next Introduction

Realistic Models For Expanding Atmospheres

A. W. A. Pauldrach, M. Lennon, T.L. Hoffmann, F. Sellmaier, R.-P.Kudritzki, and J. Puls

In: Boulder-Munich Workshop II, PASP conf. series, ed. I. Howarth, 131, 258


In this paper we describe the status of the continuing effort to construct realistic models for expanding atmospheres (e.g.,radiation driven winds of hot stars, SNIa, and novae). The potential of our theoretical concept is demonstrated by an application to the O3Iaf star HD 93129A. We present our method of O-star diagnostics, which is based on a comparison of calculated synthetic high-resolution spectra covering the observable UV region with observed spectra. As a result we get physical constraints on the properties of stellar winds, and the stellar parameters and abundances can be determined.

Figure 1: Observed Copernicus (900-1500Å; Morton & Underhill 1977) and IUE (1500-1800Å; Walborn et al. 1985) high-resolution UV spectrum of the O4I(f) star $ \zeta$ Puppis. The most important strong and weak winds lines are identified and marked. The large number of wind contaminated FeVlines between 1250 and 1500Å is striking. (From Pauldrach et al. 1994b).

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Figure 2: Comparison of observed and calculated synthetic spectrum of the O3If* star HD 93129A. The upper two panels show the ORFEUS spectrum, where the interstellar molecular lines of H2 and HD are included in the spectrum fit. The lower three panels show the usual IUE spectrum where the narrow sharp interstellar lines are not included in the spectral fit (from Taresch et al. 1997).

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Although such models already reproduce the observed quantities satisfactorily the method is still affected by shortcomings. Special emphasis is therefore given to the latest improvements which involve a fundamental step towards a realistic description of stationary wind models. These improvements comprise the use of accurate atomic data for a very detailed multilevel non-LTE treatment of the metal ions, the revised inclusion of EUV and X-ray radiation by shock-heated matter, and, most importantly, the consistent calculation of line blocking and blanketing. With the solution of the latter problem the astrophysically important information about the ionizing fluxes of O stars is obtained as a by-product.

stars: atmospheres, early-type, mass-loss, blanketing, X-rays