance
corrections'' for individual lines, which have to be applied to
standard abundance determinations based on homogeneous 1D model
atmospheres in order to correct for the influence of the photospheric
temperature fluctuations. In general, we find a line strengthening in
the presence of temperature inhomogeneities as a consequence of the
non-linear temperature dependence of the line opacity. The resulting
corrections are negligible for lines with an excitation potential around
Ei=5 eV, regardless of element and ionization stage. Moderate
granulation effects (Deltagran ~ -0.1 dex) are obtained
for weak, high-excitation lines (Ei >~ 10 eV) of C I,
N I, O I as well as Mg II and Si II. The largest corrections are found
for ground state lines (Ei=0 eV) of neutral atoms with an
ionization potential between 6 and 8 eV like Mg I, Ca I, Ti I, Fe I,
amounting to Delta_gran ~ -0.3 dex in the case of Ti I. For many lines
of practical relevance, the magnitude of the abundance correction may
be estimated from interpolation in the tables and graphs provided with
this paper. The application of abundance corrections may often be an
acceptable alternative to a detailed fitting of individual line profiles
based on hydrodynamical simulations. The present study should be helpful
in providing upper bounds for possible errors of spectroscopic abundance
analyses, and for identifying spectral lines which are least sensitive
to the influence of photospheric temperature inhomogeneities.
Title: Photospheric abundances: Problems, updates, implications
Authors: Holweger, H.
Bibcode: 2001AIPC..598...23H
Altcode: 2001sgc..conf...23H; 2001astro.ph..7426H
Current problems encountered in the spectroscopic determination of
photospheric abundances are outlined and exemplified in a reevaluation
of C, N, O, Ne, Mg, Si, and Fe, taking effects of NLTE and granulation
into account. Updated abundances of these elements are given in
Table 2. Specific topics addressed are (1) the correlation between
photospheric matter and CI chondrites, and the condensation temperature
below which it breaks down (Figure 1), (2) the question whether the
metallicity of the Sun is typical for its age and position in the
Galaxy. .
Title: Measuring Solar Abundances
Authors: von Steiger, R.; Vial, J. -C.; Bochsler, P.; Chaussidon, M.;
Cohen, C. M. S.; Fleck, B.; Heber, V. S.; Holweger, H.; Issautier, K.;
Lazarus, A. J.; Ogilvie, K. W.; Paquette, J. A.; Reisenfeld, D. B.;
Teriaca, L.; Wilhelm, K.; Yusainee, S.; Laming, J. M.; Wiens, R. C.
Bibcode: 2001AIPC..598...13V
Altcode: 2001sgc..conf...13V
This is the rapporteur paper of Working Group 2 on Measuring Solar
Abundances. The working group presented and discussed the different
observations and methods for obtaining the elemental and isotopic
composition of the Sun, and critically reviewed their results and
the accuracies thereof. Furthermore, a few important yet unanswered
questions were identified, and the potential of future missions to
provide answers was assessed. .
Title: Acoustic Energy Generated by Convection: 3-D Numerical
Simulations for the Sun
Authors: Wedemeyer, Sven; Freytag, Bernd; Holweger, Hartmut; Ludwig,
Hans-Günter; Steffen, Matthias
Bibcode: 2001AGM....18..P01W
Altcode:
Dissipation of acoustic waves may be an efficient heating mechanism for
the lower and middle chromosphere of the quiet Sun. The basic idea is
that turbulent motions at the top of the solar convection zone generate
acoustic waves which propagate upwards and dissipate in the lower and
middle chromosphere, transporting energy into the higher layers. But
still the question remains if this amount of energy is sufficient to
explain the observed temperature increase without invoking magnetic
fields. With a new version of the COBOLD radiation hydrodynamics code
we are able to compute 3-D models extending all the way from the upper
convection zone to the middle chromosphere. First 3-D simulations reveal
a complex, inhomogenous and highly dynamical structure of the lower and
middle chromosphere which evolves on rather short timescales. On small
spatial dimensions very cool regions are present next to a "network"
of hotter matter. The code is being developed further to provide a
more detailed analysis and comparison with observations.
Title: Radiation Hydrodynamics Simulations of the Solar Chromosphere
Authors: Wedemeyer, Sven; Freytag, Bernd; Steffen, Matthias; Holweger,
Hartmut
Bibcode: 2000AGM....17..P01W
Altcode:
While heating of the solar corona is commonly attributed to
reconnection of magnetic field lines, the mechanism responsible for
heating the chromosphere of the quiet Sun, away from active regions,
is still under debate1,2. The basic question which we will
address in this contribution i s: Can generation of acoustic waves by
turbulent convection in photospheric and subphotospheric layers explain
the chromospheric emission of the quiet Sun? With a new 3D radiation
hydrodynamics code3 we are able to compute models ex tending
from the upper convection zone to the middle chromosphere. The code
can handle shocks with a minimum of numerical dissipation. Therefore
generation and propagation of acoustic waves can be investigated,
permitting the evaluation of wave dissipation in the chromosphere in
a physically consistent manner. We present first results and discuss
the principal problems and future prospects.
Title: Neon as a Tracer for the Detection of Weak Stellar Winds:
NLTE Abundance Corrections for B Stars
Authors: Graf, Jörg; Hempel, Marc; Holweger, Hartmut
Bibcode: 2000AGM....17..P28G
Altcode:
Weak stellar winds in B stars can influence the chemical composition
of the stellar atmosphere. In the temperature range of late B stars
theoretical models predict neon to be a tracer for the detection of
these stellar winds. Therefore detailed NLTE abundance calculations
are necessary. The modelling of neon became more reliable since the
Opacity Project provided new atomic data, though only a few spectral
lines exist, which can be used for reliable abundance determinations. We
present a Ne I/II model atom and show the results of a parameter study
for the range of B stars. Our calculations show that NLTE corrections
are indispensable for the search of weak stellar winds. This is
strengthened by the results obtained for several B stars (see poster
by Hempel et al.), the model atom also was used for.
Title: Non-LTE Abundance Analysis of Late B Stars
Authors: Hempel, Marc; Graf, Jörg; Holweger, Hartmut; Belyakkova,
Elena V.; Galazutdinov, Gazinur A.; Musaev, Faig A.
Bibcode: 2000AGM....17..P27H
Altcode:
Due to their shallow surface convection zones, the composition of
main-sequence A and B stars responds sensitively to any 'contamination'
by processes of diffusion or accretion. Accurate surface abundances
and a sensitive search for circumstellar lines perm its to trace
the photospheric signatures of accretion differentially and at high
sensitivity. Extending our previous work on A stars (see references)
to higher temperatures we have determined abundances of He, C, O,
Ne, Mg, Si, Ca, Fe, Sr and Ba in 27 B5-B9 stars. Non-LTE corrections
were taken into account. Our program stars occupy the interesting
temperature regime where the transition between diffusion dominated
atmospheres of A stars and massive radiative-driven winds of OB stars
occurs. Therefore they provide an excellent tool to investigate
the theoretically predicted onset of weak stellar winds producing
mild overabundances of certain elements (Landstreet et al. 1998). In
terms of diffusion and weak stellar winds we discuss results based on
high S/N spectra obtained at La Silla, Chile and Terskol Observatory,
Russia. References: Holweger H., Rentzsch-Holm I., 1995, A&A 303,
819 Holweger H., Hempel M., Kamp I., 1999, A&A 350, 603 Landstreet
J.D., Dolez N., Vauclair S.,1998, A&A 333, 977
Title: A search for circumstellar gas around normal A stars and
Lambda Bootis stars
Authors: Holweger, H.; Hempel, M.; Kamp, I.
Bibcode: 1999A&A...350..603H
Altcode:
We have searched for interstellar or circumstellar absorption lines
in the center of Ca II K towards bright A-type stars that are mostly
within 80 pc of the Sun. Narrow absorption features are found in about
30 % of the 28 normal main-sequence A stars and 18 metal-deficient
lambda Bootis stars studied. We have determined surface gravities and
projected rotational velocities. Most of the stars with detectable Ca K
features have comparatively low gravities and high projected rotational
velocities. This correlation with stellar properties implies that
most of the narrow absorption features are of circumstellar rather
than interstellar origin. The preference of low gravity and rapid
rotation furthermore suggests that most of the gas shells around A
stars develop in the pre-main-sequence phase of evolution, and disappear
largely before the star arrives at the ZAMS. Among the normal A stars
studied, about 50 % are known to have dust disks. Unlike A stars with
circumstellar gas, these dusty stars do not prefer low log g and high v
sin i. This results in an apparent lack of correlation between gas and
dust, and indicates that normal A stars with gas shells and those with
dust disks are not in the same evolutionary stage. We conjecture that
dust disks tend to develop after most of the gas has disappeared. Based
on observations collected at the European Southern Observatory, La
Silla, Chile
Title: The Fe/O elemental abundance ratio in the solar wind
Authors: Aellig, M. R.; Holweger, H.; Bochsler, P.; Wurz, P.;
Grünwaldt, H.; Hefti, S.; Ipavich, F. M.; Klecker, B.
Bibcode: 1999AIPC..471..255A
Altcode: 1999sowi.conf..255A
We analyze the Fe/O elemental abundance ratio in the solar wind from
SOHO/CELIAS/CTOF data. Analyzed in different solar wind regimes this
ratio is indicative of the strength of the FIP fractionation process
because iron is a low FIP element and oxygen is a high FIP element. It
is investigated whether there is a significant fractionation of the
Fe/O ratio in the coronal hole solar wind. For the first time, to our
knowledge, we attempt to eliminate the influence of model-dependent
parameters on the derivation of the photospheric Fe/O ratio thereby
increasing the accuracy of its determination. The Fe/O ratio in coronal
hole solar wind is slightly higher than in the photosphere. Even with
our optimistic estimates of the uncertainties of the photospheric Fe/O
ratio the observed fractionation is only marginally significant.
Title: Selected Fe II lifetimes and f-values suitable for a solar
abundance study
Authors: Schnabel, R.; Kock, M.; Holweger, H.
Bibcode: 1999A&A...342..610S
Altcode:
A selected number of Fe II level lifetimes have been measured anew
with an improved experimental equipment and evaluation procedure
yielding data with uncertainties around 1%. The lifetimes have been
used to rescale the corresponding oscillator strengths and to derive
solar abundances. On average, the iron abundance, log N(Fe) = 7.42 +/-
0.09 on the scale log N(H) = 12, is further reduced supporting the
lower abundance results in the literature.
Title: Thermal structure of circumstellar discs around A stars
Authors: Kamp, I.; Holweger, H.
Bibcode: 1999AGAb...15...17K
Altcode: 1999AGM....15..B05K
IRAS and ISO observations revealed that a large number of A stars is
surrounded by dust discs. At least for a subgroup, the lambda Bootis
stars, there is growing evidence that these are pre-main-sequence stars
surrounded by gas and dust discs (Holweger & Rentzsch-Holm 1995;
Holweger, Hempel & Kamp 1999). In order to understand the physical
and chemical processes in such circumstellar discs, we developed
thin hydrostatic equilibrium models which contain a sophisticated
chemical network and account for the detailed photospheric flux of
the central star (Kamp & Bertoldi 1999). In a first approximation
we assumed that gas and dust have the same temperature due to strong
collisional coupling, and that the temperature is determined by the
radiative equilibrium of the dust. Now we present disc models where the
chemical equilibrium is solved subject to the energy balance of gas
and dust. We take into account a large number of heating and cooling
processes in detail, like for example heating by photodissociation or
formation of H_2 or cooling by C and O fine structure lines. We find
that frictional heating by dust grains may be the dominant heating
source depending on the drift velocity of dust grains and hence the
efficiency of radiation pressure. In the absence of a large grain
drift velocity gas-dust collisions determine the gas temperature for
densities larger than 10^6 cm^{-3}.
Title: Silicon as a cosmic reference element: a reassessment of the
solar SI abundance
Authors: Wedemeyer, Sven; Holweger, Hartmut; Steffen, Matthias
Bibcode: 1999AGAb...15..113V
Altcode: 1999AGM....15..P53V; 1999AGM....15..P54W
Silicon is an important reference elements for comparing various
types of cosmic matter with the Sun. The most widely used sources
of solar (photospheric) abundances, the compilation by Anders &
Grevesse (1989) and its updates (e.g. Grevesse & Sauval 1998), are
based on standard abundance analyses employing 1D solar models and,
in most cases, assuming LTE. We report NLTE calculations for Si and
a first attempt to determine the effect of horizontal temperature
inhomogeneities associated with convection on the photospheric
abundance of Si. We combine the result with that obtained previously
for O and Fe (Aellig et al. 1999; Schnabel et al. 1999) and compare
the photospheric Si/Fe, Si/O and Si/H abundance ratios with literature
data for meteorites, the corona and solar wind, energetic particles and
galactic B stars and H ii regions. References: Aellig M.R., Holweger H.,
Bochsler P., et al., 1999, Solar Wind Nine, AIP Conf. Proc. Vol. 471,
255 Anders E., Grevesse N., 1989, Geochim. Comochim. Acta 53, 197
Grevesse N., Sauval A.J., 1998, Space Sci. Rev. 85, 161 Schnabel R.,
Kock M., Holweger H., 1999, A&A 342, 610
Title: Line Formation in Convective Stellar Atmospheres
Authors: Steffen, Matthias; Holweger, Hartmut
Bibcode: 1999AGb....15..107S
Altcode: 1999AGM....15..P40S
Convection affects the temperature structure of a stellar atmosphere
in a twofold way: it influences the mean vertical stratification and
introduces horizontal inhomogeneities. This poses several questions: (i)
What is the ``right'' alpha_MLT to produce the correct mean temperature
stratification in the framework of mixing-length theory ? (ii) What
errors are introduced, in the context of spectroscopic abundance
determinations, by representing the horizontally averaged spectrum
of an inhomogeneous atmosphere by the spectrum of a plane-parallel
mean stratification? (iii) Is there something like a spectroscopically
equivalent mean stratification of an inhomogeneous atmosphere? In order
to address these questions, we have computed synthetic line profiles for
a sample of fictitious spectral lines of different chemical elements,
based on both mixing-length atmospheres and 2D hydrodynamical solar
granulation models. Through a differential comparison of the equivalent
widths computed from the inhomogeneous atmospheres and different 1D
mean models, respectively, we derive correction factors to be applied
to standard 1D spectroscopic abundance determinations in order to
correct for the effects of stellar `granulation'. We find that the
abundance correction depends sensitively on the ionization stage of
the chemical element and on the excitation potential of the spectral
line considered. In some cases the `granulation correction' can amount
to -0.2 dex.
Title: Abundance analysis of late B stars
Authors: Hempel, Marc; Holweger, Hartmut; Galazutdinov, Gazinur A.;
Musaev, Faig A.; Kaufer, Andreas
Bibcode: 1999AGAb...15..106H
Altcode: 1999AGM....15..P39H
Due to their shallow surface convection zones, the composition of
main-sequence A and B stars responds sensitively to any 'contamination'
by processes of diffusion or accretion. Accurate surface abundances
and a sensitive search for circumstellar lines perm its to trace
the photospheric signatures of accretion differentially and at high
sensitivity. Extending our previous work on A stars (see references)
to higher temperatures we have determined LTE abundances of He,
C, O, Ne, Mg, Si, Ca, Fe, Sr and Ba in 27 B5-B9 stars. Our program
stars occupy the interesting temperature regime where the transition
between diffusion dominated atmospheres of A stars and massive
radiative-driven winds of OB stars occurs. Therefore they provide
an excellent tool to investigate the theoretically predicted onset
of weak stellar winds producing mild overabundances of certain
elements (Landstreet et al. 1998). We present results based on high
S/N spectra obtained at La Silla, Chile and Terskol Observatory,
Russia (http://www.sao.ru). Non-LTE analysis is currently under
way. References: Holweger H., Rentzsch-Holm I., 1995, A&A 303, 819
Holweger H., Hempel M., Kamp I., 1999, A&A (submitted) Landstreet
J.D., Dolez N., Vauclair S., 1998, A&A 333, 977
Title: Lithium Depletion in the Sun: A Study of Mixing Based on
Hydrodynamical Simulations
Authors: Blöcker, T.; Holweger, H.; Freytag, B.; Herwig, F.; Ludwig,
H. -G.; Steffen, M.
Bibcode: 1998SSRv...85..105B
Altcode: 1998astro.ph..6310B
Based on radiation hydrodynamics modeling of stellar convection zones,
a diffusion scheme has been devised describing the downward penetration
of convective motions beyond the Schwarzschild boundary (overshoot)
into the radiative interior. This scheme of exponential diffusive
overshoot has already been successfully applied to AGB stars. Here
we present an application to the Sun in order to determine the time
scale and depth extent of this additional mixing, i.e. diffusive
overshoot at the base of the convective envelope. We calculated the
associated destruction of lithium during the evolution towards and on
the main-sequence. We found that the slow-mixing processes induced by
the diffusive overshoot may lead to a substantial depletion of lithium
during the Sun's main-sequence evolution.
Title: Dusty and dust-free A stars
Authors: Hempel, M.; Holweger, H.; Kamp, I.
Bibcode: 1998CoSka..27..246H
Altcode: 1998astro.ph..5073H
We present preliminary results of our search for circumstellar
absorption features in the Ca K lines based on high S/N observations
obtained with the ESO CAT/CES system.
Title: Dust and gas around lambda Bootis stars
Authors: Kamp, I.; Holweger, H.
Bibcode: 1998CoSka..27..408K
Altcode: 1998astro.ph..5053K
High-resolution spectra of lambda Bootis stars reveal the presence
of circumstellar gas for example in the Ca K line. The example of the
normal A star beta Pictoris shows, that the narrow stable absorption
component in Ca K can be reproduced using appropriate disk models
and a calcium underabundance in the circumstellar gas of a factor of
appr. 30. Similar models are suggested for the group of metal-deficient
lambda Bootis stars, but the observational material is still very poor.
Title: Lithium Depletion in the Sun: A Study of Mixing Based on
Hydrodynamical Simulations
Authors: Blöcker, T.; Holweger, H.; Freytag, B.; Herwig, F.; Ludwig,
H. -G.; Steffen, M.
Bibcode: 1998sce..conf..105B
Altcode:
No abstract at ADS
Title: Toward solving the `CO-Problem': chemistry in the disks around
VEGA and beta Pictoris
Authors: Rentzsch-Holm, I.; Holweger, H.; Bertoldi, F.
Bibcode: 1998ASPC..132..275R
Altcode: 1998sfis.conf..275R
Detailed modeling of the chemistry in the disks around Vega-like stars
reveals that photodissociation is indeed capable of destroying CO
molecules in the circumstellar environment. The amount of dissociation
strongly depends on the disk mass, on the dust extinction properties,
and on the effective temperature of the star. The non-detection of CO
therefore does not necessarily imply a general gas depletion.
Title: Dusty and dust-free A stars
Authors: Hempel, Marc; Holweger, Hartmut
Bibcode: 1998AGAb...14R.124H
Altcode: 1998AGM....14..P51H
Main-sequence A stars have shallow convection zones, therefore their
composition responds sensitively to any 'contamination' by processes
of diffusion or accretion. For example, the metal deficiency of
the \lambda Bootis stars indicates accretion of depleted gas after
separation of gas and dust in the stellar environment. Yet not all A
stars with circumstellar (CS) matter show chemical anomalies indicative
of accretion. A prominent example is \beta Pictoris. However, in most
cases nothing is known about their composition and the presence of
CS gas. Accurate surface abundances of A stars that are positive or
negative IRAS detections and a sensitive search for CS lines permits
to trace the signature of accretion differentially and at high
sensitivity. Results of our model-atmosphere analysis are presented
(see also Holweger H., Rentzsch-Holm I.,\ 1995,\ A&A\ 303,\ 819).
Title: Circumstellar discs around A stars
Authors: Kamp, I.; Holweger, H.; Bertoldi, I.
Bibcode: 1998AGAb...14...20K
Altcode: 1998AGM....14..B23K
Since the IRAS mission it is known that a couple of nearby young stars
are surrounded by dust disks (Aumann 1995); two prominent examples
are Vega and \beta Pictoris. CO radio observations of these stars,
carried out to trace the gas component of these disks, revealed a
strong depletion of CO (Dent et al. 1995). This has been interpreted
as a general gas depletion, and models for the formation of gas-giant
planets have been called in question. Detailed disc models concentrating
on the discs' gas component show that CO has been selectively depleted
in the dusty and gaseous discs by photodissociation and freezing out
of CO on the cold dust grain surfaces (Rentzsch-Holm, Holweger &
Bertoldi (1998), Kamp & Bertoldi 1998). We will now compare our
models with the observation to fix the remaining free parameters. The
disc mass, the main free parameter, can be inferred from modeling
the infrared excess using dust models with various grain sizes and
chemical composition. References: Aumann, H.H. 1985. PASP 97, 885 Dent,
W.R.F., et al. 1995. MNRAS 277, L25 Rentzsch-Holm, I., Holweger, H.,
Bertoldi, F. 1998. ASP Conference Series 132, 275 Kamp, I., Bertoldi,
F. 1998. in preparation
Title: "Discovery" of a β Pictoris-like circumstellar disk in
the Internet.
Authors: Hempel, M.; Holweger, H.; Rentzsch-Holm, I.; Freytag, B.
Bibcode: 1997AGAb...13..201H
Altcode:
No abstract at ADS
Title: The surface composition of Beta Pictoris.
Authors: Holweger, H.; Hempel, M.; van Thiel, T.; Kaufer, A.
Bibcode: 1997A&A...320L..49H
Altcode:
We present an element-by-element analysis of the surface composition of
β Pic (A5V) based on high-resolution broad-band optical spectra. The
abundances (relative to H) of C, Ca, Ti, Cr, Fe, Sr, and Ba are
solar. Obviously β Pic does not show the "λ-Boo phenomenon" - the
metal deficiency of certain cool A-type stars attributed to accreting
circumstellar matter.
Title: Chemistry in the disks around young A stars.
Authors: Rentzsch-Holm, I.; Holweger, H.; Bertoldi, F.
Bibcode: 1997AGAb...13...22R
Altcode:
No abstract at ADS
Title: On the Scale of Photospheric Convection
Authors: Freytag, B.; Holweger, H.; Steffen, M.; Ludwig, H. -G.
Bibcode: 1997svlt.work..316F
Altcode:
No abstract at ADS
Title: The surface composition of β Pictoris.
Authors: Hempel, M.; Holweger, H.; van Thiel, T.; Kaufer, A.
Bibcode: 1996AGAb...12..185H
Altcode:
No abstract at ADS
Title: CO around young stars with dust disks: Vega and β Pictoris.
Authors: Rentzsch-Holm, I.; Holweger, H.; Bertoldi, F.
Bibcode: 1996AGAb...12...25R
Altcode:
No abstract at ADS
Title: Solar element abundances, non-LTE line formation in cool
stars and atomic data.
Authors: Holweger, H.
Bibcode: 1996PhST...65..151H
Altcode:
The composition of solar and meteoritic matter serves as a primary
reference for cosmochemical studies. Element abundances in the Sun -
and in cool stars in general - are usually determined by spectroscopy
of a stellar atmosphere whose properties differ from most laboratory
sources: (1) there are strong gradients of temperature and pressure,
(2) the main constituents are neutral hydrogen and helium, while the
fractional abundance of electrons is only ≍10-4, (3) the
plasma is immersed in an intense, anisotropic radiation field, and is
highly turbulent. The present contribution discusses meteoritic and
solar abundances and their suitability as cosmic reference data. Also
addressed are mayor diagnostic problems encountered in the analysis
of the photospheric line spectrum of cool stars - in particular line
broadening and deviations from LTE in neutral iron. This paper is an
update of a review, given at the 1987 Meudon symposium on high-S/N
stellar spectroscopy.
Title: Lambda Bootis Stars and 'Dusty' A Stars
Authors: Holweger, H.; Rentzsch-Holm, I.
Bibcode: 1996rdfs.conf..179H
Altcode:
No abstract at ADS
Title: High-resolution spectroscopy of λ Bootis stars and `dusty'
normal A stars: circumstellar gas, rotation, and accretion.
Authors: Holweger, H.; Rentzsch-Holm, I.
Bibcode: 1995A&A...303..819H
Altcode:
We present results of a high-S/N search for circumstellar Ca K lines
in two classes of A stars: (i) metal-deficient stars of the λBootis
type whose surface anomalies are believed to be due to accretion
of depleted gas, and (ii) stars known to possess circumstellar dust
disks, including Vega and βPictoris. We derive T_eff_ and logg and
combine model-atmosphere analysis with spectrum synthesis to determine
projected rotational velocities, calcium abundances, and the motion of
circumstellar gas with respect to the star. Narrow components in Ca K
are present in five of the eleven λBoo stars studied. This exceptional
high incidence suggests that the λBoo phenomenon is related to the
presence of circumstellar gas. Specific topics discussed (Sect. 6)
include: (1) a connection between rotation, the presence of detectable
amounts of CS gas, and metal deficiency, (2) Vega and βPic as suspected
λBoo stars, (3) λBoo stars as probable pre-main-sequence objects, and
(4) episodes of massive accretion in βPic and in the λBoo star HR4881.
Title: On the determination of the solar iron abundance using Fe I
lines. Comments on a paper by D.E. Blackwell et al. and presentation
of new results for weak lines.
Authors: Holweger, H.; Kock, M.; Bard, A.
Bibcode: 1995A&A...296..233H
Altcode:
We examine the critical remarks by Blackwell, Lynas-Gray &
Smith (1995; A&A, this issue). Points discussed in detail include
equivalent widths, oscillator strengths, microturbulence, damping, and
models of the solar photosphere. In addition, we present new results
based on the Fe i oscillator strengths of Bard & Kock (1994). The
sample of weak solar lines, which are the most reliable abundance
indicators, is greatly increased. The result is fully consistent with
our earlier determinations based on lines of Fe i and Fe ii.
Title: Abundance Patterns in Unevolved A Stars and in Blue Stragglers
Authors: Holweger, H.; Lemke, M.; Rentzsch-Holm, I.; Stürenburg, S.
Bibcode: 1995AIPC..327...41H
Altcode: 1995nct3.conf...41H
On the basis of high-resolution spectrometry and NLTE analysis
we investigate abundance patterns of non-nuclear origin in normal
main-sequence A stars and in their metal-deficient counterparts, the
Lambda Bootis stars. We try to identify and separate the effects of
diffusion (gravitational settling, radiative levitation) and accretion
(separation of gas and dust) on the surface composition. Two blue
stragglers in the old open cluster M67 are compared with the normal
A stars in an attempt to trace the signature of anomalous stellar
evolution.
Title: Institut für Astronomie und Astrophysik. Jahresbericht
für 1994.
Authors: Holweger, H.
Bibcode: 1995MitAG..78..411H
Altcode:
No abstract at ADS
Title: Identification of the 1600A feature in Lambda Bootis stars
Authors: Holweger, H.; Koester, D.; Allard, N. F.
Bibcode: 1994A&A...290L..21H
Altcode:
The nature of the absoprtion feature near 1600A in λ Bootis stars,
which is one of the strongest features in these objects, is a
longstanding puzzle. In this study we demonstrate that it is caused
by quasimolecular absorption leading to a satellite in the Lyman α
profile due to perturbations by neutral hydrogen. This feature has also
been observed in the hydrogen-rich DA white dwarfs. The satellite is not
observable in normal A stars because of the extremely strong distortion
of the UV flux by metal lines, especially of C, Si, and Fe. Although
the C abundance seems to be close to solar in λ Bootis stars, the Si,
Fe, and other metal abundances are sufficiently reduced to make the
feature visible. For the same reason the feature is conspicuous in
metal-deficient horizontal branch stars of spectral type A.
Title: Shocks in the solar photosphere and their spectroscopic
signature
Authors: Steffen, M.; Freytag, B.; Holweger, H.
Bibcode: 1994smf..conf..298S
Altcode:
No abstract at ADS
Title: Analysis of the DA white dwarf HZ 43A and its companion star.
Authors: Napiwotzki, R.; Barstow, M. A.; Fleming, T.; Holweger, H.;
Jordan, S.; Werner, K.
Bibcode: 1993A&A...278..478N
Altcode:
The DA white dwarf HZ 43 A (WD 1314+293) is analyzed based on a newly
obtained optical spectrogram. We demonstrate that the derived parameters
Teff = 49.000 K and log g = 7.7 are in agreement with the
observed Ly-alpha line, the slope of the UV continuum, and the measured
trigonometric parallax. The EXOSAT spectrograms of Paerels et al. (1986)
are used to obtain upper limits for the atmospheric abundance of helium,
carbon, nitrogen, and oxygen of HZ 43 A by applying the new parameters
and up-to-date Non Local Thermodynamic Equilibrium (NLTE) model
atmospheres. The result is discussed within the framework of diffusion
calculations. It turns out that the resulting abundances of the CNO
elements are below the predictions of theory making HZ 43 A an unique
object. A red/near-infrared spectrum of the companion star HZ 43 B is
used to reclassify it and to estimate temperature and metallicity. We
calculate EUV fluxes from models with the derived stellar parameters
and use them to check the flux calibrations of EXOSAT and ROSAT. The
agreement between predicted and measured count rates is reasonable
for the ROSAT-Wide Field Camera (WFC) filters. Most EXOSAT photometric
filters exhibit deviations. These are marginally consistent with our
error limits for the LX 3000, LX 4000, and the PPL filters. The Al/P
calibration is in error. Discrepant results are obtained for the EXOSAT
spectrograph and the ROSAT Position Sensitive Proportional Counter
(PSPC). These inconsistencies may cause systematic errors, if for
instance PSPC measurements are combined with WFC data for an analysis.
Title: VizieR Online Data Catalog: Equivalent Widths in Pollux
(Ruland+ 1980)
Authors: Ruland, F.; Griffin, R.; Griffin, R.; Biehl, D.; Holweger, H.
Bibcode: 1993yCat..40420391R
Altcode:
Not Available (2 data files).
Title: Carbon and Silicon in Normal A-Stars and in Lambda-Bootis Stars
Authors: Holweger, H.; Sturenburg, S.
Bibcode: 1993ASPC...44..356H
Altcode: 1993IAUCo.138..356H; 1993pvnp.conf..356H
No abstract at ADS
Title: Abundance patterns in a stars: Carbon and silicon
Authors: Holweger, Hartmut
Bibcode: 1992LNP...401...48H
Altcode: 1992aets.conf...48H
It is shown that the seemingly erratic abundance variation of carbon
among normal A stars is in fact a tight anticorrelation with silicon
and other elements that may be explained by gas-dust separation in
the protostellar or circumstellar environment.
Title: Statistical equilibrium of Al I/II in a stars and the abundance
of aluminium in Vega
Authors: Steenbock, W.; Holweger, H.
Bibcode: 1992LNP...401...57S
Altcode: 1992aets.conf...57S
No abstract at ADS
Title: High-resolution spectrometry of lambda Bootis stars : selected
diagnosticlines and possible detection of a beta Pic-type shell star.
Authors: Holweger, H.; Stuerenburg, S.
Bibcode: 1991A&A...252..255H
Altcode:
CCD observations of diagnostic features in the optical spectra of eight
southern Lambda Boo stars and one normal A star are presented. The
general weakness of MgII 4481A is confirmed, yet a wide range in
strength and magnesium abundance exists. Narrow interstellar or
circumstellar absorption components of NaI 5890 + 5896A are detected in
three stars; in HR 4881 they exceed in strength those of the shell star
Beta Pictoris and are probably of circumstellar origin. HR 4881 also
exhibits a conspicuous absorption feature in CaII 3933A, resembling
Beta Pic in appearance.
Title: A redetermination of the solar iron abundance based on new
Fe I oscillator strengths
Authors: Holweger, H.; Bard, A.; Kock, M.; Kock, A.
Bibcode: 1991A&A...249..545H
Altcode:
The solar abundance of iron is derived from photospheric Fe I lines
whose f-values have been determined recently in a hollow-cathode
experiment in combination with accurate lifetime measurements. Taking
into account a small (+0.03 dex) abundance correction for photospheric
non-LTE effects, a solar iron abundance of log N(Fe) = 7.50 +/-0.07 on
the scale log N(H) = 12 is inferred. This result is in close agreement
with that derived earlier from lines of ionized iron whose f-values
have been obtained by the same technique, but it is 0.17 dex smaller
than the currently accepted standard value based on absorption furnace
f-values. The new result strengthens the evidence that the solar Fe/Si
ratio agrees with the meteoritic value found in C1 chondrites.
Title: Erratum - Statistical Equilibrium and Photospheric Abundance
of Carbon in the Sun and in VEGA
Authors: Sturenburg, S.; Holweger, H.
Bibcode: 1991A&A...246..644S
Altcode:
No abstract at ADS
Title: Generation of Acoustic Flux Derived from Numerical Simulations
of the Solar Granular Convection (With 3 Figures)
Authors: Steffen, M.; Krüss, A.; Holweger, H.
Bibcode: 1991mcch.conf..380S
Altcode:
No abstract at ADS
Title: Statistical equilibrium and photospheric abundance of carbon
in the the sun and Vega.
Authors: Stuerenburg, S.; Holweger, H.
Bibcode: 1990A&A...237..125S
Altcode:
The statistical equilibrium of carbon is investigated for the atmosphere
of the sun and for the prototype A star Vega using a model atom with
88 levels and 66 line transitions of C I and C II. A quantitative
assessment is made of the magnitude of non-LTE effects in photospheric
abundance determinations for the sun and for Vega. In the sun, non-LTE
abundance corrections are typically -0.05 dex, so that the solar
carbon abundance becomes log N(C) = 8.58 + or - 0.13 on the scale
log N(H) = 12, implying that even the most primitive meteorites,
the C1 chondrites, are deficient in carbon by a factor of 10. The
photospheric abundance of carbon in Vega is log N(C) = 8.34 + or -
0.13, implying a marginal underabundance with respect to the sun. It
is concluded that detailed non-LTE calculations are required for the
accurate analysis of photospheric C I lines in main sequence stars of
intermediate and late spectral type.
Title: The abundance of iron in the Sun derived from photospheric
Fe II lines.
Authors: Holweger, H.; Heise, C.; Kock, M.
Bibcode: 1990A&A...232..510H
Altcode:
The solar abundance of iron is determined from photospheric Fe II
lines whose f-values have been measured recently in a hollow-cathode
experiment. In contrast to lines of Fe I these lines are perfectly in
LTE in the sun, and the derived abundance is insensitive to imperfect
modeling of the solar photosphere. The resulting iron abundance, log N
(Fe) = 7.48 + or - 0.09 on the scale log N (H) = 12, is significantly
lower than the currently accepted value based on lines of Fe I. The
solar Fe/Si abundance ratio agrees with the meteoritic value found in
C1 chrondrites. The resulting solar Fe I/Fe II abundance discrepancy
is discussed.
Title: Generation of acoustic flux by turbulent convection.
Authors: Holweger, H.; Krüß, A.; Steffen, M.
Bibcode: 1990AGAb....5...72H
Altcode:
No abstract at ADS
Title: Results from 2-D Numerical Simulations of Solar Granules
Authors: Steffen, M.; Gigas, D.; Holweger, H.; Krüss, A.; Ludwig,
H. -G.
Bibcode: 1990IAUS..138..213S
Altcode:
No abstract at ADS
Title: Statistical equilibrium and photospheric abundance of carbon
in the Sun and in Vega.
Authors: Stürenburg, S.; Holweger, H.
Bibcode: 1990AGAb....5...15S
Altcode:
No abstract at ADS
Title: An abundance analysis of the Hyades giant gamma Tauri :
an exercise in caution.
Authors: Griffin, R. E. M.; Holweger, H.
Bibcode: 1989A&A...214..249G
Altcode:
A model-atmosphere analysis is used to derive chemical abundances
in the Hyades giant Gamma Tau relative to the standard K0 giant Beta
Gem. An appraisal of the various factors which can influence this type
of investigation leads to the disappointing conclusion that the many
uncertainties are probably at least as great as the reported enrichment
of elements in the Hyades dwarfs; the smallest uncertainty appears
to be associated with the analysis of Fe I lines, which indicate an
enhancement of Fe in Gamma Tau, relative to Beta Gem, of 0.04 dex, or
(with greater uncertainty) a deficiency of 0.06 dex relative to the sun.
Title: Spatially Resolved Spectra of Solar Granules
Authors: Holweger, H.; Kneer, F.
Bibcode: 1989ASIC..263..173H
Altcode: 1989ssg..conf..173H
No abstract at ADS
Title: Results from 2-D Numerical Simulations of the Solar Granulation
Authors: Steffen, M.; Gigas, D.; Holweger, H.; Krüß, A.; Ludwig,
H. -G.
Bibcode: 1989AGAb....3...12S
Altcode:
No abstract at ADS
Title: COSTEP: A comprehensive suprathermal and energetic particle
analyzer for SOHO
Authors: Kunow, Horst; Fischer, Harald; Green, Guenter; Mueller-Mellin,
Reinhold; Wibberenz, Gerd; Holweger, Hartmut; Evenson, Paul; Meyer,
Jean-Paul; Hasebe, Nabuyuki; von Rosenvinge, Tycho
Bibcode: 1988sohi.rept...75K
Altcode:
The group of instruments involved in the COSTEP (comprehensive
suprathermal and energetic particle analyzer) project are
described. Three sensors, the LION (low energy ion and electron)
instrument, the MEICA (medium energy ion composition analyzer) and
the EPHIN (electron proton helium instrument) are described. They are
designed to analyze particle emissions from the sun over a wide range
of species (electrons through iron) and energies (60 KeV/particle to
500 MeV/nucleon). The data collected is used in studying solar and
space plasma physics.
Title: Accurate Spectroscopy of Intermediate and Late Spectral Types
Authors: Holweger, H.
Bibcode: 1988IAUS..132..411H
Altcode:
Elemental abundances in the Sun and in meteorites are examined
with respect to their qualifications as a standard of population I
composition. Some problems that arise in connection with spectroscopic
determinations of abundances in the Sun, and in other late-type stars,
are discussed with emphasis on photospheric models and departures
from LTE.
Title: CN Bandhead and the Measurement of Magnetic Fields
Authors: Livingston, W.; Huang, Y. -R.; Holweger, H.
Bibcode: 1987BAAS...19..940L
Altcode:
No abstract at ADS
Title: A non-LTE study of the solar emission lines near 12 microns
Authors: Lemke, M.; Holweger, H.
Bibcode: 1987A&A...173..375L
Altcode:
The formation of the peculiar FIR emission lines in the solar spectrum,
identified by Chang and Noyes (1983) as transitions between highly
excited states of Mg I and Al I, is investigated. The statistical
equilibrium of Mg I and the influence of various input data on the
line profile are studied. An emission core is not easily generated. The
chromospheric contribution to these rather faint lines turns out to be
negligible unless it is assumed ad hoc that the line source function
exceeds the non-LTE prediction by a large factor. An alternative
requiring less severe assumptions is pointed out. In this scheme
the emission is purely photospheric. Disk-center and limb profiles
of Mg I (818.058/cm) can be reproduced by postulating that a slight
overexcitation prevails in the upper photosphere, with log tau(5000)
= about -2, in the sense that the population ratio of upper to lower
level exceeds the LTE value by a few percent.
Title: Simulation solarer Konvektionszellen
Authors: Krüss, A.; Holweger, H.; Steffen, M.
Bibcode: 1987MitAG..70..325K
Altcode:
No abstract at ADS
Title: Atmospheric Structure and the Activity Cycle
Authors: Holweger, H.
Bibcode: 1987rfsm.conf....1H
Altcode:
Contents: Granulation: quiet photospheres - active regions; granulation
and the activity cycle; size distribution of granules. Ephemeral active
regions. X-ray bright points. Network bright points. Full-disk total
magnetic flux. Full-disk photospheric spectrum.
Title: Compositional differences among "normal" A stars inferred
from high-resolution spectroscopy.
Authors: Holweger, H.; Steffen, M.; Gigas, D.
Bibcode: 1986A&A...163..333H
Altcode:
A previous study of sharp-lined B 9.5-A 2 V stars classified as normal
to ten additional objects, including Sirius (A 1 Vm) is extended. The
occurrence of significant star-to-star abundance variations is
confirmed. Elements studied are He, C, Mg, Ti, Fe, and Ba. Variations
of the iron group and of magnesium or barium are generally correlated,
but carbon varies independently. Anomalously strong He I lines are found
in HR 3963 (A 0 V), which may be an intermediate helium star. Another
star (HR 4138) with very sharp lines has been found.
Title: High-resolution spectra of "normal" A stars : evidence for
compositional differences.
Authors: Holweger, H.; Gigas, D.; Steffen, M.
Bibcode: 1986A&A...155...58H
Altcode:
High-resolution Reticon spectra of seven reputedly normal B9.5 - A2
V stars with v sin i < 50 km s-1 were recorded using
the ESO Coudé Echelle Spectrometer. A selection of these spectra is
presented here: two wavelength bands containing lines of He, C, Mg,
the iron group, and Ba. Significant abundance variations from star
to star are indicated for carbon and, apparently uncorrelated with C,
for the heavier elements. One of the stars, HR 3383 (A1 V), has very
sharp lines.
Title: Sun-as-a-star spectrum variability.
Authors: Livingston, W.; Holweger, H.; Wallace, L.; White, O. R.
Bibcode: 1985MPARp.212..184L
Altcode:
No abstract at ADS
Title: Selective enhancement of barium in the atmospheres of red
giants.
Authors: Holweger, H.; Kovacs, N.
Bibcode: 1984A&A...132L...5H
Altcode:
High-resolution spectroscopy of 13 bright red giants and Ba stars
shows selective enhancement of Ba in three of them, HD 65699 (Ba 2),
α TrA (K4 III), and ɛ Peg (K2 Ib). Infrared spectra available for
HD 65699 show that Sr is enhanced, too. This selective enhancement
is discussed in terms of a modified s-process which converts some
of the pre-existing r- and s-process matter into the magic nuclei
88Sr and 138Ba.
Title: Fraunhofer line variability, 1975-1983
Authors: Livingston, W.; Holweger, H.; White, O. R.
Bibcode: 1984stp..conf..427L
Altcode:
No abstract at ADS
Title: Statistical equilibrium of lithium in cool stars of different
metallicity
Authors: Steenbock, W.; Holweger, H.
Bibcode: 1984A&A...130..319S
Altcode:
The authors investigate non-LTE effects in the Li I resonance lines
of the Sun, a K 3Ib supergiant, halo dwarfs and a halo giant. Special
attention is given to a realistic treatment of the ionizing ultraviolet
radiation field, including absorption lines, and to the thermalizing
effect of inelastic collisions with hydrogen atoms. The solar Li
abundance is hardly affected by departures from LTE. The recommended
value is log ɛLi = 1.16±0.10 on the standard scale log
ɛH = 12.
Title: Barium stars observed with the Coudé Echelle Spectrometer.
Authors: Holweger, H.
Bibcode: 1983Msngr..34...30H
Altcode:
The ESO's Coude Echelle Spectrometer is used to obtain spectra of
sufficiently high resolution to yield true stellar line profiles,
for the case of the Ba stars that make up at least 1 percent of all
red giants. An attempt is made to determine the mechanism by which
unorthodox mixing events and neutron releases occur in the lower
red giant branch. Data are obtained which suggest an entire sequence
of combined neutron irradiation and mixing processes, although the
standard stellar evolution theory does not predict heavy element
production at the relatively high effective temperatures and low
luminosities of the objects presently studied.
Title: Sunspot cycle and associated variation of the solar spectral
irradiance
Authors: Holweger, H.; Livingston, W.; Steenbock, W.
Bibcode: 1983Natur.302..125H
Altcode:
Precise monitoring of the solar absorption-line spectrum in the
period 1976-80 has revealed systematic changes of the strength of
photospheric lines during the ascending part of the current solar
cycle1. The most likely cause is a slight cooling of the
lower photosphere and a concomitant heating of higher layers. The
total energy radiated into space thereby remains unchanged, in
accordance with high-precision radiometry2 covering
the same period. Nevertheless, a flattening of the photospheric
temperature gradient will be accompanied by a redistribution of energy
in the solar spectrum. Its magnitude is predicted here using stellar
model-atmosphere techniques. This `change of colour' is characterized
by a 0.2% decrease of the irradiance in the blue, and an increase
of the same order in the red and near IR. In this way solar activity
may modulate terrestrial climate even in the absence of perceptible
changes of the solar constant.
Title: Barium Stars and Normal Red Giants - Evidence for a Modified
S-Process
Authors: Holweger, H.
Bibcode: 1983nuas.proc...86H
Altcode:
No abstract at ADS
Title: Barium stars and normal red giants: evidence for a modified
s-process.
Authors: Holweger, H.
Bibcode: 1983MPARp..90...86H
Altcode:
No abstract at ADS
Title: Kurzzeitige Variationen im Spektrum des integrierten
Sonnenlichts
Authors: Holweger, H.; Livingston, W.
Bibcode: 1983MitAG..60..225H
Altcode:
No abstract at ADS
Title: The Solar Abundance of Tungsten
Authors: Holweger, H.; Werner, K.
Bibcode: 1982SoPh...81....3H
Altcode:
Recent measurements of WI oscillator strengths (Obbarius and Kock, 1982)
lead to a solar photospheric abundance of tungsten, log ɛW
= 1.06 ± 0.15 on the scale log ɛH = 12. The solar W/Si
abundance ratio, 0.32 W atoms/106 Si, coincides with that
found in carbonaceous chrondrites. Implications for solar-system
r-processes abundances are pointed out.
Title: Erratum - Solar Luminosity Variation - Part Four - the
Photospheric Lines 1976-1980
Authors: Livingston, W.; Holweger, H.
Bibcode: 1982ApJ...258..904L
Altcode:
No abstract at ADS
Title: Solar luminosity variation. IV - The photospheric lines,
1976-1980
Authors: Livingston, W.; Holweger, H.
Bibcode: 1982ApJ...252..375L
Altcode:
Kitt Peak full disk spectrophotometric records covering the period
1976-1980 have been analyzed to study the behavior of seven spectrum
lines sensitive to photospheric parameters. A secular decrease of
equivalent widths ranging from 0 to 2.3% is observed. From the lack
of correlation with localized, short-lived features like sunspots and
plages, it is concluded that the line weakenings are due to global
variations of surface properties. Model atmosphere analysis suggests
that the observed response pattern reflects a slight flattening of
the lower photospheric temperature gradient, corresponding to a 15%
increase in mixing length, at constant, effective temperature. The
associated increase in the efficiency of convection can be reconciled
with a constant luminosity if the change is assumed to occur only in
the outer 100 km of the convection zone.
Title: Einfluß von Temperaturinhomogenitäten in der
Sonnenatmosphäre auf die Bestimmung von Elementhäufigkeiten
Authors: Hermsen, W.; Holweger, H.; Mattig, W.
Bibcode: 1982MitAG..55...91H
Altcode:
No abstract at ADS
Title: Observed variability in the Fraunhofer line spectrum of solar
flux, 1975 - 1980
Authors: Livingston, W.; Holweger, H.; White, O. R.
Bibcode: 1981NASCP2191...95L
Altcode: 1981vsc..conf...95L
Over the five years double-pass spectrometer observations of the
Sun-as-a-star revealed significant changes in line intensities. The
photospheric component weakened linearly with time 0 to 2.3%. From a
lack of correlation between these line weakenings and solar activity
indicators like sunspots and plage, a global variation of surface
properties is inferred. Model-atmosphere analysis suggests a slight
reduction in the lower-photospheric temperature gradient corresponding
to a 15% increase in the mixing length within the granulation
layer. Chromospheric lines such as Ca II H and K, Ca II 8543 and the CN
band head weaken synchronously with solar activity. Thus, the behavior
of photospheric and chromospheric lines is markedly different, with
the possibility of secular change for the former.
Title: Isotopes of nickel in the sun
Authors: Brault, J. W.; Holweger, H.
Bibcode: 1981ApJ...249L..43B
Altcode:
High-resolution Fourier transform spectrometer spectra of near-infrared
Ni I lines reveal isotopic structure both in a laboratory source and
in the spectrum of the quiet photosphere. The solar Ni-58/Ni-60 ratio
agrees with that found in terrestrial and meteoritic matter
Title: EPS ERI : active chromosphere associated with enhanced
microturbulence.
Authors: Steenbock, W.; Holweger, H.
Bibcode: 1981A&A....99..192S
Altcode:
High-resolution spectra of late-type dwarfs including the sun
show Epsilon Eri to be exceptional by its intense small-scale
photospheric velocity field. This is discussed in relation to the
star's well-documented high chromospheric activity. Abundance analysis
suggests that the chromosphere of Epsilon Eri is less massive than
reported previously.
Title: Spektroskopische Analyse von Pollux
Authors: Ruland, F.; Holweger, H.; Griffin, R.; Beihl, D.
Bibcode: 1981MitAG..52..127R
Altcode:
No abstract at ADS
Title: Modellatmosphären und Ba/Fe-Verhältnis alter
Hauptreihensterne
Authors: Steenbock, W.; Holweger, H.
Bibcode: 1981MitAG..52R.145S
Altcode:
No abstract at ADS
Title: Modellatmospharen und Ba/Fe Verhaltnis alter Hauptreihensterne.
Authors: Steenbock, W.; Holweger, H.
Bibcode: 1981MitAG..52..145S
Altcode:
No abstract at ADS
Title: Langzeitverhalten solarer Spektrallinien
Authors: Livingston, W. C.; Holweger, H.
Bibcode: 1981MitAG..52Q.108L
Altcode:
No abstract at ADS
Title: Thorium in Arktur und Pollux
Authors: Holweger, H.
Bibcode: 1981MitAG..52...96H
Altcode:
No abstract at ADS
Title: Solare und meteoritische Häufigkeit von Silizium
Authors: Becker, U.; Zimmermann, P.; Holweger, H.
Bibcode: 1981MitAG..52Q..21B
Altcode:
No abstract at ADS
Title: Line blocking and equivalent widths in the spectrum of Pollux.
Authors: Ruland, F.; Griffin, R.; Griffin, R.; Biehl, D.; Holweger, H.
Bibcode: 1980A&AS...42..391R
Altcode:
High-dispersion spectrograms of Pollux (β Gem, KO III) have been
used to derive line blocking coefficients for the spectral range
λλ4900-9300 Å, and equivalent widths of lines of 43 atoms, ions,
and molecules.
Title: Spectroscopic analysis of Pollux relative to the sun with
special reference to Arcturus.
Authors: Ruland, F.; Holweger, H.; Griffin, R.; Griffin, R. F.;
Biehl, D.
Bibcode: 1980A&A....92...70R
Altcode:
A model-atmosphere analysis of the MK K0 III standard Pollux (Beta
Gem) is presented which is based on high-resolution photographic and
FTS spectra. Stellar surface parameters are found to be effective
temperature equals 4840 + or - 50 K, and log g equals 2.24 + or -
0.35. In conjunction with the radius, R equals 9.1 solar radii,
this value of log g leads to a mass (0.2-1.2 solar masses) for
Pollux 2.3 times that of Arcturus. Recent controversy concerning
the gravity of Arcturus is critically examined. Evidence is found
for chromospheric inhomogeneities, large-scale photospheric flow
patterns (giant granules), and severe departures from LTE that vitiate
abundances derived from low-excitation lines of neutral atoms. The
chemical composition determined for 30 elements, lithium to thorium,
characterizes Pollux as a normal Population I object with a mean
deficiency of the heavy elements (Z not less than 20) equals -0.17.
Title: Solar and meteoritic abundance of silicon
Authors: Becker, U.; Zimmermann, P.; Holweger, H.
Bibcode: 1980GeCoA..44.2145B
Altcode:
Recent lifetime measurements on excited electronic states of
neutral silicon ( BECKERet al., Phys. Lett. In press, 1980) lead to a
reassessment of widely used experimental transition probabilities GARZ,
Astron. Astrophys., 26, 471-477, 1973 of Si I lines. This translates
into a 25% downward revision of the Si abundance determined from the
solar spectrum. A solar atomic ratio, Si/Ca = 15.5 is inferred. This
value coincides with that found in carbonaceous chondrites, but
contrasts with ordinary and enstatite chondrites.
Title: Thorium in Arcturus, Pollux, Procyon and the Sun
Authors: Holweger, H.
Bibcode: 1980Obs...100..155H
Altcode:
No abstract at ADS
Title: Solar Flux Spectrum Variability, 1975-1980, as Indicative of
a Change in the Photospheric Temperature Gradient
Authors: Holweger, H.; Livingston, W.
Bibcode: 1980BAAS...12..897H
Altcode:
No abstract at ADS
Title: Abundances of the elements in the sun - Introductory report
Authors: Holweger, H.
Bibcode: 1979LIACo..22..117H
Altcode: 1979eisu.conf..117H; 1979eiu..conf..117H
Current solar models are reviewed with reference to their ability to
reproduce the observed spectrum. Theoretical and experimental f-values
are used to check the internal consistency of abundances derived from
different transitions of the same element. Present solar abundance
data confirm the relationship between solar and chondritic matter and
indicate that C1 chondrites are an unfractioned solar condensate. The
primordial solar system abundance pattern is reconstructed by
supplementing accurate meteoritic data by photospheric and coronal
abundances for the gases.
Title: Räumlich gemittelte Eigenschaften des photosphärischen
Strömungsfeldes
Authors: Holweger, H.; Gehlsen, M.; Ruland, F.
Bibcode: 1979MitAG..45..148H
Altcode:
No abstract at ADS
Title: Spatially-averaged Properties of the Photospheric Velocity
Field
Authors: Holweger, H.; Gehlsen, M.; Ruland, F.
Bibcode: 1978A&A....70..537H
Altcode:
Summary. A comprehensive set of solar Fe I lines taken from high-quality
spectral atlases is shown to define 4 basic statistical parameters
of the photospheric flow pattern. Taking advantage of complementary
diaguo stic properties of total absorption (equivalent width)
and line shape, we separate small-scale (micro) and large- scale
(macro) velocity dispersions. We confirm a distinctive center-limb
variation of both micro and macro, and demonstrate that this cannot
be due to height-dependence. The conclusion seems inescapable that the
photospheric flow pattern is an isotropic both in the small-scale and
large-scale limit. Vertical and horizontal most probable velocities
are, respectively, micro =1.0 km - 1 (vertical) and 1.6 km - 1
(horizontal), macro =1.63 km - 1 (vertical) and 2.14 km 1 (horizontal),
with an uncertainty of + 0.15 km s- . These results are discussed in
relation with spatially resolved structures and possible hydrodynamic
scenarios. Key words: photospheric velocity field - solar granulation
Title: A solar abundance study using recent Ti I oscillator strengths.
Authors: Gehlsen, M.; Holweger, H.; Danzmann, K.; Kock, M.; Kuehne, M.
Bibcode: 1978A&A....64..285G
Altcode:
Summary. The f-values measured by Kiihne et al. (1977) lead to a solar
abundance of titanium, log eTi = 4.94 1 0.12 on the scale log eR =
12. Comparison with abundances following from two independent sets of
f-values (Ellis, 1976; Whaling et al., 1977) shows basic consistency
of absolute scales. The solar ratio Ti/Ca = 3.8 x 10-2(125%) matches
that found in chondritic meteorites of types Cl or C2, but contrasts
with other types. Further subjects of abundance analysis are the solar
velocity field, constraints on departures from LTE, and the accuracy
of the STFD oscillator strengths of Kurucz and Peytremann (1975). Key
words: oscillator strengths - solar Ti abundance - solar atmosphere
Title: Wie eng ist die Verwandtschaft zwischen solarer und
meteoritischer Materie?
Authors: Holweger, H.
Bibcode: 1978MitAG..43R.137H
Altcode:
No abstract at ADS
Title: The solar Na/Ca and S/Ca ratios: A close comparison with
carbonaceous chondrites
Authors: Holweger, H.
Bibcode: 1977E&PSL..34..152H
Altcode:
Solar abundances based on recent laboratory oscillator strengths
confirm the relationship between solar matter and carbonaceous
chondrites. Within spectroscopic uncertainties (typically ±40%)
these meteorites contain refractory and volatile elements in solar
proportions. Significant improvement of accuracy at present seems
restricted to a few abundant elements having reliable quantum-mechanical
oscillator strengths, and necessitates strictly differential spectrum
analysis. Taking this into account, the solar abundance ratios Na/Ca
and S/Ca have been determined to an accuracy of ±15%. The results are:
Na/Ca= 0.91and S/Ca= 6.8. These volatile/refractory ratios just match
type 1 carbonaceous chondrites, but contrast with other types. These
and related interstellar abundance features place constraints on
the condensation process and a potential heterogeneity of the solar
nebula. There is evidence that no drastic pre-solar separation of
interstellar gas and grains has occurred, but minor imbalance may be
a common mechanism co-determining stellar metal content.
Title: A comparison of solar and meteoritic abundances.
Authors: Holweger, H.
Bibcode: 1977cami.coll..385H
Altcode: 1977IAUCo..39..385H
Estimates of solar S/Ca and Na/Ca ratios, with uncertainties of about
15%, are presented. A preliminary estimate of solar Mg/Ca ratio is
also presented. These ratios are found to be similar to the ratios
found in C1 chondrites and dissimilar to the C2 and C3 chondrite
ratios. It is concluded that C1 matter is a well-preserved condensate
from parts of the solar nebula whose composition was very close to
solar. Composition differences between C1 chondrites and interstellar
grains that escaped vaporization are considered, and the possibility
of metal fractionation involving these two forms of matter during star
formation is suggested. Problems in determining accurate solar element
ratios are discussed.
Title: 5-Minuten-Oszillationen solarer Äquivalentbreiten
Authors: Holweger, H.; Testermann, L.
Bibcode: 1976MitAG..38..204H
Altcode:
No abstract at ADS
Title: A model-atmosphere analysis of the spectrum of Arcturus.
Authors: Mäckle, R.; Holweger, H.; R.; Griffin, R.
Bibcode: 1976IAUS...72...19M
Altcode:
No abstract at ADS
Title: Five-Minute Oscillations of Solar Equivalent Widths
Authors: Holweger, H.; Testerman, L.
Bibcode: 1975SoPh...43..271H
Altcode:
Equivalent widths of weak and moderately strong Fraunhofer lines
observed in an area roughly 3500 × 10000 km in extent are found
to show small variations of the order of 1 mÅ, on a time scale of
minutes. The dependence of amplitude on line strength and excitation
closely fits that predicted for a compressional disturbance associated
with temperature variations that manifest themselves in the equivalent
widths. The rms amplitude is about 20K near τ5000 =
10-2.
Title: Elementenhäufigkeiten im Sonnensystem und Elementenentstehung
in der Galaxis. Anfängliche Häufigkeiten im Sonnensystem und
galaktische Nukleosynthese.
Authors: Holweger, H.
Bibcode: 1975S&W....14..233H
Altcode:
Questions concerning the significance of the greater abundance of
elements with an even number of protons compared to those with an odd
number are considered along with the characteristics of thermonuclear
element synthesis, the s-process component of the heavy nuclei, and
the synthesis of neutron-rich and proton-rich heavy nuclei. Aspects
regarding the time and place of origin of the heavy elements are
discussed. The hypotheses of galactic nucleosynthesis of the elements
include a hypothesis of an element synthesis in stars and a hypothesis
which considers a further processing of primary matter, which was
possibly formed in galactic explosions, by the s process.
Title: A model-atmosphere analysis of the spectrum of Arcturus
(basic spectroscopic data)
Authors: Mäckle, R.; Griffin, R.; Griffin, R.; Holweger, H.
Bibcode: 1975A&AS...19..303M
Altcode:
The following 5 tables supplement the analysis of the Arcturus
spectrum by et at. (1975). They contain basic observational data
and computational results for individual spectral lines. Key words:
Arcturus - line blanketing - equivalent widths - abundances
Title: Eine Feinanalyse des Spektrums von Arcturus
Authors: Mäckle, R.; Holweger, H.; Griffin, R. F.; Griffin, R. E. M.
Bibcode: 1975MitAG..36...71M
Altcode:
No abstract at ADS
Title: Elementenhäufigkeiten im Sonnensystem und Elemententstehung
in der Galaxis.
Authors: Holweger, H.
Bibcode: 1975S&W....14..189H
Altcode:
No abstract at ADS
Title: A model-atmosphere analysis of the spectrum of Arcturus.
Authors: Maeckle, R.; Holweger, H.; Griffin, R.; Griffin, R.
Bibcode: 1975A&A....38..239M
Altcode:
The spectrum of the high-velocity red giant, alpha Boo (Arcturus), is
analyzed relative to that of the sun, using spectral-line data from
the Arcturus Atlas and a differential technique employing empirical
atmospheric models for both stars. The line data and several photometric
observations are used to determine the effective temperature and
the surface gravity, and a very low mass (between 0.1 and 0.6 solar
mass) is calculated, implying a substantial mass loss. The chemical
composition of the red giant is determined from the atomic, ion, and
molecular lines of 32 elements, and an average underabundance of about
a factor of 4 is found along with a significantly different abundance
pattern than the sun's. Evidence is presented which indicates that
Arcturus is not in the first giant phase following the main sequence,
but is a more evolved star which may have experienced the helium flash.
Title: The Photospheric Barium Spectrum: Solar Abundance and Collision
Broadening of Ba II Lines by Hydrogen
Authors: Holweger, H.; Mueller, E. A.
Bibcode: 1974SoPh...39...19H
Altcode:
A study of the solar Ba II spectrum leads to a solar abundance of
barium of logεBa = = 2.11±0.12, on the scale logεH = 12. The observed
asymmetry of the resonance line λ4554 is consistent with an isotopic
abundance ratio equal to the terrestrial one. The meteoritic Ba/Si
abundance ratio found in carbonaceous chondrites appears to exceed
the solar ratio by 0.1 to 0.2 dex (Section 5).
Title: The Solar Abundance of Silicon
Authors: Holweger, H.
Bibcode: 1973A&A....26..275H
Altcode:
Summary. An analysis of 19 photospheric Si ilines whose oscillator
strengths have recently been determined by Garz (1973) leads to a
solar abundance of silicon, log =7.65+0.07, on the scale where log =
12. Together with the sodium abundance determined earlier by `the
same method, a solar abundance ratio = 0.045 (+ 10 %) results. Within
the error limits this agrees with the meteoritic ratio found in
carbonaceous chondrites. Results concerning line-broadening by hydrogen
are discussed in section 3a. Key words: solar silicon abundance -
Na/Si ratio - damping
Title: Microturbulence and the Effect of Departures from LTE on
Photospheric Iron Lines
Authors: Holweger, H.
Bibcode: 1973SoPh...30...35H
Altcode:
It is shown that depth-dependent departures from LTE such as obtained by
Athay and Lites (1972) will not notably affect the solar curve-of-growth
of Fe I. This implies that both abundance and microturbulence may be
determined from this curve-of-growth assuming LTE, and excludes that
microturbulence is an artefact produced by non-LTE effects.
Title: The solar abundance of calcium and collision broadening of
Ca i- and Ca ii-Fraunhofer lines by hydrogen
Authors: Holweger, H.
Bibcode: 1972SoPh...25...14H
Altcode:
An abundance analysis of the solar calcium spectrum is carried out
using 46 lines with known f-values in the visible and near infrared
spectral region. Resonance, forbidden and autoionizing lines are
included. The solar abundance of calcium resulting from the 25 weaker,
nearly damping-independent lines only is log εCa=6.36±0.07,
on the scale log ɛH = 12. The great variety of transitions involved
in the solar calcium spectrum, ranging from 0 eV lines of CaI to 7.5
eV lines of CaII and including autoionizing lines, are in reasonable
agreement (Figure 1b). Therefore notable non-LTE effects on their
equivalent widths can be excluded.
Title: The Broadening by Neutral Hydrogen in the Solar
Atmosphere. Comments to the Note by Roueff and Van Regemorter (1971)
Authors: Holweger, H.
Bibcode: 1971A&A....12..319H
Altcode:
If the collisional broadening of solar lines by neutral hydrogen
Is partly due to rept lsive forces, our empirically derived solar
interaction constants C6 can stffl onna1ly be used for describing the
broadening by neutral hydrogen of the same lines in other stars. Key
words: atomic physics - spectral line broadening - interatomic potentiaL
Title: Influence of Hyperfine Structure on the Solar Cobalt Abundance
Authors: Holweger, H.; Oertel, K. B.
Bibcode: 1971A&A....10..434H
Altcode:
Recent laboratory measurements of the hyperfine structure (hfs) are
used to determine the effect of hfs on 25 Fraunhofer lines of Co
I. Those lines having equlvalent widths between 40 and 80 mA will
simulate an average cobalt abundance co too high by about A = 0.25
if hfs-broadening is neglected. Key words: solar cobalt abundance -
Fraunhofer lines - hyperfine structure
Title: Damping and Solar Abundance of Sodium from NA i Fraunhofer
Lines
Authors: Holweger, H.
Bibcode: 1971A&A....10..128H
Altcode:
Empirical damping constants of six strong solar Na 1 lines (
4497-23348 A) are determined by comparing, similar to Weidemann
(1955), the corresponding abundances with those computed from weak,
damping-independent sodium lines, the I-values being known with
sufficient accuracy. Agreement between strong and weak lines may be
obtained by increasing their van der Waals interaction constants,
C6, by A logC6 = + 0.8 + 0.2 over the theoretical valne predicted by
Unsbld's (1938, 1955) approximation. Within these limits this correction
is independent of the term properties. Bepnlsive interatomic forces,
whose astrophysical importance for collisional broadening by hydrogen
atoms was suspected by Roueff and Van Regemorter (1969) and Roueff
(1970), are therefore either insignificant or their effect on solar
sodium lines can quantitatively be represented by uniformly increased
van der Waals attraction. Stark broadening and radiative damping are
found to be of minor importance for the line abundances (Section 3). If
Ce is modified accordingly, the scatter of abundances, including the
D lines, becomes remarkably low, due to the accuracy of I-values and
equivalent widths. A mean solar sodinm abundance log 8 = 6.30 + 0.07
(referring to log CR 12.00) is deduced (Section 4). Deviations from
LTE or from true absorption are shown to have a negligible effect on
abundances (Section 5). Section 2 contains some remarks on the solar
abundance of magnesium and silicon. Key words: solar spectrum - sodium
abundance - collisional broadening
Title: Depression of the Solar Continuous Spectrum by Line Absorption
and the Balmer Continuum
Authors: Holweger, H.
Bibcode: 1970A&A.....4...11H
Altcode:
It is shown that line absorption - mainly due to faint Fraunhofer lines
(WA 5 mA) - can acconnt tor ditjerence between observed fl 0! solar
radiation and model predictions in the wavelengt range 3300 to 5000
A. Shortward of 4000 A several faint lines may lay within 0.1 A, thus
producing a quasi-continuous absorption of 10% or more. Equivalent
widths WA of these lines cannot be measured individually; we have
predicted them by means of laboratory.intensity tables. Other, rable
solar lines of the same element were used to transform laboratory
intensities into solar WA. In the region 3647 to 4000 A strong lines are
also important, especially merging high members of the Balmer series and
Ca U H+K. Despite of rather large uncertainties connected with predicted
lines, our calculated corrections for the absorption due to all lines
leads to good agreement (Fig. 2) between the observations of Labs and
Neckel (1968) and the fiux calculated according to solar models which
are fitted to the observed fiux at > 6000 A. The solar Balmer mp
appears to be completely hidden by line absorption (Fig. 2). It seems
therefore impossible to determine its value, D, from spectrograms alone,
i.e. without detailed line-absorption analysis. Our calculations are
consistent with D = 0.13 but are stffl not reliable enough to be used
as a model criterion.
Title: Experimental Oscillator Strengths of Fe II Lines and the
Solar Iron Abundance.
Authors: Baschek, B.; Garz, T.; Holweger, H.; Richter, J.
Bibcode: 1970A&A.....4..229B
Altcode:
Experimental Oscfflator Strengths of Fe II Lines and the Solar Iron
Abundance The wall-stabilized arc burning in argon with a small
admixture of iron chloride used by Garz and Kock (1969) to measure
oscffiator strengths of Fe I lines also allows the determination of
oscillator strengths of Fe U lines. We present oscffiator strengths
of 14 Fe U lines based on the absolute scale of Garz and Kock for Fe I
lines. A solar abundance log s (Fe) = 7.63 + 0.20, normalized to log S
(H) = 12.00, is derived out of ionized iron lines. A comparison with
previous experimental and stellar oscfflator strengths of Fe U lines
is carried out and some implications on analyses of stellar spectra
are discussed. Key words: oscillator strengths - solar abundance
Title: Abundance of Iron in the Solar Photosphere. Remarks Concerning
a Paper by John E. Ross (1970)
Authors: Garz, T.; Richter, J.; Holweger, H.; Unsöld, A.
Bibcode: 1970A&A.....7..336G
Altcode:
No abstract at ADS
Title: Experimental oscillator strengths and the solar abundances
of iron and nickel.
Authors: Garz, T.; Heise, H.; Holweger, H.; Richter, J.
Bibcode: 1970eoss.book.....G
Altcode:
No abstract at ADS
Title: Revised Solar Iron Abundance and its Influence on the
Photospheric Model
Authors: Garz, T.; Holweger, H.; Kock, M.; Richter, J.
Bibcode: 1969A&A.....2..446G
Altcode:
Revised Solar Iron Abundance and its Influence on the Photo spheric
Model Using the new 1-values of Garz and Kock (1969), an analysis
of 26 photospheric Fe I lines is carried out yielding a solar iron
abundance loge(Fe) = 7.60 (loge(H) = 12). This new value - 10 times
greater than recently determined photospheric values - is a consequence
of the revised scale of 1-values and agrees with coronal abundance
determinations. As a by-product we find from the dependence of abundance
on equivalent width, that in the solar model of Holweger (1967) the
microturbulence has to be decreased by 0.7 km/s, which leads to 1.0
km/s at T5550 0.1. In order to obtain the same central intensities of
Fraunhofer lines the macroturbulence must be increased to about 1.6
km/s. At any depth T5505 S 0.2 in solar-type stars, the increase of s
(Fe) by a factor of 10 leads to an increase of the electron pressure
by A log Pe = 0.1 and to a corresponding decrease of the gas pressure
by the same amount. In the UV, especially in the range 1700 to 2300
A, iron (together with magnesium and silicon) becomes an important
source 0! continuous opacity. Thus, like Mg and Si, Fe will affect
radiative-equilibrium models of stellar atmospheres.
Title: Center-to-Limb Analysis of the Solar Oxygen Lines
Authors: Müller, Edith A.; Baschek, Bodo; Holweger, Hartmut
Bibcode: 1968SoPh....3..125M
Altcode:
Several lines of neutral oxygen observed at various positions on the
solar disk were used to study the influence of (1) the temperature
distribution, (2) the velocity field, and (3) the damping on the line
profiles and the abundance of oxygen in the photosphere. Theoretical
profiles were calculated on the basis of four different model
atmospheres in LTE. It was found that the model proposed by HOLWEGER
(1967) best reproduced the center-to-limb observations of the lines
studied. The weighted mean of the oxygen abundance turned out to be
log ɛO = 8.83 on the basis of log ɛH = 12.00.
Title: Quantitative Analyse des Spektrums des F8 V-Sterns Beta
Virginis
Authors: Baschek, B. H.; Holweger, H.; Namba, O.; Traving, G.
Bibcode: 1967ZA.....65..418B
Altcode:
No abstract at ADS
Title: Ein empirisches Modell der Sonnenatmosphäre mit lokalem
thermodynamischem Gleichgewicht Title: Ein empirisches Modell der
Sonnenatmosphäre mit lokalem thermodynamischem Gleichgewicht Title:
An empirical model of the solar atmosphere with local thermodynamic
equilibrium;
Authors: Holweger, Hartmut
Bibcode: 1967PhDT.......146H
Altcode:
No abstract at ADS
Title: Ein empirisches Modell der Sonnenatmosphäre mit lokalem
thermodynamischem Gleichgewicht
Authors: Holweger, H.
Bibcode: 1967ZA.....65..365H
Altcode:
No abstract at ADS
Title: CI- und CH-Linien im Sonnenspektrum
Authors: Baschek, B.; Holweger, H.
Bibcode: 1967ZA.....67..143B
Altcode:
No abstract at ADS
Title: Ein ALGOL-Programm fur die quantitative Analyse von
Sternspektren
Authors: Baschek, B.; Holweger, H.; Traving, G.
Bibcode: 1966AAHam...8...26B
Altcode:
No abstract at ADS
Title: Tabellen fur die Berechnung von Zustandssummen
Authors: Traving, G.; Baschek, B.; Holweger, H.
Bibcode: 1966AAHam...8....1T
Altcode:
No abstract at ADS
Title: The Correlation Between Metal Deficiency of Stars and Their
Distance from the Galactic Plane.
Authors: Böhm-Vitense, Erika; Holweger, H.; Kohl, K.
Bibcode: 1963ApJ...138..604B
Altcode:
No abstract at ADS
Title: Die Genauigkeit von Sternatmosphären Modellen im
Strahlungsgleichgewicht. Mit 2 Textabbildungen
Authors: Holweger, H.; Unsöld, A.
Bibcode: 1963ZA.....57..235H
Altcode:
No abstract at ADS
Title: Ausbreitung magnetohydrodynamischer Wellen. Mit 7
Textabbildungen
Authors: Holweger, H.
Bibcode: 1963ZA.....56..269H
Altcode:
No abstract at ADS