RAPID DYNAMIC PROCESSES IN Ap STAR ATMOSPHERES

Abstract

Long-term observations with short exposures in 1999-2001 allowed us to reveal the rapid variation in light velocities and equivalent widths of various spectral lines in the spectra of Ap stars w Psc and g Equ with pulsation periods 17 min and 12 min respectively. To determine the pulsation periods more precisely, a frequency analysis has been applied. Our observations show that, apart from the variability related to an axial rotation of the star, two more types of variability in an observable group of stars have been detected: firstly, short-term oscillations with 12-17 min periods; secondly, a relatively slow variability with 1.5-2.5 h characteristic times. The short-term spectrum variability is shown to be observed for all programmed stars, but only w Psc and g Equ spectra variations are periodic. The second, a slower type of spectrum variability (1.5-3 h), is also reliably observed for w Psc and g Equ stars. According to the observed spectral characteristics, the star y Aur may be referred to a subgroup of roAp stars.