Line profile variability in b Supergiants

Abstract

Many B-Type supergiants are reported to show both spectroscopic and photometric variability. In addition, their line profiles show an excess broadening, typically referred to as macroturbulence. While the cause for these variabilities and the macroturbulence are not clear yet, pulsations seem to play an important role. They influence the measured radial velocity, width and shape of photospheric lines. We study a sample of Galactic B-Type super-giants based on high-quality spectroscopic data. Applying the moment method to selected atmospheric absorption lines, we find that the line profile variability in our objects is caused by pulsations. In addition, Hc displays strong, often night-To-night variability, suggesting time-variable stellar winds. The photospheric lines show large contributions of macroturbulent broadening, which render it difficult to determine proper values of the projected rotational velocities.