Detection of high-velocity material from the wind-wind collision zone of Eta Carinae across the 2009.0 periastron passage

Jose H. Groh (1), Krister E. Nielsen (2,3), Augusto Damineli (4), Theodore R. Gull (2), Thomas I. Madura (5), D. J. Hillier (6), Mairan Teodoro (4), Thomas Driebe (1), Gerd Weigelt (1), Henrik Hartman (7), Florian Kerber (8), Atsuo T. Okazaki (9), Stan P. Owocki (5), Florentin Millour (1), Koji Murakawa (1), Stefan Kraus (10), Karl-Heinz Hofmann (1), Dieter Schertl (1)

(1) Max-Planck-Institute for Radioastronomy, (2) NASA/GSFC, (3) CUA, (4) IAG/U Sao Paulo, (5) U Delaware, (6) U Pittsburgh, (7) Lund U, (8) ESO, (9) Hokkai-Gakuen U, (10) U Michigan

We report near-IR spectroscopic observations of the Eta Carinae massive binary system during 2008-2009 using VLT/CRIRES. We detect a strong, broad absorption wing in He I 10833 extending up to -1900 km/s across the 2009.0 spectroscopic event. Archival HST/STIS ultraviolet and optical data shows a similar high-velocity absorption (up to -2100 km/s) in the UV resonance lines of Si IV 1394, 1403 across the 2003.5 event. UV lines from low-ionization species, such as Si II 1527, 1533 and C II 1334, 1335, show absorption up to -1200 km/s, indicating that the absorption with v from -1200 to -2100 km/s originates in a region markedly faster and more ionized than the nominal wind of the primary star. Observations obtained at the OPD/LNA during the last 4 spectroscopic cycles (1989-2009) also display high-velocity absorption in He I 10833 during periastron. Based on the OPD/LNA dataset, we determine that material with v < -900 km/s is present in the phase range 0.976 < phi < 1.023 of the spectroscopic cycle, but absent in spectra taken at phi < 0.947 and phi > 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We suggest that the high-velocity absorption originates from shocked gas in the wind-wind collision zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. Using 3-D hydrodynamical simulations of the wind-wind collision zone, we find that the dense high-velocity gas is in the line-of-sight to the primary star only if the binary system is oriented in the sky so that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of omega ~ 240 to 270 degrees. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i=40 to 60 degrees.

Reference: A&A, in press
Status: Manuscript has been accepted