The Luminosity Function of MS2255.7+2039 at z=0.288

The luminosity function of MS2255.7+2039 at z=0.288 is determined down to atotal magnitude of R ~ 24, corresponding to M_R ~ -17 (H_0 = 50 km/s/Mpc). Thedata are corrected for incompleteness and crowding using detailed simulations.We find that the luminosity function is steeper than a standard Schechterfunction at faint magnitudes, and shows an excess of galaxies below M_R ~ -19.After corrections for light loss and crowding, the data can be described by asum of two Schechter functions, one with M_R = -22.8 and alpha = -1.0, and onesteeper with M_R = -18.9 and alpha = -1.5, representing the dwarf population. Astraight-line fit to the faint part yields a slope similar to the Schechteralpha = -1.5 of the dwarf population. The luminosity function of MS2255.7+2039is compared to other clusters at lower redshifts, and does not show anysignificant difference. The redshift range for clusters in which increasednumber of dwarf galaxies have been found is therefore extended to higherredshifts