He II 4686 IN ETA CARINAE: COLLAPSE OF THE WIND-WIND COLLISION REGION DURING PERIASTRON PASSAGE

TEODORO M.; DAMINELI A.; ARIAS J.I.; DE ARAUJO F.X.; BARBÁ R.; CORCORAN M.F.; BORGES FERNANDES M.; FERNÁNDEZ LAJÚS, E.; FRAGA L.; GAMEN R.C.; GONZÁLEZ J.F.; GROH J. H.; MARSHALL J.L.; MCGREGOR P.J.; MORRELL N.; NICHOLLS D.C.; PARKIN E.R.; PEREIRA C.B.; PHILLIPS M.M.; SOLIVELLA G.R.; STEINER J.E.; STRITZINGER M.; THOMPSON I.; TORRES C.A.O.; TORRES M.A.P.; ZEVALLOS HERENCIA M.I.

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Hamilton, Ontario; Año: 2012 vol. 746 p. 73 - 88

0004-637X

The periodic spectroscopic events in Eta Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All 3 of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of Carinae with 5 Southern telescopes during the 2009 low excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II 4686 emission line (L = 310 L⊙) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the wind-wind collision (WWC) region. Clumps in the primary’s wind probably explain the flare-like behavior of both the X-ray and He II 4686 light-curves. After a short-lived minimum, He II 4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the “surface” of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondary’s wind and the clumps in the primary’s wind.