Author name code: kupka
ADS astronomy entries on 2022-09-14
author:"Kupka, Friedrich" 
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Title: Stellar evolution models with overshooting based on 3-equation
    non-local theories, II. Main-sequence models of A- and B-type stars
Authors: Ahlborn, Felix; Kupka, Friedrich; Weiss, Achim; Flaskamp,
   Martin
Bibcode: 2022arXiv220712512A
Altcode:
  Convective overshoot mixing is a critical ingredient of stellar
  structure models, but is treated in most cases by ad hoc extensions of
  the mixing-length theory for convection. Advanced theories which are
  both more physical and numerically treatable are needed. Convective
  flows in stellar interiors are highly turbulent. This poses a number
  of numerical challenges for the modelling of convection in stellar
  interiors. We include an effective turbulence model into a 1D stellar
  evolution code in order to treat non-local effects within the same
  theory. We use a turbulent convection model which relies on the
  solution of second order moment equations. We implement this into a
  state of the art 1D stellar evolution code. To overcome a deficit
  in the original form of the model, we take the dissipation due to
  buoyancy waves in the overshooting zone into account. We compute
  stellar models of intermediate mass main-sequence stars between 1.5
  and 8 $M_\odot$. Overshoot mixing from the convective core and modified
  temperature gradients within and above it emerge naturally as a solution
  of the turbulent convection model equations. For a given set of model
  parameters the overshooting extent determined from the turbulent
  convection model is comparable to other overshooting descriptions, the
  free parameters of which had been adjusted to match observations. The
  relative size of the mixed cores decreases with decreasing stellar
  mass without additional adjustments. We find that the dissipation by
  buoyancy waves constitutes a necessary and relevant extension of the
  turbulent convection model in use.

Title: Stellar evolution models with overshooting based on 3-equation
    non-local theories I. Physical basis and the computation of the
    dissipation rate
Authors: Kupka, F.; Ahlborn, F.; Weiss, A.
Bibcode: 2022arXiv220712296K
Altcode:
  Context. Mixing by convective overshooting has long been suggested
  to play an important role for the amount of hydrogen available to
  nuclear burning in convective cores of stars. The best way to model
  this effect is still debated. Aims. We suggest an improved model for
  the computation of the dissipation rate of turbulent kinetic energy
  which can be used in non-local models of stellar convection and
  can readily be implemented and self-consistently used in 1D stellar
  evolution calculations. Methods. We review the physics underlying
  various models to compute the dissipation rate of turbulent kinetic
  energy, {\epsilon}, in local and particularly in non-local models of
  convection in stellar astrophysics. The different contributions to
  the dissipation rate and their dependence on local stratification and
  on non-local transport are analysed and a new method to account for
  at least some of these physical mechanisms is suggested. Results. We
  show how the new approach influences predictions of stellar models of
  intermediate-mass main-sequence stars and how these changes differ
  from other modifications of the non-local convection model that
  focus on the ratio of horizontal to vertical (turbulent) kinetic
  energy. Conclusions. The new model is shown to allow for a physically
  more complete description of convective overshooting and mixing in
  massive stars. Dissipation by buoyancy waves is found to be a key
  ingredient which has to be accounted for in non-local models of
  turbulent convection.

Title: On the Potential of the Reynolds Stress Approach to Model
    Convective Overshooting in Grids of Stellar Evolution Models
Authors: Kupka, Friedrich
Bibcode: 2021plat.confE..88K
Altcode:
  Convection is one of the main physical processes probed by means
  of asteroseismology these days and it is a key topic of several
  workpackages within the PLATO mission. A lot of attention in this
  field is currently given to the parameter calibration of fairly simple
  models by means of 3D RHD numerical simulations or the direct use of
  the latter in asteroseismological analyses. However, this approach is
  not available to all situations of interest where convection plays a
  role in stellar mixing and in the evolution of the thermal structure
  of a star, particularly not for overshooting and mixing when they take
  place deeply inside a star. For such cases Reynolds stress models
  provide an interesting alternative. In this talk I will report on
  the potential of this method, also for future calculations of model
  grids for asteroseismology, and summarize earlier results and recent
  progress made with this approach.

Title: Stellar evolution models with entropy-calibrated mixing-length
parameter: application to red giants
Authors: Spada, Federico; Demarque, Pierre; Kupka, Friedrich
Bibcode: 2021MNRAS.504.3128S
Altcode: 2021arXiv210408067S; 2021MNRAS.tmp.1089S
  We present evolutionary models for solar-like stars with an improved
  treatment of convection that results in a more accurate estimate of
  the radius and effective temperature. This is achieved by improving
  the calibration of the mixing-length parameter, which sets the length
  scale in the 1D convection model implemented in the stellar evolution
  code. Our calibration relies on the results of 2D and 3D radiation
  hydrodynamics simulations of convection to specify the value of the
  adiabatic specific entropy at the bottom of the convective envelope in
  stars as a function of their effective temperature, surface gravity, and
  metallicity. For the first time, this calibration is fully integrated
  within the flow of a stellar evolution code, with the mixing-length
  parameter being continuously updated at run-time. This approach replaces
  the more common, but questionable, procedure of calibrating the length
  scale parameter on the Sun, and then applying the solar-calibrated
  value in modelling other stars, regardless of their mass, composition,
  and evolutionary status. The internal consistency of our current
  implementation makes it suitable for application to evolved stars, in
  particular to red giants. We show that the entropy calibrated models
  yield a revised position of the red giant branch that is in better
  agreement with observational constraints than that of standard models.

Title: Accurate Short-Characteristics Radiative Transfer in A
    Numerical Tool for Astrophysical RESearch (ANTARES)
Authors: Kostogryz, Nadiia M.; Kupka, Friedrich; Piskunov, Nikolai;
   Fabbian, Damian; Krüger, Daniel; Gizon, Laurent
Bibcode: 2021SoPh..296...46K
Altcode:
  We aim to improve the accuracy of radiative energy transport in
  three-dimensional radiation hydrodynamical simulations in ANTARES
  (A Numerical Tool for Astrophysical RESearch). We implement in the
  ANTARES short-characteristics numerical schemes a modification of
  the Bézier interpolant solver. This method yields a smoother surface
  structure in simulations of solar convection and reduces the artifacts
  appearing due to the limited number of rays along which the integration
  is done. Reducing such artifacts leads to increased stability of the
  code. We show that our new implementation achieves a better agreement
  of the temperature structure and its gradient with a semi-empirical
  model derived from observations, as well as of synthetic spectral-line
  profiles with the observed solar spectrum.

Title: Surface effects and turbulent pressure. Assessing the
    Gas-Γ<SUB>1</SUB> and Reduced-Γ<SUB>1</SUB> empirical models
Authors: Belkacem, K.; Kupka, F.; Philidet, J.; Samadi, R.
Bibcode: 2021A&A...646L...5B
Altcode: 2021arXiv210106065B
  The application of the full potential of stellar seismology is made
  difficult by the improper modelling of the upper-most layers of
  solar-like stars and their influence on the modelled frequencies. Our
  knowledge of these so-called `surface effects' has improved thanks to
  the use of 3D hydrodynamical simulations, however, the calculation
  of eigenfrequencies relies on empirical models for the description
  of the Lagrangian perturbation of turbulent pressure, namely: the
  reduced-Γ<SUB>1</SUB> model (RGM) and the gas-Γ<SUB>1</SUB> model
  (GGM). Starting from the fully compressible turbulence equations,
  we derived both the GGM and RGM models by using a closure to model
  the flux of turbulent kinetic energy. We find that both models
  originate from two terms: the source of turbulent pressure due to
  compression produced by the oscillations and the divergence of the
  flux of turbulent pressure. We also demonstrate that they are both
  compatible with the adiabatic approximation and, additionally, that
  they imply a number of questionable assumptions, mainly with respect
  to mode physics. Among other hypotheses, it is necessary to neglect
  the Lagrangian perturbation of the dissipation of turbulent kinetic
  energy into heat and the Lagrangian perturbation of buoyancy work.

Title: The ANTARES code: recent developments and applications
Authors: Kupka, Friedrich; Zaussinger, Florian; Fabbian, Damian;
   Krüger, Daniel
Bibcode: 2020JPhCS1623a2016K
Altcode:
  ANTARES (A Numerical Tool for Astrophysical RESearch) is a
  multi-purpose numerical tool to solve different variants of the
  equations of hydrodynamics as they appear in problems of astrophysics,
  geophysics, and engineering sciences and which require the construction
  of detailed numerical simulation models. A presentation of the current
  feature set of the code with a focus on recent add-ons is given here
  in addition to a summary on several results from recent applications of
  ANTARES to solar physics, the physics of planets, and basic convection
  studies including the damping of pressure modes (solar oscillations)
  in numerical simulations of convection at the solar surface and the
  coupling of layers in numerical simulations of sheared and non-sheared
  double-diffusive convection.

Title: On long-duration 3D simulations of stellar convection using
    ANTARES
Authors: Kupka, F.; Fabbian, D.; Krüger, D.; Kostogryz, N.; Gizon, L.
Bibcode: 2020IAUGA..30..373K
Altcode:
  We present initial results from three-dimensional (3-D) radiation
  hydrodynamical simulations for the Sun and targeted Sun-like stars. We
  plan to extend these simulations up to several stellar days to study
  p-mode excitation and damping processes. The level of variation of
  irradiance on the time scales spanned by our 3-D simulations will
  be studied too. Here we show results from a first analysis of the
  computational data we produced so far.

Title: 3D Hydrodynamical Simulations of Stellar Convection for Helio-
    and Asteroseismology
Authors: Kupka, F.
Bibcode: 2020svos.conf..209K
Altcode:
  Hydrodynamical simulations of stellar convection are an essential
  theoretical tool for gaining insight into the physics of mixing
  and heat transport by convection, and also into the interaction of
  convection with pulsation. They are particularly useful for obtaining
  an accurate description of the structure of the superadiabatic layer,
  which is important to explain the observed frequencies of $p$-modes
  in solar-like oscillating stars. The simulations can also be used to
  probe analytical models of excitation and damping of modes, and thus
  explain their amplitudes, and eventually the physical completeness of
  such models. This presentation discussed general challenges of such 3D
  hydrodynamical simulations developed for helio- and asteroseismology;
  it summarized some recent results in this field for the Sun, and which
  are also relevant to other lower main-sequence stars.

Title: Thermal Convection in Stars and in Their Atmosphere
Authors: Kupka, Friedrich
Bibcode: 2020mdps.conf...69K
Altcode: 2020arXiv200111540K
  Thermal convection is one of the main mechanisms of heat transport and
  mixing in stars in general and also in the photospheric layers which
  emit the radiation that we observe with astronomical instruments. The
  present lecture notes first introduce the role of convection in
  astrophysics and explain the basic physics of convection. This is
  followed by an overview on the modelling of convection. Challenges
  and pitfalls in numerical simulation based modelling are discussed
  subsequently. Finally, a particular application for the previously
  introduced concepts is described in more detail: the study of convective
  overshooting into stably stratified layers around convection zones
  in stars.

Title: Shine BRITE: shedding light on stellar variability through
    advanced models
Authors: Fabbian, D.; Kupka, F.; Krüger, D.; Kostogryz, N. M.;
   Piskunov, N.
Bibcode: 2020svos.conf..155F
Altcode: 2020arXiv200201560F
  The correct interpretation of the large amount of complex data from
  next-generation (in particular, space-based) observational facilities
  requires a very strong theoretical underpinning. One can predict
  that, in the near future, the use of atmospheric models obtained with
  three-dimensional (3-D) radiation magneto-hydrodynamics (RMHD) codes,
  coupled with advanced radiative transfer treatment including non-local
  thermodynamic equilibrium (non-LTE) effects and polarisation, will
  become the norm. In particular, stellar brightness variability in cool
  stars (i.e., spectral types F-- M) can be caused by several different
  effects besides pulsation. In this review we have briefly discussed
  some published results, and mentioned aspects of recent progress. It
  then attempted to peek into what the future may hold for understanding
  this important aspect of the lives of stars.

Title: Layer formation in double-diffusive convection over resting
    and moving heated plates
Authors: Zaussinger, Florian; Kupka, Friedrich
Bibcode: 2019ThCFD..33..383Z
Altcode: 2018arXiv181111800Z
  We present a numerical study of double-diffusive convection
  characterized by a stratification unstable to thermal convection,
  while at the same time a mean molecular weight (or solute
  concentration) difference between top and bottom counteracts this
  instability. Convective zones can form in this case either by the
  stratification being locally unstable to the combined action of both
  temperature and solute gradients or by another process, the oscillatory
  double-diffusive convective instability, which is triggered by the
  faster molecular diffusivity of heat in comparison with that one of
  the solute. We discuss successive layer formation for this problem
  in the case of an instantaneously heated bottom (plate) which forms
  a first layer with an interface that becomes temporarily unstable and
  triggers the formation of further, secondary layers. We consider both
  the case of a Prandtl number typical for water (oceanographic scenario)
  and of a low Prandtl number (giant planet scenario). We discuss the
  impact of a Couette like shear on the flow and in particular on layer
  formation for different shear rates. Additional layers form due to the
  oscillatory double-diffusive convective instability, as is observed for
  some cases. We also test the physical model underlying our numerical
  experiments by recovering experimental results of layer formation
  obtained in laboratory setups.

Title: Solar p-mode damping rates: Insight from a 3D hydrodynamical
    simulation
Authors: Belkacem, K.; Kupka, F.; Samadi, R.; Grimm-Strele, H.
Bibcode: 2019A&A...625A..20B
Altcode: 2019arXiv190305479B
  Space-borne missions such as CoRoT and Kepler have provided a rich
  harvest of high-quality photometric data for solar-like pulsators. It is
  now possible to measure damping rates for hundreds of main-sequence and
  thousands of red-giant stars with an unprecedented precision. However,
  among the seismic parameters, mode damping rates remain poorly
  understood and thus barely used for inferring the physical properties
  of stars. Previous approaches to model mode damping rates were based on
  mixing-length theory or a Reynolds-stress approach to model turbulent
  convection. While they can be used to grasp the main physics of the
  problem, such approaches are of little help to provide quantitative
  estimates as well as a definitive answer on the relative contribution
  of each physical mechanism. Indeed, due to the high complexity of the
  turbulent flow and its interplay with the oscillations, those theories
  rely on many free parameters which inhibits an in-depth understanding of
  the problem. Our aim is thus to assess the ability of 3D hydrodynamical
  simulations to infer the physical mechanisms responsible for damping of
  solar-like oscillations. To this end, a solar high-spatial resolution
  and long-duration hydrodynamical 3D simulation computed with the
  ANTARES code allows probing the coupling between turbulent convection
  and the normal modes of the simulated box. Indeed, normal modes
  of the simulation experience realistic driving and damping in the
  super-adiabatic layers of the simulation. Therefore, investigating
  the properties of the normal modes in the simulation provides a
  unique insight into the mode physics. We demonstrate that such an
  approach provides constraints on the solar damping rates and is able
  to disentangle the relative contribution related to the perturbation
  (by the oscillation) of the turbulent pressure, the gas pressure,
  the radiative flux, and the convective flux contributions. Finally,
  we conclude that using the normal modes of a 3D numerical simulation
  is possible and is potentially able to unveil the respective role of
  the different physical mechanisms responsible for mode damping provided
  the time-duration of the simulation is long enough.

Title: Numerical simulation of DA white dwarf surface convection
Authors: Zaussinger, F.; Kupka, F.; Montgomery, M.; Egbers, Ch.
Bibcode: 2018JPhCS1031a2013Z
Altcode:
  White dwarfs are compact objects with masses comparable to our Sun,
  but a radius similar to our Earth. They are the final evolutionary
  stage for about 95% of all stars in the Galaxy, i.e., for all stars
  that have a final mass less than the Chandrasekhar mass (about 1.4
  times the solar mass), the upper mass limit for which hydrostatic
  equilibrium can be maintained by the degeneracy pressure of electrons
  at very high densities. The outermost shell of most white dwarfs
  contains a convective layer. Even if the latter is very thin (≲
  10 km), it is important for mixing properties, observed radiation,
  and pulsational stability of the whole object. During a long phase
  white dwarfs have effective temperatures T<SUB>eff</SUB> of about
  10000K ∼ 14000K, since the time scale to reach such temperatures
  by cooling is already ≈ 10<SUP>9</SUP> years. Here, we focus on DA
  (hydrogen-rich) white dwarfs with T<SUB>eff</SUB> ≈ 12000K. This is
  at the transition from shallow to deep convection zones. Due to very
  high gravitational acceleration (∼ 10<SUP>6</SUP> g at the surface)
  the material is overturned about five times per second over the distance
  of a few kilometers. Numerical simulations of such objects have to
  be done for a compressible flow and feature highly turbulent granules
  at the surface, which are qualitatively comparable to the convection
  cells observed at the surface of the Sun. For this study we compare
  three white dwarf surface simulations with realistic microphysical
  properties and full 3D radiative transport. The simulations differ
  in effective temperature, namely, T<SUB>eff</SUB> = 11800K, 12100K,
  and 12400K. A statistical analysis of the convective processes as
  function of T<SUB>eff</SUB> is presented.

Title: Mixing and overshooting in surface convection zones of DA
white dwarfs: first results from ANTARES
Authors: Kupka, F.; Zaussinger, F.; Montgomery, M. H.
Bibcode: 2018MNRAS.474.4660K
Altcode: 2017arXiv171200641K
  We present results of a large, high-resolution 3D hydrodynamical
  simulation of the surface layers of a DA white dwarf (WD) with
  T<SUB>eff</SUB> = 11 800 K and log (g) = 8 using the ANTARES code,
  the widest and deepest such simulation to date. Our simulations are in
  good agreement with previous calculations in the Schwarzschild-unstable
  region and in the overshooting region immediately beneath it. Farther
  below, in the wave-dominated region, we find that the rms horizontal
  velocities decay with depth more rapidly than the vertical ones. Since
  mixing requires both vertical and horizontal displacements, this could
  have consequences for the size of the region that is well mixed by
  convection, if this trend is found to hold for deeper layers. We discuss
  how the size of the mixed region affects the calculated settling times
  and inferred steady-state accretion rates for WDs with metals observed
  in their atmospheres.

Title: Studying p-mode damping and the surface effect with
    hydrodynamical simulations
Authors: Kupka, F.; Belkacem, K.; Samadi, R.; Deheuvels, S.
Bibcode: 2017sbcs.conf..222K
Altcode:
  Hydrodynamical simulations can be used as a complementary tool
  to observations for the study of the damping of p-modes and the
  so-called surface effect in solar-like oscillators. Here, we present
  the state-of-the-art in this research. Examples of applications include
  our Sun and the CoRoT target stars HD 49385 and HD 49933.

Title: Modelling of stellar convection
Authors: Kupka, Friedrich; Muthsam, Herbert J.
Bibcode: 2017LRCA....3....1K
Altcode:
  The review considers the modelling process for stellar convection rather
  than specific astrophysical results. For achieving reasonable depth and
  length we deal with hydrodynamics only, omitting MHD. A historically
  oriented introduction offers first glimpses on the physics of stellar
  convection. Examination of its basic properties shows that two very
  different kinds of modelling keep being needed: low dimensional models
  (mixing length, Reynolds stress, etc.) and "full" 3D simulations. A list
  of affordable and not affordable tasks for the latter is given. Various
  low dimensional modelling approaches are put in a hierarchy and basic
  principles which they should respect are formulated. In 3D simulations
  of low Mach number convection the inclusion of then unimportant sound
  waves with their rapid time variation is numerically impossible. We
  describe a number of approaches where the Navier-Stokes equations are
  modified for their elimination (anelastic approximation, etc.). We
  then turn to working with the full Navier-Stokes equations and deal
  with numerical principles for faithful and efficient numerics. Spatial
  differentiation as well as time marching aspects are considered. A list
  of codes allows assessing the state of the art. An important recent
  development is the treatment of even the low Mach number problem without
  prior modification of the basic equation (obviating side effects) by
  specifically designed numerical methods. Finally, we review a number
  of important trends such as how to further develop low-dimensional
  models, how to use 3D models for that purpose, what effect recent
  hardware developments may have on 3D modelling, and others.

Title: Semi-convective layer formation
Authors: Zaussinger, F.; Kupka, F.; Egbers, Ch.; Neben, M.; Hücker,
   S.; Bahr, C.; Schmitt, M.
Bibcode: 2017JPhCS.837a2012Z
Altcode:
  Semi-convective mixing, as an example of double-diffusive convection,
  is of general importance in multi-component fluid mixing processes. In
  astrophysics it occurs when the mean molecular weight gradient caused
  by a mixture of light material on top of heavier one counteracts
  the convective instability caused by a temperature gradient. Direct
  numerical simulations of double-diffusive fluid flows in a realistic
  stellar or planetary parameter space are currently non-feasible. Hence,
  a model describing incompressible semi-convection was developed,
  which allows to investigate semi-convective layer formation. A
  detailed parameter study with varying Rayleigh number and stability
  parameter has been performed for the giant planet case. We conclude
  that semi-convective layering may not play that important role as
  suggested in earlier works for the planetary case.

Title: Multidimensional modelling of classical pulsating stars
Authors: Muthsam, H. J.; Kupka, F.
Bibcode: 2016CoKon.105..117M
Altcode: 2016arXiv160103325M
  After an overview of general aspects of modelling the pulsation-
  convection interaction we present reasons why such simulations
  (in multidimensions) are needed but, at the same time, pose a
  considerable challenge. We then discuss, for several topics, what
  insights multidimensional simulations have either already provided or
  can be expected to yield in the future. We finally discuss properties
  of our ANTARES code. Many of these features can be expected to be
  characteristic of other codes which may possibly be applied to these
  physical questions in the foreseeable future.

Title: The ANTARES Code: New Developments
Authors: Blies, P. M.; Kupka, F.; Muthsam, H. J.
Bibcode: 2015ASPC..498..191B
Altcode:
  We give an update on the ANTARES code. It was presented by Muthsam
  et al. (2010) and has since experienced various improvements and
  has also been extended by new features which we will mention in this
  paper. Two new features will be presented in a bit more detail: the
  parallel multigrid solver for the 2D non-linear, generalized Helmholtz
  equation by Happenhofer (2014) and the capability to use curvilinear
  grids by Grimm-Strele (2014).

Title: Multidimensional realistic modelling of Cepheid-like variables
    - II. Analysis of a Cepheid model
Authors: Mundprecht, Eva; Muthsam, Herbert J.; Kupka, Friedrich
Bibcode: 2015MNRAS.449.2539M
Altcode: 2015arXiv150200449M
  Non-local, time-dependent convection models have been used to explain
  the location of double-mode pulsations in Cepheids in the HR diagram as
  well as the existence and location of the red edge of the instability
  strip. These properties are highly sensitive to model parameters. We use
  2D radiation-hydrodynamical simulations with realistic microphysics and
  grey radiative transfer to model a short-period Cepheid. The simulations
  show that the strength of the convection zone varies significantly
  over the pulsation period and exhibits a phase shift relative to the
  variations in radius. We evaluate the convective flux and the work
  integral as predicted by the most common convection models. It turns out
  that over one pulsation cycle the model parameter α<SUB>c</SUB>, has
  to be varied by up to a factor of beyond 2 to match the convective flux
  obtained from the simulations. To bring convective fluxes integrated
  over the He II convection zone and the overshoot zone below into
  agreement, this parameter has to be varied by a factor of up to ∼7.5
  (Kuhfuß). We then present results on the energetics of the convection
  and overshoot zone by radially symmetric and fluctuating quantities. To
  successfully model this scenario by a static, 1D or even by a simple
  time-dependent model appears extremely challenging. We conclude that
  significant improvements are needed to make predictions based on 1D
  models more robust and to improve the reliability of conclusions on
  the convection-pulsation coupling drawn from them. Multidimensional
  simulations can provide guidelines for developing descriptions of
  convection then applied in traditional 1D modelling.

Title: Achievable efficiency of numerical methods for simulations
    of solar surface convection
Authors: Grimm-Strele, H.; Kupka, F.; Muthsam, H. J.
Bibcode: 2015CoPhC.188....7G
Altcode: 2014arXiv1406.1891G
  We investigate the achievable efficiency of both the time and the space
  discretisation methods used in Antares for mixed parabolic-hyperbolic
  problems. We show that the fifth order variant of WENO combined with a
  second order Runge-Kutta scheme is not only more accurate than standard
  first and second order schemes, but also more efficient taking the
  computation time into account. Then, we calculate the error decay rates
  of WENO with several explicit Runge-Kutta schemes for advective and
  diffusive problems with smooth and non-smooth initial conditions. With
  this data, we estimate the computational costs of three-dimensional
  simulations of stellar surface convection and show that SSP RK(3,2)
  is the most efficient scheme considered in this comparison.

Title: Realistic simulations of stellar surface convection with
ANTARES: I. Boundary conditions and model relaxation
Authors: Grimm-Strele, H.; Kupka, F.; Löw-Baselli, B.; Mundprecht,
   E.; Zaussinger, F.; Schiansky, P.
Bibcode: 2015NewA...34..278G
Altcode: 2013arXiv1305.0743G
  We have implemented open boundary conditions into the ANTARES
  code to increase the realism of our simulations of stellar surface
  convection. Even though we greatly benefit from the high accuracy
  of our fifth order numerical scheme (WENO5) the broader stencils
  needed for the numerical scheme complicate the implementation of
  boundary conditions. We show that the effective temperature of a
  numerical simulation cannot be changed by corrections at the lower
  boundary since the thermal stratification does only change on the
  Kelvin-Helmholtz time scale. Except for very shallow models this time
  scale cannot be covered by multidimensional simulations due to the
  enormous computational requirements. We demonstrate to what extent
  numerical simulations of stellar surface convection are sensitive to
  the initial conditions and the boundary conditions. An ill-conceived
  choice of parameters for the boundary conditions can have a severe
  impact. Numerical simulations of stellar surface convection will
  only be (physically) meaningful and realistic if the initial model,
  the extent and position of the simulation box and the parameters from
  the boundary conditions are chosen adequately.

Title: The PLATO 2.0 mission
Authors: Rauer, H.; Catala, C.; Aerts, C.; Appourchaux, T.; Benz,
   W.; Brandeker, A.; Christensen-Dalsgaard, J.; Deleuil, M.; Gizon,
   L.; Goupil, M. -J.; Güdel, M.; Janot-Pacheco, E.; Mas-Hesse,
   M.; Pagano, I.; Piotto, G.; Pollacco, D.; Santos, Ċ.; Smith, A.;
   Suárez, J. -C.; Szabó, R.; Udry, S.; Adibekyan, V.; Alibert, Y.;
   Almenara, J. -M.; Amaro-Seoane, P.; Eiff, M. Ammler-von; Asplund, M.;
   Antonello, E.; Barnes, S.; Baudin, F.; Belkacem, K.; Bergemann, M.;
   Bihain, G.; Birch, A. C.; Bonfils, X.; Boisse, I.; Bonomo, A. S.;
   Borsa, F.; Brandão, I. M.; Brocato, E.; Brun, S.; Burleigh, M.;
   Burston, R.; Cabrera, J.; Cassisi, S.; Chaplin, W.; Charpinet, S.;
   Chiappini, C.; Church, R. P.; Csizmadia, Sz.; Cunha, M.; Damasso, M.;
   Davies, M. B.; Deeg, H. J.; Díaz, R. F.; Dreizler, S.; Dreyer, C.;
   Eggenberger, P.; Ehrenreich, D.; Eigmüller, P.; Erikson, A.; Farmer,
   R.; Feltzing, S.; de Oliveira Fialho, F.; Figueira, P.; Forveille,
   T.; Fridlund, M.; García, R. A.; Giommi, P.; Giuffrida, G.; Godolt,
   M.; Gomes da Silva, J.; Granzer, T.; Grenfell, J. L.; Grotsch-Noels,
   A.; Günther, E.; Haswell, C. A.; Hatzes, A. P.; Hébrard, G.; Hekker,
   S.; Helled, R.; Heng, K.; Jenkins, J. M.; Johansen, A.; Khodachenko,
   M. L.; Kislyakova, K. G.; Kley, W.; Kolb, U.; Krivova, N.; Kupka, F.;
   Lammer, H.; Lanza, A. F.; Lebreton, Y.; Magrin, D.; Marcos-Arenal,
   P.; Marrese, P. M.; Marques, J. P.; Martins, J.; Mathis, S.; Mathur,
   S.; Messina, S.; Miglio, A.; Montalban, J.; Montalto, M.; Monteiro,
   M. J. P. F. G.; Moradi, H.; Moravveji, E.; Mordasini, C.; Morel, T.;
   Mortier, A.; Nascimbeni, V.; Nelson, R. P.; Nielsen, M. B.; Noack,
   L.; Norton, A. J.; Ofir, A.; Oshagh, M.; Ouazzani, R. -M.; Pápics,
   P.; Parro, V. C.; Petit, P.; Plez, B.; Poretti, E.; Quirrenbach, A.;
   Ragazzoni, R.; Raimondo, G.; Rainer, M.; Reese, D. R.; Redmer, R.;
   Reffert, S.; Rojas-Ayala, B.; Roxburgh, I. W.; Salmon, S.; Santerne,
   A.; Schneider, J.; Schou, J.; Schuh, S.; Schunker, H.; Silva-Valio,
   A.; Silvotti, R.; Skillen, I.; Snellen, I.; Sohl, F.; Sousa, S. G.;
   Sozzetti, A.; Stello, D.; Strassmeier, K. G.; Švanda, M.; Szabó,
   Gy. M.; Tkachenko, A.; Valencia, D.; Van Grootel, V.; Vauclair,
   S. D.; Ventura, P.; Wagner, F. W.; Walton, N. A.; Weingrill, J.;
   Werner, S. C.; Wheatley, P. J.; Zwintz, K.
Bibcode: 2014ExA....38..249R
Altcode: 2014ExA...tmp...41R; 2013arXiv1310.0696R
  PLATO 2.0 has recently been selected for ESA's M3 launch opportunity
  (2022/24). Providing accurate key planet parameters (radius, mass,
  density and age) in statistical numbers, it addresses fundamental
  questions such as: How do planetary systems form and evolve? Are there
  other systems with planets like ours, including potentially habitable
  planets? The PLATO 2.0 instrument consists of 34 small aperture
  telescopes (32 with 25 s readout cadence and 2 with 2.5 s candence)
  providing a wide field-of-view (2232 deg <SUP>2</SUP>) and a large
  photometric magnitude range (4-16 mag). It focusses on bright (4-11
  mag) stars in wide fields to detect and characterize planets down to
  Earth-size by photometric transits, whose masses can then be determined
  by ground-based radial-velocity follow-up measurements. Asteroseismology
  will be performed for these bright stars to obtain highly accurate
  stellar parameters, including masses and ages. The combination of
  bright targets and asteroseismology results in high accuracy for
  the bulk planet parameters: 2 %, 4-10 % and 10 % for planet radii,
  masses and ages, respectively. The planned baseline observing strategy
  includes two long pointings (2-3 years) to detect and bulk characterize
  planets reaching into the habitable zone (HZ) of solar-like stars
  and an additional step-and-stare phase to cover in total about 50 %
  of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect
  and characterize hundreds of small planets, and thousands of planets
  in the Neptune to gas giant regime out to the HZ. It will therefore
  provide the first large-scale catalogue of bulk characterized planets
  with accurate radii, masses, mean densities and ages. This catalogue
  will include terrestrial planets at intermediate orbital distances,
  where surface temperatures are moderate. Coverage of this parameter
  range with statistical numbers of bulk characterized planets is unique
  to PLATO 2.0. The PLATO 2.0 catalogue allows us to e.g.: - complete
  our knowledge of planet diversity for low-mass objects, - correlate the
  planet mean density-orbital distance distribution with predictions from
  planet formation theories,- constrain the influence of planet migration
  and scattering on the architecture of multiple systems, and - specify
  how planet and system parameters change with host star characteristics,
  such as type, metallicity and age. The catalogue will allow us to study
  planets and planetary systems at different evolutionary phases. It
  will further provide a census for small, low-mass planets. This will
  serve to identify objects which retained their primordial hydrogen
  atmosphere and in general the typical characteristics of planets
  in such low-mass, low-density range. Planets detected by PLATO 2.0
  will orbit bright stars and many of them will be targets for future
  atmosphere spectroscopy exploring their atmosphere. Furthermore,
  the mission has the potential to detect exomoons, planetary rings,
  binary and Trojan planets. The planetary science possible with PLATO
  2.0 is complemented by its impact on stellar and galactic science via
  asteroseismology as well as light curves of all kinds of variable stars,
  together with observations of stellar clusters of different ages. This
  will allow us to improve stellar models and study stellar activity. A
  large number of well-known ages from red giant stars will probe the
  structure and evolution of our Galaxy. Asteroseismic ages of bright
  stars for different phases of stellar evolution allow calibrating
  stellar age-rotation relationships. Together with the results of ESA's
  Gaia mission, the results of PLATO 2.0 will provide a huge legacy to
  planetary, stellar and galactic science.

Title: Improved Time Integration for WENO Methods in Astrophysical
    Applications
Authors: Kupka, F.; Grimm–Strele, H.; Happenhofer, N.; Higueras,
   I.; Koch, O.; Muthsam, H. J.
Bibcode: 2014ASPC..488..243K
Altcode:
  Weighted essentially non-oscillatory methods are a powerful approach to
  discretize advection and pressure gradient terms in the hydrodynamical
  equations, since they yield higher effective resolution than traditional
  methods. But in some astrophysical problems, low Mach number flows have
  to be tackled or the flow may change from a low to a high Mach number
  flow, spatially or in time, and diffusion or radiative transfer can
  impose severe limitations on time steps allowed in explicit time
  integration methods. We provide a summary of new developments on
  semi-implicit time integration methods useful for astrophysical problems
  such as numerical simulations of stellar surfaces and envelopes, and
  the basic physical question of how to improve models of double-diffusive
  convection. We discuss several applications of these new methods.

Title: The effects of rotation on a double-diffusive layer in a
    rotating spherical shell
Authors: Blies, Patrick; Kupka, Friedrich; Zaussinger, Florian;
   Hollerbach, Rainer
Bibcode: 2014arXiv1404.6086B
Altcode:
  So far, numerical studies of double-diffusive layering in turbulent
  convective flows have neglected the effects of rotation. We undertake
  a first step into that direction by investigating how Coriolis
  forces affect a double-diffusive layer inside a rotating spherical
  shell. For this purpose we have run simulations in a parameter regime
  where these layers are expected to form and successively increased
  the rate of rotation with the result that fast rotation is found to
  have a similar stabilising effect on the overall convective flux as
  an increase of the stability ratio $R_{\rho}$ has in a non-rotating
  setup. We have also studied to what extent the regimes of rotational
  constraints suggested by King, Stellmach, and Buffett (2013) for
  rotation in the case of Rayleigh-Bénard convection are influenced
  by double-diffusive convection: their classification could also be
  applicable to the case of double-diffusive convection in a spherical
  shell if it is extended to be also a function of the stability ratio
  $R_{\rho}$. Furthermore, we examined the ratio of saline and thermal
  Nusselt numbers and compared our results with models of Spruit (2013),
  Rosenblum et al. (2011) and Wood, Garaud, and Stellmach (2013). We
  find our data to be fitted best by Spruit's model. Our result that
  fast rotation further decreases the convective transport, which is
  already lowered by double-diffusive convection, could play a major
  role for e.g. the modeling of the interior of some rapidly rotating
  giant planets, as gaseous giant planets have recently been proposed
  to be influenced by double-diffusive convection.

Title: Curvilinear grids for WENO methods in astrophysical simulations
Authors: Grimm-Strele, H.; Kupka, F.; Muthsam, H. J.
Bibcode: 2014CoPhC.185..764G
Altcode: 2013arXiv1308.3066G
  We investigate the applicability of curvilinear grids in the context of
  astrophysical simulations and WENO schemes. With the non-smooth mapping
  functions from Calhoun et al. (2008), we can tackle many astrophysical
  problems which were out of scope with the standard grids in numerical
  astrophysics. We describe the difficulties occurring when implementing
  curvilinear coordinates into our WENO code, and how we overcome
  them. We illustrate the theoretical results with numerical data. The
  WENO finite difference scheme works only for high Mach number flows
  and smooth mapping functions, whereas the finite volume scheme gives
  accurate results even for low Mach number flows and on non-smooth grids.

Title: Pulsation - convection interaction
Authors: Kupka, F.; Mundprecht, E.; Muthsam, H. J.
Bibcode: 2014IAUS..301..177K
Altcode:
  A lot of effort has been devoted to the hydrodynamical modelling
  of Cepheids in one dimension. While the recovery of the most basic
  properties such as the pulsational instability itself has been achieved
  already a long time ago, properties such as the observed double-mode
  pulsation of some objects and the red-edge of the classical instability
  strip and their dependence on metallicity have remained a delicate
  issue. The uncertainty introduced by adjustable parameters and further
  physical approximations introduced in one-dimensional model equations
  motivate an investigation based on numerical simulations which use
  the full hydrodynamical equations. In this talk, results from such
  two-dimensional numerical simulations of a short period Cepheid are
  presented. The importance of a carefully designed numerical setup, in
  particular of sufficient resolution and domain extent, is discussed. The
  problematic issue of how to reliably choose fixed parameters for the
  one-dimensional model is illustrated. Results from an analysis of
  the interaction of pulsation with convection are shown concerning the
  large-scale structure of the He ii ionization zone. We also address
  the influence of convection on the atmospheric structure. Considering
  the potential of hydrodynamical simulations and the wealth of ever
  improving observational data an outlook on possible future work in
  this field of research is given.

Title: Multidimensional realistic modelling of Cepheid-like variables
    - I. Extensions of the ANTARES code
Authors: Mundprecht, Eva; Muthsam, Herbert J.; Kupka, Friedrich
Bibcode: 2013MNRAS.435.3191M
Altcode: 2012arXiv1209.2952M; 2013MNRAS.tmp.2236M
  We have extended the ANTARES code to simulate the coupling of pulsation
  with convection in Cepheid-like variables in an increasingly realistic
  way, in particular in multidimensions, 2D at this stage. Present-day
  models of radially pulsating stars assume radial symmetry and have the
  pulsation-convection interaction included via model equations containing
  ad hoc closures and moreover parameters whose values are barely
  known. We intend to construct ever more realistic multidimensional
  models of Cepheids. In this paper, the first of a series, we describe
  the basic numerical approach and how it is motivated by physical
  properties of these objects which are sometimes more, sometimes less
  obvious. For the construction of appropriate models a polar grid
  comoving with the mean radial velocity has been introduced to optimize
  radial resolution throughout the different pulsation phases. The grid is
  radially stretched to account for the change of spatial scales due to
  vertical stratification and a new grid refinement scheme is introduced
  to resolve the upper, hydrogen ionization zone where the gradient of
  temperature is steepest. We demonstrate that the simulations are not
  conservative when the original weighted essentially non-oscillatory
  method implemented in ANTARES is used and derive a new scheme which
  allows a conservative time evolution. The numerical approximation of
  diffusion follows the same principles. Moreover, the radiative transfer
  solver has been modified to improve the efficiency of calculations on
  parallel computers. We show that with these improvements, the ANTARES
  code can be used for realistic simulations of the convection-pulsation
  interaction in Cepheids. We discuss the properties of several numerical
  models of this kind which include the upper 42 per cent of a Cepheid
  along its radial coordinate and assume different opening angles. The
  models are suitable for an in-depth study of convection and pulsation
  in these objects.

Title: Semi-convection
Authors: Zaussinger, F.; Kupka, F.; Muthsam, H. J.
Bibcode: 2013LNP...865..219Z
Altcode:
  Double-diffusive processes play an important role in various
  astrophysical and geophysical systems. Especially the case which
  considers a thermally unstable configuration stabilized by mean
  molecular weight and which is known as semi-convection has been
  studied for several decades. Whether a semi-convective region in
  a star should be treated layered or fully mixed has not yet been
  conclusively answered. However, in recent years numerical simulations
  have been used to investigate this fluid dynamical instability. With
  high resolution methods we can now develop a better understanding
  of this mixing process. For this review our intention is to present
  semi-convection from different points of view. At first, a summary
  of studies made during the last decades is used to demonstrate the
  continuous importance of semi- convection for stellar evolution. The
  physical process itself as well as linear stability criteria are
  explained subsequently. Finally, models, experiments, and the study
  through numerical simulations are discussed. Semi-convective mixing and
  related questions in stellar evolution and, recently, also in exoplanet
  science continue to be a vivid research field and have never ceased
  to surprise.

Title: Total-variation-diminishing implicit-explicit Runge-Kutta
    methods for the simulation of double-diffusive convection in
    astrophysics
Authors: Kupka, Friedrich; Happenhofer, Natalie; Higueras, Inmaculada;
   Koch, Othmar
Bibcode: 2012JCoPh.231.3561K
Altcode: 2011arXiv1106.5672K
  We put forward the use of total-variation-diminishing (or
  more generally, strong stability preserving) implicit-explicit
  Runge-Kutta methods for the time integration of the equations of
  motion associated with the semiconvection problem in the simulation
  of stellar convection. The fully compressible Navier-Stokes equation,
  augmented by continuity and total energy equations, and an equation
  of state describing the relation between the thermodynamic quantities,
  is semi-discretized in space by essentially non-oscillatory schemes and
  dissipative finite difference methods. It is subsequently integrated
  in time by Runge-Kutta methods which are constructed such as to
  preserve the total variation diminishing (or strong stability) property
  satisfied by the spatial discretization coupled with the forward Euler
  method. We analyse the stability, accuracy and dissipativity of the
  time integrators and demonstrate that the most successful methods
  yield a substantial gain in computational efficiency as compared to
  classical explicit Runge-Kutta methods.

Title: Divisions Iv-V / Working Group ap &amp; Related Stars
Authors: Mathys, Gautier; Cunha, Margarida; Dworetsky, Michael;
   Kochukhov, Oleg; Kupka, Friedrich; LeBlanc, Francis; Monier, Richard;
   Paunzen, Ernst; Pintado, Olga; Piskunov, Nikolai; Ziznovsky, Jozef
Bibcode: 2012IAUTA..28..203M
Altcode:
  The purpose of the Working Group on Ap and Related Stars (ApWG) is
  to promote and facilitate research about stars in the spectral type
  range from B to early F that exhibit surface chemical peculiarities
  and related phenomena. This is a very active field of research, in
  which a wide variety of new developments have taken place since 2009,
  as illustrated by the following selected highlights.

Title: Layered convection in double diffusive fluids
Authors: Zaussinger, F.; Kupka, F.; Muthsam, H. J.; Happenhofer, N.;
   Grimm-Strele, H.
Bibcode: 2012EGUGA..14.1830Z
Altcode:
  Double diffusive convection plays an important role in astrophysics
  and oceanography where under certain conditions a thermally
  unstable temperature gradient is counteracted by a stable solute
  gradient. This configuration is well known from salt lakes, where
  the salt concentration stabilizes convective motions and a layered
  structure emerges. Similar conditions are found in stellar interiors,
  where helium as the stabilizing component inhibits the development
  of convection and the occurrence of double-diffusive staircases is
  assumed. We investigate mixing timescales and stability conditions
  using theoretical estimates and numerical simulations covering a
  broad range of parameter sets by varying Prandtl-, Lewis- and Rayleigh
  numbers. To shed light on the numerically inaccessible astrophysical
  case we extrapolate to the relevant parameter range. We investigate
  the initial layer formation process as well as the stability of evolved
  layers by performing direct numerical simulations in 2D and 3D using the
  Boussinesq approximation. A fitting formula for the Nusselt numbers and
  the effective mixing rates is given. Finally, we present a semi-implicit
  method to solve the compressible counterpart of the governing equations
  which has the advantage to cover the entire relevant Mach number range.

Title: Simulations of stellar convection, pulsation and semiconvection
Authors: Muthsam, Herbert J.; Kupka, Friedrich; Mundprecht, Eva;
   Zaussinger, Florian; Grimm-Strele, Hannes; Happenhofer, Natalie
Bibcode: 2011IAUS..271..179M
Altcode: 2010arXiv1009.2409M
  We report on modelling in stellar astrophysics with the ANTARES
  code. First, we describe properties of turbulence in solar granulation
  as seen in high-resolution calculations. Then, we turn to the first
  2D model of pulsation-convection interaction in a cepheid. We discuss
  properties of the outer and the HeII ionization zone. Thirdly, we
  report on our work regarding models of semiconvection in the context
  of stellar physics.

Title: Vamdc as a Resource for Atomic and Molecular Data and the
    New Release of Vald
Authors: Kupka, F.; Dubernet, M. -L.; VAMDC Collaboration
Bibcode: 2011BaltA..20..503K
Altcode: 2011OAst...20..503K; 2012arXiv1201.0154K
  The Virtual Atomic and Molecular Data Centre (VAMDC) is an EU-FP7
  project devoted to build a common electronic infrastructure for the
  exchange and distribution of atomic and molecular data. Within VAMDC
  scientists from many different disciplines in atomic and molecular
  physics collaborate with users of their data and also with scientists
  and engineers from the information and communication technology
  community. In this presentation, an overview of the current status
  of VAMDC and its capabilities is provided. In the second part of
  the presentation I will focus on one of the databases which have
  become a part of the VAMDC platform, the Vienna Atomic Line Data Base
  (VALD). VALD has developed into a well-known resource of atomic data for
  spectroscopy, particularly in astrophysics. A new release, VALD-3, will
  provide numerous improvements over its predecessor. This particularly
  relates to the data contents where new sets of atomic data for both
  precision spectroscopy (i.e., with data for observed energy levels) as
  well as opacity calculations (i.e., with data involving predicted energy
  levels) have been included. Data for selected diatomic molecules have
  been added, and a new system for data distribution and data referencing
  provides more convenience in using the third release of VALD.

Title: Asteroseismology of solar-type stars with Kepler I: Data
    analysis
Authors: Karoff, C.; Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.;
   Garcia, R. A.; Houdek, G.; Metcalfe, T. S.; Molenda-Żakowicz, J.;
   Monteiro, M. J. P. F. G.; Thompson, M. J.; Christensen-Dalsgaard, J.;
   Gilliland, R. L.; Kjeldsen, H.; Basu, S.; Bedding, T. R.; Campante,
   T. L.; Eggenberger, P.; Fletcher, S. T.; Gaulme, P.; Handberg, R.;
   Hekker, S.; Martic, M.; Mathur, S.; Mosser, B.; Regulo, C.; Roxburgh,
   I. W.; Salabert, D.; Stello, D.; Verner, G. A.; Belkacem, K.; Biazzo,
   K.; Cunha, M. S.; Gruberbauer, M.; Guzik, J. A.; Kupka, F.; Leroy,
   B.; Ludwig, H. -G.; Mathis, S.; Noels, A.; Noyes, R. W.; Roca Cortes,
   T.; Roth, M.; Sato, K. H.; Schmitt, J.; Suran, M. D.; Trampedach,
   R.; Uytterhoeven, K.; Ventura, R.
Bibcode: 2010AN....331..972K
Altcode: 2010arXiv1005.0507K
  We report on the first asteroseismic analysis of solar-type stars
  observed by Kepler. Observations of three G-type stars, made at
  one-minute cadence during the first 33.5 days of science operations,
  reveal high signal-to-noise solar-like oscillation spectra in all three
  stars: About 20 modes of oscillation can clearly be distinguished
  in each star. We discuss the appearance of the oscillation spectra,
  including the presence of a possible signature of faculae, and the
  presence of mixed modes in one of the three stars.

Title: VAMDC: The Virtual Atomic and Molecular Data Centre: a Service
    Orientated Data Infrastructure for e- Research
Authors: Mason, N. J.; Dubernet, M. L.; Benson, K. M.; Bureau, J.;
   Heiter, U.; Kupka, F.; Le Sidaner, P.; Piskunov, N.; Rixon, G. T.;
   Schlemmer, S.; Shih, A.; Tennyson, J.; Walton, N.; Witherick, D. W.
Bibcode: 2010epsc.conf..861M
Altcode:
  No abstract at ADS

Title: ANTARES - A Numerical Tool for Astrophysical RESearch with
    applications to solar granulation
Authors: Muthsam, H. J.; Kupka, F.; Löw-Baselli, B.; Obertscheider,
   C.; Langer, M.; Lenz, P.
Bibcode: 2010NewA...15..460M
Altcode: 2009arXiv0905.0177M
  We discuss the general design of the ANTARES code which is intended
  for simulations in stellar hydrodynamics with radiative transfer and
  realistic microphysics in 1D, 2D and 3D. We then compare the quality of
  various numerical methods. We have applied ANTARES in order to obtain
  high resolution simulations of solar granulation which we describe and
  analyze. In order to obtain high resolution, we apply grid refinement
  to a region predominantly occupied by an exploding granule. Strong,
  rapidly rotating vortex tubes of small diameter (∼100km) generated
  by the downdrafts and ascending into the photosphere near the granule
  boundaries evolve, often entering the photosphere from below in an
  arclike fashion. They essentially contribute to the turbulent velocity
  field near the granule boundaries.

Title: INTER-DIVISION IV-V WORKING GROUP on Ap and Related Stars
Authors: Cunha, Margarida S.; Weiss, Werner; Dworetsky, Mike;
   Kochukhov, Oleg; Kupka, Friedrich; Leblanc, Francis; Monier, Richard;
   Paunzen, Ernst; Piskunov, Nikolai; Shibahashi, Hiromoto; Smalley,
   Barry; Ziznovsky, Jozef
Bibcode: 2010IAUTB..27..205C
Altcode:
  The business meeting started at 11h00, in the presence of 18 members,
  with a brief summary of the activities and achievements of the Working
  group during the triennium 2006-2009.

Title: The Asteroseismic Potential of Kepler: First Results for
    Solar-Type Stars
Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; García,
   R. A.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz,
   J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Brown, T. M.;
   Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Borucki,
   W. J.; Koch, D.; Jenkins, J. M.; Ballot, J.; Basu, S.; Bazot, M.;
   Bedding, T. R.; Benomar, O.; Bonanno, A.; Brandão, I. M.; Bruntt,
   H.; Campante, T. L.; Creevey, O. L.; Di Mauro, M. P.; Doǧan,
   G.; Dreizler, S.; Eggenberger, P.; Esch, L.; Fletcher, S. T.;
   Frandsen, S.; Gai, N.; Gaulme, P.; Handberg, R.; Hekker, S.; Howe,
   R.; Huber, D.; Korzennik, S. G.; Lebrun, J. C.; Leccia, S.; Martic,
   M.; Mathur, S.; Mosser, B.; New, R.; Quirion, P. -O.; Régulo, C.;
   Roxburgh, I. W.; Salabert, D.; Schou, J.; Sousa, S. G.; Stello, D.;
   Verner, G. A.; Arentoft, T.; Barban, C.; Belkacem, K.; Benatti, S.;
   Biazzo, K.; Boumier, P.; Bradley, P. A.; Broomhall, A. -M.; Buzasi,
   D. L.; Claudi, R. U.; Cunha, M. S.; D'Antona, F.; Deheuvels, S.;
   Derekas, A.; García Hernández, A.; Giampapa, M. S.; Goupil, M. J.;
   Gruberbauer, M.; Guzik, J. A.; Hale, S. J.; Ireland, M. J.; Kiss,
   L. L.; Kitiashvili, I. N.; Kolenberg, K.; Korhonen, H.; Kosovichev,
   A. G.; Kupka, F.; Lebreton, Y.; Leroy, B.; Ludwig, H. -G.; Mathis, S.;
   Michel, E.; Miglio, A.; Montalbán, J.; Moya, A.; Noels, A.; Noyes,
   R. W.; Pallé, P. L.; Piau, L.; Preston, H. L.; Roca Cortés, T.;
   Roth, M.; Sato, K. H.; Schmitt, J.; Serenelli, A. M.; Silva Aguirre,
   V.; Stevens, I. R.; Suárez, J. C.; Suran, M. D.; Trampedach, R.;
   Turck-Chièze, S.; Uytterhoeven, K.; Ventura, R.; Wilson, P. A.
Bibcode: 2010ApJ...713L.169C
Altcode: 2010arXiv1001.0506C
  We present preliminary asteroseismic results from Kepler on three G-type
  stars. The observations, made at one-minute cadence during the first
  33.5 days of science operations, reveal high signal-to-noise solar-like
  oscillation spectra in all three stars: about 20 modes of oscillation
  may be clearly distinguished in each star. We discuss the appearance of
  the oscillation spectra, use the frequencies and frequency separations
  to provide first results on the radii, masses, and ages of the stars,
  and comment in the light of these results on prospects for inference
  on other solar-type stars that Kepler will observe.

Title: Effects of resolution and helium abundance in A star surface
    convection simulations
Authors: Kupka, F.; Ballot, J.; Muthsam, H. J.
Bibcode: 2009CoAst.160...30K
Altcode: 2009arXiv0905.0070K
  We present results from 2D radiation-hydrodynamical simulations of fully
  compressible convection for the surface layers of A-type stars with
  the ANTARES code. Spectroscopic indicators for photospheric convective
  velocity fields show a maximum of velocities near Teff ∼ 8000 K with
  the largest values measured for the subgroup of Am stars. Thus far,
  no prognostic model, neither theoret ical nor numerical, is able to
  exactly reproduce the line profiles of sharp line A and Am stars in that
  temperature range. As the helium abundance of A stars is not known from
  observations, we have considered two extreme cases for our simulations:
  a solar helium abundance as an upper limit and zero helium abundance
  as a lower limit. The simulation for the helium free case is found to
  differ from the case with solar helium abundance by larger velocities,
  larger flow structures, and by a sign reversal of the flux of kinetic
  energy inside the hydrogen ionisation zone. Both simulations show
  extended shock fronts emerg- ing from the optical surface, as well
  as mixing far below the region of partial ionisation of hydrogen, and
  vertical oscillations emerging after initial perturba- tions have been
  damped. We discuss problems related to the rapid radiative cooling at
  the surface of A-type stars such as resolution and efficient relax-
  ation. This includes identifying the radiative cooling rate Qrad ,
  which poses the most severe time step limitation for the dynamical
  equation for the evolution of energy density, as a stiff term. It is
  thus a numerical rather than a physical constraint for the numerical
  simulation of these objects. The present work is considered as a
  step towards a systematic study of convection in A- to F-type stars,
  encouraged by the new data becoming available for these objects from
  both asteroseismological missions and from high resolution spectroscopy.

Title: Atmospheric velocity fields in tepid main sequence stars
Authors: Landstreet, J. D.; Kupka, F.; Ford, H. A.; Officer, T.;
   Sigut, T. A. A.; Silaj, J.; Strasser, S.; Townshend, A.
Bibcode: 2009A&A...503..973L
Altcode: 2009arXiv0906.3824L
  Context: The line profiles of the stars with {v<SUB>e</SUB> sin i} below
  a few km s<SUP>-1</SUP> can reveal direct signatures of local velocity
  fields such as convection in stellar atmospheres. This effect is well
  established in cool main sequence stars, and has been detected and
  studied in three A stars. <BR />Aims: This paper reports observations
  of main sequence B, A and F stars (1) to identify additional stars with
  sufficiently low values of {v<SUB>e</SUB> sin i} to search for spectral
  line profile signatures of local velocity fields and (2) to explore how
  the signatures of the local velocity fields in the atmosphere depend
  on stellar parameters such as effective temperature and peculiarity
  type. <BR />Methods: We have carried out a spectroscopic survey of B and
  A stars of low {v<SUB>e</SUB> sin i} at high resolution. Comparison of
  model spectra with those observed allows us to detect signatures of the
  local velocity fields such as asymmetric excess line wing absorption,
  best-fit {v<SUB>e</SUB> sin i} parameter values that are found to be
  larger for strong lines than for weak lines, and discrepancies between
  observed and modelled line profile shapes. <BR />Results: Symptoms
  of local atmospheric velocity fields are always detected through
  a non-zero microturbulence parameter for main sequence stars having
  {T<SUB>e</SUB>} below about 10 000 K, but not for hotter stars. Direct
  line profile tracers of the atmospheric velocity field are found in six
  very sharp-lined stars in addition to the three reported earlier. Direct
  signatures of velocity fields are found to occur in A stars with and
  without the Am chemical peculiarities, although the amplitude of the
  effects seems larger in Am stars. Velocity fields are also directly
  detected in spectral line profiles of A and early F supergiants, but
  without significant line asymmetries. <BR />Conclusions: We confirm
  that several atmospheric velocity field signatures, particularly excess
  line wing absorption which is stronger in the blue line wing than
  in the red, are detectable in the spectral lines of main sequence A
  stars of sufficiently low {v<SUB>e</SUB> sin i}. We triple the sample
  of A stars known to show these effects, which are found both in Am
  and normal A stars. We argue that the observed line distortions are
  probably due to convective motions reaching the atmosphere. These data
  still have not been satisfactorily explained by models of atmospheric
  convection, including numerical simulations. <P />Based in part on
  observations obtained at the <P />Canada-France-Hawaii Telescope
  (CFHT) which is operated by the <P />National Research Council of
  Canada, the Institut National des <P />Sciences de l'Univers of the
  Centre National de la Recherche <P />Scientifique of France, and the
  University of <P />Hawaii. <P />Based in part on observations made at
  <P />Observatoire de Haute Provence (CNRS), France.

Title: Using p-mode excitation rates for probing convection in
    solar-like stars
Authors: Kupka, F.; Belkacem, K.; Goupil, J. -M.; Samadi, R.
Bibcode: 2009CoAst.159...24K
Altcode:
  We discuss how the possibility to measure mode excitation rates through
  means of helio- and asteroseismology has improved our capabilities to
  test convection models and numerical simulations of surface convection
  and avoids ambiguities that have limited previous approaches.

Title: 3D stellar atmospheres for stellar structure models and
    asteroseismology.
Authors: Kupka, F.
Bibcode: 2009MmSAI..80..701K
Altcode: 2009arXiv0911.3353K
  Convection is the most important physical process that determines the
  structure of the envelopes of cool stars. It influences the surface
  radiation flux and the shape of observed spectral line profiles and is
  responsible for both generating and damping solar-like oscillations,
  among others. 3D numerical simulations of stellar surface convection
  have developed into a powerful tool to model and analyse the physical
  mechanisms operating at the surface of cool stars. This review
  discusses the main principles of 3D stellar atmospheres used for such
  applications. The requirements from stellar structure and evolution
  theory to use them as boundary conditions are analysed as well as the
  capabilities of using helio- and asteroseismology to reduce modelling
  uncertainties and probing the consistency and accuracy of 3D stellar
  atmospheres as part of this process. Simulations for the solar surface
  made by different teams are compared and some issues concerning the
  uncertainties of this modelling approach are discussed.

Title: An Introduction to Turbulence
Authors: Hillebrandt, W.; Kupka, F.
Bibcode: 2009LNP...756....1H
Altcode:
  No abstract at ADS

Title: Turbulent Convection and Numerical Simulations in Solar and
    Stellar Astrophysics
Authors: Kupka, F.
Bibcode: 2009LNP...756...49K
Altcode:
  No abstract at ADS

Title: Interdisciplinary Aspects of Turbulence
Authors: Hillebrandt, Wolfgang; Kupka, Friedrich
Bibcode: 2009LNP...756.....H
Altcode:
  No abstract at ADS

Title: Inter-Division IV-V / Working Group Ap and Related Stars
Authors: Cunha, Margarida S.; Weiss, Werner W.; Dworetsky, Michael M.;
   Kochukhov, Oleg; Kupka, Friedrich; Leblanc, Francis; Monier, Richard;
   Paunzen, Ernst; Piskunov, Nikolai E.; Shibahashi, Hiromoto; Smalley,
   Barry; Ziznovsky, Jozef
Bibcode: 2009IAUTA..27..245C
Altcode:
  The diversity of physical phenomena embraced by the study of Chemically
  Peculiar (CP) stars results in an associated research community
  with interests that are equally diverse. This fact became once more
  evident during the CP#Ap Workshop that took place in Vienna (Austria)
  in September 2007, and which gathered over 80 members of this research
  community. Besides the excellent scientific outcome of the meeting,
  during the workshop the community had the opportunity to discuss its
  organization and plans for the future. Following on those plans,
  the Working Group has submitted a proposal for a Joint Discussion
  during the IAU XXVII General Assembly, in Rio de Janeiro, which has
  meanwhile been accepted. Moreover, through an ApN newsletter forum,
  the Working Group has compiled requests from the community concerning
  atomic and related data. These requests have been put together and
  will be shared with Commission 14.

Title: Vald
Authors: Obbrugger, M.; Heiter, U.; Kupka, F.; Lüftinger, T.;
   Nesvacil, N.; Piskunov, N.; Ryabchikova, T. A.; Stempels, H. C.;
   Stütz, Ch.; Weiss, W. W.
Bibcode: 2008asvo.proc..215O
Altcode:
  VALD is a collection of atomic transition parameters and supporting
  extraction software. VALD services are available via Email (VALD-EMS)
  and the Web interface. Different kinds of requests are useful for
  several needs like abundance analysis, radial velocity measurements,
  or line identification. Since 1994, the early days of VALD, the database
  has been constantly improved and the release of VALD-3 - incorporating,
  e.g., molecular data and new line lists - is in preparation. With
  meanwhile more than 5 000 000 requests VALD developed to a much
  appreciated tool.

Title: Analysing the Contributions in Moment Equations of Reynolds
    Stress Models of Convection with Numerical Simulations
Authors: Kupka, F.; Muthsam, H. J.
Bibcode: 2008IAUS..252..463K
Altcode:
  We discuss how 3D numerical simulations can be used to analyse the
  different contributions within dynamical equations of non-local Reynolds
  stress models of convection.

Title: Shear Driven Turbulence and Coherent Structures in Solar
    Surface Simulations
Authors: Kupka, F.
Bibcode: 2008IAUS..252..451K
Altcode:
  Numerical simulations of convection near the solar surface are now
  advanced enough to reproduce both a large set of observational data and
  provide tests for convection models. We discuss the role of coherent
  structures in models of solar p-mode excitation, for which the analysis
  of numerical simulations has provided key inputs in the modelling. The
  robustness of these simulations is shown by a comparison illustrating
  the influence of boundary conditions on ensemble averaged quantities. In
  a concluding example advanced high resolution simulations are shown
  to resolve the onset of shear driven turbulence generated by up-
  and downflow structures.

Title: Modeling the excitation of acoustic modes in α Centauri A
Authors: Samadi, R.; Belkacem, K.; Goupil, M. J.; Dupret, M. -A.;
   Kupka, F.
Bibcode: 2008A&A...489..291S
Altcode: 2008arXiv0806.0725S
  From different seismic observations we infer the energy supplied
  per unit of time by turbulent convection to the acoustic modes of α
  Centauri A (HD 128620), a star that is similar but not identical to
  the Sun. The inferred rates of energy supplied to the modes (i.e. mode
  excitation rates) are found to be significantly higher than in the
  Sun. They are compared with those computed with an excitation model that
  includes two sources of driving, the Reynolds stress contribution and
  the advection of entropy fluctuations. The model also uses a closure
  model, the Closure Model with Plumes (CMP hereafter), that takes
  the asymmetry between the up- and down-flows (i.e. the granules and
  plumes, respectively) into account. Different prescriptions for the
  eddy-time correlation function are also compared to observational
  data. Calculations based on a Gaussian eddy-time correlation
  underestimate excitation rates compared with the values derived from
  observations for α Centauri A. On the other hand, calculations based
  on a Lorentzian eddy-time correlation lie within the observational
  error bars. This confirms results in the solar case. Compared to
  the helioseismic data, those obtained for α Centauri A constitute
  an additional support for our model of excitation. We show that mode
  masses must be computed taking turbulent pressure into account. Finally,
  we emphasize the need for more accurate seismic measurements in order
  to distinguish between the CMP closure model and the quasi-normal
  approximation in the case of α Centauri A, as well as to confirm or
  not the need to include the excitation by the entropy fluctuations.

Title: VALD — an atomic and molecular database for astrophysics
Authors: Heiter, U.; Barklem, P.; Fossati, L.; Kildiyarova, R.;
   Kochukhov, O.; Kupka, F.; Obbrugger, M.; Piskunov, N.; Plez, B.;
   Ryabchikova, T.; Stempels, H. C.; Stütz, Ch; Weiss, W. W.
Bibcode: 2008JPhCS.130a2011H
Altcode:
  The VALD database of atomic and molecular data aims to ensure a robust
  and consistent analysis of astrophysical spectra. We offer a convenient
  e-mail and web-based user interface to a vast collection of spectral
  line parameters for all chemical elements and in the future also for
  molecules. An international team is working on the following tasks:
  collecting line parameters from relevant theoretical and experimental
  publications, computing line parameters, evaluating the data quality by
  comparison of similar data from different sources and by comparison
  with astrophysical observations, and incorporating the data into
  VALD. A unique feature of VALD is its capability to provide the most
  comprehensive spectral line lists for specific astrophysical plasma
  conditions defined by the user.

Title: High-resolution models of solar granulation: the
    two-dimensional case
Authors: Muthsam, H. J.; Löw-Baselli, B.; Obertscheider, Chr.;
   Langer, M.; Lenz, P.; Kupka, F.
Bibcode: 2007MNRAS.380.1335M
Altcode: 2007arXiv0706.3349M; 2007MNRAS.tmp..777M
  Using advanced numerical schemes and grid refinement, we present 2D
  high-resolution models of solar granulation with particular emphasis on
  downflowing plumes. In the high-resolution portion of our simulation,
  a box measuring 1.97 × 2.58Mm<SUP>2</SUP> (vertical × horizontal),
  the grid size is 1.82 × 2.84km<SUP>2</SUP>. Calculations at the
  resolution usually applied in this type of simulations amount to only a
  few horizontal gridpoints for a downflowing plume. Due to the increased
  number of gridpoints in our high-resolution domain, the simulations
  show the development of vigorous secondary instabilities of both the
  plume's head and stem. The plume's head produces counterrotating vortex
  patches, a topology due to the 2D nature of the simulations. Below a
  depth of about 1Mm, the plume's head and stem instabilities produce,
  in these 2D models, patches of low density, temperature, pressure
  and high vorticity which may last for all of our simulation time,
  ~10min, and probably considerably longer. Centrifugal forces acting
  in these patches counteract the strong inward pressure. Probably most
  importantly, the plume's instabilities give rise to acoustic pulses
  created predominantly down to ~1.5Mm. The pulses proceed laterally
  as well as upwards and are ubiquitous. Ultimately, most of them
  emerge into the photosphere. A considerable part of the photospheric
  `turbulence' in these models is due to those pulses rather than to some
  sort of eddies. The upflows in granules are smooth where they reach
  the photosphere from below even in the present calculations; however,
  the pulses may enter in the photosphere also in granular upflows.

Title: Eclipsing binaries as a test for synthetic photometry
Authors: Heiter, U.; Smalley, B.; Stütz, Ch.; Kupka, F.; Kochukhov, O.
Bibcode: 2007IAUS..240..328H
Altcode:
  Narrow band photometry is a viable tool to characterize large numbers
  of stars. The connection between observed colors and astrophysical
  parameters has to rely on synthetic photometry calculated from stellar
  atmosphere models. Here, we present synthetic Hbeta indices calculated
  from 1D model atmospheres, which implement various treatments of
  convection. The calculated indices are transformed to the standard
  system using observed medium-resolution spectra from recently published
  stellar libraries. We test how well the synthetic photometry reproduces
  observed indices by using a number of eclipsing binary systems. For
  these stars, atmospheric parameters can be determined independently
  from the models with highest possible accuracy. As a preliminary
  conclusion, the computed indices deviate from the observed ones by an
  amount expected from the observational errors and the accuracy of the
  atmospheric parameters.

Title: Convection in Astrophysics (IAU S239)
Authors: Kupka, Friedrich; Roxburgh, Ian; Chan, Kwing Lam
Bibcode: 2007IAUS..239.....K
Altcode:
  Preface; Session A. Modelling convection and radiative transfer; Session
  B. Observational probes of convection; Session C. Convection in planets
  and brown dwarfs; Session D. Stellar evolution, nucleosynthesis and
  convective mixing; Session E. Oscillations, mass loss and convection;
  Session F. Convection and rotation; Session G. MHD convection and
  dynamos.

Title: Two-scale mass-flux closure models for turbulence: p-mode
    amplitudes in solar-like stars
Authors: Belkacem, K.; Samadi, R.; Goupil, M. -J.; Kupka, F.; Dupret,
   M. -A.
Bibcode: 2007CoAst.150..153B
Altcode:
  A new closure model has been developed, which takes into account both
  the skewness of the velocity distribution induced by the presence of
  two flows in the convection zone, and the effects of turbulence onto
  each flow (Belkacem et al. 2006a). Applied to the formalism of p-mode
  excitation, it has been possible to validate this theoretical model
  by a comparison with the observational excitation rates in the solar
  case using GOLF data (see Belkacem et al. 2006b). The next step is
  to consider α Cen A for which observations of the mode-damping rates
  are available.

Title: Reynolds stress models of convection in convective cores
Authors: Roxburgh, Ian W.; Kupka, Friedrich
Bibcode: 2007IAUS..239...77R
Altcode:
  No abstract at ADS

Title: Probing Reynolds stress models of convection with numerical
simulations: I. Overall properties: fluxes, mean profiles
Authors: Kupka, F.; Muthsam, H. J.
Bibcode: 2007IAUS..239...80K
Altcode:
  No abstract at ADS

Title: Mixing length model of convection in stellar cores
Authors: Roxburgh, Ian W.; Kupka, Friedrich
Bibcode: 2007IAUS..239...98R
Altcode:
  No abstract at ADS

Title: Some open questions concerning the modelling of non-locality
    in Reynolds stress type models of stellar convection.
Authors: Kupka, F.
Bibcode: 2007IAUS..239...92K
Altcode:
  No abstract at ADS

Title: Coherent structures in granulation convection and their
    importance for higher order closure models
Authors: Kupka, F.; Robinson, F. J.
Bibcode: 2007IAUS..239...74K
Altcode:
  No abstract at ADS

Title: A closure model for turbulent convection. Application to the
    excitation of p modes
Authors: Belkacem, K.; Samadi, R.; Goupil, M. -J.; Kupka, F.;
   Baudin, F.
Bibcode: 2007IAUS..239..376B
Altcode:
  No abstract at ADS

Title: Eclipsing binaries as a test for synthetic photometry
Authors: Heiter, U.; Smalley, B.; Stütz, Ch.; Kupka, F.; Kochukhov, O.
Bibcode: 2007IAUS..239..169H
Altcode:
  No abstract at ADS

Title: Modelling of solar granulation
Authors: Muthsam, H. J.; Löw-Baselli, B.; Obertscheider, Chr.;
   Langer, M.; Lenz, P.; Kupka, F.
Bibcode: 2007IAUS..239...89M
Altcode:
  No abstract at ADS

Title: Probing Reynolds stress models of convection with numerical
simulations: II. Non-locality and third order moments.
Authors: Kupka, F.; Muthsam, H. J.
Bibcode: 2007IAUS..239...83K
Altcode:
  No abstract at ADS

Title: Solar-like oscillation amplitudes and line-widths as a probe
    for turbulent convection in stars
Authors: Samadi, R.; Belkacem, K.; Goupil, M. -J.; Kupka, F.; Dupret,
   M. -A.
Bibcode: 2007IAUS..239..349S
Altcode: 2006astro.ph.11760S
  Excitation of solar-like oscillations is attributed to turbulent
  convection and takes place at the upper-most part of the outer
  convective zones. Amplitudes of these oscillations depend on the
  efficiency of the excitation processes as well as on the properties
  of turbulent convection. We present past and recent improvements on
  the modeling of those processes. We show how the mode amplitudes and
  mode line-widths can bring information about the turbulence in the
  specific cases of the Sun and Alpha Cen A.

Title: Probing Reynolds stress models of convection with numerical
simulations: III. Compressibility modelling and dissipation
Authors: Kupka, F.; Muthsam, H. J.
Bibcode: 2007IAUS..239...86K
Altcode:
  No abstract at ADS

Title: Effect of the microturbulence parameter on the Color-Magnitude
    Diagram
Authors: Montalbán, J.; Nendwich, J.; Heiter, U.; Kupka, F.; Paunzen,
   E.; Smalley, B.
Bibcode: 2007IAUS..239..166M
Altcode:
  No abstract at ADS

Title: Round table discussion of session A: modelling convection
    and radiative transfer
Authors: Kupka, F.
Bibcode: 2007IAUS..239...64K
Altcode:
  No abstract at ADS

Title: On the effects of coherent structures on higher order moments
    in models of solar and stellar surface convection
Authors: Kupka, F.; Robinson, F. J.
Bibcode: 2007MNRAS.374..305K
Altcode:
  Non-local models of stellar convection usually rely on the assumption
  that the transfer of convective heat flux, turbulent kinetic energy
  and related quantities can be described as a diffusion process or that
  the fourth-order moments of velocity and temperature fluctuations
  follow a Gaussian distribution (quasi-normal approximation). The
  latter is also assumed in models of solar p-mode excitation. <P />We
  have used realistic numerical simulations of solar granulation and of
  granulation in a K dwarf to test the quasi-normal approximation and
  several alternatives. For the superadiabatic layer of the Sun and for
  the quasi-adiabatic zone underneath, we find that the hypothesis of
  quasi-normality is a rather poor approximation. In the superadiabatic
  layer, it overestimates some of the fourth-order moments of vertical
  velocity and temperature by up to a factor of 2 while it underestimates
  them in the quasi-adiabatic layers by up to a factor of 3.5. The model
  proposed by Gryanik &amp; Hartmann and Gryanik et al. reduces the
  discrepancies within the quasi-adiabatic zone to typically less than 30
  per cent and is partially comparable and partially in better agreement
  with the simulation data than two earlier models by Grossman &amp;
  Narayan. Simulation data for the K dwarf confirm these results. However,
  none of the proposed models works well in the superadiabatic layer nor
  in the photospheric layers above. For the Sun, we provide evidence that
  the fourth-order moments of horizontal velocity fields can be estimated
  to within about 30 per cent with the quasi-normal approximation despite
  the complexity of the horizontal flow. Comparing our results to those
  from solar simulations with idealized microphysics and with related
  studies of geophysical convection zones confirms our conclusions about
  the quasi-normal approximation and the new models. <P />The improvements
  come from including the effects of coherent structures (such as granules
  or plumes), while the limitations are tied to the transition regions
  or boundaries such as the rapid radiative cooling that occurs at the
  top of the convection zone. Incorporating the model of Gryanik &amp;
  Hartmann and Gryanik et al. into non-local convection models may well
  produce a significant improvement in the modelling of convection or of
  solar-like p-mode excitation in the quasi-adiabatic part of convection
  zones. For application to entire convection zones, modifications are
  necessary which can account for the change in background properties
  of the convective medium near boundaries or transition regions.

Title: A closure model with plumes. I. The solar convection
Authors: Belkacem, K.; Samadi, R.; Goupil, M. J.; Kupka, F.
Bibcode: 2006A&A...460..173B
Altcode: 2006astro.ph..7568B
  Context: .Oscillations of stellar p modes, excited by turbulent
  convection, are investigated. In the uppermost part of the solar
  convection zone, radiative cooling is responsible for the formation
  of turbulent plumes, hence the medium is modelled with downdrafts and
  updrafts.<BR /> Aims: .We take into account the asymmetry of the up-
  and downflows created by turbulent plumes through an adapted closure
  model. In a companion paper, we apply it to the formalism of excitation
  of solar p modes developed by Samadi &amp; Goupil (2001).<BR /> Methods:
  .Using results from 3D numerical simulations of the uppermost part of
  the solar convection zone, we show that the two-scale mass-flux model
  (TFM) is valid only for quasi-laminar or highly skewed flows (Gryanik
  &amp; Hartmann 2002) and does not reproduce turbulent properties
  of the medium such as velocity-correlation products. We build a
  generalized two-scale mass-flux Model (GTFM) model that takes both
  the skew introduced by the presence of two flows and the effects of
  turbulence in each flow into account. In order to apply the GTFM to
  the solar case, we introduce the plume dynamics as modelled by Rieutord
  &amp; Zahn (1995) and construct a closure model with plumes (CMP).<BR
  /> Results: .The CMP enables expressing the third- and fourth-order
  correlation products in terms of second-order ones. When compared
  with 3D simulation results, the CMP improves the agreement for the
  fourth-order moments by a factor of two approximately compared with the
  use of the quasi-normal approximation or a skewness computed with the
  classical TFM.<BR /> Conclusions: .The asymmetry of turbulent convection
  in the solar case has an important impact on the vertical-velocity
  fourth-order moment, which has to be accounted for by models. The CMP
  is a significant improvement and is expected to improve the modelling
  of solar p-mode excitation.

Title: A closure model with plumes. II. Application to the stochastic
    excitation of solar p modes
Authors: Belkacem, K.; Samadi, R.; Goupil, M. J.; Kupka, F.; Baudin, F.
Bibcode: 2006A&A...460..183B
Altcode: 2006astro.ph..7570B
  Context: . Amplitudes of stellar p modes result from a balance between
  excitation and damping processes taking place in the uppermost part
  of convective zones in solar-type stars and can therefore be used as
  a seismic diagnostic for the physical properties of these external
  layers. <BR /> Aims: . Our goal is to improve the theoretical modelling
  of stochastic excitation of p modes by turbulent convection. <BR />
  Methods: . With the help of the closure model with plume (CMP) developed
  in a companion paper, we refine the theoretical description of the
  excitation by the turbulent Reynolds stress term. The CMP is generalized
  for two-point correlation products so as to apply it to the formalism
  developed by Samadi &amp; Goupil (2001, A&amp;A, 370, 136). The
  excitation source terms are then computed with this improvement, and a
  comparison with solar data from the GOLF instrument is performed. <BR
  /> Results: .The present model provides a significant improvement when
  comparing absolute values of theoretical amplitudes with observational
  data. It gives rise to a frequency dependence of the power supplied
  to solar p modes, which agrees with GOLF observations. It is shown
  that the asymmetry of the turbulent convection zone (up and downflows)
  plays a major role in the excitation processes. Despite an increase in
  the Reynolds stress term contribution due to our improved description,
  an additional source of excitation, identified as the entropy source
  term, is still necessary for reproducing the observational data. <BR />
  Conclusions: .Theoretical excitation rates in the frequency range ν in
  [2.5 mHz, 4 mHz] now are in agreement with the observational data from
  the GOLF instrument. However, at lower frequencies, it exhibits small
  discrepancies at the maximum level of a few per cent. Improvements are
  likely to come from a better physical description of the excitation
  by entropy fluctuations in the superadiabatic zone.

Title: Seismic diagnostics inferred from the amplitudes of
    stochastically-excited modes
Authors: Samadi, R.; Belkacem, K.; Goupil, M. -J.; Kupka, F.
Bibcode: 2006IAUJD..17E..14S
Altcode:
  Solar-like oscillations have been detected in numerous main-sequence
  stars as well as in red giant stars. The excitation of such oscillations
  is ensured by turbulent convection at the upper most part of the
  convective zones. From the measurement of the mode amplitude and
  line-width it is possible to infer the power supplied to the modes by
  turbulent convection. Apart from the Sun, α Cen A is the only star for
  which both mode amplitudes and mode line-widths have been derived. I
  will first present the diagnostics inferred from the measurement of the
  amplitudes and line-widths in the Sun and in α Cen A. For other stars,
  despite the lack of direct constraints on the excitation mechanisms,
  I will show that the solar-like oscillations observed in different
  stars can nevertheless offer interesting constraints on the properties
  of turbulent convection.

Title: Excitation of solar p modes. Effect of the asymmetry of the
    convection zone
Authors: Belkacem, K.; Samadi, R.; Goupil, M. J.; Kupka, F.; Baudin, F.
Bibcode: 2006sf2a.conf..523B
Altcode:
  Excitation of stellar p modes by turbulent convection is
  investigated. The aim is to take into account the asymmetry of up-
  and downflows created by turbulent plumes through an adapted closure
  model. We built a generalized two scale mass flux model (GTFM) that
  includes both the skew introduced by the presence of two flows and
  the effect of turbulence within each flow. The plume dynamics modelled
  according to Rieutord &amp; Zahn (1995) is used to construct a closure
  model with plumes (CMP). We apply it to the formalism of excitation
  of stellar p modes developed by Samadi &amp; Goupil (2001). The new
  excitation model leads to a frequency dependence, of the power supplied
  to solar p modes, which is in agreement with GOLF observations. Despite
  an increase of the Reynolds stress contribution due to our improved
  description, an additional source of excitation -identified as the
  entropy source term- is still necessary to reproduce the maximum of
  excitation rate. Our modelling including the entropy contribution
  reproduces the maximum but <P />over-estimates, at low frequencies,
  the power and calls for further theoretical improvements.

Title: Prospects for population synthesis in the H band: NeMo grids
    of stellar atmospheres compared to observations
Authors: Frémaux, J.; Kupka, F.; Boisson, C.; Joly, M.; Tsymbal, V.
Bibcode: 2006A&A...449..109F
Altcode: 2005astro.ph.11125F
  Context: .For applications in population synthesis, libraries of
  theoretical stellar spectra are often considered an alternative
  to template libraries of observed spectra, because they allow a
  complete sampling of stellar parameters. Most of the attention in
  published theoretical spectral libraries has been devoted to the
  visual wavelength range.Aims.The goal of the present work is to
  explore the near-infrared range where few observed fully calibrated
  spectra and no theoretical libraries are available.Methods.We make
  a detailed comparison of theoretical spectra in the range 1.57-1.67
  μm for spectral types from A to early M and for giant and dwarf
  stars, with observed stellar spectra at resolutions around 3000,
  which would be sufficient to disentangle the different groups of
  late-type stars. We selected the NeMo grids of stellar atmospheres
  to perform this comparison.Results.We first demonstrate that observed
  spectral flux distributions can be matched very well with theoretical
  ones for almost the entire parameter range covered by the NeMo grids at
  moderate resolution in the visual range. In the infrared range, although
  the overall shape of the observed flux distributions still matches
  reasonably well, the individual spectral features are reproduced by the
  theoretical spectra only for stars earlier than mid F type. For later
  spectral types the differences increase, and theoretical spectra of K
  type stars have systematically weaker line features than those found
  in observations. These discrepancies are traced back to stem primarily
  from incomplete data on neutral atomic lines, although some of them are
  also related to molecules.Conclusions.Libraries of theoretical spectra
  for A to early M type stars can be successfully used in the visual
  regions for population synthesis, but their application in the infrared
  is restricted to early and intermediate type stars. Improving atomic
  data in the near infrared is a key element in making the construction
  of reliable libraries of stellar spectra feasible in the infrared.

Title: Limb-darkening coefficients for the purpose of pulsation mode
    identification for A-F stars. .
Authors: Barban, C.; Goupil, M. J.; van't Veer-Menneret, C.; Garrido,
   R.; Heiter, U.; Kupka, F.
Bibcode: 2006MmSAI..77..101B
Altcode:
  Limb-darkening coefficients are computed from a set of model atmospheres
  with: a solar chemical composition, 6000 K&lt; T<SUB>eff</SUB> &lt;
  8500 K (Delta T_eff=250 K), 2.5 &lt; logg &lt; 4.5 (Delta log g=0.1)
  and a microturbulent velocity of 2 km/s. Convection is included assuming
  either the turbulent convection approach of \citet{cm} or the classical
  mixing length prescription with alpha =0.5 and 1.25. Four limb-darkening
  laws have been used: quadratic, cubic, square root and the one of
  \citet{cl}. We compare the ATLAS 9 intensities and the ones computed
  from these laws. We find that Claret's law is the best law for almost
  all the models, independently of the convection prescription used.

Title: Influence of local treatments of convection upon solar p mode
    excitation rates
Authors: Samadi, R.; Kupka, F.; Goupil, M. J.; Lebreton, Y.; van't
   Veer-Menneret, C.
Bibcode: 2006A&A...445..233S
Altcode: 2005astro.ph..7243S
  We compute the rates P at which acoustic energy is injected into
  the solar radial p modes for several solar models. The solar models
  are computed with two different local treatments of convection: the
  classical mixing-length theory (MLT) and the formulation by Canuto et
  al. (1996, ApJ, 473, 550, CGM). Among the models investigated here,
  our best models reproduce both (i) the solar radius and the solar
  luminosity at solar age and (ii) the observed Balmer line profiles. For
  the MLT treatment, the rates P do significantly depend on the properties
  of the atmosphere, whereas for the CGM treatment, the dependence of
  P on the properties of the atmosphere is found to be smaller than
  the error bars attached to the seismic measurements. The excitation
  rates P for modes associated with the MLT models are significantly
  underestimated compared with the solar seismic constraints. The CGM
  models yield values for P closer to the seismic data than do the MLT
  models. We conclude that the solar p-mode excitation rates provide
  valuable constraints and, according to the present investigation,
  clearly favor the CGM treatment with respect to the MLT, although
  neither of them yields values of P as close to the observations as
  recently found for 3D numerical simulations.

Title: Workshop on "Interdisciplinary Aspects of Turbulence"
Authors: Kupka, F.; Hillebrandt, W.
Bibcode: 2005iat..work.....K
Altcode:
  The Workshop on Interdisciplinary Aspects of Turbulence was organized
  within the framework of the Max-Planck-Institute for Astrophysics in
  Garching, Germany, and held at Ringberg Castle. It brought together
  researchers from the fields of Astrophysics, Atmospheric and Ocean
  Physics, Engineering and Laboratory Turbulence Research, as well
  as Non-linear Dynamics and Statistical Mechanics who share a common
  interest in turbulence and its properties of mixing, self-organisation
  of large scale structures, and related issues and the interdisciplinary
  aspects underlying these topics. The proceedings volume contains a
  collection of extended abstracts as well as short review papers based
  on 30 from a total of 40 contributions presented at the workshop as well
  as links and references to further material discussed at the workshop.

Title: Turbulent convection in astrophysics and geophysics -
    a comparison
Authors: Kupka, F.
Bibcode: 2005iat..work..141K
Altcode:
  Energy transport by turbulent convection is studied in both astrophysics
  and geophysics. We briefly outline the physics of convection as well
  as the differences between astrophysical and geophysical turbulent
  convective flows. The case of convection in stars including our
  sun is described in more detail. Reynolds stress models have been
  suggested for quantitative predictions for both stellar and geophysical
  convection. One of the main problems of such models is how to account
  for the influence of the observed large scale coherent structures. We
  discuss a possible solution which has first been suggested for the
  convective planetary boundary layer and show how it performs when
  applied to convection in our sun.

Title: Spectrum synthesis of sharp-line B, A and F stars
Authors: Silaj, J.; Townshend, A.; Kupka, F.; Landstreet, J.; Sigut, A.
Bibcode: 2005EAS....17..345S
Altcode:
  The spectra of a number of reportedly sharp-line B, A and F stars
  have been observed in a 60-Å window with a resolving power of
  120 000. As a first step in analysis of these data, the spectra have
  been synthesized to see how well simple models fit. The information
  obtained from both successful modelling and from discrepant fits
  is discussed.

Title: Direct Simulations of Radiative and Convective Zones
Authors: Kupka, F.
Bibcode: 2005EAS....17..177K
Altcode:
  Numerical simulations have become one of the main tools in the research
  on stellar convection zones and they can be expected to become very
  important for the study of the convection-diffusion interaction as
  well. In this review, I will first provide some historical background
  and then select a few sample problems where numerical simulations of
  stellar convection have provided useful results or are expected to do
  so in the near future: solar granulation, interacting convection zones,
  and semi-convection.

Title: Some Physics We Can Learn from Spectroscopy of A-Type Stars
Authors: Kupka, F.
Bibcode: 2005PhST..119...20K
Altcode:
  Stars of spectral type A are distinguished from others by the
  interesting fact that several physical processes are of equal importance
  in their outer envelope. The competing processes include diffusion
  driven by either gravitational settling or radiation pressure, thermal
  convection driven by partial ionisation of hydrogen and/or helium, their
  interaction with a global stellar magnetic field in some cases, and
  large rotation rates or pulsational instabilities in others. Whether one
  of them dominates over the others is also determined by their initial
  and present environment. Most of the information on the physics of
  these processes is obtained from spectroscopy of the surface layers of
  these stars. In spectroscopic studies of A-stars we can either attempt
  to obtain a better understanding of the physical processes, if our
  atomic data are good enough, or alternatively, if the stellar physics
  provides strong enough constraints, we can learn about atomicphysics:
  wavelengths, oscillator strengths, pressure broadening, and other
  quantities which characterise electronic transitions in neutral and
  ionised atoms within the stellar plasma. <P />Professor Charles R
  Cowley has made many important contributions to the spectroscopy
  of A-type stars throughout his research work and he is also very
  active in this field today. I have enjoyed being able to work with
  him on this subject on several occasions. In this paper I present an
  overview as to why the spectroscopy of A-type stars is of interest
  to both astrophysicists and laboratory spectroscopists, and I will
  use various opportunities to illustrate the selected topics through
  contributions made by Professor Cowley to this field.

Title: Observational signatures of atmospheric velocity fields in
    Main Sequence stars
Authors: Kupka, F.; Landstreet, J. D.; Sigut, A.; Bildfell, C.; Ford,
   A.; Officer, T.; Silaj, J.; Townshend, A.
Bibcode: 2004IAUS..224..573K
Altcode:
  In stars with sufficiently small projected rotational velocities
  (less than a few km s<SUP>-1</SUP>), it is often possible to detect
  signatures of the atmospheric velocity field in line profiles. These
  signatures may be as subtle as small asymmetries in the profile ("line
  bisector curvature") or as obvious as profile shapes that strongly
  depart from those predicted by simple microturbulence models. We have
  recently carried out a high resolution survey of sharp-line stars
  to search for these symptoms of local velocity fields. We report the
  first results of a comparison of models with the observed profiles.

Title: Convection in stars
Authors: Kupka, F.
Bibcode: 2004IAUS..224..119K
Altcode:
  Convection is one of the most intricate processes studied in stellar
  astrophysics and has challenged both theorists and observers since
  the beginnings of astrophysics. But during the last two decades
  observational data of unprecedented resolution and accuracy have
  been collected in solar and stellar research which permit a new look
  at the field. An enormous increase of computer speed now permits
  solving more complete model equations with more accurate numerical
  approximations. Modelling and theoretical understanding of convection,
  however, are lagging behind observational progress and are still
  wanting.

Title: Stellar model atmospheres with emphasis on velocity dynamics
Authors: Stütz, Ch.; Kupka, F.
Bibcode: 2004IAUS..224..570S
Altcode:
  Recently a formalism for solving the open set of non-local hydrodynamic
  moment equations has been applied to the envelopes of A-stars by
  Kupka &amp; Montgomery (2002). Tests on numerical simulations and
  selected properties derived from stellar spectra such as average
  surface velocities and velocity skewness have shown the applicability
  of this RSM approach. In addition, a variety of improvements over
  existing modeling standards have been developed within and around
  the AMS group at the Institute for Astronomy in Vienna during the
  last couple of years. For example, individual elemental abundance
  patterns (Piskunov &amp; Kupka 2001) or stratification as an observed
  parameter (Shuliak et al. 2004) can be taken into account in our model
  atmospheres. Once the underlying programs, which currently operate as
  stand alone applications, are combined with a model atmosphere code,
  we will obtain a powerful and efficient tool that will allow us the
  investigation of a number of open problems in the physics of A-stars,
  such as more realistic models of the temperature gradients of cool
  CP2 stars.

Title: Panel discussion section I
Authors: Kupka, F.
Bibcode: 2004IAUS..224..465K
Altcode:
  No abstract at ADS

Title: Effect of Local Treatments of Convection upon the Solar P-Mode
    Excitation Rates
Authors: Samadi, R.; Goupil, M. J.; Lebreton, Y.; van't Veer, C.;
   Kupka, F.
Bibcode: 2004ESASP.559..611S
Altcode: 2004soho...14..611S; 2004astro.ph..9324S
  We compute, for several solar models, the rates P at which the
  solar radial p modes are expected to be excited. The solar models
  are computed with two different local treatments of convection : the
  classical mixing-length theory (MLT hereafter) and Canuto, Goldmann
  and Mazzitelli(1996, CGM hereafter)'s formulation. For one set of
  solar models (EMLT and ECGM models), the atmosphere is gray and
  assumes Eddington's approximation. For a second set of models (KMLT
  and KCGM models), the atmosphere is built using a T(tau) law which has
  been obtained from a Kurucz's model atmosphere computed with the same
  local treatment of convection. The mixing-length parameter in the model
  atmosphere is chosen so as to provide a good agreement between synthetic
  and observed Balmer line profiles, while the mixing-length parameter
  in the interior model is calibrated so that the model reproduces
  the solar radius at solar age. For the MLT treatment, the rates P do
  depend significantly on the properties of the atmosphere. On the other
  hand, for the CGM treatment, differences in P between the ECGM and the
  KCGM models are very small compared to the error bars attached to the
  seismic measurements. The excitation rates P for modes from the EMLT
  model are significantly under-estimated compared with the solar seismic
  constraints. The KMLT model results in intermediate values for P and
  shows also an important discontinuity in the temperature gradient and
  the convective velocity. On the other hand, the KCGM model and the ECGM
  model yield values for P closer to the seismic data than the EMLT and
  KMLT models. We conclude that the solar p-mode excitation rates provide
  valuable constraints and according to the present investigation cleary
  favor the CGM treatment with respect to the MLT.

Title: The 5200-Åflux depression of chemically peculiar stars -
    II. The cool chemically peculiar and λ Bootis stars
Authors: Kupka, F.; Paunzen, E.; Iliev, I. Kh.; Maitzen, H. M.
Bibcode: 2004MNRAS.352..863K
Altcode: 2004MNRAS.tmp..204K
  After establishing the synthetic Δa photometric system in the first
  paper of this series, we now present model atmospheres computed with
  individual abundances for a representative sample of chemically
  peculiar (CP) stars and either confirm or redetermine their input
  parameters through comparisons with photometric, spectrophotometric
  and high-resolution spectroscopic data. The final models obtained from
  this procedure were used to compute synthetic Δa indices which were
  compared with observations. The observed behaviour of Δa is reproduced
  for several types of CP stars: models for Am stars show negligible
  (or marginally positive) values of a few mmag, while for λ Bootis
  stars - and for metal deficient A stars in general - we obtain negative
  values (as low as -12 mmag in one case). For the coolest CP2 stars with
  effective temperatures below about 8500 K, we obtain mild (~+10 mmag)
  to moderately large (~+30 mmag) flux depressions in agreement with
  observations. However, Δa values for slightly hotter members of the CP2
  group (for which still T<SUB>eff</SUB> &lt; 10000 K) are underestimated
  from these new models. The effect of the microturbulence parameter on
  the Δa index is revisited and its different role in various types of
  CP stars for reproducing the flux depression at 5200 Åis explained. We
  also provide reasons why models based on enhanced microturbulence and
  scaled solar abundance could not explain the observed flux depression
  for all types of CP stars. We discuss potential improvements of
  the current models including the possibility of still missing line
  opacities (unidentified and autoionization lines), modifications due
  to an explicit account of a global stellar magnetic field, and the
  effect of vertical abundance stratification.

Title: Interpolation of Stellar Model Grids and Application to the
    NEMO Grid
Authors: Nendwich, J.; Heiter, U.; Kupka, F.; Nesvacil, N.; Weiss,
   W. W.
Bibcode: 2004CoAst.144...43N
Altcode: 2004astro.ph..6381N
  NEMO Grid of Stellar Atmospheres is a DVD with 91,520 stellar model
  atmospheres representing a 5D grid of modified ATLAS atmospheres;
  the purpose of the modifications was to include different treatments
  of convection and higher vertical resolution. In addition, for every
  model fluxes are provided and color indices for 14 different photometric
  systems. Because the model grid contained gaps due to non-converging
  models, we developed and applied a set of 4D interpolation routines to
  complete the grid. All the data, which will continuously be updated,
  can be found on the NEMO homepage http://ams.astro.univie.ac.at/nemo/
  and are available via DVD.

Title: White dwarf envelopes: further results of a non-local model
    of convection
Authors: Montgomery, M. H.; Kupka, F.
Bibcode: 2004MNRAS.350..267M
Altcode: 2004astro.ph..1489M
  We present results of a fully non-local model of convection for white
  dwarf envelopes. We show that this model is able to reproduce the
  results of numerical simulations for convective efficiencies ranging
  from very inefficient to moderately efficient; this agreement is made
  more impressive given that no closure parameters have been adjusted
  in going from the previously reported case of A-stars to the present
  case of white dwarfs. For comparison, in order to match the peak
  convective flux found in numerical simulations for both the white dwarf
  envelopes discussed in this paper and the A-star envelopes discussed
  in our previous work requires changing the mixing length parameter of
  commonly used local models by a factor of 4. We also examine in detail
  the overshooting at the base of the convection zone, both in terms of
  the convective flux and in terms of the velocity field; we find that
  the flux overshoots by ~1.25 H<SUB>P</SUB> and the velocity by ~2.5
  H<SUB>P</SUB>. Because of the large amount of overshooting found at the
  base of the convection zone, the new model predicts the mixed region
  of white dwarf envelopes to contain at least 10 times more mass than
  local mixing length theory (MLT) models having similar photospheric
  temperature structures. This result is consistent with the upper limit
  given by numerical simulations which predict an even larger amount of
  mass to be mixed by convective overshooting. Finally, we attempt to
  parametrize some of our results in terms of local MLT-based models,
  insofar as is possible given the limitations of MLT.

Title: Convection in the atmospheres and envelopes  of Pre-Main
    Sequence stars
Authors: Montalbán, J.; D'Antona, F.; Kupka, F.; Heiter, U.
Bibcode: 2004A&A...416.1081M
Altcode: 2003astro.ph.10690M
  The T<SUB>eff</SUB> location of Pre-Main Sequence (PMS) evolutionary
  tracks depends on the treatment of over-adiabaticity (D'Antona
  &amp; Mazzitelli \cite{Antona1994}, \cite{Antona1998}). Since the
  convection penetrates into the stellar atmosphere, also the treatment
  of convection in the modeling of stellar atmospheres will affect the
  location of the Hayashi tracks. In this paper we present new non-grey
  PMS tracks for T<SUB>eff</SUB>,&gt;4000 K. We compute several grids of
  evolutionary tracks varying: i) the treatment of convection: either
  the Mixing Length Theory (MLT) or Canuto et al. (\cite{Canuto1996e},
  CGM) formulation of a Full Spectrum of Turbulence; ii) the atmospheric
  boundary conditions: we use the new Vienna grids of ATLAS9 atmospheres
  (Heiter et al. \cite{Heiter2002a}), which were computed using either MLT
  (with α=Λ/H<SUB>p</SUB>=0.5) or CGM treatments. For comparison, we
  also compute grids of models with the NextGen (Allard &amp; Hauschildt
  \cite{Allard1997}, AH97) atmosphere models, and a 1 {M<SUB>⊙</SUB>}
  grey MLT evolutionary track using the α calibration based on
  2D-hydrodynamical models (Ludwig et al. \cite{Ludwig1999}). These
  different grids of models allow us to analyze the effects of convection
  modeling on the non-grey PMS evolutionary tracks. We disentangle
  the effect of the wavelength dependent opacity on a self-consistent
  treatment of convection in the atmosphere from the role of the
  convection model itself in the atmosphere and in the interior. While
  for some parts of the HR diagram (e.g., A stars) a low efficiency of
  atmospheric convection is clearly indicated by the data, for others the
  evidence is conflicting, showing the weaknesses of all the presently
  adopted local convection models. Nevertheless, the assumption of a
  low photospheric efficiency permits us to reproduce a larger amount of
  data and we have hence restricted our study to this case and draw the
  following conclusions for it: i) in spite of the solar calibration,
  if MLT convection is adopted a large uncertainty results in the shape
  and location of PMS tracks, and the MLT calibration loses sense. ii)
  As long as the model of convection is not the same in the interior
  and in the atmosphere, the optical depth at which we take the boundary
  conditions is an additional parameter of the models. iii) Furthermore,
  very different sub-atmospheric structures are obtained (for MS and PMS
  stellar models) depending not only on the treatment of convection,
  but also on the optical depth at which the boundary conditions are
  taken. iv) The comparison between NextGen based models and ATLAS9 based
  models shows that in the T<SUB>eff</SUB> domain they have in common
  (4000-10 000 K) the improved opacities in NextGen atmosphere models have
  no relevant role on the PMS location, this being determined mainly by
  the treatment of the over-adiabatic convection. v) In the framework of
  standard stellar modeling (i.e., non-magnetic, non-rotating, spherical
  models), the comparison between theoretical models and observational
  data in very young binary systems indicates that, for both treatments
  of convection (MLT and CGM) and for any of the atmosphere grids
  (including those based on the 2D-hydrodynamical atmosphere models),
  the same assumption for convection cannot be used in PMS and MS: either
  the models fit the MS - and the Sun in particular - or they fit the
  PMS. Convection in the PMS phase appears to be less efficient than
  what is necessary to fit the Sun.

Title: New grids of ATLAS9 atmospheres. II. Limb-darkening
    coefficients for the Strömgren photometric system  for A-F stars
Authors: Barban, C.; Goupil, M. J.; Van't Veer-Menneret, C.; Garrido,
   R.; Kupka, F.; Heiter, U.
Bibcode: 2003A&A...405.1095B
Altcode:
  Using up-to-date model atmospheres (Heiter et al. \cite{Heiter02})
  with the turbulent convection approach developed by Canuto et
  al. (\cite{Canuto96}, CGM), quadratic, cubic and square root limb
  darkening coefficients (LDC) are calculated with a least square
  fit method for the Strömgren photometric system. This is done for a
  sample of solar metallicity models with effective temperatures between
  6000 and 8500 K and with log g between 2.5 and 4.5. A comparison is
  made between these LDC and the ones computed from model atmospheres
  using the classical mixing length prescription with a mixing length
  parameter alpha =1.25 and alpha =0.5. For CGM model atmospheres,
  the law which reproduces better the model intensity is found to
  be the square root one for the u band and the cubic law for the v
  band. The results are more complex for the b and y bands depending
  on the temperature and gravity of the model. Similar conclusions are
  reached for MLT alpha =0.5 models. As expected much larger differences
  are found between CGM and MLT with alpha =1.25. In a second part,
  the weighted limb-darkening integrals, b<SUB>l</SUB>, and their
  derivatives with respect to temperature and gravity, are then computed
  using the best limb-darkening law. These integrals are known to be
  very important in the context of photometric mode identification of
  non-radial pulsating stars. The effect of convection treatment on these
  quantities is discussed and as expected differences in the b<SUB>l</SUB>
  coefficients and derivatives computed with CGM and MLT alpha =0.5 are
  much smaller than differences obtained between computations with CGM
  and MLT alpha =1.25. <P />Table 1 is only available in electronic form
  at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
  or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/1095

Title: Observations of Rapid Radial Velocity Variations of Spectral
    Lines in Rapidly Oscillating Ap (roAp) Stars
Authors: Landstreet, J. D.; Kochukhov, O.; Kupka, F.; Ryabchikova,
   T.; Weiss, W. W.
Bibcode: 2003aahd.conf..347L
Altcode:
  No abstract at ADS

Title: VizieR Online Data Catalog: Limb-darkening coefficients from
    ATLAS9 models (Barban+, 2003)
Authors: Barban, C.; Goupil, M. J.; van't Veer-Menneret, C.; Garrido,
   R.; Kupka, F.; Heiter, U.
Bibcode: 2003yCat..34051095B
Altcode:
  Using up-to-date model atmospheres (Heiter et
  al. 2002A&amp;A...392..619H) with the turbulent convection approach
  developed by Canuto, Goldman &amp; Mazzitelli (1996ApJ...473..550C,
  CGM), quadratic, cubic and square root limb darkening coefficients
  (LDC) are calculated with a least square fit method for the Stroemgren
  photometric system. This is done for a sample of solar metallicity
  models with effective temperatures between 6000 and 8500K and with logg
  between 2.5 and 4.5. A comparison is made between these LDC and the
  ones computed from model atmospheres using the classical mixing length
  prescription with a mixing length parameter α=1.25 and α=0.5. For CGM
  model atmospheres, the law which reproduces better the model intensity
  is found to be the square root one for the u band and the cubic law for
  the v band. The results are more complex for the b and y bands depending
  on the temperature and gravity of the model. Similar conclusions are
  reached for Mixing Length Theory (MLT) α=0.5 models. As expected much
  larger differences are found between CGM and MLT with α=1.25. In a
  second part, the weighted limb-darkening integrals, b<SUB>ell</SUB>,
  and their derivatives with respect to temperature and gravity, are then
  computed using the best limb-darkening law. These integrals are known
  to be very important in the context of photometric mode identification
  of non-radial pulsating stars. The effect of convection treatment
  on these quantities is discussed and as expected differences in the
  b<SUB>ell</SUB> coefficients and derivatives computed with CGM and MLT
  α=0.5 are much smaller than differences obtained between computations
  with CGM and MLT α=1.25. <P />The limb darkening coefficients are
  given here for the u, v, b and y bands and for CGM models, MLT α=0.5
  models and MLT α=1.25 models. <P />(3 data files).

Title: The 5200-Å flux depression of chemically peculiar stars -
I. Synthetic Δa photometry: the normality line
Authors: Kupka, F.; Paunzen, E.; Maitzen, H. M.
Bibcode: 2003MNRAS.341..849K
Altcode: 2003astro.ph..3225K
  The Δa photometric system provides an efficient observational method
  to identify and distinguish magnetic and several other types of
  chemically peculiar (CP) stars of spectral types B to F from other
  classes of stars in the same range of effective temperatures. We
  have developed a synthetic photometric system that can be used to
  explore the capability of model atmospheres with individual element
  abundances to predict photometric Δa magnitudes, which measure the
  extent of the flux depression around 5200 Å found in different types
  of CP stars. In this first paper, we confirm the observed dependency
  of the a index as a function of various colour indices sensitive to
  the effective temperature of stars as well as its average scatter
  expected from surface gravity variations within the main-sequence
  band. The behaviour of the so-called `normality line' of Δa systems
  used in photometric observations of CP stars is well reproduced. The
  metallicity dependence of the normality line of the Δa system was
  computed for several grids of model atmospheres where the abundances
  of elements heavier than He had been scaled +/-0.5 dex with respect to
  the solar value. We estimate a lowering of Δa magnitudes for CP stars
  within the Magellanic Clouds by ~-3 mmag relative to those in the solar
  neighbourhood assuming an average metallicity of [Fe/H]=-0.5 dex. Using
  these results on the metallicity bias of the Δa system we find the
  observational systems in use suitable to identify CP stars in other
  galaxies or distant regions of our own Galaxy and capable to provide
  data samples on a statistically meaningful basis. In turn, the synthetic
  system is suitable to test the performance of model atmospheres for CP
  stars. This work will be presented in follow-up papers of this series.

Title: Colors of ATLAS9 Atmospheres and Their Interpolation
Authors: Nendwich, J.; Nesvacil, N.; Weiss, W. W.; Heiter, U.;
   Kupka, F.
Bibcode: 2003IAUS..210P..A9N
Altcode:
  No abstract at ADS

Title: Problems and Difficulties in Building up Stellar Models with
    Non-grey Boundary Conditions
Authors: Montalbán, J.; D'Antona, F.; Kupka, F.
Bibcode: 2003IAUS..210P..C6M
Altcode:
  No abstract at ADS

Title: Non-local Convection Models for Stellar Atmospheres and
    Envelopes
Authors: Kupka, F.
Bibcode: 2003IAUS..210..143K
Altcode:
  No abstract at ADS

Title: Pre-Main Sequence and Main Sequence Models Using the Vienna
    Grids of ATLAS9 Atmospheres
Authors: Montalbán, J.; Kupka, F.; D'Antona, F.; Heiter, U.
Bibcode: 2003IAUS..210P..C5M
Altcode:
  No abstract at ADS

Title: Convection in A Stars
Authors: Kupka, F.
Bibcode: 2003ASPC..305..190K
Altcode: 2003mfob.conf..190K
  No abstract at ADS

Title: Application of New ATLAS9 Model Atmosphere Grids
Authors: Heiter, U.; Kupka, F.; Samadi, R.; Barban, C.; van't-Veer
   Menneret, C.; Lebreton, Y.; Goupil, M. -J.; Garrido, R.; Weiss, W. W.
Bibcode: 2003IAUS..210P.E10H
Altcode:
  No abstract at ADS

Title: Using Balmer Line Profiles to Investigate Convection in A
    and F Stars
Authors: Smalley, B.; Kupka, F.
Bibcode: 2003IAUS..210P.C10S
Altcode: 2002astro.ph..7388S
  Balmer lines are an important diagnostic of stellar atmospheric
  structure, since they are formed at a wide range of depths within the
  atmosphere. The different Balmer lines are formed at slightly different
  depths making them useful atmospheric diagnostics. The low sensitivity
  to surface gravity for stars cooler than ~8000 K makes them excellent
  diagnostics in the treatment of atmospheric convection. For hotter
  stars Balmer profiles are sensitive to both effective temperature and
  surface gravity. Provided we know the surface gravity of these stars
  from some other method (e.g. from eclipsing binary systems), we can
  use them to determine effective temperature. In previous work, we have
  found no significant systematic problems with using uvby photometry
  to determine atmospheric parameters of fundamental (and standard)
  stars. In fact, uvby was found to be very good for obtaining both Teff
  and log g. Using Halpha and Hbeta profiles, we have found that both
  the Canuto &amp; Mazzitteli and standard Kurucz mixing-length theory
  without approximate overshooting are both in agreement to within the
  uncertainties of the fundamental stars. Overshooting models were always
  clearly discrepant. Some evidence was found for significant disagreement
  between all treatments of convection and fundamental values around
  8000~9000K, but these results were for fundamental stars without
  fundamental surface gravities. We have used stars with fundamental
  values of both Teff and log g to explore this region in more detail.

Title: Tools and Methods for Abundance Analysis
Authors: Knoglinger, P.; Nesvacil, N.; Kupka, F.; Mittermayer, P.;
   Piskunov, N.; Weiss, W. W.; Bruntt, H.
Bibcode: 2003IAUS..210P.E66K
Altcode:
  No abstract at ADS

Title: Discovery of rapid radial velocity variations in the roAp
    star 10 Aql and possible pulsations of β CrB
Authors: Kochukhov, O.; Landstreet, J. D.; Ryabchikova, T.; Weiss,
   W. W.; Kupka, F.
Bibcode: 2002MNRAS.337L...1K
Altcode:
  We report discovery of radial velocity variations in rare earth spectral
  lines of the roAp star 10 Aql with amplitudes of between 30 and 130 m
  s<SUP>-1</SUP> and periods of about 11 min. Radial velocity variations
  with amplitude 70 m s<SUP>-1</SUP> may also have been detected in
  one spectral line of Fe I in β CrB. If confirmed, our results may
  indicate that all Ap stars in a certain temperature range pulsate,
  which means that roAp stars do not exist as a separate class but are
  only distinguished by higher pulsational amplitudes.

Title: On the anomaly of Balmer line profiles of A-type
    stars. Fundamental binary systems
Authors: Smalley, B.; Gardiner, R. B.; Kupka, F.; Bessell, M. S.
Bibcode: 2002A&A...395..601S
Altcode: 2002astro.ph..9239S
  In previous work, Gardiner et al. (\cite{GKS99}) found evidence
  for a discrepancy between the T<SUB>eff</SUB> obtained from Balmer
  lines with that from photometry and fundamental values for A-type
  stars. An investigation into this anomaly is presented using Balmer
  line profiles of stars in binary system with fundamental values of both
  T<SUB>eff</SUB> and log g. A revision of the fundamental parameters
  for binary systems given by Smalley &amp; Dworetsky (\cite{SD95}) is
  also presented. The T<SUB>eff</SUB> obtained by fitting Hα and Hβ
  line profiles is compared to the fundamental values and those obtained
  from uvby photometry. We find that the discrepancy found by Gardiner et
  al. (\cite{GKS99}) for stars in the range 7000 K &lt;~ T<SUB>eff</SUB>
  &lt;~ 9000 K is no longer evident. Partly based on DENIS data obtained
  at the European Southern Observatory.

Title: New grids of ATLAS9 atmospheres I: Influence of convection
    treatments on model structure and on observable quantities
Authors: Heiter, U.; Kupka, F.; van't Veer-Menneret, C.; Barban, C.;
   Weiss, W. W.; Goupil, M. -J.; Schmidt, W.; Katz, D.; Garrido, R.
Bibcode: 2002A&A...392..619H
Altcode: 2002astro.ph..6156H
  We present several new sets of grids of model stellar atmospheres
  computed with modified versions of the ATLAS9 code. Each individual set
  consists of several grids of models with different metallicities ranging
  from [M/H] = -2.0 to +1.0 dex. The grids range from 4000 to 10 000 K
  in T<SUB>eff</SUB> and from 2.0 to 5.0 dex in log {g}. The individual
  sets differ from each other and from previous ones essentially in the
  physics used for the treatment of the convective energy transport, in
  the higher vertical resolution of the atmospheres and in a finer grid
  in the (T<SUB>eff</SUB>, log {g}) plane. These improvements enable
  the computation of derivatives of color indices accurate enough for
  pulsation mode identification. In addition, we show that the chosen
  vertical resolution is necessary and sufficient for the purpose of
  stellar interior modelling. To explain the physical differences between
  the model grids we provide a description of the currently available
  modifications of ATLAS9 according to their treatment of convection. Our
  critical analysis of the dependence of the atmospheric structure and
  observable quantities on convection treatment, vertical resolution and
  metallicity reveals that spectroscopic and photometric observations are
  best represented when using an inefficient convection treatment. This
  conclusion holds whatever convection formulation investigated here is
  used, i.e. MLT(alpha =0.5), CM and CGM are equivalent. We also find that
  changing the convection treatment can lead to a change in the effective
  temperature estimated from Strömgren color indices from 200 to 400 K.

Title: Mode identification using the exoplanetary camera
Authors: Garrido, R.; Moya, A.; Goupil, M. J.; Barban, C.; van't
   Veer-Menneret, C.; Kupka, F.; Heiter, U.
Bibcode: 2002CoAst.141...48G
Altcode:
  No abstract at ADS

Title: A-star envelopes: a test of local and non-local models of
    convection
Authors: Kupka, F.; Montgomery, M. H.
Bibcode: 2002MNRAS.330L...6K
Altcode: 2001astro.ph.12401K
  We present results of a fully non-local, compressible model of
  convection for A-star envelopes. This model quite naturally reproduces
  a variety of results from observations and numerical simulations which
  local models based on a mixing length do not. Our principal results,
  which are for models with T <SUB>eff</SUB> between 7200 and 8500K, are
  the following. First, the photospheric velocities and filling factors
  are in qualitative agreement with those derived from observations of
  line profiles of A-type stars. Secondly, the Heii and Hi convection
  zones are separated in terms of convective flux and thermal interaction,
  but joined in terms of the convective velocity field, in agreement with
  numerical simulations. In addition, we attempt to quantify the amount
  of overshooting in our models at the base of the Heii convection zone.

Title: Colors in Eddington: implications for mode identification
Authors: Garrido, R.; Claret, A.; Moya, A.; Kupka, F.; Heiter, U.;
   Barban, C.; Goupil, M. -J.; van't Veer-Menneret, C.
Bibcode: 2002ESASP.485..103G
Altcode: 2002sshp.conf..103G
  Theoretical radial and non-radial modes of low n orders in main sequence
  stars, like δ Scuti and β Cephei, do not show regular pattern in their
  power spectra. Although Barban et al. (2001) have shown that assuming an
  amplitude distribution certain patterns could be recovered, a method to
  identify the mode is needed in order to perform real asteroseismology of
  these objects. Examples are given in the literature where for several
  stars showing many periods: FG Vir (24): Breger et al. (1999), XX Pyx
  (22): Handler et al. (2000), 4 CVn (30): Breger et al. (1999) and BI CMi
  (20): Breger et al. (2002), a physical modeling was not successful,
  the reason being the mode identification. Multicolor photometry,
  as well as line profile spectroscopy, have been the usual methods to
  identify modes. In this work we will focus on the capabilities of color
  information to discriminate the different angular degrees l of the
  spherical harmonic associated to a radial or non-radial mode excited
  in a given δ Scuti pulsating star. Some numerical simulations are
  also presented for the exoplanetary camera in the space mission COROT
  where it is shown that, under some physical assumptions, color can be
  very important in order to identify the angular degree l. Furthermore
  colors can give relevant information of the non-adiabatic properties
  of some pulsating stars which, in the case of the δ Scuti stars,
  are related with the treatment of the convection. Arguments are also
  given to support the inclusion of color information in Eddington.

Title: The Böhm-Vitense Gap: The Role of Turbulent Convection
Authors: D'Antona, F.; Montalbán, J.; Kupka, F.; Heiter, U.
Bibcode: 2002ApJ...564L..93D
Altcode:
  ``Böhm-Vitense gaps,'' discontinuities in the color distribution
  of A-F type stars along the main sequence, have traditionally
  been attributed to the abrupt onset of strong convection (8000
  K&gt;=T<SUB>eff</SUB>&gt;=6400 K) in stellar atmospheres and
  envelopes. Using the full spectrum of turbulence model to describe
  convective transport (Canuto, Goldman, &amp; Mazzitelli) both in
  the interior and in the atmosphere yields a very sharp transition
  between structures that are convective only in the surface layers
  and structures that show a well-developed convection also in the
  interior. This produces a sudden change in the T<SUB>eff</SUB> of stars,
  around T<SUB>eff</SUB>~=6800 K. Using numerical simulations, we show
  that this feature produces a stellar depletion that is consistent with
  the gap at 0.33&lt;~B-V&lt;~0.38. The standard mixing-length theory
  does not show this behavior. Consequently, this particular gap is a
  ``T<SUB>eff</SUB>'' gap and not a ``color'' gap. In fact, it is also
  present in the V-I color distribution of the Hyades stars.

Title: TEMPLOGG for determining stellar parameters of MONS targets
Authors: Kupka, F.; Bruntt, H.
Bibcode: 2001JAD.....7Q...8K
Altcode:
  We describe the TEMPLOGG tool which has been developed at the Institute
  of Astronomy in Vienna for the determination of fundamental stellar
  parameters from photometric observations. TEMPLOGG provides a very
  convenient access to a variety of calibrations for the Strömgren-β
  and the Geneva photometric systems. Using observed photometric indices
  the program automatically selects the most suitable transformation
  between observed colours and stellar fundamental parameters. We have
  used it here for a parameter determination with a preliminary list of
  primary MONS targets. The results of this study are presented as an
  example for the application and capabilities of TEMPLOGG.

Title: Using TEMPLOGG for determining stellar parameters of MONS
    targets
Authors: Kupka, F.; Bruntt, H.
Bibcode: 2001fcm..book...39K
Altcode:
  We describe the TEMPLOGG tool which has been developed at the Institute
  of Astronomy in Vienna for the determination of fundamental stellar
  parameters from photometric observations. TEMPLOGG provides a very
  convenient access to a variety of calibrations for the Stromgren-beta
  and the Geneva photometric systems. Using observed photometric indices
  the program automatically selects the most suitable transformation
  between observed colours and stellar fundamental parameters. We have
  used it here for a parameter determination with a preliminary list of
  primary MONS targets. The results of this study are presented as an
  example for the application and capabilities of TEMPLOGG.

Title: Convection in the atmospheres and envelopes of turnoff and
    giant branch stars of globular clusters
Authors: Montalbán, J.; Kupka, F.; D'Antona, F.; Schmidt, W.
Bibcode: 2001A&A...370..982M
Altcode:
  We explore the dependence of {T_eff}'s and colors of stellar
  models on the treatment of over-adiabatic convection, both in the
  atmosphere and in the interior. We compute main sequence, turnoff,
  and subgiant models for low metallicity stars (Z=2 10<SUP>-4</SUP>)
  using as boundary conditions two new sets of model atmospheres by the
  Wien group (Kupka \cite{kup96}; Smalley &amp; Kupka \cite{sma97};
  Heiter et al. \cite{hei01}). In these models convection is treated
  either in the Mixing Length Theory (MLT) or in the Full Spectrum of
  Turbulence (FST) formulation. We check the dependence of the {T_eff}
  location of the HR diagram both on the optical depth tau at which the
  atmospheric boundary conditions are fixed, and on the convective model
  adopted in the atmosphere and interior. Obviously, full selfconsistency
  of the result is obtained only if the treatment of convection is the
  same in the outer layers and in the interior. We show that it is not
  appropriate to use MLT convection in the atmosphere and FST in the
  interior; if we wish to test the effect of changing the l/H_p in the
  MLT, the atmospheric integration must be limited to tau =1. We construct
  isochrones for ages of 10 Gyr and greater, and transform the theoretical
  {T_eff} and gravity values to the Johnson B and V magnitudes. The two
  sets of model atmospheres give small differences (up to ~ 0.03 mag) for
  the B-V color, a result of the different temperature stratification in
  the model atmosphere with FST convection treatment compared to that one
  based on MLT. The FST boundary conditions provide relative locations
  of turnoff and giant branch which differ from the MLT solutions, and
  are in better agreement with the HR diagram morphology of the Globular
  Cluster M 92.

Title: Model Atmospheres with Individualized Abundances
Authors: Piskunov, N.; Kupka, F.
Bibcode: 2001ApJ...547.1040P
Altcode:
  We describe a new method for computing opacity distribution functions
  (ODFs) for model atmosphere calculations. The method is tailored to
  model the atmospheres of individual stars on a modern workstation. Our
  goal is the computation of model atmospheres for stars with abundances
  significantly different from the solar or scaled solar composition
  typically used for grid calculations. As a consistency test, we show
  that the new procedure is able to reproduce the ODFs and existing model
  atmospheres for solar abundances, and we describe models for stars
  with peculiar abundances. We demonstrate that while mild chemical
  peculiarities can be well represented by scaled solar models, the
  extreme cases result in a very different atmospheric structure with no
  analogs in scaled solar grids. Such a structure influences the emerging
  spectrum as is clearly seen both in the observed flux distribution and
  in the line ratios that are much better represented by the new models.

Title: A New Project for Theoretical Colors of Globular Cluster Stars
Authors: Montalban, J.; D'Antona, F.; Kupka, F.; Schmidt, W.
Bibcode: 2001coev.conf..243M
Altcode:
  The following sections are included: <P />* Summary <P />* References

Title: Abundances in Przybylski's star
Authors: Cowley, C. R.; Ryabchikova, T.; Kupka, F.; Bord, D. J.;
   Mathys, G.; Bidelman, W. P.
Bibcode: 2000MNRAS.317..299C
Altcode:
  We have derived abundances for 54 elements in the extreme roAp star
  HD101065. ESO spectra with a resolution of about 80000, and S/N of 200
  or more were employed. The adopted model has T<SUB>eff</SUB>=6600K, and
  log(g)=4.2. Because of the increased line opacity and consequent low
  gas pressure, convection plays no significant role in the temperature
  structure. Lighter elemental abundances through the iron group scatter
  about standard abundance distribution (SAD) (solar) values. Iron
  and nickel are about one order of magnitude deficient while cobalt
  is enhanced by 1.5dex. Heavier elements, including the lanthanides,
  generally follow the solar pattern but enhanced by 3 to 4dex. Odd-Z
  elements are generally less abundant than their even-Z neighbours. With
  a few exceptions (e.g. Yb), the abundance pattern among the heavy
  elements is remarkably coherent, and resembles a displaced solar
  distribution.

Title: Abundance analysis of roAp stars. V. HD 166473
Authors: Gelbmann, M.; Ryabchikova, T.; Weiss, W. W.; Piskunov, N.;
   Kupka, F.; Mathys, G.
Bibcode: 2000A&A...356..200G
Altcode:
  This fifth paper in a sequence on abundance analyses of roAp stars
  features several improvements and complements over the previous
  investigations: i. The new VALD-2 atomic data base was used which
  significantly improves the analysis of C, N, O, and rare earth
  elements (REE) and in particular includes also some doubly ionized
  REE species. ii. An individual opacity distribution function table
  was generated for a successful synthesis of photometric indices of
  this very peculiar star. iii. The influence of a (rather strong)
  magnetic field on abundance determinations is studied and presented
  for 30 elements. iv. Our investigation of 33 elements (45 ions) is
  the hitherto most complete chemical analysis of a chemically peculiar
  star, using modern tools. Similar to the four roAp stars analysed
  by us so far (alpha Cir: Kupka et al. 1996, HD 203932: Gelbmann
  et al. 1997, gamma Equ: Ryabchikova et al. 1997a, and HD 24712:
  Ryabchikova et al. 1997b) we find nearly solar abundances of Fe and
  Ni, and a definite overabundance of Cr and especially Co. Rare earth
  elements have large overabundances, whereas C and O are underabundant
  relative to the Sun. This pattern seems to be a common property of the
  chemically peculiar (CP2, Ap) stars. A new and most striking result
  is the discovery of the anomalous line strengths of the second ions
  of REE resulting in an abundance increase of up to +1.5 dex, compared
  to values obtained from lines of the first ions. This anomaly is not
  found in non-roAp and ``normal'' stars. Based on observations obtained
  at the European Southern Observatory (La Silla, Chile)

Title: Spectroscopic Survey of Rapidly Oscillating Ap Stars
Authors: Weiss, W. W.; Ryabchikova, T. A.; Kupka, F.; Lueftinger,
   T. R.; Savanov, I. S.; Malanushenko, V. P.
Bibcode: 2000ASPC..203..487W
Altcode: 2000ilss.conf..487W; 2000IAUCo.176..487W
  A spectroscopic survey of roAp stars has been initiated in Vienna
  in order to determine their fundamental astrophysical parameters and
  abundances. We report here on our attempt to confirm and elaborate an
  atmospheric peculiarity recently discovered (Ryabchikova et al. 1999)
  which should allow to identify roAp stars with a single spectrum.

Title: VALD-2 -- The New Vienna Atomic Line Database
Authors: Kupka, F. G.; Ryabchikova, T. A.; Piskunov, N. E.; Stempels,
   H. C.; Weiss, W. W.
Bibcode: 2000BaltA...9..590K
Altcode: 2000OAst....9..590K
  We provide a brief outline of the concepts and facilities of the Vienna
  Atomic Line DataBase in its new version 2. A summary of contents and
  recommendations how to use the VALD-2 are given. We conclude by a few
  applications planned for future releases of VALD.

Title: Line Blanketing in Przybylski's Star
Authors: Cowley, C. R.; Kupka, F.; Mathys, G.
Bibcode: 1999AAS...195.5002C
Altcode: 1999BAAS...31.1447C
  Przybylski's star (HD 101065) may be the most heavily blanketed
  star known. It therefore provides a test of our techniques for line
  blanketing. The current abstract draws on a paper in preparation by
  CRC, T. Ryabchikova, F. Kupka, G. Mathys, and D. J. Bord, based on
  ESO spectra obtained by GM. Unfortunately, the atomic species that
  provide the majority of the line blanketing in Przybylski's star
  does not have enough atomic data for realistic calculations of the
  blanketing. We therefore discuss three models in which iron-group
  elements were articifically elevated in abundance in the calculation
  of opacity used to construct the models. We thank Drs. R. L. Kurucz,
  and Bengt Edvardsson for calculating respectively Models 1 (dashed
  [Fe/H]=+3) and 2 (dot-dash, [Fe/H]=+2) at our request. Model 3
  (line, [Fe/H]) was calculated by FK, using the Canuto-Mazzitelli
  formalism. Figure 1 (www.astro.lsa.umich.edu/usrs/cowley/models.gif),
  shows these 3 models in good agreement with one another, and clearly
  different from a standard solar-abundance Atlas9 model (dashed)
  with the same effective temperature. All three models are scaled to
  Te=6600K. The blanketed models have little or no convection, and show
  the lowered boundary temperature of classical picket-fence models. The
  true boundary temperature may be still lower than in these numerical
  models. Abundances from Pr I and Nd I are systematically higher than
  those from the corresponding second spectra, as are those from Pr III
  and Nd III. It was noted long ago by Przybylski and others that the
  Balmer profiles had cores indicative of temperatures of some 6000K;
  the wings could be fit with much higher temperatures--perhaps
  as high as 7500K. Molecular species have been sought but not
  identified. Calculations show CN and CH lines would be very weak, even
  if the temperature between log(tau5000)=-3.5 and -5.4 were allowed to
  drop to 3000K.

Title: The Hydrodynamic Moment Equations: An Alternative Treatment
    For Stellar Convection
Authors: Kupka, F.
Bibcode: 1999POBeo..65...13K
Altcode:
  No abstract at ADS

Title: Turbulent Convection: Comparing the Moment Equations to
    Numerical Simulations
Authors: Kupka, F.
Bibcode: 1999ApJ...526L..45K
Altcode: 1999astro.ph..9331K
  The nonlocal hydrodynamic moment equations for compressible convection
  are compared to numerical simulations. Convective and radiative flux
  typically deviate less than 20% from the three-dimensional simulations,
  while mean thermodynamic quantities are accurate to at least 2%
  for the cases we have investigated. The moment equations are solved
  in minutes rather than days as required on standard workstations. We
  conclude that this convection model has the potential to considerably
  improve the modeling of convection zones in stellar envelopes and cores,
  in particular those of A and F stars.

Title: VALD - The Vienna Atomic Line Database: A Survey
Authors: Kupka, F.; Ryabchikova, T. A.
Bibcode: 1999POBeo..65..223K
Altcode:
  No abstract at ADS

Title: Interacting convection zones
Authors: Muthsam, Herbert J.; Göb, Wolfgang; Kupka, Friedrich;
   Liebich, Wolfgang
Bibcode: 1999NewA....4..405M
Altcode:
  3D Numerical simulations of convection zones separated by a stable
  layer (according to the Schwarzschild criterion) are presented. The
  compressible case is considered. We make use of idealized microphysics
  closely related to polytropes. Decreasing the importance of the
  separating stable layer by diminishing its vertical extent in a series
  of models we investigate how the two convection zones merge into
  one. In our parameter range it is the upper zone which increases in
  size and ultimately squeezes the lower convection zone more or less
  out of existence. Properties of various fluxes and other physical
  quantities are discussed.

Title: VALD-2: Progress of the Vienna Atomic Line Data Base
Authors: Kupka, F.; Piskunov, N.; Ryabchikova, T. A.; Stempels, H. C.;
   Weiss, W. W.
Bibcode: 1999A&AS..138..119K
Altcode:
  We describe the updated version of the Vienna Atomic Line Data
  Base (VALD, \cite[Piskunov et al. 1995)]{pis95} which represents a
  considerable improvement over the first installation from 1994. The
  original line lists have been complemented with critically evaluated
  data obtained from experimental measurements and theoretical
  calculations which are necessary for computing state-of-the-art line
  opacities in stellar atmospheres, as well as for synthesizing spectra
  for high precision analyses. In this paper, we present new and improved
  data sets for neutral species and ions of Si, P, Sc, Ti, V, Cr, Mn, Fe,
  Co, Ni, Cu, Zn, Y, Zr, Ru, Xe, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er,
  Tm, Yb, Lu, Re, Pt, Au, Hg, and Pb. For some species data are available
  in VALD for the first time. We explain our choice of quality rankings by
  reviewing the literature for the new data and by comparison with source
  lists included into VALD. For some cases, we produced new line data
  by weighted averaging of data from different sources with individual
  error estimates in order to increase the reliability of VALD line
  lists. Software modifications allow remote users of VALD to specify
  individual extraction parameters as an alternative to the default
  settings of the VALD team and to have direct control over the quality
  ranking of line data. A World-Wide-Web interface is described which
  provides easy access to all new features. To simplify proper crediting
  of all authors of atomic data, VALD now includes a compilation of all
  publications used in each type of reply. Finally, we briefly discuss
  the future roadmap of VALD developments, including the incorporation
  of molecular transitions and integration with external data
  bases. http://www.astro.univie.ac.at/~vald http://www.astro.uu.se/~vald

Title: Testing convection theories using Balmer line profiles of A,
    F, and G stars
Authors: Gardiner, R. B.; Kupka, F.; Smalley, B.
Bibcode: 1999A&A...347..876G
Altcode:
  We consider the effects of convection on the Balmer line profiles
  ({H_α} and {H_β}) of A, F, and G stars. The standard mixing-length
  theory (MLT) atlas9 models of Kurucz (1993), with and without
  overshooting, are compared to atlas9 models based on the turbulent
  convection theory proposed by Canuto &amp; Mazzitelli (1991, 1992)
  and implemented by Kupka (1996), and the improved version of this model
  proposed by Canuto et al. (1996) also implemented by Kupka. The Balmer
  line profiles are a useful tool in investigating convection because
  they are very sensitive to the parameters of convection used in the
  stellar atmosphere codes. The {H_α} and {H_β} lines are formed at
  different depths in the atmosphere. The {H_α} line is formed just
  above the convection zone. The {H_β} line, however, is partially
  formed inside the convection zone. We have calculated the {T_eff} of
  observed stars by fitting Balmer line profiles to synthetic spectra
  and compared this to: (i) the {T_eff} of the fundamental stars; (ii)
  the {T_eff} of stars determined by the Infra-Red Flux Method and (iii)
  the {T_eff} determined by Geneva photometry for the stars in the Hyades
  cluster. We find that the results from the {H_α} and {H_β} lines are
  different, as expected, due to the differing levels of formation. The
  tests are inconclusive between three of the four models; MLT with no
  overshooting, CM and CGM models, which all give results in reasonable
  agreement with fundamental values. The results indicate that for the
  MLT theory with no overshooting it is necessary to set the mixing
  length parameter alpha equal to 0.5 for stars with {T_eff &lt;= 6000}
  K or {T_eff &gt;= 7000} K. However for stars with {6000} K{&lt;= T_eff
  &lt;= 7000} K the required value for the parameter is {alpha &gt;=
  1.25}. Models with overshooting are found to be clearly discrepant,
  consistent with the results with uvby photometry by Smalley &amp; Kupka
  (1997). Based on observations made at the Observatorio del Roque de
  los Muchachos using the Richardson-Brealey Spectrograph on the 1.0m
  Jacobs Kapteyn Telescope.

Title: Eu III identification and Eu abundance in CP stars
Authors: Ryabchikova, T.; Piskunov, N.; Savanov, I.; Kupka, F.;
   Malanushenko, V.
Bibcode: 1999A&A...343..229R
Altcode:
  We report the first identification of the Eu iii lambda 6666.347 line
  in optical spectra of CP stars. This line is clearly present in the
  spectra of HR 4816, 73 Dra, HR 7575, beta CrB, and alpha (2) CVn,
  while it is marginally present or absent in spectra of the roAp stars
  (rapidly oscillating Ap stars, cf. Kurtz 1990) alpha Cir, gamma Equ,
  HD 203932, GZ Lib (33 Lib), and HD 24712. Careful synthetic spectrum
  calculations for the Eu ii lambda 6645.11 line taking into account
  hyperfine, isotopic, and magnetic splittings allow us to obtain more
  accurate Eu abundances in the atmospheres of 9 CP stars. In most
  cases the derived abundances are significantly lower than the previous
  results reported for some of the stars based on coarse analysis of the
  famous blue Eu ii lines. Assuming an ionization balance in the stellar
  atmospheres we give an estimate of the astrophysical oscillator strength
  log (gf)=1.18 +/- 0.14 for the Eu iii lambda 6666.347 line. This value
  is obtained without taking into account a possible hyperfine-splitting
  which is unknown for this Eu iii line. We also provide astrophysical
  gf-values for Eu iii lambda lambda 7221.838, 7225.151, and 8079.071.

Title: Observational Evidence for Convection in Main Sequence Star
    Atmospheres
Authors: Weiss, W. W.; Kupka, F.
Bibcode: 1999ASPC..173...21W
Altcode: 1999sstt.conf...21W
  No abstract at ADS

Title: Testing Convection Theories Using Balmer Line Profiles of A,
    F and G Stars
Authors: Gardiner, R.; Smalley, B.; Kupka, F.
Bibcode: 1999ASPC..173..213G
Altcode: 1999sstt.conf..213G
  No abstract at ADS

Title: Computing Solar and Stellar Overshooting with Turbulent
    Convection Models. First Tests of a Fully Non-Local Model
Authors: Kupka, F.
Bibcode: 1999ASPC..173..157K
Altcode: 1999sstt.conf..157K
  No abstract at ADS

Title: The acoustic cut-off frequency of roAp stars
Authors: Audard, N.; Kupka, F.; Morel, P.; Provost, J.; Weiss, W. W.
Bibcode: 1998A&A...335..954A
Altcode: 1997astro.ph.12126A
  Some of the rapidly oscillating (roAp) stars, have frequencies which are
  larger than the acoustic cut-off frequency determined from published
  stellar models which usually assume a grey atmosphere. As the cut-off
  frequency depends on the T(tau ) relation, we have computed models
  and adiabatic frequencies for pulsating Ap stars with more realistic
  atmospheres which include a frequency dependent treatment of radiative
  transfer, take blanketing effects into account, and which have a better
  treatment of the radiative pressure. In addition, we are using opacity
  distribution functions specific to the atmospheric composition. With
  these improvements over the classical stellar models the theoretical
  acoustic cut-off frequency for roAp stars are increased by about
  200 mu Hz, which brings them close to the observations. We restrict
  the comparison of our computations with observations to those two
  `pathological' roAp stars for which more reliable astrophysical
  parameters are available, HD 24712 and alpha Cir, and comment briefly
  on a third one, HD 134214. For alpha Cir we find models which have
  indeed a cut-off frequency beyond the largest observed frequency and
  which are well within the T<SUB>eff</SUB> - L/L_⊙ error box. For HD
  24712 only models which are hotter by about 100 K and less luminous
  by nearly 10% than what is actually the most probable value derived by
  spectroscopy would have an acoustic cut-off frequency large enough. HD
  134214 fits our models best, however, the error box for T<SUB>eff</SUB>
  - L/L_⊙ is the largest of all three stars. One may thus speculate
  that the old controversy about a mismatch between observed largest
  frequencies and theoretical cut-off frequencies of roAp star models
  is resolved. Based on hipparcos data.

Title: Abundance analysis of the lambda Bootis stars HD 192640,
    HD 183324, and HD 84123
Authors: Heiter, U.; Kupka, F.; Paunzen, E.; Weiss, W. W.; Gelbmann, M.
Bibcode: 1998A&A...335.1009H
Altcode:
  The classification of lambda Bootis stars based on photometric indices
  or low resolution spectra is not sufficient for a final decision
  concerning a membership to this group. A detailed spectroscopic
  investigation is necessary to rule out stars with similar classification
  spectra but different abundance patterns. Therefore a program on
  abundance analyses of lambda Bootis candidates was established, which
  makes use of a software package that enables the analysis of high
  signal-to-noise spectra with large resolution. In this paper we present
  the results of the application of these tools on two lambda Bootis stars
  (HD 192640 and HD 183324) for which the derived abundances agree very
  well with the literature. For a third star (HD 84123), which shows a
  very low projected rotational velocity, the newly determined abundance
  pattern confirms its membership to the lambda Bootis group. We also
  investigated the effect of using several different codes for the
  calculation of the model atmospheres on the synthetic spectra of the
  program stars, which span a wide range in effective temperature, gravity
  and metallicity. The substitution of opacity distribution functions,
  which where pretabulated for metal abundances scaled according to the
  solar composition, by ones calculated for the individual abundance
  patterns does not change the synthetic spectra significantly. On the
  other hand, the derived abundances are sensitive to the treatment of
  overshooting within the calculation of the convective flux for cool
  stars. Based on observations obtained at the Observatoire de Haute
  Provence, the Osservatorio Astronomico di Padua-Asiago and with the
  Hipparcos satellite

Title: CP star atmospheres based on individual ODFs
Authors: Kupka, F.; Piskunov, N. E.
Bibcode: 1998CoSka..27..228K
Altcode: 1998astro.ph..5057K
  We describe a new method for the computation of opacity distribution
  functions (ODFs) useful to calculate one-dimensional model atmospheres
  in local thermal equilibrium (LTE). The new method is fast enough to
  be applied on current workstations and allows the computation of model
  atmospheres which deviate significantly from (scaled) solar chemical
  composition. It has reproduced existing ODFs and model atmospheres
  for solar abundances. Depending on the type of chemical peculiarity
  the "individual" model atmosphere may have a structure and surface
  fluxes similar to atmospheres based on (scaled) solar abundances or
  deviate in a way that cannot be reproduced by any of the conventional
  models. Examples are given to illustrate this behavior. The availability
  of models with "individualized" abundances is crucial for abundance
  analyses and Doppler imaging of extreme CP stars.

Title: The effects of convection on the colours of A and F stars
Authors: Smalley, B.; Kupka, F.
Bibcode: 1998CoSka..27..233S
Altcode: 1998astro.ph..5058S
  We present a discussion on the effects of convection on the uvby colours
  of A and F stars. The mixing-length theory used in ATLAS9 is compared to
  the turbulent convection theory of Canuto &amp; Mazzitelli. Comparison
  with fundamental stars reveals that colours calculated using the Canuto
  &amp; Mazzitelli convection theory are generally in better agreement
  than those obtained using mixing-length theory.

Title: EU III identification and EU abundance in cool CP stars
Authors: Ryabchikova, T.; Piskunov, N.; Savanov, I.; Kupka, F.
Bibcode: 1998CoSka..27..359R
Altcode: 1998astro.ph..5206R
  We report the first identification of the Eu III lambda 6666.317
  line in optical spectra of CP stars. This line is clearly present in
  the spectra of HR 4816, 73 Dra, HR 7575, and beta CrB, while it is
  marginally present or absent in spectra of the roAp stars alpha Cir,
  gamma Equ, BI Mic, 33 Lib, and HD 24712.

Title: Atmospheric structure and acoustic cut-off frequency of
    roAp stars
Authors: Audard, N.; Kupka, F.; Morel, P.; Provost, J.; Weiss, W. W.
Bibcode: 1998CoSka..27..304A
Altcode: 1998astro.ph..5091A
  Some of the rapidly oscillating (CP2) stars, have frequencies which are
  larger than the theoretical acoustic cut-off frequency. As the cut-off
  frequency depends on the T(tau) relation in the atmosphere, we have
  computed models and adiabatic frequencies for pulsating Ap stars with
  T(tau) laws based on Kurucz model atmospheres and on Hopf's purely
  radiative relation. The frequency-dependent treatment of radiative
  transfer as well as an improved calculation of the radiative pressure
  in Kurucz model atmospheres increase the theoretical acoustic cut-off
  frequency by about 200 microHz, which is closer to the observations. For
  alpha Cir we find models with Kurucz atmospheres which have indeed a
  cut-off frequency beyond the largest observed frequency and which are
  well within the T(eff) - L error box. For HD 24712 only models which
  are hotter by about 100 K and less luminous by nearly 10% than what
  is actually the most probable value would have an acoustic cut-off
  frequency large enough. One may thus speculate that the old controversy
  about a mismatch between observed largest frequencies and theoretical
  cut-off frequencies of roAp star models is resolved. However, the
  observational errors for the astrophysical fundamental parameters have
  to be reduced further and the model atmospheres refined.

Title: The acoustic cut-off frequency of A to F stars
Authors: Audard, N.; Kupka, F.; Morel, P.; Provost, J.; Weiss, W. W.
Bibcode: 1998IAUS..185..299A
Altcode:
  For some Ap stars, frequencies are observed which are larger than the
  theoretical acoustic cut-off frequency, which strongly depends on the T
  tau relation in the atmosphere. We have computed models and eigenmodes
  for pulsating Ap stars. The internal stellar structure is obtained
  with the CESAM code, and improved model atmospheres are constructed
  with T tau laws derived from Kurucz's model atmospheres. These
  models are compared to models whose atmospheres are derived from
  the purely radiative Hopf's T tau law. Our main result is that the
  frequency-dependent treatment of radiative transfer in Kurucz's model
  atmospheres induces an increase of the theoretical acoustic cut-off
  frequency, which brings us closer to the observations. As the cut-off
  frequency is determined by the very outer layers, we point out the
  necessity to compute very accurate model atmospheres.

Title: The role of convection on the UVBY colours of A, F, and G stars
Authors: Smalley, B.; Kupka, F.
Bibcode: 1997A&A...328..349S
Altcode:
  We discuss the effects of convection on the theoretical uvby colours of
  A, F, and G stars. The standard mixing-length theory atlas9 models of
  Kurucz (1993), with and without approximate overshooting, are compared
  to models using the turbulent convection theory proposed by Canuto &amp;
  Mazzitelli (1991, 1992) and implemented by Kupka (1996a). Comparison
  with fundamental T_eff and log g stars reveals that the Canuto &amp;
  Mazzitelli models give results that are generally superior to standard
  mixing-length theory (MLT) without convective overshooting. MLT
  models with overshooting are found to be clearly discrepant. This is
  supported by comparisons of non-fundamental stars, with T_eff obtained
  from the Infrared Flux Method and log g from stellar evolutionary
  models for open cluster stars. The Canuto &amp; Mazzitelli theory
  gives values of (b-y)_0 and c_0 that are in best overall agreement
  with observations. Investigations of the m_0 index reveal that all
  of the treatments of convection presented here give values that are
  significantly discrepant for models with T_eff &lt; 6000 K. It is
  unclear as to whether this is due to problems with the treatment of
  convection, missing opacity, or some other reason. None of the models
  give totally satisfactory m_0 indices for hotter stars, but the Canuto
  &amp; Mazzitelli models are in closest overall agreement above 7000
  K. Grids of uvby colours, based on the CM treatment of convection,
  are presented. These grids represent an improvement over the colours
  obtained from models using the mixing-length theory. The agreement with
  fundamental stars enables the colours to be used directly without the
  need for semi-empirical adjustments that were necessary with the earlier
  colour grids. Table~5 is only available at the CDS via anonymous ftp
  130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html

Title: VizieR Online Data Catalog: Role of Convection in A, F,
    and G stars (Smalley+ 1997)
Authors: Smalley, B.; Kupka, F.
Bibcode: 1997yCat..33280349S
Altcode:
  We discuss the effects of convection on the theoretical uvby
  colours of A, F, and G stars. The standard mixing-length theory
  atlas9 models of Kurucz (1993, ATLAS9, SAO, Cambridge, USA), with
  and without approximate overshooting, are compared to models using
  the turbulent convection theory proposed by Canuto &amp; Mazzitelli
  (1991ApJ...370..295C, 1992ApJ...389..724C) and implemented by Kupka
  (1996, ASPConf. Proc. 108, 73). Comparison with fundamental Teff
  and log g stars reveals that the Canuto &amp; Mazzitelli models give
  results that are generally superior to standard mixing-length theory
  (MLT) without convective overshooting. MLT models with overshooting
  are found to be clearly discrepant. This is supported by comparisons
  of non-fundamental stars, with Teff obtained from the Infrared Flux
  Method and log g from stellar evolutionary models for open cluster
  stars. The Canuto &amp; Mazzitelli theory gives values of (b-y)0 and c0
  that are in best overall agreement with observations. Investigations
  of the m0 index reveal that all of the treatments of convection
  presented here give values that are significantly discrepant for
  models with Teff&lt;6000K. It is unclear as to whether this is
  due to problems with the treatment of convection, missing opacity,
  or some other reason. None of the models give totally satisfactory
  m0 indices for hotter stars, but the Canuto &amp; Mazzitelli models
  are in closest overall agreement above 7000K. Grids of uvby colours,
  based on the CM treatment of convection, are presented. These grids
  represent an improvement over the colours obtained from models using
  the mixing-length theory. The agreement with fundamental stars enables
  the colours to be used directly without the need for semi-empirical
  adjustments that were necessary with the earlier colour grids. For a
  description of the uvby photometric system, see e.g. &lt;GCPD/04&gt;
  (6 data files).

Title: (Erratum) Abundance analysis of roAp stars.
Authors: Gelbmann, M.; Kupka, F.; Weiss, W. W.; Mathys, G.
Bibcode: 1997A&A...322.1026G
Altcode:
  Erratum to Astron. Astrophys. 319, 630-636 (1997).

Title: Abundance analysis of roAp stars. II. HD 203932
Authors: Gelbmann, M.; Kupka, F.; Weiss, W. W.; Mathys, G.
Bibcode: 1997A&A...319..630G
Altcode:
  A new tool to simplify abundance analyses which is based on stand-alone
  programs has been applied to the rapidly oscillating Ap star HD
  203932 (BI Mic, CD -30 18600, SAO 212996; Ap(SrEu), V=8.82mag). The
  spectroscopically determined T_eff_=7450+/-100K and logg=4.3+/-0.15 put
  this star close to the ZAMS. Other fundamental atmospheric parameters
  are v_micro_&lt;0.6km/s and the total abundance of all iron peak
  elements [M/H]=0.0+/-0.1. The fundamental parameters put HD 203932 in a
  region of the HR-diagram where convection starts becoming efficient and
  the standard mixing length theory models lead to severe problems in the
  determination of the atmospheric parameters. The difference between the
  upper limit for logg obtained from several variants of the mixing length
  theory and the Canuto-Mazzitelli model indicates that the choice of a
  particular convection model can influence the determination of basic
  stellar parameters. For the first time abundances were determined for
  HD 203932 showing a pattern for the 35 investigated elements which is
  similar to α Cir (Kupka et al. 1996A&amp;A...308..886K, Paper I). Fe
  and Ni have about solar abundance, Cr and especially Co are clearly
  overabundant as well as rare earth elements. The most underabundant
  element is Sc, followed by C, N, and O, which is a common property of
  CP2 stars. The lack of a correlation in our data between individual line
  abundances and their effective Lande factors implies a mean magnetic
  field modulus not exceeding few kG. Compared to the last homogeneous
  spectroscopic investigation of a large sample of chemically peculiar
  stars (21 cool Ap stars, Adelman 1973ApJ...183...95A), our analysis
  is based on data with higher spectral resolution and signal-to-noise
  ratio. Even more important, we are using a much larger atomic line
  data base with more precise atomic parameters than available more than
  twenty years ago.

Title: The Vienna Atomic Line Database : Present State and Future
    Development
Authors: Ryabchikova, T. A.; Piskunov, N. E.; Kupka, F.; Weiss, W. W.
Bibcode: 1997BaltA...6..244R
Altcode: 1997OAst....6..244R
  We describe the main structure of the Vienna Atomic Line Database,
  the tools provided for the users and the statistics of its use in
  the last two years. Our plans for future developments of the database
  are discussed.

Title: Abundance analysis of roAp stars. I. α Circini.
Authors: Kupka, F.; Ryabchikova, T. A.; Weiss, W. W.; Kuschnig, R.;
   Rogl, J.; Mathys, G.
Bibcode: 1996A&A...308..886K
Altcode:
  Based on high resolution, low noise spectroscopy in the spectral region
  from 4200A to 6700A we derived T_eff_=7900+/-200K, logg=4.2+/-0.15,
  vsin(i)=12.5(-0.5,+1.5)km/s, and elemental abundances for the rapidly
  oscillating (ro)Ap star αCir(HD128898, HR5463). We used the spectrum
  synthesis and the equivalent width technique and confirmed the presence
  of a magnetic field in αCir. The underabundance of C, N, and O, and
  the overabundances of rare-earth and some other heavy elements are
  comparable to other cool Ap-stars. The most important peculiarity is
  that of Co, which is almost as overabundant as Cr, the most overabundant
  iron peak element in cool Ap-stars.

Title: New models for the convective flux in stellar atmospheres
Authors: Kupka, F.
Bibcode: 1996IAUS..176..557K
Altcode:
  No abstract at ADS

Title: Beyond Mixing Length Theory
Authors: Kupka, F.
Bibcode: 1996ASPC..108...73K
Altcode: 1996mass.conf...73K
  No abstract at ADS

Title: Introduction
Authors: Griffin, R. E. M.; Kupka, F.
Bibcode: 1996ASPC..108..299G
Altcode: 1996mass.conf..299G
  No abstract at ADS

Title: M.A.S.S., Model Atmospheres and Spectrum Synthesis
Authors: Adelman, Saul J.; Kupka, Friedrich; Weiss, Warner W.
Bibcode: 1996ASPC..108.....A
Altcode: 1996mass.conf.....A
  No abstract at ADS

Title: M.A.S.S. Model atmospheres and stellar spectra. 5th Vienna
    workshop
Authors: Adelman, Saul J.; Kupka, Friedrich; Weiss, Werner W.
Bibcode: 1996mssm.conf.....A
Altcode:
  No abstract at ADS

Title: VALD: The Vienna Atomic Line Data Base.
Authors: Piskunov, N. E.; Kupka, F.; Ryabchikova, T. A.; Weiss, W. W.;
   Jeffery, C. S.
Bibcode: 1995A&AS..112..525P
Altcode:
  The "Vienna Atomic Line Data Base" (VALD) consists of a set of
  critically evaluated lists of astrophysically important atomic
  transition parameters and supporting extraction software. VALD contains
  about 600000 entries and is one of the largest collections of accurate
  and homogeneous data for atomic transitions presently available. It
  also includes specific tools for extracting data for spectrum synthesis
  and model atmosphere calculations. The different accuracies of data
  available in the literature made it necessary to introduce a ranking
  system and to provide a flexible method for extracting the best possible
  set of atomic line parameters for a given transition from all the
  available sources. The data base is presently restricted to spectral
  lines which are relevant for stars in which the LTE approximation is
  sufficient and molecular lines do not have to be taken into account. The
  provision was made that these requirements should not restrict the
  general design of VALD and the possibility of future expansion. In
  this paper we describe the structure of VALD, the available data sets
  and specific retrieval tools. The electronic-mail interface (VALD-EMS)
  created to allow remote access to VALD is also described. Both users
  and producers of atomic data are invited to explore the database,
  and to collaborate in improving and extending its contents.

Title: Fine Analysis of Pulsating CP Stars
Authors: Kupka, F.; Gelbmann, M.; Heiter, U.; Kuschnig, R.; Weiss,
   W. W.; Ryabchikova, T. A.
Bibcode: 1995ASPC...83..317K
Altcode: 1995IAUCo.155..317K; 1995aasp.conf..317K
  No abstract at ADS

Title: A numerical study of compressible convection.
Authors: Muthsam, H. J.; Goeb, W.; Kupka, F.; Liebich, W.; Zoechling,
   J.
Bibcode: 1995A&A...293..127M
Altcode:
  We perform numerical investigations of (mainly 3D) compressible
  convection by using simple microphysics (closely related to piecewise
  polytropes). The convective layer is embedded between stable layers
  at the top and the bottom. Overshooting above is found to be quite
  effective within the present parameter range, overshooting below
  less so. However, consistent with prior 2D calculation the induced
  motions outside of the directly convectively influenced region are more
  developed below than above the convection zone. Typical features of the
  lower parts of the convection zone leading to a downwardly pointing
  convective flux are discussed as is the existence of a specific cell
  system near the lower boundary of the convection zone proper. Also,
  the influence of parameters is discussed. 2D convection tends to lead to
  more intensive convection than 3D (the physical parameters being equal).

Title: The Vienna Atomic Line Data-Base
Authors: Piskunov, N. E.; Kupka, F.; Ryabchikova, T. A.; Weiss, W. W.;
   Jeffery, C. S.
Bibcode: 1995ASPC...81..610P
Altcode: 1995lahr.conf..610P
  No abstract at ADS

Title: The Evolutionary Status of Lambda Boo Stars
Authors: Paunzen, E.; Gelbmann, M.; Heiter, U.; Kupka, F.; Kuschnig,
   R.; Weiss, W. W.
Bibcode: 1995ASPC...83..315P
Altcode: 1995IAUCo.155..315P; 1995aasp.conf..315P
  No abstract at ADS

Title: Abundance analysis of cool oscillating CP stars
Authors: Kupka, F.; Ryabchikova, T.; Bolgova, G.; Kuschnig, R.; Weiss,
   W. W.; Mathys, G.; Le Contel, J. M.
Bibcode: 1994cpms.conf..130K
Altcode:
  No abstract at ADS

Title: Interaction of convection zones: the nonmagnetic case
Authors: Muthsam, H. J.; Göb, W.; Kupka, F.; Liebich, W.
Bibcode: 1994smf..conf..152M
Altcode:
  No abstract at ADS

Title: The peculiar binary system HR 8891 (ET And)
Authors: Kuschnig, R.; Weiss, W. W.; Piskounov, N.; Ryabchikova,
   T.; Kreidl, T. J.; Alvarez, M.; Bedolla, S. G.; Bus, S. J.; Guo, Z.;
   Hao, J.; Huang, L.; Kupka, F.; Le Contel, D.; Le Contel, J. M.; Osip,
   D. J.; Panov, K.; Polosukchina, N.; Sareyan, J. P.; Schneider, H.;
   Valtier, J. C.; Zboril, M.; Ziznovsky, J.; Zverko, J.
Bibcode: 1994IAUS..162...43K
Altcode:
  No abstract at ADS

