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Astron. Astrophys. 317, 108-113 (1997)

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Intermediate-age metal deficient stellar populations:
the case of metallicity Z=0.00001

S. Cassisi 1, 2, M. Castellani 3 and V. Castellani 1, 4

1 Osservatorio Astronomico Collurania,Via Mentore Maggini, I-64100 Teramo, Italy
2 Universitá de L'Aquila, Dipartimento di Fisica, Via Vetoio, I-67010 L'Aquila, Italy
3 Universitá "La Sapienza", Istituto Astronomico, Via Lancisi 29, I-00161 Roma, Italy
4 Universitá di Pisa, Dipartimento di Fisica, Piazza Torricelli 2, I-56100 Pisa, Italy

Received 3 August 1995 / Accepted 20 April 1996

Abstract

We investigate the evolution of metal deficient stars, presenting H-burning isochrones covering cluster ages from 800 Myr to 7 Gyr. Evolutionary evidences for selection effects in the metallicity distribution of very metal poor H-burning red giants are reported. The evolution of stars during central and shell He burning is further investigated, discussing the occurrence of He burning pulsators as a function of cluster age.

Key words: stars: evolution — stars: HR diagram — stars: horizontal branch — stars: Population II — galaxies: stellar content

Send offprint requests to: S. Cassisi

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© European Southern Observatory (ESO) 1997

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