scholarly journals Testing common classical LTE and NLTE model atmosphere and line-formation codes for quantitative spectroscopy of early-type stars

2011 ◽  
Vol 328 ◽  
pp. 012015 ◽  
Author(s):  
Norbert Przybilla ◽  
Maria-Fernanda Nieva ◽  
Keith Butler
Keyword(s):  
Model Atmosphere ◽  
Line Formation ◽  
Early Type ◽  
Early Type Stars ◽  
Quantitative Spectroscopy

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).

scholarly journals Discovery of weak magnetic fields in early B-type stars

2003 ◽  
Vol 212 ◽  
pp. 202-203 ◽  
Author(s):  
Huib F. Henrichs ◽  
Coralie Neiner ◽  
Vincent C. Geers
Keyword(s):  
Magnetic Properties ◽  
Stellar Wind ◽  
Magnetic Measurements ◽  
Magnetic Phase ◽  
Model Atmosphere ◽  
Early Type ◽  
Chemical Abundance ◽  
Weak Magnetic Fields ◽  
Magnetic Dipole Field ◽  
Early Type Stars

We summarize recent results of magnetic measurements of three bright early B-type stars, β Cep, ζ Cas, and V2052 Oph, which were found to be oblique rotators with a weak magnetic dipole field with typical strength of a few hundred Gauss. From stellar wind studies we could derive their rotational periods very accurately, and match the stellar wind with the magnetic phase. From model atmosphere fits we derive the angles of rotational and magnetic axis. All three stars show some chemical abundance anomaly, presumably associated with the magnetic properties. The stars are also pulsating variables. This is of high asteroseismological interest, since these are the only early-type stars known with observationally determined rotation, pulsation and magnetic properties.

scholarly journals Theoretical Wavelength Dependence of Polarization in Early-Type Stars

1976 ◽  
Vol 70 ◽  
pp. 375-376
Author(s):  
Bernhard M. Haisch ◽  
Joseph P. Cassinelli
Keyword(s):  
Steady State ◽  
Radiation Pressure ◽  
Electron Scattering ◽  
Wavelength Dependence ◽  
Model Atmosphere ◽  
Be Stars ◽  
Early Type ◽  
Steady State Flow ◽  
Early Type Stars ◽  
Rayet Star

We have examined the theoretical wavelength dependence of linear polarization produced by electron scattering and modified by an absorptive opacity in the extended, distorted atmospheres of Be and Wolf-Rayet stars. A model atmosphere representing a Wolf-Rayet star recently calculated by Cassinelli and Hartmann was used. This model takes into consideration the subsonic portions of a radial, steady-state flow together with the requirement of radiative equilibrium. The model was then scaled down in temperature to approximate the cooler Be stars, again assuming radiative equilibrium. There were four models altogether, one WR star, and three Be models. All the atmospheres are quite extended by radiation pressure.

scholarly journals Observations of Strong Stellar Lines with the OAO

1970 ◽  
Vol 36 ◽  
pp. 173-177
Author(s):  
A.D. Code ◽  
R. C. Bless
Keyword(s):  
Preliminary Analysis ◽  
Temperature Scale ◽  
Model Atmosphere ◽  
Astronomical Observatory ◽  
Qualitative Description ◽  
Spectral Interval ◽  
Early Type ◽  
Stellar Temperature ◽  
Early Type Stars

This paper reports on preliminary analysis of spectral scans of early-type stars obtained with the Orbiting Astronomical Observatory. The discussion is confined to the spectra of 50 stars observed with a resolution of approximately 10 Å over the spectral interval from 1050 Å to 2000 Å. Following a qualitative description of the spectra, observed equivalent widths of the Siiv (1400 Å) and Civ (1550 Å) lines are compared with model atmosphere calculations. The results suggest an upward revision of the stellar temperature scale for stars earlier than B3 V.

scholarly journals Model atmosphere and kinematical analyses of early-type stars from the Edinburgh--Cape Survey

2001 ◽  
Vol 324 (3) ◽  
pp. 747-756 ◽  
Author(s):  
H. R. M. Magee ◽  
P. L. Dufton ◽  
F. P. Keenan ◽  
W. R. J. Rolleston ◽  
D. Kilkenny ◽  
...  
Keyword(s):  
Model Atmosphere ◽  
Early Type ◽  
Early Type Stars

scholarly journals Winds of Hot Stars as a Diagnostic Tool of Stellar Evolution

1988 ◽  
Vol 108 ◽  
pp. 114-126 ◽  
Author(s):  
R.P. Kudritzki ◽  
A. Pauldrach ◽  
J. Puls
Keyword(s):  
Quantitative Analysis ◽  
Stellar Evolution ◽  
Stellar Wind ◽  
Model Atmosphere ◽  
Stellar Winds ◽  
Line Formation ◽  
Hot Stars ◽  
Long Time ◽  
Quantitative Spectroscopy

Modern quantitative spectroscopy of hot stars has two aspects: the analysis of photospheric lines and stellar wind lines. The first one is meanwhile established as an almost classical tool to determine stellar parameters. NLTE model atmosphere and line formation calculations yield Teff, log g and abundances with high precision (see recent reviews by Husfeld (this meeting), Kudritzki (1987), Kudritzki and Hummer (1986), Kudritzki, (1985)). The second aspect, however, the quantitative analysis of stellar wind lines is still at its very beginning. For long time the stellar wind lines have been used to determine mass-loss rates and terminal velocities v∞ only. While these studies were pioneering and of enormous importance, it was also clear that very approximate calculations were done with respect to NLTE ionization and excitation and the radiative transfer in stellar winds. Thus, stellar wind lines could be used only in a more qualitative comparative sense, with no theory behind, which allowed the determination of precise and reliable numbers.

scholarly journals Empirical wind models from detail ed UV-line fits: Tau Scorpii

1981 ◽  
Vol 59 ◽  
pp. 161-165
Author(s):  
W.-R. Hamann
Keyword(s):  
Main Sequence ◽  
The Other ◽  
Line Formation ◽  
Early Type ◽  
Systematic Comparison ◽  
Early Type Stars ◽  
Sobolev Approximation

The main-sequence BO star Tau Sco has been studied previously by Lamers and Rogerson (1978). However, their line fit was restricted to the blue wings of the UV resonance lines because the line formation was calculated in Sobolev approximation. We now repeat this investigation by means of the comoving-frame (CMF) method, which we have extended to the treatment of overlapping doublets. From a systematic comparison (Hamann 1980b) we know that the results may deviate considerably from those of the Sobolev method. Our method has been applied previously to the other “prototype” of mass loosing early-type stars, the Of star Zeta Puppis (Hamann 1980a).

scholarly journals Resonance Line Profiles from Radial Accretion Flows

1988 ◽  
Vol 103 ◽  
pp. 127-128
Author(s):  
R. Tylenda
Keyword(s):  
Resonance Line ◽  
Compact Star ◽  
Stellar Winds ◽  
Line Formation ◽  
Line Profiles ◽  
Early Type ◽  
Principal Mechanism ◽  
Accretion Flows ◽  
Early Type Star ◽  
Early Type Stars

A compact star in a detached binary system can accrete the matter from the stellar wind of the companion. In this case a more or less radial accretion flow is formed. By analogy to stellar winds from early type stars it is usually believed that the accretion of this sort should produce inverse P-Cygni profiles in resonance lines. However, there are physical differences between the wind and the radial accretion which can alter the outgoing profile significantly.The matter outflowing from an early type star cools off very fast due to the adiabatic expansion. However, it remains highly ionized as the quickly decreasing density does not allow it to recombine. Therefore the principal mechanism for the resonance line formation here is the scattering of the stellar continuum photons in the wind.

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