XUV Detections of Comets in the ROSAT All-Sky Survey

EXTREME-ULTRAVIOLET DETECTIONS OF COMETS
     J. P. Pye and R. G. West, Leicester University; and K. Dennerl,
Max-Planck-Institut fur Extraterrestrische Physik, Garching, report
the discovery of extreme-ultraviolet (EUV) emission from two comets
in data acquired by the Wide-Field Camera (WFC) during the ROSAT
all-sky survey.  Accompanying x-ray emission has previously been
reported by Dennerl et al. (IAUC 6413).  Significant EUV detections
have been made in the following observing intervals:  C/1990 K1
(Levy), 1990 Sept. 6.50-7.43 UT, 1991 Jan. 9.96-11.96, and Jan.
17.36-18.02; C/1990 N1 (Tsuchiya-Kiuchi), 1990 Nov. 18.16-20.70.
All detections were made in the WFC S1 filter, nominal passband 90-
206 eV (14-6 nm).  The upper-limit countrates derived for the WFC
S2 filter (passband 62-110 eV; 20-11 nm), when compared with the S1
measurements, yield spectral parameters consistent with those
previously reported for some comets (IAUC 6394, 6404).