An EUVE Observation of the polar AN UMa

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Session 63 -- Intrinsic and Cataclysmic Variables
Display presentation, Thursday, 9:20-4:00, Heller Lounge Room

[63.13] An EUVE Observation of the polar AN UMa

K.~Mukai (USRA, NASA/GSFC), J.~V.~Vallerga \& F.~Paerels (UCB)

AN UMa is a member of the polar, or AM Her, class of magnetic cataclysmic variables. They are strong soft X-ray/EUV sources due to the heating of a small area of the white dwarf surface onto which the accretion flow is collimated. There remains a controversy over the ``soft X-ray puzzle,'' i.e., whether the polars are overluminous in EUV compared with other (hard X-ray, UV/optical/IR) wavelength ranges, given theoretical expectations. Spectroscopic observations of the EUV component of a large number of polars is essential if we are to resolve this issue.

AN UMa is a known soft X-ray source; furthermore, the ROSAT WFC survey detected this system with count rates of 0.175$\pm$0.011 and 0.226$\pm$0.014 counts per second, respectively, in S1 and S2 bands. The brightness and the high S2/S1 ratio (possibly indicating low interstellar absorption, although the measurements were not simultaneous) make AN UMa an ideal candidate for an EUVE observation. We have carried out such an observation on 1993 Feb 28, and will present preliminary results.

Thursday program listing