The Be Star Gamma Cassiopeiae: X-Ray, Far-UV, and Optical Observations in Early 1989

This is the authors' abstract. We don't add key points for this paper.

The state of γ Cas in early 1989 is presented as the result of joint observations in the X-ray, far-UV, and optical regions. Particular attention has been paid to short- and long-term variations within these spectral ranges. In X-ray observations with the Ginga satellite we have found no specific periodic variabilities in the 64 to 13,000 s range, although a highly variable nature with no appreciable changes in the hardness ratios has been confirmed. The X-ray spectrum has been fitted with that of a thin thermal plasma (16–17 keV) with an iron emission line centered at 6.7 keV. For the resonance lines of SiIV, CIV, and NV observed with the IUE satellite in the far-UV region, no high-velocity narrow absorption components were detected. The presence of very broad wings in their profiles extending to expansion velocities (≳ 1,000 km s–1) much larger than the photospheric escape velocity provides evidence for the existence of high-velocity mass-loss processes from the star. The optical spectrum shows that γ Casis still in the state of V / R > 1 for Hα, Hβ and Hγ. A series of high-resolution, high-S/N, He I λ4471 and Mg II λ4481 line profiles indicates evidence of nonradial pulsation (|m| ≃ 8–10) of the star. The UBV photometric observations show that γ Cas was in a rather stable state in early 1989, although some fluctuation was recorded on time scales of minutes and hours. We cannot find any correlation between the time variations of the X-ray and other wavelength regions. We discuss the X-ray characteristics of γ Cas, which is uncommon among Be star X-ray sources regarding its spectral feature and variability.