On the gap in horizontal branches at B - V about zero
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 about zero is due to a surface phenomenon. Stars on the hotter side of the gap - 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
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© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999