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2000ApJ...538..289Z - Astrophys. J., 538, 289-294 (2000/July-3)
On the helium content of galactic globular clusters via the r-parameter.
ZOCCALI M., CASSISI S., BONO G., PIOTTO G., RICH R.M. and DJORGOVSKI S.G.
Abstract (from CDS):
The trend in the R-parameter toward solar metallicity is consistent with an upper limit to the He-to-metal enrichment ratio of the order of 2.5. Detailed calculations of central He burning times as a function of the horizontal-branch (HB) morphology suggest that He lifetimes for hot HB stars are on average ~20% longer than for RR Lyrae and red HB stars. Therefore, the increase in the empirical R-values of metal-poor clusters characterized by blue HB morphologies is due to an increase in the HB lifetime and not due to an increase in the He abundance.
Abstract Copyright: ∼
Journal keyword(s): Galaxy: Globular Clusters: General - Stars: Abundances - Stars: Evolution - Stars: Horizontal-Branch
Simbad objects: 30
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