scholarly journals The Stagger-grid: A Grid of 3D Stellar Atmosphere Models

2013 ◽  
Vol 63 ◽  
pp. 367-371 ◽  
Author(s):  
Z. Magic ◽  
R. Collet ◽  
M. Asplund
Keyword(s):  
Stellar Atmosphere ◽  
Stagger Grid

scholarly journals The Stagger-grid: A grid of 3D stellar atmosphere models

2014 ◽  
Vol 573 ◽  
pp. A89 ◽  
Author(s):  
Z. Magic ◽  
A. Weiss ◽  
M. Asplund
Keyword(s):  
Stellar Atmosphere ◽  
Stagger Grid

scholarly journals The Stagger-grid: A grid of 3D stellar atmosphere models

2013 ◽  
Vol 557 ◽  
pp. A26 ◽  
Author(s):  
Z. Magic ◽  
R. Collet ◽  
M. Asplund ◽  
R. Trampedach ◽  
W. Hayek ◽  
...  
Keyword(s):  
Stellar Atmosphere ◽  
Stagger Grid

scholarly journals The Stagger-grid: A grid of 3D stellar atmosphere models

2014 ◽  
Vol 573 ◽  
pp. A90 ◽  
Author(s):  
Z. Magic ◽  
A. Chiavassa ◽  
R. Collet ◽  
M. Asplund
Keyword(s):  
Stellar Atmosphere ◽  
Stagger Grid

scholarly journals 3D NLTE spectral line formation of lithium in late-type stars

2020 ◽  
Vol 500 (2) ◽  
pp. 2159-2176
Author(s):  
Ella Xi Wang ◽  
Thomas Nordlander ◽  
Martin Asplund ◽  
Anish M Amarsi ◽  
Karin Lind ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Gaussian Process Regression ◽  
Feedforward Neural Networks ◽  
Big Bang ◽  
Stellar Atmosphere ◽  
Multilayer Perceptrons ◽  
Stagger Grid ◽  
Big Bang Nucleosynthesis ◽  
Wide Range ◽  
Fully Connected

ABSTRACT Accurately known stellar lithium abundances may be used to shed light on a variety of astrophysical phenomena such as big bang nucleosynthesis, radial migration, ages of stars and stellar clusters, and planet engulfment events. We present a grid of synthetic lithium spectra that are computed in non-local thermodynamic equilibrium (NLTE) across the stagger grid of three-dimensional (3D) hydrodynamic stellar atmosphere models. This grid covers three Li lines at 610.4, 670.8, and 812.6 nm for stellar parameters representative of FGK-type dwarfs and giants, spanning Teff = 4000–7000 K, log g = 1.5–5.0, $[\rm {Fe}/\rm {H}]= -4.0$–0.5, and A(Li) = −0.5–4.0. We find that our abundance corrections are up to 0.15 dex more negative than in previous work, due to a previously overlooked NLTE effect of blocking of UV lithium lines by background opacities, which has important implications for a wide range of science cases. We derive a new 3D NLTE solar abundance of A(Li) = 0.96 ± 0.05, which is 0.09 dex lower than the commonly used value. We make our grids of synthetic spectra and abundance corrections publicly available through the breidablik package. This package includes methods for accurately interpolating our grid to arbitrary stellar parameters through methods based on Kriging (Gaussian process regression) for line profiles, and multilayer perceptrons (a class of fully connected feedforward neural networks) for NLTE corrections and 3D NLTE abundances from equivalent widths, achieving interpolation errors of the order of 0.01 dex.

scholarly journals The Stagger-grid: A grid of 3D stellar atmosphere models

2013 ◽  
Vol 560 ◽  
pp. A8 ◽  
Author(s):  
Z. Magic ◽  
R. Collet ◽  
W. Hayek ◽  
M. Asplund
Keyword(s):  
Stellar Atmosphere ◽  
Stagger Grid

scholarly journals The STAGGER-grid: A grid of 3D stellar atmosphere models

2018 ◽  
Vol 611 ◽  
pp. A11 ◽  
Author(s):  
A. Chiavassa ◽  
L. Casagrande ◽  
R. Collet ◽  
Z. Magic ◽  
L. Bigot ◽  
...  
Keyword(s):  
Turbulent Flows ◽  
Three Dimensional ◽  
Stellar Atmosphere ◽  
Resolving Power ◽  
Convective Velocity ◽  
Stagger Grid ◽  
Synthetic Spectra ◽  
Convective Motions ◽  
Effective Temperatures ◽  
Hydrodynamical Simulations

Context. The surface structures and dynamics of cool stars are characterised by the presence of convective motions and turbulent flows which shape the emergent spectrum. Aims. We used realistic three-dimensional (3D) radiative hydrodynamical simulations from the STAGGER-grid to calculate synthetic spectra with the radiative transfer code OPTIM3D for stars with different stellar parameters to predict photometric colours and convective velocity shifts. Methods. We calculated spectra from 1000 to 200 000 Å with a constant resolving power of λ∕Δλ = 20 000 and from 8470 and 8710 Å (Gaia Radial Velocity Spectrometer – RVS – spectral range) with a constant resolving power of λ∕Δλ = 300 000. Results. We used synthetic spectra to compute theoretical colours in the Johnson-Cousins UBV (RI)C, SDSS, 2MASS, Gaia, SkyMapper, Strömgren systems, and HST-WFC3. Our synthetic magnitudes are compared with those obtained using 1D hydrostatic models. We showed that 1D versus 3D differences are limited to a small percent except for the narrow filters that span the optical and UV region of the spectrum. In addition, we derived the effect of the convective velocity fields on selected Fe I lines. We found the overall convective shift for 3D simulations with respect to the reference 1D hydrostatic models, revealing line shifts of between −0.235 and +0.361 km s−1. We showed a net correlation of the convective shifts with the effective temperature: lower effective temperatures denote redshifts and higher effective temperatures denote blueshifts. We conclude that the extraction of accurate radial velocities from RVS spectra need an appropriate wavelength correction from convection shifts. Conclusions. The use of realistic 3D hydrodynamical stellar atmosphere simulations has a small but significant impact on the predicted photometry compared with classical 1D hydrostatic models for late-type stars. We make all the spectra publicly available for the community through the POLLUX database.

Polarimetric Observations of Red Variables: A Study of Gas and Particle Interactions

1979 ◽  
Vol 46 ◽  
pp. 386-408 ◽  
Author(s):  
G. V. Coyne ◽  
I. S. McLean
Keyword(s):  
Wavelength Dependence ◽  
Stellar Atmosphere ◽  
Molecular Absorption ◽  
Absorption Bands ◽  
Absorption And Emission ◽  
Mira Variables ◽  
Stellar Photosphere ◽  
Regular Variable ◽  
Red Supergiants ◽  
Balmer Lines

AbstractIn recent years the wavelength, dependence of the polarization in a number of Mira variables, semi-regular variables and red supergiants has been measured with resolutions between 0.3 and 300 A over the range 3300 to 11000 A. Variations are seen across molecular absorption bands, especially TiO bands, and across atomic absorption and emission lines, especially the Balmer lines. In most cases one can ignore or it is possible to eliminate the effects due to interstellar polarization, so that one can study the polarization mechanisms operating in the stellar atmosphere and environment. The stars Omicron Ceti. (Mira), V CVn (semi-regular variable) and Mu Cephei (M2 la), in addition to other stars similar to them, will be discussed in some detail.Models to explain the observed polarization consider that the continuum flux is polarized either by electron, molecular and/or grain scattering or by temperature variations and/or geometrical asymmetries over the stellar photosphere. This polarized radiation is affected by atomic and molecular absorption and emission processes at various geometric depths in the stellar atmosphere and envelope. High resolution spectropolarimetry promises, therefore, to be a power-rul tool for studying stratification effects in these stars.

scholarly journals A Spherical Non‐LTE Line‐blanketed Stellar Atmosphere Model of the Early B GiantεCanis Majoris

1998 ◽  
Vol 498 (2) ◽  
pp. 837-850 ◽  
Author(s):  
J. P. Aufdenberg ◽  
P. H. Hauschildt ◽  
S. N. Shore ◽  
E. Baron
Keyword(s):  
Stellar Atmosphere ◽  
Atmosphere Model

scholarly journals The Use of Model Atmospheres for Temperature-Gravity Calibration

1973 ◽  
Vol 54 ◽  
pp. 173-221
Author(s):  
J. C. Pecker
Keyword(s):  
Model Building ◽  
Stellar Atmosphere ◽  
Line Formation ◽  
Early Type ◽  
New Concepts ◽  
Total Luminosity ◽  
Classical Models ◽  
Early Type Stars ◽  
Two Parameters

Regardless of the degree of elaboration of series of models, just how can they be used for calibration purposes? And how much is this calibration sensitive to the quality of the model theory? These two questions are the basis of our discussion, which covers : I – The general principles of the use of model atmospheres in stellar calibration (1 – The two dimensional classifications; 2 – The use of the total luminosity; 3 – The cases of Vega and Sirius; 4 – The calibration of ST – Teff relation); II – The failures of the two parameters model atmospheres (1 – The observational need for more-than-two-parameters classification; 2 – The abundance of elements, the line formation, and the model atmospheres; 3 – Various sources of unadequacy of models; 4 – Envelopes or shell features; their influence on model-building; 5 – The case of HD 45677. Diagnostic of early-type stars; 6 – Various unexplained spectral features); III – The present state of the model factory (1 – The classical models; 2 – New concepts in the description of a stellar atmosphere; 3 – New approaches in model making; 4 – Conclusions).

Thermosolutal-convective instability in a stellar atmosphere

1987 ◽  
Vol 8 (4) ◽  
pp. 305-314 ◽  
Author(s):  
R. C. Sharma ◽  
Bakshis Singh
Keyword(s):  
Convective Instability ◽  
Stellar Atmosphere
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