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Astron. Astrophys. 354, 150-156 (2000)

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The puzzling theoretical predictions for the luminosity of clumping He burning stars

V. Castellani 1,2, S. Degl'Innocenti 1,2, L. Girardi 3, M. Marconi 4, P.G. Prada Moroni 1 and A. Weiss 5

1 Dipartimento di Fisica, Universitá di Pisa, piazza Torricelli 2, 56126 Pisa, Italy
2 Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, via Livornese 1291, 56010 S. Piero a Grado, Pisa, Italy
3 Dipartimento di Astronomia, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
4 Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
5 Max-Planck-Institut für Astrophysik, K. Schwarzschild Strasse 1, 85740 Garching bei München, Germany

Received 16 July 1999 / Accepted 3 December 1999

Abstract

This paper deals with theoretical predictions for He burning models in a range of masses covering the so-called Red Giant Branch phase transition. Taking as a guideline the observational constraints given by Hipparcos parallaxes to the predicted luminosity of models originated from Red Giant progenitors with He core undergoing electron degeneracy, we compare models by various authors as recently appeared in the literature, disclosing sensitive differences in the predicted luminosity. The "solidity" of these theoretical predictions is investigated by exploring the effects of varying the assumptions about the efficiency of core overshooting or the amount of mass loss, giving quantitative estimates of the related uncertainties. However, one finds that theoretical predictions concerning the luminosity of the red giant clump in the Hipparcos sample is scarcely affected by these mechanisms. A comparison among theoretical predictions as recently given by different authors convincingly demonstrates that the different luminosity predictions are the natural results of evolutionary codes with different - but all reasonable- input physics. In this context observations suggests that stellar models based on the "most updated" input physics are possibly overestimating the luminosity of these structures, raising doubts on several current predictions concerning the luminosity of HB stars in galactic globulars.

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

Send offprint requests to: S. Degl'Innocenti (scilla@astr18pi.difi.unipi.it)

This article contains no SIMBAD objects.

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© European Southern Observatory (ESO) 2000

Online publication: January 31, 2000
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