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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. We wished to spatially resolve the photosphere and gaseous environment of 51 Oph, a peculiar star with a very high vsin(i) of 267km s$^{-1}$ and an evolutionary status that remains unsettled. It has been classified by different authors as a Herbig, a $beta$ Pic, or a classical Be star. We used the VEGA visible beam combiner installed on the CHARA array that reaches a submilliarcsecond resolution. Observation were centered on the H$alpha$ emission line. We derived, for the first time, the extension and flattening of 51 Oph photosphere. We found a major axis of $theta_{{mathrm{eq}}}$=8.08$pm$0.70$R_odot$ and a minor axis of $theta_{{mathrm{pol}}}$=5.66$pm$0.23$R_odot$ . This high photosphere distortion shows that the star is rotating close to its critical velocity. Finally, using spectro-interferometric measurements in the H$ alpha$ line, we constrained the circumstellar environment geometry and kinematics and showed that the emission is produced in a 5.2$pm$2R$_{*}$ disk in Keplerian rotation. From the visible point of view, 51 Oph presents all the features of a classical Be star: near critical-rotation and double-peaked H$alpha $ 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.
The Vega planetary system hosts the archetype of extrasolar Kuiper belts, and is rich in dust from the sub-au region out to 100s of au, suggesting intense dynamical activity. We present ALMA mm observations that detect and resolve the outer dust belt
Vega, the second brightest star in the northern hemisphere, serves as a primary spectral type standard. While its spectrum is dominated by broad hydrogen lines, the narrower lines of the heavy elements suggested slow to moderate rotation, giving conf
Optical and infrared interferometers definitively established that the photometric standard Vega (alpha Lyrae) is a rapidly rotating star viewed nearly pole-on. Recent independent spectroscopic analyses could not reconcile the inferred inclination an
We present ten young ($lesssim$10 Myr) late-K and M dwarf stars observed in K2 Campaign 2 that host protoplanetary disks and exhibit quasi-periodic or aperiodic dimming events. Their optical light curves show $sim$10-20 dips in flux over the 80-day o
Circumstellar disc evolution is paramount for the understanding of planet formation. The GASPS program aims at determining the circumstellar gas and solid mass around ~250 pre-main-sequence Herbig Ae and TTauri stars. We aim to understand the origin