Be stars: one ring to rule them all?

Abstract

Aims. We report theoretical spectral energy distributions (SEDs), Br$γ$ line profiles and visibilities for two scenarios that can explain the disk dissipation of active hot stars an account for the transition from the Be to the B spectroscopic phase. Methods. We use the SIMECA code to investigate these 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, where a slowly decreasing mass loss, for instance due to a decrease of the radiative force through an opacity change at the base of the photosphere, may also be responsible for the vanishing of the circumstellar disk. Results. We obtain 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 peaks separation. Moreover, we found that following the ring-like scenario the visibilities must show an increasing second lobe, an increase of 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 is been excavate. We propose to use the AMBER instrument on the VLTI to probe if the the ring scenario is the one that rule the Be phenomenon.