AAS Meeting #193 - Austin, Texas, January 1999
Session 99. Stellar Atmospheric Activity and Luminous Blue Variables
Display, Saturday, January 9, 1999, 9:20am-4:00pm, Exhibit Hall 1

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[99.08] Study of the Atmospheric Conditions in Luminous Blue Variables

Th. G\"ang (GSFC)

Luminous Blue Variables (LBVs) have recently been recognized as keys to the evolution of massive stars; understanding the physical mechanisms causing their changing spectral type and huge mass loss rates are thus of great importance.

We have obtained two data sets of high resolution optical spectra to address the following questions:

\begin{enumerate} \item which physical mechanisms are responsible for the observed spectral variability? \item do LBV winds have inhomogeneities and/or substructures? \end{enumerate}

For the first question we have obtained high resolution spectra (R\approx 60\,000, \lambda\approx3600--7000\,Å) of a sample of 20 LBVs and LBV-candidates in the Milky Way and the Magellanic Clouds. Substructures have been detected in almost all our observed objects suggesting that inhomogeneities exist in the wind of at least some LBVs.

To address the second question we have observed the galactic LBV HD\,160529 over 4 years to study the variability of its optical spectrum. We found that all spectral lines are variable. The lines with P Cygni-type profiles show variations in the emission as well as in the absorption components. Even pure absorption lines, forming deep in the atmosphere (e.g.\ He\,I\,\lambda5876 and Mg\,II\,\lambda4481), show signs of wind-influence, indicating that the observed variations are caused at the very base of the wind (e.g.\ by propagating density fluctuations starting at the photosphere).

The results from the analyzes of this data with static NLTE-codes (Hubeny et al.: TLUSTY, SYNSPEC) and with dynamical and pulsational models (Rivinius et al.: SEIDYNAMIC; Kaufer et al.: Monte Carlo code) will be discussed in the paper presentation.

The author(s) of this abstract have provided an email address for comments about the abstract: gaeng@chippewa.nascom.nasa.gov

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