The Be star Gamma Cassiopeiae: X-ray, far-UV, and optical observations in early 1989

Details The Be star Gamma Cassiopeiae: X-ray, far-UV, and optical observations in early 1989 The Be star Gamma Cassiopeiae: X-ray, far-UV, and optical observations in early 1989

Feb 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994pasj...46....9h&link_type=abstract

PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264), vol. 46, no. 1, p. 9-26

Astronomy and Astrophysics

Astronomy

25

B Stars, Cassiopeia Constellation, Light (Visible Radiation), Line Shape, Ultraviolet Astronomy, Ultraviolet Spectra, Variations, X Ray Astronomy, X Ray Spectra, Astronomical Photometry, Astronomical Spectroscopy, Carbon, Ginga Satellite, H Alpha Line, H Beta Line, H Gamma Line, Helium, Iron, Iue, Magnesium, Nitrogen, Silicon

Scientific paper

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 Si IV, C IV, and N V 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 (greater than or approximately equal to 1,000 km/s) 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 greater than 1 for H alpha, H beta, and H gamma. A series of high-resolution, high-S/N, He I lambda 4481 line profiles and Mg II lambda 4481 line profiles indicates evidence of nonradial pulsation (absolute value of m approx. = 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.

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