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Astron. Astrophys. 320, 852-864 (1997)


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Line formation in Be star envelopes

II. Disk oscillations

W. Hummel 1, 2 and R.W. Hanuschik 3

1 Astrofysisch Instituut, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium
2 now at: Universitätssternwarte München, Scheinerstr. 1, D-81679 München, Germany
3 Astronomisches Institut, Ruhr-Universität Bochum, D-44780 Bochum, Germany

Received 23 April 1996 / Accepted 13 September 1996

Abstract

We present numerical model calculations for an especially interesting class of H [FORMULA] emission line profiles from Be star disks, those with asymmetric shape and long-term variability (so-called class 2 profiles). As an underlying model for the disk we investigate the hypothesis of Okazaki (1991) that these profiles are caused by a distortion of a quasi-Keplerian disk. The distortion has the form of a one-armed global disk oscillation (density and velocity wave).

The radiation transfer in the disk is calculated with an improved version of the spatially implicit 3D radiative transfer code of Hummel (1994).

The resulting sets of H [FORMULA] emission line profiles reproduce well the observed structures of fully-resolved class 2 H [FORMULA] emission lines, like double peaks and winebottle-type shoulders. For high inclinations, shell-type profiles result. It is shown that the full variety of observed profile shapes is caused by the interaction of kinematical and non-coherent scattering broadening. While this result has already been found by Hummel (1994) for the symmetric (class 1) H [FORMULA] profiles, it is proven here for the second major profile class as well.

The comparison between observed and theoretical emission shows that the model of global disk oscillations is in full agreement with the observed shapes and the cyclic long-term variability of class 2 profiles.

Key words: line: profiles – line: formation – radiative transfer – stars: Be – circumstellar matter

Send offprint requests to: W. Hummel, München address

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998

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