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Astron. Astrophys. 336, 200-208 (1998)


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ASCA observation of the polar RX J1802.1+1804

M. Ishida 1, J. Greiner 2, R.A. Remillard 3 and C. Motch 4

1 Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229, Japan (ishida@astro.isas.ac.jp)
2 Max-Planck-Institut für Extraterrestrische Physik, D-85740 Garching, Germany
3 Center for Space Research, MIT, 77 Mass Ave, Cambridge, MA 02139, USA (rr@space.mit.edu)
4 Observatoire de Strasbourg, 11 rue de l'Université, F-67000 Strasbourg, France (motch@astro.u-strasbg.fr)

Received 22 December 1997 / Accepted 14 April 1998

Abstract

We present X-ray data of RX J1802.1+1804 obtained by ASCA . Although it shows a clear orbital intensity modulation with an amplitude of nearly 100% below 0.5 keV in ROSAT data, the ASCA light curves are nearly flat except for a possible dip lasting about one-tenth of the orbital period. We discuss this within the model assumption of a stream-eclipsing geometry as derived from the ROSAT observations.

The ASCA X-ray spectrum can be represented by a two temperature optically thin thermal plasma emission model with temperatures of [FORMULA]1 keV and [FORMULA]7 keV, suggesting postshock cooling as observed in EX Hya. A remarkable feature of the spectrum is the strong iron [FORMULA] emission line whose equivalent width is [FORMULA]4 keV. To account for this, an iron abundance of greater than at least 1.3 times Solar is required. A combined spectral analysis of the ROSAT PSPC and ASCA data indicates that the [FORMULA]-corrected flux ratio of the soft blackbody (0.1-2.4 keV) to the hard optically thin thermal plasma emission (2-10 keV) is as large as [FORMULA].

Key words: stars: novae, cataclysmic variables – accretion, accretion disks – X-rays: stars – stars: individual: RX J1802.1+1804 = V884 Her

Present address: Astrophysical Institute Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany (jgreiner@aip.de)

Send offprint requests to: M. Ishida

© European Southern Observatory (ESO) 1998

Online publication: July 7, 1998

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