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E. L. Robinson, I. I. Ivans, W. F. Welsh (Dept. of Astronomy, Univ. of Texas at Austin)
The transient X-ray source XTE~J0421+560 erupted on 1998 March 31 and its optical counterpart was soon found to be the obscure and rarely-observed variable star CI~Cam. During the eruption CI~Cam became the brightest known X-ray transient at optical wavelengths, rising from R ~10.6 at minimum light to R ~7.1. In addition, VLA observations in April suggested that CI~Cam was emitting relativistic corkscrew jets. We obtained high-dispersion spectroscopy of CI~Cam with the 2D-coudé spectrograph on the 2.7-m telescope at McDonald Observatory in April, near the end of the eruption. CI~Cam had a uniquely-rich emission-line spectrum at that time. The emission lines fell into three distinct groups: (1) H and He~I lines with wings extending from -1500~km/s to +500 km/s; (2) Metal lines, mostly Fe II, with half widths at half maximum of 32 km/s; (3)) Highly forbidden lines of, for example, [O III] with half-widths at half maximum of 16 km/s. The permitted metal lines and the highly-forbidden lines arise in two kinematically and thermally distinct shells around CI~Cam. The broad lines of H and He arise in a strong wind.
Additional observations this fall show that the spectrum has changed radically since April. The H and He emission lines are much narrower and their broad wings have disappeared; the metallic lines have retained their width, but their profile has changed; and the higher members of the Balmer series have developed broad, dish-shaped absorption wings.