1111.2487 (Anthony Meilland et al.)

First spectro-interferometric survey of Be stars I. Observations and constraints on the disks geometry and kinematics    [PDF]

Anthony Meilland, Florentin Millour, Samer Kanaan, Philippe Stee, Romain Petrov

Context. Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar disk responsible for the observed infrared-excess and emission lines. The phenomena involved in the disk formation still remain highly debated. Aims. To progress in the understanding of the physical process or processes responsible for the mass-ejection and test the hypothesis that they depends on the stellar parameters, we initiate a survey on the circumstellar environment of the brightest Be stars. Methods. To achieve this goal, we used spectro-interferometry, the only technique combining high spectral (R=12000) and high spatial (\thetamin=4mas) resolutions. Observations were carried out at Paranal observatory with the VLTI/AMBER instrument. We concentrate our observations on the Br{\gamma} emission line to be able to study the kinematics within the circumstellar disk. Our sample is composed of eight bright classical Be stars : \alph Col, \kappa CMa, \omega Car, p Car, \delta Cen, \mu Cen, \alpha Ara, and o Aqr. Results. We managed to determine the disk extension in the line and the nearby continuum for most targets. We also constrained the disk kinematics showing that it is dominated by rotation with a rotation law close to the Keplerian one. On the other hand, our survey also suggests that these stars are rotating below their critical velocities (Vc) with a mean rotational rate of 0.82$\pm$0.08 Vc Conclusions. We did not detect any correlation between the stellar parameters and the structure of the circumstellar environment. Moreover, it seems that a simple model of a geometrically thin Keplerian disk can explain most of our spectrally-resolved K-band data. Nevertheless, some small departures from this model have been detected for at least two objects (i.e, \kappa CMa and \alpha Col). Finally, our Be stars sample suggests that rotation alone cannot explain the origin of the Be phenomenon and that other mechanisms are playing a non-negligible role in the ejection of matter.

View original: http://arxiv.org/abs/1111.2487