  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.
