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

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1. Introduction

HD 76534 is a bright B2Ve star with V [FORMULA] 8. By virtue of its H [FORMULA] emission and claimed circumstellar nebulosity, it was thought at first to be a Herbig Be star (van den Bergh & Herbst 1975, Herbst 1975). It is one of the exciting stars of the Vela-R2 association, and lies close to its main sequence (Herbst, 1975). Its status as a Herbig Be star was questioned however by Thé et al. (1985) who argued that since HD 76534 does not have a significant near-infrared excess, it should not be classified as such.

In view of the above, we will regard HD 76534 as a classical Be star in the remainder of this paper, although it will not affect any of our conclusions. Here we report on the discovery of dramatic variations in its H [FORMULA] line on unusually short timescales.

Such variations have been detected in few Be stars, notably µ Cen (Peters, 1986; Hanuschik et al. 1993) and [FORMULA] Eri (Smith, Peters & Grady 1991). These stars have long periods without significant H [FORMULA] emission, but sometimes undergo an H [FORMULA] outburst where the emission rises to an equivalent width (EW) as high as -6 Å within days. The emission then fades on somewhat longer timescales until only a photospheric profile remains. The above authors propose that the H [FORMULA] outburst traces the build-up of a circumstellar disk which neither reaches steady state nor exceeds the local escape velocity, and falls back onto the stellar photosphere. Observations such as these can provide important clues on the manner of the formation of disks around Be stars.

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998