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O.K. Krienke (Seattle Pacific University), P.W. Hodge (U. Washington)
As a follow up to the automated cluster search of 13 HST pointings in M31 carried out by Williams and Hodge (2001), we have re-examined the images to locate and study additional clusters. The Williams technique was effective in finding only young clusters, not intermediate age or old clusters. Our searches have shown that M31 has many of these intermediate and older open clusters, undetected by both the Williams survey and earlier ground-based searches. We have carried out integrated multi-color photometry for a sample of these clusters to ascertain ages and to compare their properties with cluster systems of other galaxies. Compared to the Magellanic Clouds, the open clusters of M31 have relatively fewer young, massive clusters, but otherwise show a similar distribution in color and absolute magnitude. Compared to M33 and M81, the M31 cluster system is deficient in luminous red clusters. The open cluster specific frequency is intermediate between that for the MCs and that for cluster-poor galaxies like IC 1613. The M31 cluster luminosity function can be fitted to a power law with a slope that agrees well with those determined from studies of other spiral galaxies’ clusters by Larsen (2002).
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.