¹ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária, São Paulo, SP 05508-900, Brazil
² LUAN, Université de Nice-Sophia Antipolis (UNSA), CNRS, Observatoire de la Côte d'Azur (OCA), 28 avenue de Valrose, Parc Valrose, F-06108 Nice - France
³ University of Toledo, Department of Physics & Astronomy MS111, 2801 W. Bancroft Street, Toledo, OH 43606 USA

The recent interferometric study of Achernar, leading to the conclusion that its geometrical oblateness cannot be explained in the Roche approximation, has stirred substantial interest in the community, in view of its potential impact in many fields of stellar astrophysics. It is the purpose of this paper to reinterpret the interferometric observations with a fast rotating, gravity darkened central star surrounded by a small equatorial disk, whose presence is consistent with contemporaneous spectroscopic data. We find that we can only fit the available data assuming a critically rotating central star. We identified two different disk models that simultaneously fit the spectroscopic, polarimetric, and interferometric observational constraints: a tenuous disk in hydrostatic equilibrium (i.e., with small scale height) and a smaller, scale height enhanced disk. We believe that these relatively small disks correspond to the transition region between the photosphere and the circumstellar environment, and that they are probably perturbed by some photospheric mechanism. The study of this interface between photosphere and circumstellar disk for near-critical rotators is crucial to our understanding of the Be phenomenon, and the mass and angular momentum loss of stars in general. This work shows that it is nowadays possible to directly study this transition region from simultaneous multi-technique observations.

Accepted by ApJL
Preprints from carciofi@usp.br