Low-Luminosity Early-Type Galaxies in the Coma Cluster: Variations in Spectral Properties

We present spectra of nine low-luminosity early-type galaxies (M_B > -17.5)in the Coma cluster. The spectra, which were obtained with the Multiple MirrorTelescope and cover the spectral region 3300-5350 A, exhibit a large variationin Balmer line strengths. In fact the line strength variation among the Comalow-luminosity galaxies is as large as that found among a sample oflow-luminosity ellipticals in the Virgo cluster and lower density environments.When compared to detailed population synthesis models, the variation in Balmerline strengths among the Coma galaxies indicates a range in luminosity-weightedmean age of from 1 Gyr to 12 Gyr. The two youngest galaxies are shown to be ina post-starburst state, i.e., they are not simply former spirals whose starformation was recently terminated. Moreover, the 1 Gyr ages of these twoyoungest low-luminosity galaxies are similar to those of the brighterpost-starburst galaxies in Coma.Comment: To appear in the Astronomical Journa