Instability of the kinematic state in the atmosphere of the hypergiant ρ Cas outside outburst

Abstract

Multiple observations of the yellow hypergiant ρ Cas obtained in 2007–2011 in a wide wavelength range with spectroscopic resolving power R ≥ 60 000 have enabled studies of features of its optical spectrum in detail and brought to light previously unknown characteristics of the star’s extended atmosphere. The radial velocity measured from symmetric absorption lines of metals varies with an amplitude of about ±7 km/s around the systemic velocity V sys = −47 km/s, due to low-amplitude pulsations of the atmospheric layers near the photosphere. At some times, a velocity gradient was observed in deep atmospheric layers of the star. A slight velocity stratification in the stellar atmosphere was detected for the first time, manifest as a difference of 3–4 km/s in the velocities measured from absorption lines of neutral metals and of ions. The long-wavelength components of split absorption lines of BaII, SrII, TiII, and other strong lines with low excitation potentials for their lower levels are distorted by nearby emission lines. It is suggested that the short-wavelength components, whose locations correspond to the narrow velocity range V r (blue) from approximately −60 to −70 km/s, are formed in a circumstellar envelope; one component of the D NaI doublet and the emission components of the FeII 6369.46 and 6432.68 Å ions are also formed there.