Star Clusters and Stellar Populations in Nearby Galaxies

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The study of stellar clusters in the galaxy M33 has provided much information concerning the stellar cluster system itself, chemical evolution of the disk and some kinematics. This survey will be extended to deeper limits taking advantage of the quality of observing conditions on Mauna Kea, Hawaii. Deep luminosity functions of clusters will be obtained as clues to the formation and cluster dissolution processes occurring in M33. The wavelength range will be extended to the Ultraviolet (UV) band and to the near infrared (IR) wavelength using arrays to obtain improved reddening, age and metallicity estimates for a larger sample of clusters. The region of the brightest open clusters in the disk will be probed. High spatial resolution cameras will be used to resolve the fields at the best quality offered at ground-based facilities. Spectroscopy will be used to study the kinematics of the cluster system and to calibrate the metallicity estimates. The stellar content of M33 will be examined as well, using the same data taken to survey the clusters. The variation of the stellar population from place to place in the disk will be investigated. Coupled with the metallicity gradient seen in M33 traced by HII regions and the clusters, the age-metallicity and population variations across the disk will be unveiled. The proximity and inclination of M33 allows optimal sampling of parameters that provide constraints for galactic structure and evolution theories, in contrast to studies of M31 and the Galaxy which are severely restricted by extinction. The M33 samples will be compared to data for the Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC) to understand how much of stellar and cluster evolution is determined by the parent galaxy. Continuing the M33 study to fainter magnitudes achievable from the ground permits a smooth transition from the "brighter" surveys (V=14-20) currently published to fields selected for Hubble Space Telescope (HST). The ground based studies will be used to choose the "most profitable" fields for space observations. Stars in other galaxies, sampled at only the brightest fraction of the population, will be measured using existing data. Blue, violet, ultraviolet, red and infrared protometry will be obtained. Characterization of the properties of the stellar content of Local Group galaxies, as they vary within each galaxy and from galaxy to galaxy, will be used to understand the integrated properties of more distant systems.