Issue |
A&A
Volume 422, Number 1, July IV 2004
|
|
---|---|---|
Page(s) | 177 - 191 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20047035 | |
Published online | 06 July 2004 |
Wind clumping and the wind-wind collision zone in the Wolf-Rayet binary γ2 Velorum *
XMM-Newton observations at high and low state
1
Institut für Astronomie, ETH-Zentrum, 8092 Zürich, Switzerland e-mail: hschild@astro.phys.ethz.ch
2
Paul Scherrer Institut, Würenlingen & Villigen, 5232 Villigen PSI, Switzerland
3
SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands e-mail: [a.j.j.raassen;k.a.van.der.hucht;r.mewe]@sron.nl
4
Physikalisch-Meteorologisches Observatorium Davos, Dorfstrasse 33, 7260 Davos Dorf, Switzerland e-mail: w.schmutz@pmodwrc.ch
5
Astronomical Institute “Anton Pannekoek”, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: raassen@science.uva.nl
6
Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA e-mail: [audard;maurice]@astro.columbia.edu
7
Center for Astrophysics and Space Astronomy, University of Colorado, Campus Box 389, Boulder, CO 80309-0389, USA e-mail: skinner@origins.colorado.edu
Corresponding author: M. Güdel, guedel@astro.phys.ethz.ch
Received:
8
January
2004
Accepted:
13
April
2004
We present XMM-Newton observations of γ2 Velorum (WR 11,
WC8+O7.5III, P = 78.53 d),
a nearby Wolf-Rayet binary system, at its X-ray high and low states.
At high state, emission from a hot collisional
plasma dominates from about 1 to 8 keV. At low state, photons between 1 and 4 keV are absorbed. The hot plasma
is identified with the shock zone between the winds of the primary
Wolf-Rayet star and the secondary O giant. The absorption at
low state is interpreted as photoelectric absorption in the Wolf-Rayet
wind. This absorption allows us to measure the absorbing column density
and to derive a mass loss rate
= 8
10-6
yr-1
for the WC8 star.
This mass loss rate, in conjunction with a previous Wolf-Rayet wind model,
provides evidence for a clumped WR wind. A clumping factor of 16 is
required.
The X-ray spectra below 1 keV (12 Å)
show no absorption and are essentially similar in both states.
There is a rather clear separation
in that emission from a plasma hotter than 5 MK is heavily absorbed in low state
while the cooler plasma is not.
This cool plasma must come from a much more extended region
than the hot material. The Neon
abundance in the X-ray emitting material is 2.5 times
the solar value.
The unexpected detection of C v (25.3 Å) and C vi (31.6 Å)
radiative recombination continua at both phases indicates the presence of a cool
(~40 000 K) recombination region located far out in the
binary system.
Key words: stars: binaries: spectroscopic / stars: early-type / stars: individual: γ2 Vel / stars: circumstellar matter / X-rays: individual: WR 11
© ESO, 2004
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