ON THE He Ⅱ EMISSION IN η CARINAE AND THE ORIGIN OF ITS SPECTROSCOPIC EVENTS

摘要

We describe and analyze Hubble Space Telescope (HST) observations of transient emission near 4680 A in η Car, reported earlier by Steiner & Damineli. If, as seems probable, this is He Ⅱ λ4687, then it is a unique clue to η Car's 5.5 yr cycle. According to our analysis, several aspects of this feature support a mass-ejection model of the observed spectro-scopic events, and not an eclipse model. The He n emission appeared in early 2003, grew to a brief maximum during the 2003.5 spectroscopic event, and then abruptly disappeared. It did not appear in any other HSTspectra before or after the event. The peak brightness was larger than previously reported and is difficult to explain even if one allows for an uncertainty factor of order 3. The stellar wind must provide a temporary larger-than-normal energy supply, and we describe a special form of radiative amplification that may also be needed. These characteristics are consistent with a class of mass-ejection or wind-disturbance scenarios, which have implications for the physical structure and stability of η Car.