FAST AND SUPER-FAST VARIATIONS OF LINE PROFILE IN SPECTRA OF EARLY-TYPE STARS

Abstract

The results of our search for the fast line prole variations (LPVs) in spectra of selected OBA stars presented. The regular  variations of the line profiles with periods ranging from several hours to days in spectra of OBA stars are well known. Our recent observations of the A0 supergiant HD 92207 using FOcal reducer low dispersion spectrographs FORS 2 in spectropolarimetric
mode mounted on the 8-m telescopes of the VLT showed moderate line profile variations of various lines on a time-scale of minutes or maybe even of a fraction of a minute. This nding triggers our program of looking for the short time-scale LPVs in spectra of early-type stars. Such LPVs were detected in our spectral time series for HD 93521 (O9.5III), rho Leo (B1Iab), a² CVn,
and other stars obtained with the multi-mode focal reducer SCORPIO at the 6-meter telescope (Northern Caucasus, Russia). Both regular LPVs with periods from 1 to 90 minutes and non-regular LPVs with amplitudes of 1-2% of the continuum level are detected. The presence of such short-term spectral variability in spectra of massive OBA stars, which are suggested to be the
progenitors of Type II supernova, was not studied systematically in the past and can be critical for the current theoretical understanding of the supernova physics and for the stellar evolution modeling.