ULTRAVIOLET IMAGING OF THE Z=0.23 CLUSTER ABELL-2246

We present deep ultraviolet observations of a field containing the clu ster Abell 2246 (z = 0.225), which provide far-ultraviolet (FUV) image s of some of the faintest galaxies yet observed in that bandpass. Abel l 2246 lies within the field of view of Ultraviolet Imaging Telescope (UIT) observations of the quasar HS 1700+64, which accumulated over 71 00 s of UIT FUV exposure time during the Astro-2 mission in 1995 March . For objects found on both the far-ultraviolet (FUV) and ground-based V-band images, we obtain FUV (lambda similar to 1520 Angstrom) photom etry and V-band photometry, as well as mid-UV (lambda similar to 2490 Angstrom) photometry from UIT Astro-1 observations and ground-based I- band photometry. We find five objects in the images that are probably galaxies at the distance of Abell 2246, with FUV magnitudes [m(FUV)] b etween 18.6 and 19.6 and V magnitudes between 18.4 and 19.6. We find t hat their absolute FUV fluxes and colors imply strongly that they are luminous galaxies with significant current star formation, as well as some relatively recent, but not current (>400 Myr ago) star formation. We interpret the colors of these five objects by comparing them with local objects, redshift-corrected template spectra, and stellar popula tion models, finding that they are plausibly matched by 10 Gyr-old pop ulation models with decaying star formation, with decay time constants in the range 3 Gyr < tau < 5 Gyr, with an additional color component from a single burst of moderate (similar to 400-500 Myr) age. From der ived FUV luminosities we compute current star formation rates. We comp are the UV properties of Abell 2246 with those of the Coma Cluster, fi nding that Abell 2246 has significantly more recent star formation, co nsistent with the Butcher-Oemler phenomenon.