THE X-RAY ECLIPSE OF THE DWARF-NOVA HT-CASSIOPEIAE - RESULTS FROM ASCA AND ROSAT-HRI OBSERVATIONS

We report on a 1 day ASCA observation and ROSAT HRI observations of th e eclipsing dwarf nova HT Gas. The presence of the X-ray eclipse, orig inally detected in a ROSAT PSPC observation, is confirmed at a much hi gher significance level. The quality of the ASCA light curve is high e nough to allow detailed investigation of the eclipse depth, width, and shape. The eclipse is found to be deep, compatible with being total T he eclipse width is comparable to that of the white dwarf, as derived from optical light curves, and in fact may be narrower. The eclipse tr ansition is also found to be short, which puts a limit of 1.15 times t he white dwarf radius as the total size of the X-ray emission region. The out-of-eclipse spectrum of HT Cas is found to be consistent with a single temperature (kT similar to 10 keV), absorbed (N-H similar to 3 .3 x 10(21) cm(-2)), thermal model.