Binary Nature and Long‐Term Variations of γ Cassiopeiae

Abstract

ABSTRACTWe present the results of high‐resolution spectroscopic observations of the bright Be star γ Cas obtained at the Ritter Observatory of the University of Toledo in 1993–2002. Two components in the emission‐line profile variations, a long‐term and a periodic one, are found. The periodic component is represented by changes of the mean radial velocity of the Hα line with a period of 205 days, which is most likely related to the orbital motion in a binary system. This finding confirms a recently reported result of Harmanec et al., although our data suggest a circular orbit rather than the eccentric one they derived. The zero eccentricity favors a nondegenerate nature of the secondary and supports a hypothesis that the companion is not connected with the X‐ray generation. The long‐term variations are represented by changes in the peak intensities and radial velocities of the spectral lines on a timescale of a few years and include a continuous decrease of the line intensities in 1993–2001. We also found a different behavior of the Hα line profile shape and those of nonhydrogen lines. This suggests the presence of an additional component in the Hα line profile that may originate in the outer regions of the primary's disk. This might manifest the beginning of a new phase in the evolution of γ Cas, which could lead to a new normal B star phase.