Peculiarities of radial velocity variability of lines in the spectrum of α Cyg supergiant

Abstract

ABSTRACT We use about 430 CCD spectra obtained in 1998–2001 and in 2007 to study temporal radial velocity variations of the ion, He i, and H β lines in the spectrum of the α Cyg. We found that these variations are caused by pulsation-type motions. In case of the ion and He i lines, fluctuations occur in the fundamental radial mode with the period of about 12.5 ± 1.0 d and the amplitude of 5.0 ± 0.5 km s−1. The oscillation lasts about ∼34 ± 1 d. In the case of the H β line the radial velocity variability was studied separately for the blue and red halves of the line profile. Such a methodical approach allowed to discover three characteristic cases of radial velocity variability for the blue and red halves of the H β line profile. In 1999 and 2001, the period P and amplitude A variability parameters are the same for the blue and red halves, and hence for the line bisector too. In 1998, P and A are the same for the blue and red halves of the profile, however, there is a phase shift between the fluctuations of their radial velocity by 0.6P. In 2000, P and A are different for the two halves of the line profile. Relative to the center of the star’s mass, the average expansion rate for the atmospheric layers, where the H β line is formed, is about −10.0 km s−1. It varies over time with a semi-amplitude of around ±3.3 km s−1.