Eta Carinae’s 2014.6 Spectroscopic Event: The Extraordinary He II and N II Features

Abstract

Eta Carinae’s spectroscopic events (periastron passages) in 2003, 2009, and 2014 differed progressively. He ii λ4687 and nearby N ii multiplet 5 have special significance because they respond to very soft X-rays and the ionizing UV radiation field (EUV). Hubble Space Telescope (HST)/STIS observations in 2014 show dramatic increases in both features compared to the previous 2009.1 event. These results appear very consistent with a progressive decline in the primary wind density, proposed years ago on other grounds. If material falls onto the companion star near periastron, the accretion rate may now have become too low to suppress the EUV.

Based on observations made with the NASA/ESA Hubble Space Telescope, which is opera ted by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.