OBSERVATIONS OF A HIGH SURFACE BRIGHTNESS ARCLET ASSOCIATED WITH THE CLUSTER OF GALAXIES GHO-2154+0508

We present the results of photometric and spectroscopic observations o f a high surface brightness arclet associated with the cluster of gala xies GHO 2154 + 0508. High-resolution imaging (FWHM almost-equal-to 0. ''45) of this arclet, presumably the result of gravitational lensing o f a background galaxy, show it to be resolved, having FWHM almost-equa l-to 1.''1, with lengths of 3.''3 and 4.''5 in the V band and R band, respectively. We find the arclet to have V = 22.07 +/- 0.08, (V - R)KC = 0.7, and a mean central surface brightness in the V band of 23.7 ma g arsec-2. The spectrum of the arclet has a single strong emission lin e, which we identify as [O II] lambda3727 at a redshift of 0.721. This redshift is supported by several weaker features in the spectrum. Spe ctra of two bright cluster galaxies confirm the cluster redshift of 0. 32, with a third galaxy found to be at a redshift of 0.468. The presen ce of this high surface brightness arclet and the irregular structure of GHO 2154 + 0508 suggest the mass responsible for producing the lens ing is not as centrally concentrated as other known lensing clusters. GHO 2154 + 0508 may be a rich cluster of galaxies in the early stages of formation.