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Astron. Astrophys. 350, 485-490 (1999)

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4. Concluding remarks

In this paper we have investigated whether the H[FORMULA] flaring star HD 76534 is variable on short timescales of order minutes and hours. We find no evidence for statistically significant variations. One of our original suggestions to explain the H[FORMULA] outburst in 1995 was to invoke a pulsation-type behaviour of the star. If this would have been the case, we might have seen at least some variability on short time scales, but these are not seen.

Including the current data, H[FORMULA] measurements for this object have now been reported 9 times in the astronomical literature (see the Introduction), and all but one show the line in emission. Considering this, one would conclude that the observed collapse and the subsequent rapid recovery of the H[FORMULA] emission is only a sporadic event. If we were to associate the brightening of the object in the Hipparcos photometric data to a strong emission variability, it may be that the relevant timescale is the hundreds of days between events. A monitoring programme sampling a range of timescales is needed to clear this up.

In terms of variability, HD 76534 can be regarded as belonging to the same class as µ Cen and [FORMULA] Eri. But there are some striking differences. In the first place, the H[FORMULA] variations in 1995 were the strongest and fastest ones observed to date in a Be star. Secondly, whereas µ Cen and [FORMULA] Eri are most often observed in a quiescent state, interrupted by bursts of emission that gradually declines, HD 76534 is most often observed with H[FORMULA] emission, interrupted by absorption, suggesting a different process governing the H[FORMULA] behaviour. Indeed, the H[FORMULA] line that was observed only two hours after it had been in absorption showed a smooth doubly-peaked emission profile, similar to what has been observed now, suggesting that a neutral disk was present before the source of ionizing photons increased in strength contrary to the common idea that a disk has been built up in the case of µ Cen and [FORMULA] Eri.

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© European Southern Observatory (ESO) 1999

Online publication: October 4, 1999
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