EDP Sciences
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Volume 366, Number 1, January IV 2001
Page(s) 91 - 99
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20000210

A&A 366, 91-99 (2001)
DOI: 10.1051/0004-6361:20000210

Mixing, enhanced helium and blue tails in globular clusters

V. Caloi

Istituto di Astrofisica Spaziale C.N.R., Via Fosso del Cavaliere, 00133 Roma, Italy

(Received 14 September 2000 / Accepted 6 November 2000 )

We investigate the consequences of an increase in the envelope helium abundance of pre-helium flash red giants in globular clusters, an occurrence suggested by chemical peculiarities in many red giant atmospheres. Comparing predictions with the CM diagrams of a few crucial globular clusters, one finds no evidence for a substantial increase in the surface helium content of horizontal branch members of these clusters, at least for objects in the RR Lyrae region or close to it. The possibility that the most peculiar giants belong to the asymptotic giant branch is discussed. The consequences of a delay in the helium flash are briefly examined.

Key words: stars: horizontal branch -- stars: AGB and post-AGB -- globular clusters: general -- stars: chemically peculiar

Offprint request: V. Caloi, caloi@saturn.ias.rm.cnr.it

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