CORONAL ACTIVITY IN THE COMA BERENICES OPEN CLUSTER

We present ROSAT PSPC observations of the similar to 500 Myr old Coma Berenices cluster. The X-ray survey in Coma consists of a) a raster sc an of short duration PSPC pointings, b) ROSAT All-Sky Survey data, and c) a 16 ksec deep PSPC pointing. The raster scan and the survey data were merged together covering an area of about 36 square degrees, whil e the deep pointing was analyzed separately. No major differences were found between the two datasets. Our ROSAT observations indicate that Coma is much more similar in its X-ray properties to the coeval Hyades than to the also coeval Praesepe cluster. As in the Hyades, almost al l late-F and G stars were detected, also showing a comparable range in X-ray luminosity. X-ray luminosity distribution functions (XLDFs) for solar-type members are in close agreement with those of the Hyades, c onfirming that the majority of Praesepe's members are less luminous th an what one would expect for stars of their age. The Coma Berenices cl uster is known for its apparent deficit of low mass stars of spectral type K and later. We present 12 new possible low-mass Coma candidates, identified through this X-ray survey.