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

Abstract

The state of gamma 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 gamma Cas is still in the state of V/R >1 for Hα , Hβ , and Hγ . A series of high-resolution, high-S/N, HeI lambda4471 and MgII lambda4481 line profiles indicates evidence of nonradial pulsation (|m| =~ 8--10) of the star. The UBV photometric observations show that gamma 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 gamma Cas, which is uncommon among Be star X-ray sources regarding its spectral feature and variability.