1999A&A...345..203B

We present spectrally resolved interferometry of the Be star γ Cas in '88, '91, '93 and '94, obtained with the GI2T interferometer. The analysis of high spatial resolution data across the Hα line reveals azimuthally asymmetric variations which are correlated with those of V/R of the Hα profile. This correlation supports a prograde one-armed oscillation precessing in the equatorial disk of γ Cas due to the confinement by a radiative effect. We examine the occurrence of such oscillations in the context of the latitude dependent radiative wind model developed for previous GI2T interferometric observations of this star. We find that this enhanced equatorial density pattern may be located at 1.5 stellar radii from the stellar surface. We follow its possible rotation through the -99km/s, +92km/s, +140km/s and +41km/s iso-velocity regions which results in approximate stellar longitudes: 224°, 42°, 153° and 184° for '88, '91, '93, '94 epochs respectively. Thus, γ Cas is the second Be star after ζ Tau for which interferometric observations directly evidence a prograde one-armed oscillations of its equatorial disk.