New results from the VLTI on massive hot stars: First direct detection of a Keplerian disk around α Arae

We use the VLTI/AMBER instrument operating in the K band which combine a high angular resolution with a medium spectral resolution to study the kinematics of the inner part of α Arae’s disk and try to infer its rotation law. We obtain for the first time the direct evidence that the disk is in keplerian rotation, answering a question that occurs since the discovery of the first Be star γ Cas by father Secchi in 1866. We also present the global geometry of the disk showing that it is compatible with a thin disk + polar enhanced winds modeled with the SIMECA code. We found that the disk around α Arae is compatible with a dense equatorial matter confined in the central region whereas a polar wind is contributing along the rotational axis of the central star. Between these two regions the density must be low enough to reproduce the large visibility modulus (small extension) obtained for two of the four VLTI baselines. Moreover, we obtain that α Arae is rotating very close to its critical rotation.