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Astron. Astrophys. 343, 904-908 (1999)

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On the gap in horizontal branches at B - V about zero

V. Caloi

Istituto di Astrofisica Spaziale CNR, Via Fosso del Cavaliere, I-00133 Roma, Italy (caloi@victoria.ias.rm.cnr.it)

Received 19 October 1998 / Accepted 3 December 1998


It is proposed that the gap observed in the horizontal branch sequence of many globular clusters at [FORMULA] about zero is due to a surface phenomenon. Stars on the hotter side of the gap - [FORMULA] [FORMULA] 10000 K - have an atmospheric chemical composition altered as in peculiar A and B stars. The appearance of a convective regime in the surface layers at the temperature and gravity of the gap cancel the peculiarities: it is proposed that the ensuing changes in surface physical conditions give origin to the observed gap.

Key words: Galaxy: globular clusters: general – stars: horizontal-branch – stars: chemically peculiar

Send offprint requests to: V. Caloi

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999