The peculiar fast-rotating star 51 Ophiuchi probed by VEGA/CHARA
1 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Munich, Germany
2 Laboratoire Lagrange, UMR 7293, Univ. Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
3 Institut d’Astrophysique et de Planétologie de Grenoble, CNRS-UJF UMR 5571, 414 rue de la Piscine, 38400 St-Martin d’Hères, France
4 Georgia State University, PO Box 3969, Atlanta GA 30302-3969, USA
5 CHARA Array, Mount Wilson Observatory, 91023 Mount Wilson CA, USA
Received: 4 December 2014
Accepted: 19 May 2015
Context. Stellar rotation is a key in our understanding of both mass-loss and evolution of intermediate and massive stars. It can lead to anisotropic mass-loss in the form of radiative wind or an excretion disk.
Aims. We wished to spatially resolve the photosphere and gaseous environment of 51 Oph, a peculiar star with a very high vsini of 267 km s-1 and an evolutionary status that remains unsettled. It has been classified by different authors as a Herbig, a β Pic, or a classical Be star.
Methods. We used the VEGA visible beam combiner installed on the CHARA array that reaches a submilliarcsecond resolution. Observation were centered on the Hα emission line.
Results. We derived, for the first time, the extension and flattening of 51 Oph photosphere. We found a major axis of θeq = 8.08 ± 0.70 R⊙ and a minor axis of θpol = 5.66 ± 0.23 R⊙. This high photosphere distortion shows that the star is rotating close to its critical velocity. Finally, using spectro-interferometric measurements in the Hα line, we constrained the circumstellar environment geometry and kinematics and showed that the emission is produced in a 5.2 ± 2 R⋆ disk in Keplerian rotation.
Conclusions. From the visible point of view, 51 Oph presents all the features of a classical Be star: near critical-rotation and double-peaked Hα line in emission produced in a gaseous disk in Keplerian rotation. However, this does not explain the presence of dust as seen in the mid-infrared and millimeter spectra, and the evolutionary status of 51 Oph remains unsettled.
Key words: stars: emission-line, Be / stars: evolution / stars: rotation
© ESO, 2015