Astronomy and Astrophysics, volume 517, A9-9 (2010/7-1)
Detection of high-velocity material from the wind-wind collision zone of Eta Carinae across the 2009.0 periastron passage.
GROH J.H., NIELSEN K.E., DAMINELI A., GULL T.R., MADURA T.I., HILLIER D.J., TEODORO M., DRIEBE T., WEIGELT G., HARTMAN H., KERBER F., OKAZAKI A.T., OWOCKI S.P., MILLOUR F., MURAKAWA K., KRAUS S., HOFMANN K.-H. and SCHERTL D.
Abstract (from CDS):
We report near-infrared spectroscopic observations of the Eta Carinae massive binary system during 2008-2009 using the CRIRES spectrograph mounted on the 8m UT1 Very Large Telescope (VLT Antu). We detect a strong, broad absorption wing in HeI λ10833 extending up to -1900km/s across the 2009.0 spectroscopic event. Analysis of archival Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet and optical data identifies a similar high-velocity absorption (up to -2100km/s) in the ultraviolet resonance lines of SiIV λλ1394, 1403 across the 2003.5 event. Ultraviolet resonance lines from low-ionization species, such as SiII λλ1527, 1533 and CII λλ1334, 1335, show absorption only up to -1200km/s, indicating that the absorption with velocities -1200 to -2100km/s originates in a region markedly more rapidly moving and more ionized than the nominal wind of the primary star. Seeing-limited observations obtained at the 1.6m OPD/LNA telescope during the last four spectroscopic cycles of Eta Carinae (1989-2009) also show high-velocity absorption in HeI λ10833 during periastron. Based on the large OPD/LNA dataset, we determine that material with velocities more negative than -900km/s is present in the phase range 0.976≤φ≤1.023 of the spectroscopic cycle, but absent in spectra taken at φ≤0.947 and φ≥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 propose that the high-velocity absorption component originates in shocked gas in the wind-wind collision zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. With the aid of three-dimensional hydrodynamical simulations of the wind-wind collision zone, we find that the dense high-velocity gas is along the line-of-sight to the primary star only if the binary system is oriented in the sky such that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of ω∼240°-270°. 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°-60°.