Fast spectral variations of OBA stars

Our search for magnetic fields in selected OBA stars using FOcal Reducer low dispersion Spectrographs FORS 1 and FORS 2 in spectropolarimetric mode revealed the presence of strong line profile variations (LPV) in spectra of magnetic OBA stars. More specifically, we detected moderate line profile variations of selected lines on a time scale of minutes in FORS 2 spectra of the A0 supergiant HD 92207 (Hubrig et al. 2014). Recently, we investigated the variability of line profiles of selected OBA stars with the multi-mode focal reducer SCORPIO at the 6-meter BTA telescope. We discovered regular variations of H and He lines in the spectra of the O-type star HD 93521 (O9.5III) with periods ~4-5 and ~32-36 minutes. The possible origin of short time-scale spectral variations is discussed.