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Astron. Astrophys. 349, 151-168 (1999)

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4. Conclusions

In this paper we have reviewed long-term visual spectrophotometric (SPh) variations of Be stars using an exhaustive set of data presented in a previous paper (MZH). We studied the SPh variations as a function of fundamental stellar parameters. The data used allowed us to confirm and generalize previous results obtained by us and other authors. We noted in addition that there are [FORMULA] and [FORMULA] dependencies of SPh variations. We paid much attention to the interpretation of bivalued ([FORMULA]) SPh relations that were put forward in our preceding paper MZH. The observed SPh behaviours of Be stars were described as a function of three CE variation scenarios: (a) CE expansion by preserving ellipticity; (b) CE expansion by varying the ellipticity so that a disc-like structure is produced; (c) filling up a constant circumstellar volume with given extent and flattening. CE base densities and extents of regions producing the SPh variations were adopted according to a previous critical discussion of model consistencies with observational facts. From this discussion it follows that electron density in CE of Be stars should never exceed [FORMULA] cm-3 and that the radii of regions producing the SPh do not exceed some [FORMULA]. It was also shown that SPh observations do not always support strongly flattened CE. Models show that in such flattened CE it is not possible to produce the amount of emission currently observed in the V magnitude without violating the CE density limitations imposed by the characteristics of the second component of the Balmer discontinuity. The double valued ([FORMULA]) relations are due to the opacity evolution of CE in processes (a) and (b). These scenarios are consistent with a building up mechanism of CE in Be stars due to isolated massive ejections, followed by continuous mass loss phenomena. The models of axi-symmetrical CE used in this paper explain the global aspect angle and temperature dependencies of SPh slopes, though detailed studies of individual stars are needed to identify the CE variation scenarios which are most likely to account for the observed facts and to lead to the most reliable set of CE physical parameters.

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© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999