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
Received 16 July 1999 / Accepted 3 December 1999
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 (firstname.lastname@example.org)
This article contains no SIMBAD objects.
© European Southern Observatory (ESO) 2000
Online publication: January 31, 2000