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Astron. Astrophys. 336, 191-199 (1998)

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The X-ray stream-eclipsing polar RX J1802.1+1804

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

1 Max-Planck-Institut für Extraterrestrische Physik, D-85740 Garching, Germany
2 Center for Space Research, MIT, 77 Mass Ave, Cambridge, MA 02139 USA (rr@space.mit.edu)
3 Observatoire de Strasbourg, 11 rue de l'Université, F-67000 Strasbourg, France (motch@astro.u-strasbg.fr)

Received 22 December 1997 / Accepted 31 March 1998


We present X-ray and optical data of the newly discovered AM Her variable RX J1802.1+1804. This X-ray source was observed in the ROSAT All-Sky-Survey in September 1990 and subsequently discovered as a highly variable and soft X-ray source. Follow-up pointed observations confirmed the strong variability and revealed a periodic flux modulation including a sharp and nearly complete eclipse of the X-ray emission. Based on the shape and duration of this eclipse as well as the lack of optical eclipses we favour an interpretation in terms of a self-eclipse by the accretion stream. The X-ray spectrum averaged over the full period is dominated by soft emission below 0.5 keV. The ratio of soft (blackbody) to hard (bremsstrahlung) bolometric energy flux is 1670, distinguishing this object as another example of a polar with an extreme strong excess in soft X-rays.

Key words: cataclysmic variables – accretion – stars: magnetic fields – 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: J. Greiner

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© European Southern Observatory (ESO) 1998

Online publication: July 7, 1998