An episodic red-wing structure of SiIV, lambda 1394A, in gamma Cas

摘要

International Ultraviolet Explorer (IUE) observations of gamma Cas obtained in January 1983 show the conspicuous presence of a red-wing structure in the SiIV, 1394 A, resonance line in gamma Cas. The 1403 A, shows a much less enhanced trace of the same effect. A comparison between 1938 IUE spectra with previous ones obtained in 1980 show that in January 1983 the red absorption wing is strongly depressed relative to the 1980 profile where the red feature was absent. It is concluded that this red wing feature is in absorption rather than in emission. This same wing-structure is suggested on 1982 IUE spectra. Combining long-term variations of gamma Cas in the visual with published far-UV data, it is noted that this red feature seems to occur preferentially at epochs where the V/R ratio of the violet and red emission peaks at H-alpha is less than one. It is suggested that these two characteristics, visual and far UV, are linked to the flow-deceleration in the outer-atmosphere.