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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.
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.

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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.
2004A&A...414.1121W    Altcode: 2003astro.ph.11273W
  Three-dimensional numerical simulations with CO<SUP>5</SUP>, 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.

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Title: Abundance analysis of late B stars.  Evidence for diffusion
    and against weak stellar winds
Authors: Hempel, M.; Holweger, H.
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. <P
  />Based on observations collected at the European Southern Observatory,
  La Silla, Chile and at the Special Astrophysical Observatory, Nizhnij
  Arkhyz, Russia.

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Title: Modelling the Chromospheric Background Pattern of the
    Non-magnetic Sun
Authors: Wedemeyer, Sven; Freytag, Bernd; Steffen, Matthias; Ludwig,
   Hans-Günter; Holweger, Hartmut
2003ANS...324R..66W    Altcode: 2003ANS...324..I07W
  No abstract at ADS

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Title: Acoustic Waves in the Solar Chromosphere - Numerical
    Simulations with COBOLD
Authors: Wedemeyer, S.; Freytag, B.; Steffen, M.; Ludwig, H. -G.;
   Holweger, H.
2003IAUS..210P..C1W    Altcode:
  No abstract at ADS

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Title: 3-D hydrodynamic simulations of the solar chromosphere
Authors: Wedemeyer, S.; Freytag, B.; Steffen, M.; Ludwig, H. -G.;
   Holweger, H.
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 CO<SUP>5</SUP>BOLD. 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.

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Title: NLTE Model-Atmosphere Analysis of B Stars
Authors: Hempel, M.; Holweger, H.
2003IAUS..210P.E37H    Altcode:
  No abstract at ADS

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Title: Granulation Abundance Corrections from Hydrodynamical
    Convection Simulations
Authors: Steffen, M.; Holweger, H.
2003IAUS..210P.D15S    Altcode:
  No abstract at ADS

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Title: Do dusty A stars exhibit accretion signatures in their
    photospheres?
Authors: Kamp, I.; Hempel, M.; Holweger, H.
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.

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Title: Line formation in convective stellar
    atmospheres. I. Granulation corrections for solar photospheric
    abundances
Authors: Steffen, M.; Holweger, H.
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
  E<SUB>i</SUB>=5 eV, regardless of element and ionization stage. Moderate
  granulation effects (Delta<SUB>gran</SUB> ~ -0.1 dex) are obtained
  for weak, high-excitation lines (E<SUB>i</SUB> &gt;~ 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 (E<SUB>i</SUB>=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.

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Title: Photospheric abundances: Problems, updates, implications
Authors: Holweger, H.
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. .

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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.
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. .

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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
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.

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Title: Radiation Hydrodynamics Simulations of the Solar Chromosphere
Authors: Wedemeyer, Sven; Freytag, Bernd; Steffen, Matthias; Holweger,
   Hartmut
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 debate<SUP>1,2</SUP>. 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 code<SUP>3</SUP> 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.

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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
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.

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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.
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&amp;A 303,
  819 Holweger H., Hempel M., Kamp I., 1999, A&amp;A 350, 603 Landstreet
  J.D., Dolez N., Vauclair S.,1998, A&amp;A 333, 977

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Title: A search for circumstellar gas around normal A stars and
    Lambda Bootis stars
Authors: Holweger, H.; Hempel, M.; Kamp, I.
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

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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.
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.

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Title: Selected Fe II lifetimes and f-values suitable for a solar
    abundance study
Authors: Schnabel, R.; Kock, M.; Holweger, H.
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.

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Title: Thermal structure of circumstellar discs around A stars
Authors: Kamp, I.; Holweger, H.
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 &amp; Rentzsch-Holm 1995;
  Holweger, Hempel &amp; 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 &amp; 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}.

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Title: Silicon as a cosmic reference element: a reassessment of the
    solar SI abundance
Authors: Wedemeyer, Sven; Holweger, Hartmut; Steffen, Matthias
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 &amp;
  Grevesse (1989) and its updates (e.g. Grevesse &amp; 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&amp;A 342, 610

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Title: Line Formation in Convective Stellar Atmospheres
Authors: Steffen, Matthias; Holweger, Hartmut
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.

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Title: Abundance analysis of late B stars
Authors: Hempel, Marc; Holweger, Hartmut; Galazutdinov, Gazinur A.;
   Musaev, Faig A.; Kaufer, Andreas
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&amp;A 303, 819
  Holweger H., Hempel M., Kamp I., 1999, A&amp;A (submitted) Landstreet
  J.D., Dolez N., Vauclair S., 1998, A&amp;A 333, 977

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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.
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.

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Title: Dusty and dust-free A stars
Authors: Hempel, M.; Holweger, H.; Kamp, I.
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.

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Title: Dust and gas around lambda Bootis stars
Authors: Kamp, I.; Holweger, H.
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.

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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.
1998sce..conf..105B    Altcode:
  No abstract at ADS

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Title: Toward solving the `CO-Problem': chemistry in the disks around
    VEGA and beta Pictoris
Authors: Rentzsch-Holm, I.; Holweger, H.; Bertoldi, F.
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.

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Title: Dusty and dust-free A stars
Authors: Hempel, Marc; Holweger, Hartmut
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&amp;A\ 303,\ 819).

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Title: Circumstellar discs around A stars
Authors: Kamp, I.; Holweger, H.; Bertoldi, I.
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 &amp;
  Bertoldi (1998), Kamp &amp; 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.
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.
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.
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.
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.
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.
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.
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<SUP>-4</SUP>, (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.
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.
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.
1995A&A...296..233H    Altcode:
  We examine the critical remarks by Blackwell, Lynas-Gray &amp;
  Smith (1995; A&amp;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 &amp; 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.
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.
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.
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.
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.
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
  T<SUB>eff</SUB> = 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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
1987MitAG..70..325K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Atmospheric Structure and the Activity Cycle
Authors: Holweger, H.
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.
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.
1986A&A...155...58H    Altcode:
  High-resolution Reticon spectra of seven reputedly normal B9.5 - A2
  V stars with v sin i &lt; 50 km s<SUP>-1</SUP> 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.
1985MPARp.212..184L    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Selective enhancement of barium in the atmospheres of red
    giants.
Authors: Holweger, H.; Kovacs, N.
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
  <SUP>88</SUP>Sr and <SUP>138</SUP>Ba.

---------------------------------------------------------
Title: Fraunhofer line variability, 1975-1983
Authors: Livingston, W.; Holweger, H.; White, O. R.
1984stp..conf..427L    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Statistical equilibrium of lithium in cool stars of different
    metallicity
Authors: Steenbock, W.; Holweger, H.
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 ɛ<SUB>Li</SUB> = 1.16±0.10 on the standard scale log
  ɛ<SUB>H</SUB> = 12.

---------------------------------------------------------
Title: Barium stars observed with the Coudé Echelle Spectrometer.
Authors: Holweger, H.
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.
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
  cycle<SUP>1</SUP>. 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 radiometry<SUP>2</SUP> 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.
1983nuas.proc...86H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Barium stars and normal red giants: evidence for a modified
    s-process.
Authors: Holweger, H.
1983MPARp..90...86H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Kurzzeitige Variationen im Spektrum des integrierten
    Sonnenlichts
Authors: Holweger, H.; Livingston, W.
1983MitAG..60..225H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Solar Abundance of Tungsten
Authors: Holweger, H.; Werner, K.
1982SoPh...81....3H    Altcode:
  Recent measurements of WI oscillator strengths (Obbarius and Kock, 1982)
  lead to a solar photospheric abundance of tungsten, log ɛ<SUB>W</SUB>
  = 1.06 ± 0.15 on the scale log ɛ<SUB>H</SUB> = 12. The solar W/Si
  abundance ratio, 0.32 W atoms/10<SUP>6</SUP> 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.
1982ApJ...258..904L    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Solar luminosity variation. IV - The photospheric lines,
    1976-1980
Authors: Livingston, W.; Holweger, H.
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.
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.
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.
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.
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.
1981MitAG..52..127R    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Modellatmosphären und Ba/Fe-Verhältnis alter
    Hauptreihensterne
Authors: Steenbock, W.; Holweger, H.
1981MitAG..52R.145S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Modellatmospharen und Ba/Fe Verhaltnis alter Hauptreihensterne.
Authors: Steenbock, W.; Holweger, H.
1981MitAG..52..145S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Langzeitverhalten solarer Spektrallinien
Authors: Livingston, W. C.; Holweger, H.
1981MitAG..52Q.108L    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Thorium in Arktur und Pollux
Authors: Holweger, H.
1981MitAG..52...96H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Solare und meteoritische Häufigkeit von Silizium
Authors: Becker, U.; Zimmermann, P.; Holweger, H.
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.
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.
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.
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.
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.
1980BAAS...12..897H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Abundances of the elements in the sun - Introductory report
Authors: Holweger, H.
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.
1979MitAG..45..148H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Spatially-averaged Properties of the Photospheric Velocity
    Field
Authors: Holweger, H.; Gehlsen, M.; Ruland, F.
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.
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.
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.
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.
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.
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.
1976IAUS...72...19M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Five-Minute Oscillations of Solar Equivalent Widths
Authors: Holweger, H.; Testerman, L.
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 τ<SUB>5000</SUB> =
  10<SUP>-2</SUP>.

---------------------------------------------------------
Title: Elementenhäufigkeiten im Sonnensystem und Elementenentstehung
    in der Galaxis. Anfängliche Häufigkeiten im Sonnensystem und
    galaktische Nukleosynthese.
Authors: Holweger, H.
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.
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.
1975MitAG..36...71M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Elementenhäufigkeiten im Sonnensystem und Elemententstehung
    in der Galaxis.
Authors: Holweger, H.
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.
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.
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.
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.
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.
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 ε<SUB>Ca</SUB>=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.
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.
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.
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.
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 &gt; 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.
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.
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.
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.
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
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 ɛ<SUB>O</SUB> = 8.83 on the basis of log ɛ<SUB>H</SUB> = 12.00.

---------------------------------------------------------
Title: Quantitative Analyse des Spektrums des F8 V-Sterns Beta
    Virginis
Authors: Baschek, B. H.; Holweger, H.; Namba, O.; Traving, G.
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
1967PhDT.......146H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Ein empirisches Modell der Sonnenatmosphäre mit lokalem
    thermodynamischem Gleichgewicht
Authors: Holweger, H.
1967ZA.....65..365H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: CI- und CH-Linien im Sonnenspektrum
Authors: Baschek, B.; Holweger, H.
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.
1966AAHam...8...26B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Tabellen fur die Berechnung von Zustandssummen
Authors: Traving, G.; Baschek, B.; Holweger, H.
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.
1963ApJ...138..604B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Die Genauigkeit von Sternatmosphären Modellen im
    Strahlungsgleichgewicht. Mit 2 Textabbildungen
Authors: Holweger, H.; Unsöld, A.
1963ZA.....57..235H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Ausbreitung magnetohydrodynamischer Wellen. Mit 7
    Textabbildungen
Authors: Holweger, H.
1963ZA.....56..269H    Altcode:
  No abstract at ADS