A Complete Sample of Evolved Stars in the Globular Cluster M13 Within 10'

Details A Complete Sample of Evolved Stars in the Globular Cluster M13 Within 10' A Complete Sample of Evolved Stars in the Globular Cluster M13 Within 10'

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21344227s&link_type=abstract

American Astronomical Society, AAS Meeting #213, #442.27; Bulletin of the American Astronomical Society, Vol. 41, p.323

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Scientific paper

We have analyzed photometry from space- and ground-based cameras to identify
all bright red giant branch, horizontal branch, and asymptotic giant
branch stars within 10′ of the center of M13. Concerning the helium-sensitive R ratio, we apply our method for correcting star counts for longer lifetimes of hot horizontal branch stars, and find that M13's R ratio is in agreement with theoretical values for primordial helium abundance Y_P = 0.245 and inconsistent with an average helium enrichment as large as ΔY = 0.04. We discuss this in the context of other evidence implying enrichment of the majority of the cluster's stars. With regard to red
giant branch stars, we find that the numbers of stars on the lower red giant
branch and in the red giant bump agree very well with recent theoretical
models, although there are slight indications of a deficit of red giant stars above the bump and a ``heap'' feature similar to that identified in NGC 2808. We also use a combination of ultraviolet datasets to identify UV-bright post-HB stars and discuss their evolutionary tracks.
We gratefully acknowledge support from the National Science Foundation under grant AST-0507785.

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