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Session 80 - Star Clusters in the Milky Way.
Display session, Friday, January 09
Exhibit Hall,
We provide a comprehensive list of re-determinations of the values for the helium abundance indicators R =N_HB/N_RGB, A (the exponent of the mass-luminosity relation for RR Lyraes), and \Delta (the magnitude difference between the HB and the main sequence at (B-V)_0 = 0.7) for globular clusters in the Milky Way and Magellanic Clouds as well as nearby dwarf spheroidals. This study corrects a prevalent error in the determination of R, and provides a more comprehensive error analysis for all three indicators. We attempt to correlate the indicators to identify anomalous abundances in spite of shortcomings in each indicator. From the R determinations, we identify 6 clusters which show high values, possibly as a result of environmental factors --- each cluster has a galactocentric radius of less than 7 kpc, and 5 of the 6 appear to be post-core-collapse. From A values, all indications point toward a constant helium abundance of Y\approx0.23 for virtually all Oosterhoff class I clusters. In general, uncertainties in reddening determinations must be reduced in order to improve the worth of the \Delta indicator, which is the most sensitive to helium.
The author(s) of this abstract have provided an email address for comments about the abstract: erics@apollo.astro.nwu.edu
