Issue |
A&A
Volume 454, Number 1, July IV 2006
|
|
---|---|---|
Page(s) | 287 - 294 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20065078 | |
Published online | 03 July 2006 |
The X-ray properties of the magnetic cataclysmic variable UU Columbae
1
INAF–Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy e-mail: demartino@na.astro.it
2
Dipartimento di Fisica, Universita' degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy e-mail: matt@fis.uniroma3.it
3
Laboratory for High Energy Astrophysics, NASA/GSFC, Code 662, Greenbelt, MD 20771, USA e-mail: mukai@milkyway.gsfc.nasa.gov
4
Service d'Astrophysique, DSM/DAPNIA/SAp, CE Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: bonnetbidaud@cea.fr
5
Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, Postfach 1312, 85741 Garching, Germany e-mail: [burwitz;fwh]@mpe.mpg.de
6
Department of Physics, University of Warwick, Coventry CV4 7AL, UK e-mail: boris.gaensicke@warwick.ac.uk
7
APC, UMR 7164, University Denis Diderot, 2 place Jussieu, 75005 Paris and LUTH, Observatoire de Paris, 92195 Meudon Cedex, France e-mail: martine.mouchet@obspm.fr
Received:
23
February
2006
Accepted:
11
March
2006
Aims.XMM-Newton observations to determine for the first time the broad-band X-ray properties of the faint, high galactic latitude intermediate polar UU Col are presented.
Methods.We performed X-ray timing analysis in different energy ranges of the EPIC
cameras, which reveals the dominance of the 863 s white dwarf rotational
period. The spin pulse is strongly energy dependent. Weak
variabilities at the beat 935 s and at
the 3.5 h orbital periods are also observed, but the orbital modulation
is detected only below 0.5 keV. Simultaneous UV and optical photometry
shows that the spin pulse is anti-phased with respect to the hard
X-rays. Analysis of the EPIC and RGS spectra reveals the complexity
of the X-ray emission, which is composed of a soft 50 eV black–body
component
and two optically thin emission components at 0.2 keV and 11 keV
strongly absorbed
by dense material with an equivalent hydrogen column density of
that partially (50%) covers the X-ray
source.
Results.The complex X-ray and UV/optical temporal behaviour indicates that
accretion occurs predominantly (~) via a disc with a
partial contribution (~
) directly from the stream. The main
accreting pole dominates at high energies whilst the secondary
pole mainly contributes in the soft X-rays and at lower energies.
The bolometric flux
ratio of the soft-to-hard X-ray emissions is found to
be consistent with the prediction of the standard accretion shock model.
We find the white dwarf in UU Col accretes at a low rate and
possesses a low magnetic moment.
It is therefore unlikely that
UU Col will evolve into a moderate field strength polar, so that
the soft X-ray intermediate polars still remain an enigmatic small group
of magnetic cataclysmic variables.
Key words: stars: binaries: close / stars: individual: RX J0512.2-3241 (UU Col) / stars: novae, cataclysmic variables / X-rays: binaries / accretion, accretion disks
© ESO, 2006
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