Volume 383, Number 2, FebruaryIV 2002
|Page(s)||636 - 647|
|Published online||15 February 2002|
In hot pursuit of the hidden companion of η Carinae: An X-ray determination of the wind parameters
Department of Physics & Astronomy, The University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK
2 Universities Space Research Association, 7501 Forbes Blvd, Ste 206, Seabrook, MD 20706, USA
3 Laboratory for High Energy Astrophysics, Goddard Space Flight Center, Greenbelt, MD 20771, USA
Corresponding author: J. M. Pittard, email@example.com
Accepted: 2 January 2002
We present X-ray spectral fits to a recently obtained Chandra grating spectrum of η Carinae, one of the most massive and powerful stars in the Galaxy and which is strongly suspected to be a colliding wind binary system. Hydrodynamic models of colliding winds are used to generate synthetic X-ray spectra for a range of mass-loss rates and wind velocities. They are then fitted against newly acquired Chandra grating data. We find that due to the low velocity of the primary wind (≈ ), most of the observed X-ray emission appears to arise from the shocked wind of the companion star. We use the duration of the lightcurve minimum to fix the wind momentum ratio at . We are then able to obtain a good fit to the data by varying the mass-loss rate of the companion and the terminal velocity of its wind. We find that and . With observationally determined values of ≈500–700 for the velocity of the primary wind, our fit implies a primary mass-loss rate of . This value is smaller than commonly inferred, although we note that a lower mass-loss rate can reduce some of the problems noted by Hillier et al. ([CITE]) when a value as high as is used. The wind parameters of the companion are indicative of a massive star which may or may not be evolved. The line strengths appear to show slightly sub-solar abundances, although this needs further confirmation. Based on the over-estimation of the X-ray line strengths in our model, and re-interpretation of the HST/FOS results, it appears that the Homunculus nebula was produced by the primary star.
Key words: stars: binaries: general / stars: early-type / stars: individual: η Carinae / stars: Wolf-Rayet / X-rays: stars
© ESO, 2002
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