HeII λ4686 in η Car: The Data and Modeling

DAMINELI A.; TEODORO M.; STEINER J.; MORRELL N.; BARBÁ R; SOLIVELLA G.; GAMEN R.; FERNÁNDEZ LAJÚS E.; GONZALEZ F.; TORRES C. A. P. C. O.; GROH J. H.; FRAGA L.; PEREIRA C. B.; BORGES FERNANDES M.; ZEVALLOS M.I.; MCGREGOR P.

Río de Janeiro

Jornada; Eta Carinae in the Context of the Most Massive Stars; 2009

International Astronomical Union

The intrinsic emission of He ii is quite repeatable from cycle to cycle. The He ii λ4686line flux rises by a factor of ≈10 in the 2 months preceding phase zero. There are twolocal maxima in the month preceding the minimum and a secondary maximum ≈50 daysafter phase zero. The rising before phase zero resembles that seen in X-rays, but withremarkable differences. The He ii line flux increases by a factor of ≈10 as compared toonly a few times in X-ray emission. Both light curves collapse before phase zero, butthe collapse of He ii is shifted by 16.5 days relative to the X-ray collapse. The minimumin He ii is reached a week after phase zero. Since the X-ray variability is measured inthe range 2–10 keV, and comes mainly from the vertex of the wind-wind shock cone,it is probably not common to the He ii emitting region, which comes from gas at lowertemperature. The He ii line indicates a high luminosity source in the system, but it is notclear where it comes from. One possible source is the collision of the secondary star wind,since the SED derived from Parkin et al. 2009 (MNRAS 394, 1758) models indicates thepresence of 10 times more He+ ionizing photons than those passing through this atomictransition. Recombination of the shocked secondary wind is not the only source for theHe+ ionizing photons. As the shock cone migrates deep in the wind of the primary star, a huge amount of hard photons are free to escape and ionize the inner walls of thewind-wind collision zone.