SOME MUSINGS ON GALAXY CLASSIFICATION

This paper presents a discussion of classification systems for galaxie s, with special emphasis on possible modifications of the Hubble ''tun ing fork'' diagram, and on galaxy types not included in Hubble's origi nal scheme. Hubble's morphological types were defined in terms of stan dards observed at small look-back times that were mostly located in th e field, or in poor clusters. It is pointed out chat it is often diffi cult to shoehorn galaxies located in the cores of rich clusters, or ob jects viewed at large look-back times, into the Hubble classification system. The evolutionary relationships between E, S0, and dSph galaxie s are still controversial and poorly understood. It is suggested that S0 galaxies may have arrived at their present morphology along various evolutionary tracks. Late-type barred spirals are found to be systema tically less luminous than normal late-type galaxies. This suggests th at the dichotomy between normal and barred spirals may reflect signifi cant differences in their evolutionary histories. Such differences mig ht be explored by searching for systematic differences between the [O/ Fe] values in normal and barred spirals. Finally, it is pointed out th at the Lame Magellanic Cloud may have been a low surface brightness ga laxy for an similar to 8 Gyr period that ended 3-5 Gyr ago. This sugge sts that some galaxies can jump from one morphological classification type to another. (C) 1997 American Astronomical Society.