EUVE All-Sky Survey Observations of the Magnetic Cataclysmic Variable UZ Fornacis

The eclipsing AM Her-type cataclysmic variable UZ For was observed by the Extreme Ultraviolet Explorer (EUVE) satellite from August 1 to August 8, 1992 during its 6-month all-sky survey. It was detected in the Lexan/boron (50--180 Angstroms) scanner with a maximum count rate of ~ 2 s(-1) (7sigma ). The total exposure time on source was 2.7 kiloseconds. UZ For was not detected during the ROSAT Wide Field Camera calibration (except for a 2sigma detection in the S2a filter) or sky survey. From previous observations by EXOSAT and ROSAT, it is known that, in addition to eclipses by the secondary, the source also displays bright and faint phases which have been interpreted as due to the bright accretion spot being carried behind the white dwarf during the rotation of the system. To address the phase modulation of the EUV radiation, we folded the EUVE data onto the 2.1 hr orbital period of UZ For. We find that our observation covered these phase sections: phi = 0.03--0.10, 0.28--0.35, 0.53--0.60, and 0.78--0.85. The first and last phase sections were bright, with average count rates of ~ 1 s(-1) and ~ 1.2 s(-1) , respectively. The dim second and third sections had average count rates of ~ 0.06 s(-1) (5sigma ) and ~ 0.17 s(-1) (9sigma ), respectively. With these data, we address the nature of the EUV emitting region, including its temperature, luminosity, and geometry. For instance, in the third phase section we probably detect (5sigma ) the rise to turn-on near phase 0.58, substantially before the soft X-ray rise detected by the ROSAT PSPC at phase 0.61. This suggests that the EUV emitting region is more extended than the soft X-ray emitting region. This work has been supported by NASA grant NAGW-1290 and NASA contracts NAS5-29298 and -30180.