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Session 60 - Stellar Astrophysics I.
Oral session, Tuesday, January 16
Salon del Rey North, Hilton
We have computed the luminosity functions for the metal-rich cluster M5 and for the metal-poor cluster M30 based on wide-field photometry. The size of the stellar samples (42,000 and 20,000 stars respectively) allow us to finely bin the data. Our samples range in brightness from the tip of the red-giant branch to several magnitudes below the cluster turnoff in the color-magnitude diagram. We find that there is no evidence for the ``subgiant excesses'' previously seen in metal-poor clusters, and we believe the previous results failed to adequately account for unresolved blends of stars near the cluster's turnoff in the color-magnitude diagram. Incorporation of \alpha-element enhancements into theoretical luminosity functions can explain the majority of the discrepancy between the observed and predicted positions of the red-giant clump, reducing the need for convective overshooting. We also find that for the metal-rich clusters the observations agree with theoretical predictions of the relative numbers of stars on the red-giant branch and main sequence. For the metal-poor clusters though, there are relatively more red giants (or alternately, fewer main sequence stars) than predicted. This result introduces the disturbing possibility that evolutionary timescales for the red-giant branch or main-sequence are not correctly predicted as a function of metallicity.
Program listing for Tuesday