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Astron. Astrophys. 333, 125-140 (1998) 8. Conclusions8.1. Summary of the results for µ CenThe circumstellar variability largely consists of discrete events which can be characterized as outbursts during which matter is ejected by the star and possibly even (partly) transferred to the disk. The relative contributions of outbursts and stellar wind to the total mass of the disk are currently unconstrained. In any event, µ Cen is building up a new persistent disk which was not detected between 1977 and 1989. An outburst cycle appears to be composed of a sequence of relative quiescence, a short pre-outburst phase (precursor), the outburst, and an extended relaxation phase. However, outbursts may differ substantially not only in amplitude and duration, but also in the relative prominence of the above noted constituents. This depends on the absolute strength of the disk emission already present, i.e., on the mass and optical thickness of the disk. Especially the burst and the relaxation phases can be missing completely in outbursts during which the disk emission is strong. By contrast, the precursor phase is the stronger the higher the disk emission is. Even at low emission levels a new outburst may appear before the relaxation to the pre-outburst level is completed. Also, relaxation may proceed more slowly with increasing disk mass, so that relative quiescence as defined in this paper may eventually never be reached any more once a strong disk has been built up. The relative quiescence is a phase of merely minor variability in
the hydrogen lines, the smallest separation between double emission
peaks of all phases, and the absence of Fe ii emission lines. As a
precursor to an outburst, a sudden decrease in emission peak height
occurs. At the same time, broad emission wings appear. The outburst is
defined by a rapid increase of the emission strength, rapid cyclic
For the first time in a Be star the time scale of rapid cyclical
Especially at times of enhanced Some of the generalizations that have been attempted in this study of the outbursts of µ Cen may also apply to other Be stars. However, with no second case known in nearly as much detail, this is arbitrarily uncertain. Especially the geometry of the disk and its orientation with respect to the observer may lead to some modifications. 8.2. Comparison with other Be starsOutbursts do not seem to have been observed at the same level of detail in other classical Be stars. But those (less complete) observations that are available suggest a number of similarities which are worthwhile recalling:
It would, therefore, appear not only a necessary but perhaps even reasonably promising undertaking to search other Be stars for a similar behaviour so that it becomes clearer to what extent µ Cen is a representative case. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: April 15, 1998 ![]() |