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Astron. Astrophys. 349, 834-838 (1999)

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Theoretical zero age main sequences revisited

V. Castellani 1, S. Degl'Innocenti 1,2 and M. Marconi 3

1 Dipartimento di Fisica, Universitá di Pisa, piazza Torricelli 2, I-56126 Pisa, Italy
2 Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara, via Paradiso 12, I-44100 Ferrara, Italy
3 Osservatorio Astronomico di Capodimonte, via Moiariello 16, I-80131 Napoli, Italy

Received 7 December 1998 / Accepted 22 July 1999


Zero Age Main Sequence (ZAMS) models with updated physical inputs are presented for selected assumptions about the chemical composition, covering the ranges 0.6 [FORMULA] M [FORMULA] 1.2 [FORMULA], 0.0001 [FORMULA] Z [FORMULA] 0.04, 0.23 [FORMULA] Y [FORMULA] 0.34. The HR diagram location of the ZAMS as a function of Y and Z is discussed both in the theoretical (logL, logTeff) and in the observational (Mv, B-V) diagrams, showing that the V magnitude presents an increased dependence on Z to be taken into account when discussing observational evidences. Analytical relations quantifying both these dependences are derived. Implications for the galactic helium to heavier elements enrichment [FORMULA]Y/[FORMULA]Z are finally discussed.

Key words: stars: general – stars: Hertzsprung – Russel (HR) and C-M diagrams

Send offprint requests to: S. Degl'Innocenti, Dipartimento di Fisica Università di Pisa, piazza Torricelli 2, I-56126 Pisa, Italy (scilla@astr18pi.difi.unipi.it)

© European Southern Observatory (ESO) 1999

Online publication: September 13, 1999