Eta Car's spectroscopic event begins to differ from 2009
Kris Davidson(U. MN), Andrea Mehner(ESO-Chile), Roberta Humphreys(U MN), K. Ishibash(Nagoya U., Japan), J. C. Martin(U. Illinois, Springfield)
The middle of eta Car's 2014.6 spectroscopic event (periastron passage) occurred in mid-August (ATEL #6334, #6336, #6357, #6368, #6380). HST/STIS observations on July 13, July 30, and August 15 strongly suggest that the exotic He II 4687 emission is reappearing sooner than in the 2009.1 event. This is not entirely unexpected (ATEL #6368), and most likely it signals an early reappearance of the hard X-rays. For background and implications see Martin et al 2006, ApJ 640, 474 (M2006) and Mehner et al 2011 (M2011). --- --- Using the Treasury Program time scale (t = 0 on 2014 August 14, see M2011) and a measurement protocol defined in M2006, the estimated He II 4686 emission equivalent widths were 3.1 A at t = -32 d, 0.5 A at t = -15 d, and 1.0 A at t = +1 d. The first of these was slightly higher than the 2009 peak, and, more important, the third is either much brighter or (more likely) about a week earlier than the 2009 reappearance. A small peak was discernible on July 30 and August 15, but most of the EW is due to very broad emission resembling a heightened continuum between 4675 and 4694 A; see M2006 and 2011. --- --- Unlike the 2003 and 2009 spectroscopic events, N II multiplet 5 near 4600 A is now very conspicuous in emission. It is excited by photons near 18.5 eV (Mehner et al. 2011, ApJ 737:70). The simplest interpretation is that the stars' UV radiation is much stronger than in the previous events -- consistent with lower gas densities (M2011).
optical,ultra-violet,x-ray,star,variables