| Issue |
A&A
Volume 383, Number 2, FebruaryIV 2002
|
|
|---|---|---|
| Page(s) | 636 - 647 | |
| Section | The Sun | |
| DOI | https://doi.org/10.1051/0004-6361:20020025 | |
| Published online | 15 February 2002 | |
In hot pursuit of the hidden companion of η Carinae: An X-ray determination of the wind parameters
1
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, jmp@ast.leeds.ac.uk
Received:
28
September
2001
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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