Abstract

We use spectral energy distributions (SEDs), Hα line profiles, and visibilities available in the literature to study Achernar's envelope geometry and to propose a possible scenario for its circumstellar disk formation and dissipation. We use the SIMECA code to investigate possible geometries by comparing our synthetic results with spectroscopic and high angular resolution data from the VLTI/VINCI instrument. We compute three different kind of models : an equatorial disk, a polar wind, and a disk+wind model. We have developed a 2D axial symmetric kinematic model to study the variation of the observed Hα line profiles, which clearly evidence Achernar's equatorial disk formation and dissipation between 1991 and 2002. Our model can reproduce the polar wind extension greater than 10 Rstar and a possible equatorial disk (≤ 10 Rstar) but, due to the lack of interferometric data at short baselines, we were not able to estimate the wind opening angle. We have also reproduced the Hα line profiles variations using an outburst scenario but the disk final contraction needs an additional unkonwn physical effect to be taken into account. New interferometric observations at short baselines (5 ≤ B ≤ 20 m) are mandatory to constrain Achernar's circumstellar envelope, as well as specroscopic long term following to link Achernar's mass loss episodes with its circumstellar disk formation.