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 v sin 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 .

Methods : 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 .

Results : 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 2 R _ { \star } 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 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 .