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On the evolutionary status of Be stars
J. Fabregat 1 and
J.M. Torrejón 2
Received 18 June 1999 / Accepted 23 March 2000
We present a study of the incidence of Be stars in open clusters as a function of the cluster age, using whenever possible ages determined through Strömgren uvby photometry. For the first time in studies of this kind we have considered separately classical and Herbig Be stars.
The main results can be summarized as follows:
We interpret our results in the sense that the Be phenomenon is an evolutionary effect which appears in the second half of the main sequence lifetime of a B star. We propose that it can be related to main structural changes happening at this evolutionary phase, which also lead to the recently discovered non-monotonic helium abundance enhancement. The semiconvection or turbulent diffusion responsible of the surface helium enrichment, coupled with the high rotational velocity, can generate magnetic fields via the dynamo effect and thereby originate the Be phenomenon. Observational tests to this hypothesis are proposed.
Key words: stars: emission-line, Be stars: evolution Galaxy: open clusters and associations: general
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Online publication: June 5, 2000