He II λ4686 Emission from the Massive Binary System in λ Car: Constraints to the Orbital Elements and the Nature of the Periodic Minima

TEODORO, M.; DAMINELI, A.; HEATHCOTE, B.; RICHARDSON, N. D.; MOFFAT, A. F. J.; ST-JEAN, L.; RUSSELL, C.; GULL, T. R.; MADURA, T. I.; POLLARD, K. R.; WALTER, F.; COIMBRA, A.; PRATES, R.; FERNÁNDEZ-LAJÚS, E.; GAMEN, R. C.; 15 COAUTORES

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Londres; Año: 2016 vol. 819 p. 131 - 154

0004-637X

Eta Carinae (η Car) is an extremely massive binary system in whichrapid spectrum variations occur near periastron. Most notably, nearperiastron the He ii λ4686 line increases rapidly in strength,drops to a minimum value, then increases briefly before fading away. Tounderstand this behavior, we conducted an intense spectroscopicmonitoring of the He ii λ4686 emission line across the 2014.6periastron passage using ground- and space-based telescopes. Comparisonwith previous data confirmed the overall repeatability of the lineequivalent width (EW), radial velocities, and the timing of the minimum,though the strongest peak was systematically larger in 2014 than in 2009by 26%. The EW variations, combined with other measurements, yield anorbital period of 2022.7 ± 0.3 days. The observed variability ofthe EW was reproduced by a model in which the line flux primarily arisesat the apex of the wind?wind collision and scales inversely withthe square of the stellar separation, if we account for the excessemission as the companion star plunges into the hot inner layers of theprimary?s atmosphere, and including absorption from the disturbedprimary wind between the source and the observer. This model constrainsthe orbital inclination to 135°?153°, and the longitude ofperiastron to 234°?252°. It also suggests that periastronpassage occurred on {T}0=2456874.4\quad (+/- 1.3 days). Ourmodel also reproduced EW variations from a polar view of the primarystar as determined from the observed He ii λ 4686 emissionscattered off the Homunculus nebula.