Be stars: one ring to rule them all?

¹ Observatoire de la Côte d'Azur, CNRS-UMR 6203, Avenue Copernic, Grasse, France e-mail: anthony.meilland@obs-azur.fr
² Institut d'Astrophysique de Paris, UMR7095 CNRS, Univ. P. & M. Curie, Paris, France

Received: 14 December 2005
Accepted: 2 March 2006

Abstract

Aims.We report the theoretical spectral energy distributions (SEDs), Brγ line profiles, and visibilities for two scenarios that can explain the disk dissipation of active hot stars and account for the transition from the Be to the B spectroscopic phase.

Methods.We use the SIMECA code to investigate two scenarios, the first one where the disk is formed by successive outbursts of the central star. A low-density region is developing above the star and slowly grows outward and forms a ring-like structure that will gradually excavate the disk. The second one has a slowly decreasing mass loss due for instance, to a decrease in the radiative force through an opacity change at the base of the photosphere, and may also be responsible for the vanishing of the circumstellar disk.

Results.We find that a clear signature of the disk dissipation following the ring scenario will be the disappearance of the high velocity tails in the emission lines and a nearly constant peak separation. Moreover, we found that, following the ring-like scenario, the visibilities must show an increasing second lobe, an increase in the value of the first zero, and assuming an unresolved central star, a first zero of the visibility curves that appends at shorter baselines as far as the disk has been excavated. We propose to use the AMBER instrument on the VLTI to probe whether the ring scenario is the one to rule the Be phenomenon.