Methodical Peculiarities of Study of Pulsation-Type Motions in Stellar Atmospheres

An efficient methodical approach is proposed to the study of pulsation-type motions in the at- mospheres of hot stars. Several well-studied stars are used as examples to demonstrate the appropriateness of the method, which allows to study in detail the kinematics of the atmosphere and do asteroseismological forecasts. This approach makes it possible to separately analyze different kinematics of the rising and falling layers of the stellar atmosphere, and to spectroscopically reveal different rotation of the star if such is the case. The differential rotation of atmospheric layers of HD 93521 is confirmed by the model computations. Spectroscopic monitoring programs performed using CCD detectors combined with echelle spec- trographs since the early 1990s and until now have revealed many interesting features of nonstationarity in the atmospheres and winds of hot stars. The observed variations of the positional and photometric parameters of photospheric and wind lines; the differ- ent morphologies of the PCyg profiles of the Hα lines and their radical variations; observations of discrete absorption components (DACs) and their migration along the line profiles; observations of the high- velocity blueshifted absorption component (HVA) of the Hα line, which may also be accompanied by a redshifted absorption component; simultaneous appearance, enhancement, and disappearance of the absorption and emission components, etc. have been observed in many hot O-, B-, and A-type stars. There have been proposed several mechanisms which may cause these variations: nonradial pulsations (1, 2), rotational modulation (3, 4), clumpy structure of the stellar wind (5), weak surface mag- netic field (6, 7), bistable mechanism of the stellar wind (8, 9), etc. The attributes of these processes are difficult to reveal and discern, but their diagnostics is quite useful. This especially applies to nonradial pulsations, which form the empirical basis of astero- seismology.