EDP Sciences
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Volume 379, Number 1, November III 2001
Page(s) 257 - 269
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011335

A&A 379, 257-269 (2001)
DOI: 10.1051/0004-6361:20011335

Evolution in circumstellar envelopes of Be stars: From disks to rings?

Th. Rivinius1, D. Baade1, S. Stefl2 and M. Maintz3

1  European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
2  Astronomical Institute, Academy of Sciences, 25165 Ondrejov, Czech Republic
3  Landessternwarte Königstuhl, 69117 Heidelberg, Germany

(Received 25 June 2001 / Accepted 18 September 2001 )

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.

Key words: stars: emission-line, Be -- stars: circumstellar matter -- stars: winds, outflows

Offprint request: Th. Rivinius, triviniu@eso.org

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