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Title:
Evolution in circumstellar envelopes of Be stars: From disks to rings?
Authors:
Rivinius, Th.; Baade, D.; Štefl, S.; Maintz, M.
Affiliation:
AA( European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany), AB( European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany), AC(Astronomical Institute, Academy of Sciences, 25165 Ondřejov, Czech Republic), AD(Landessternwarte Königstuhl, 69117 Heidelberg, Germany)
Publication:
Astronomy and Astrophysics, v.379, p.257-269 (2001) (A&A Homepage)
Publication Date:
11/2001
Origin:
A&A
A&A Keywords:
STARS: EMISSION-LINE, BE, STARS: CIRCUMSTELLAR MATTER, STARS: WINDS, OUTFLOWS
DOI:
10.1051/0004-6361:20011335
Bibliographic Code:
2001A&A...379..257R

Abstract

New series of echelle spectra were obtained to study the medium- and long-term evolution of the disks of several Be stars. Subtle variations in the wings of optically thin and thick emission lines suggest that the conventional, static picture of the disk being in quasi-contact with the central star is justified primarily (or perhaps only) after an outburst event. Some weeks to months later, a low-density region seems to develop above the star and slowly grows outwards. A subsequent outburst may later replenish this cavity. In fact, in two stars this more ring-like structure is apparently at times detached far enough from the star to allow for the formation of a secondary inner disk from the ejecta of a later outburst. This behaviour is not necessarily representative of Be stars in general because in the later spectral sub-types, discrete mass loss events have not so far been observed to play a major role. In the light of the apparent life cycle of such disks, a brief discussion is given of the differences in strength and variability between the winds of Be and normal B stars. It seems possible to attribute these differences to matter that was initially in the disk and therefore largely shielded from the stellar radiation, but that during the course of the inner excavation (or even complete distruction) of the disk becomes exposed. Based on observations collected at the European Southern Observatory at La Silla, Chile, ESO proposal No. 64.H-0548 and on observations with the Wendelstein 80-cm and the Ondřejov 2-m telescopes, both equipped with the HEROS spectrograph provided by the Landessternwarte Heidelberg.
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