Momentum and energy deposition in late-type stellar atmospheres and winds

1980 ◽  
Vol 242 ◽  
pp. 260 ◽  
Author(s):  
L. Hartmann ◽  
K. B. MacGregor
Keyword(s):  
Energy Deposition ◽  
Stellar Atmospheres ◽  
Late Type

Electron density diagnostics for late-type stellar atmospheres

1988 ◽  
Vol 324 ◽  
pp. 1068 ◽  
Author(s):  
F. P. Keenan ◽  
P. L. Dufton ◽  
A. E. Kingston ◽  
K. M. Aggarwal
Keyword(s):  
Electron Density ◽  
Stellar Atmospheres ◽  
Late Type ◽  
Density Diagnostics

scholarly journals 3D non-LTE line formation of neutral carbon in the Sun

2019 ◽  
Vol 624 ◽  
pp. A111 ◽  
Author(s):  
A. M. Amarsi ◽  
P. S. Barklem ◽  
R. Collet ◽  
N. Grevesse ◽  
M. Asplund
Keyword(s):  
Three Dimensional ◽  
Solar Spectrum ◽  
Neutral Hydrogen ◽  
Stellar Atmospheres ◽  
Impact Excitation ◽  
Solar Photosphere ◽  
Late Type ◽  
Current Standard ◽  
Standard Value ◽  
Good Agreement

Carbon abundances in late-type stars are important in a variety of astrophysical contexts. However C I lines, one of the main abundance diagnostics, are sensitive to departures from local thermodynamic equilibrium (LTE). We present a model atom for non-LTE analyses of C I lines, that uses a new, physically-motivated recipe for the rates of neutral hydrogen impact excitation. We analyse C I lines in the solar spectrum, employing a three-dimensional (3D) hydrodynamic model solar atmosphere and 3D non-LTE radiative transfer. We find negative non-LTE abundance corrections for C I lines in the solar photosphere, in accordance with previous studies, reaching up to around 0.1 dex in the disk-integrated flux. We also present the first fully consistent 3D non-LTE solar carbon abundance determination: we infer log ɛC = 8.44 ± 0.02, in good agreement with the current standard value. Our models reproduce the observed solar centre-to-limb variations of various C I lines, without any adjustments to the rates of neutral hydrogen impact excitation, suggesting that the proposed recipe may be a solution to the long-standing problem of how to reliably model inelastic collisions with neutral hydrogen in late-type stellar atmospheres.

scholarly journals Mg line formation in late-type stellar atmospheres

2015 ◽  
Vol 579 ◽  
pp. A53 ◽  
Author(s):  
Y. Osorio ◽  
P. S. Barklem ◽  
K. Lind ◽  
A. K. Belyaev ◽  
A. Spielfiedel ◽  
...  
Keyword(s):  
Stellar Atmospheres ◽  
Line Formation ◽  
Late Type

scholarly journals Chromospheric Surface Structures on EI Eridani and HD 199178

1991 ◽  
Vol 130 ◽  
pp. 330-332
Author(s):  
James E. Neff
Keyword(s):  
Spatial Distribution ◽  
Effective Temperature ◽  
Three Dimensional ◽  
Stellar Atmospheres ◽  
Surface Structures ◽  
High Dispersion ◽  
The Sun ◽  
Late Type ◽  
Magnetic Topology ◽  
Radial Dimension

Several groups at this meeting are presenting maps of the spatial distribution of either brightness or effective temperature in the photospheres of rapidly-rotating, late-type stars. It is generally believed that structure seen in these maps traces the magnetic topology, in analogy with the Sun. We expect the structure of the outer atmospheres (i.e., chromosphere and corona) of these stars to be even more directly tied to the magnetic topology; the magnetic structure is three-dimensional. In order to probe the radial dimension of stellar atmospheres, we need to combine maps of the spatial distribution of emission from chromospheres and coronae with these detailed photospheric maps.Along with collaborators at Armagh, Catania, Boulder, Paris, Helsinki, and Stony Brook, I have been obtaining high-dispersion ultraviolet spectra of several rapidly-rotating, late-type stars using the IUE spacecraft. I discuss results for two stars, El Eridani and HD 199178, for which photospheric maps are presented elsewhere at this conference.

scholarly journals Sphericity Effects of Extended Atmospheres of Late-Type Giants in the HR Diagram

1978 ◽  
Vol 80 ◽  
pp. 387-390
Author(s):  
Keiichi Kodaira
Keyword(s):  
Stellar Evolution ◽  
Stellar Atmospheres ◽  
Late Type ◽  
Stellar Radius ◽  
Know How ◽  
Atmospheric Structure ◽  
The Third ◽  
Plane Parallel ◽  
Parallel Approximation ◽  
Hr Diagram

In the late phases of stellar evolution, evolutionary tracks of stars with different masses come together along the Hayashi line in the HR diagram. The theoretical HR diagram (log L, log Teff) is accordingly partially degenerate in the domain of late-type giants and supergiants, with respect to the third parameter, the stellar mass M. The stellar radius, R, being determined by log L and log Teff, the mass determines the surface gravity log g at the radius R. These parameters enable us to transform a point in the theoretical HR diagram to the corresponding point in the empirical HR diagram MV, (R-I) or spectral type. This transformation is conventionally carried out within the framework of the plane-parallel approximation in stellar atmospheres, and the parameters for the abscissa of the empirical HR diagram are dependant upon Teffand log g alone, irrespective of the mass itself. In this case, the parameter M indirectly affects the observable quantities through log g, but the effects of a variation by Δlog g=±0.5, corresponding to Δlog M=±0.5, are almost insignificant (cf. Tsuji 1976). The transformation between the theoretical and the empirical HR diagram is, therefore, almost one-to-one, within the framework of the plane-parallel approximation. Late-type giants and supergiants, however, have moderately extended atmospheres in general (cf. Schmid-Burgk and Scholz 1975), and their photometric colors and spectra are expected to be influenced by the sphericity of the atmospheric structure. Consequently, in comparing empirical HR diagrams with theoretical ones, it is important to know how atmospheric sphericity affects the transformation in the degenerate domains of the theoretical diagram.

scholarly journals Stellar masers, circumstellar envelopes and supernova remnants

2007 ◽  
Vol 3 (S242) ◽  
pp. 236-245
Author(s):  
Athol J. Kemball
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Supernova Remnants ◽  
Stellar Mass ◽  
Stellar Atmospheres ◽  
Late Type ◽  
Open Future ◽  
Circumstellar Envelopes ◽  
Recent Advances

AbstractThis paper reviews recent advances in the study or circumstellar masers and masers found toward supernova remnants. The review is organized by science focus area, including the astrophysics of extended stellar atmospheres, stellar mass-loss processes and outflows, late-type evolved stellar evolution, stellar maser excitation and chemistry, and the use of stellar masers as independent distance estimators. Masers toward supernova remnants are covered separately. Recent advances and open future questions in this field are explored.

scholarly journals Theory of stellar coronae

1987 ◽  
Vol 122 ◽  
pp. 347-356
Author(s):  
S. Serio
Keyword(s):  
High Temperature ◽  
Magnetic Confinement ◽  
Radical Change ◽  
Stellar Atmospheres ◽  
Late Type ◽  
X Ray

X-ray observations have shown in recent years that the existence of high temperature plasmas in stellar atmospheres is far more widespread than extrapolated from preexisting theories of the solar and stellar coronae, forcing a radical change in our understanding of the mechanisms of coronal physics. This paper reviews our current ideas on stellar coronae, in particular on the role of magnetic confinement in the atmospheres of late type stars.

scholarly journals Polarized Continuum Radiation from Stellar Atmospheres

2014 ◽  
Vol 10 (S305) ◽  
pp. 395-400 ◽  
Author(s):  
J. Patrick Harrington
Keyword(s):  
Rayleigh Scattering ◽  
Accurate Method ◽  
Stellar Atmospheres ◽  
Early Type ◽  
Late Type ◽  
Hydrogen Atoms ◽  
Free Electrons ◽  
Continuum Radiation ◽  
Early Type Stars ◽  
Limb Darkening

AbstractContinuum scattering by free electrons can be significant in early type stars, while in late type stars Rayleigh scattering by hydrogen atoms or molecules may be important. Computer programs used to construct models of stellar atmospheres generally treat the scattering of the continuum radiation as isotropic and unpolarized, but this scattering has a dipole angular dependence and will produce polarization. We review an accurate method for evaluating the polarization and limb darkening of the radiation from model stellar atmospheres. We use this method to obtain results for: (i) Late type stars, based on the MARCS code models (Gustafsson et al. 2008), and (ii) Early type stars, based on the NLTE code TLUSTY (Lanz and Hubeny 2003). These results are tabulated at http://www.astro.umd.edu/~jph/Stellar_Polarization.html While the net polarization vanishes for an unresolved spherical star, this symmetry is broken by rapid rotation or by the masking of part of the star by a binary companion or during the transit of an exoplanet. We give some numerical results for these last cases.

scholarly journals Ultraviolet Spectroscopic Measurements of Cool Stars

1980 ◽  
Vol 5 ◽  
pp. 263-276 ◽  
Author(s):  
A. K. Dupree
Keyword(s):  
Binary Systems ◽  
Stellar Atmospheres ◽  
Late Type ◽  
Near Ultraviolet ◽  
International Ultraviolet Explorer ◽  
Cool Stars ◽  
Late Type Star ◽  
Far Ultraviolet ◽  
Low Dispersion ◽  
Balloon Measurements

A vast increase in the amount of information on cool stars has occurred during the past 3 years starting with the spectroscopy of the brightest objects from the Princeton experiment on Copernicus, the near ultraviolet balloon measurements from BUSS, low dispersion observations in the far ultraviolet from rocket instruments, and most recently, spectra from the International Ultraviolet Explorer satellite (IUE). IUE now gives access to a wide variety of cool stars and stellar systems enabling systematic studies to be made.Drawing on the most recent material from IUE, we discuss the presence and structure of chromospheres and coronae in single stars of varying gravities, surface temperatures, and activity. Evidence of mass loss and the concurrent presence of a corona are also noted. Binary systems of late-type stars (the RS CVn and W UMa type) are briefly discussed since they display extremes of surface activity. A binary system such as VV Cep containing a late-type star and an early-type companion provides a unique probe of cool extended stellar atmospheres.

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