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Institut für Astronomie und Astrophysik

Abteilung Astronomie

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Preprint 06a/96

Periodic Changes of the Accretion Geometry in the Nearly-Synchronous Polar RX J1940.1-1025

Ralf D. Geckeler and Rüdiger Staubert

Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany

Contribution to the Conference Accretion Phenomena and Associated Outflows - IAU Colloquium 163, Port Douglas, Australia, July 15-19, 1996

Abstract. RX J1940.1-1025 is a newly discovered magnetic Cataclysmic Variable and one of only three known polars with a slightly non-synchronous (< 3%) rotation of the white dwarf primary. The accretion geometry between the infalling accretion stream and the magnetic field of the WD thus changes periodically with the beat period of 50.0 d between the orbital and the spin period of the WD. The accretion thus occurs along different field lines, depending on the beat phase.
For the first time we have observed this effect as a periodic shift in the timings of the absorption troughs in the optical and X-ray pulse profiles of RX J1940.1-1025 with phase of the beat period. There is evidence for a secular decrease of the spin period of RXJ1940.1-1025 with a synchronization time scale of the order of 10^2 y.

Paper (29k gzip'ed Postscript including figures)

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