H ii Region Oxygen Abundances in Starbursting Transition Dwarf Galaxies

We present empirical HII region oxygen abundances for a sample oflow-luminosity starburst galaxies which are in a short lived evolutionarystate. All five galaxies are characterized by centrally concentrated starformation, which is embedded in smooth stellar envelopes resembling dE-likesystems. The galaxies also have small gas contents with typical M_{HI}/L_{B} ~0.1 resulting in gas exhaustion timescales less than 1 Gyr, even when moleculargas is considered. We find, compared to other morphologically similar systems,the galaxies of this sample have surprisingly high oxygen abundances with 12 +log(O/H) ~ 9.0. We propose that these objects are a subclass of evolved bluecompact dwarfs, which have exhausted most of their gas supply while retainingtheir metals. We further propose that we are seeing these objects during ashort phase in which they are nearing the end of their starburst activity, andcould become early-type dwarfs.Comment: 13 pages, 3 figures, accepted by ApJ Letter