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Astron. Astrophys. 318, 198-203 (1997)

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7. Final remarks

The case of the rapid variability in the H [FORMULA] line of HD 76534 provides us with new data to understand the H [FORMULA] emission of Be stars, and their rapid variability in particular. However, it seems that HD 76534 is deviant from other examples of Be stars which show sudden outbursts in the H [FORMULA] line. The timescales are shorter, yet the line profile itself appears to trace a dynamically stable circumstellar environment. This contradicts the hypothesis that has been put forward to explain the observed variability in other Be stars, namely a mass ejection which results in a circularized disk after several rotation periods of the central star. In order to explain the observed behaviour of the object, we suggest another mechanism that could explain the sudden outburst, without the necessity of building up the disk on a short timescale. The variability of the Lyman continuum of this object may be responsible for an increase of the ionized volume within the circumstellar envelope, either spherical, or disk-like, that was already present around the star.

The discrimination between the two scenarios could be made when HD 76534 is observed using simultaneous rapid photometry, preferably in the U band, and rapid high resolution spectroscopy. If stellar pulsations give rise to a changing ionized volume within the circumstellar envelope, one would expect the H [FORMULA] emission to be correlated both with changes in the photometry and radial velocity, while the H [FORMULA] line profile would trace a dynamically stable region. On the other hand, the build-up of a newly ejected envelope should be visible in a less regular evolution of the H [FORMULA] line profile, and is more likely to be an irregular and infrequent occurrence.

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998
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