Ratio of Horizontal Branch Stars to Red Giant Stars in Globular Clusters

FOR any globular cluster, an observationally estimated number ratio N HB / N RG can be compared with a theoretically estimated lifetime ratio t HB / t RG to obtain an estimate of the initial abundance of helium which characterizes cluster stars. Here N HB is the total number of stars along the horiz...

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Bibliographic Details
Published in:Nature (London) 1969-01, Vol.224 (5223), p.1006-1008
Main Authors: IBEN, ICKO, ROOD, ROBERT T, STROM, KAREN M, STROM, STEPHEN E
Format: Article
Language:English
Subjects:
Humanities and Social Sciences
letter
multidisciplinary
Science
Science (multidisciplinary)
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Summary:FOR any globular cluster, an observationally estimated number ratio N HB / N RG can be compared with a theoretically estimated lifetime ratio t HB / t RG to obtain an estimate of the initial abundance of helium which characterizes cluster stars. Here N HB is the total number of stars along the horizontal branch and N RG is the number of those stars along the red giant branch that are as bright as or brighter than the horizontal branch at roughly the level of the RR Lyrae stars that lie directly above cluster turnoff. The ratio of relevant lifetimes is a moderately strong function of helium abundance 1 that varies 2 from about 0.4 when Y (helium abundance by mass) ∼0.1 to about 1 when Y ∼ 0.3.
ISSN:0028-0836
1476-4687
DOI:10.1038/2241006a0