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Astron. Astrophys. 335, 261-265 (1998)


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Evidence for one-armed oscillations in the equatorial disk of [FORMULA] Tauri from GI2T spectrally resolved interferometry

F. Vakili 1, D. Mourard 1, Ph. Stee 1, D. Bonneau 1, P. Berio 1, O. Chesneau 1, N. Thureau 1, F. Morand 1, A. Labeyrie 2 and I. Tallon-Bosc 3

1 Observatoire de la Côte d'Azur, Département Fresnel, CNRS UMR 6528, F-06460 Saint Vallier de Thiey, France
2 Observatoire de Haute Provence, F-04870 Saint Michel l'Observatoire, France
3 Centre de Recherche Astronomique de Lyon, UMR CNRS 5574, 9 avenue Charles André, F-69561 St Genis Laval Cedex, France

Received 6 February 1998 / Accepted 23 March 1998

Abstract

We report sub-mas observations of the Be Shell star [FORMULA]  Tauri with the Grand Interféromètre à 2 Télescopes (GI2T) on November '93 and October '94. In '93, the H [FORMULA] line presented a V/R ratio of 0.57 with a central absorption shell component. On October '94 the H [FORMULA] line presented a reversed V/R ratio of 1.26 with a shallower absorption component. For both epochs we analysed the amplitude and phase of the fringe signal relative to the local continuum as a function of Doppler-shift across H [FORMULA]. We clearly resolve the H [FORMULA] emitting envelope on October '93. We find that the bulge of the emission which occurs around RV=+130 km. [FORMULA] has a N-S projected position of 0.7 mas to the South of the continuum source. This value corresponds to a linear separation of 3.6 photospheric radii. For October 94, the same analysis shows that the projected position of this bulge, occuring around RV=-70 km. [FORMULA] has moved to 0.5 mas, i.e. 2.6 photospheric radii, North of the continuum source. On account of the opposite V/R values between 93 and 94 and the long term H [FORMULA] cyclic variability of [FORMULA] Tauri this apparent motion corresponds to the first interferometric detection of an axi-asymmetric envelope around a Be star that we interpret as direct evidence for a prograde one-armed oscillation of its equatorial disk.

Key words: stars: circumstellar matter – stars: emission-line, Be – stars: imaging – stars: individual: Zeta Tauri – line: profiles

Send offprint requests to: Farrokh Vakili

© European Southern Observatory (ESO) 1998

Online publication: June 12, 1998

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