Asymptotic Giant Branch predictions: Theoretical uncertainties

¹ Osservatorio Astronomico di Collurania, via M. Maggini, 64100 Teramo, Italy
² Dipartimento di Fisica, Universitá di Pisa, Piazza Torricelli 2, 56126 Pisa, Italy
³ Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, via Livornese 582/A, S. Piero a Grado, 56010 Pisa, Italy
⁴ Dipartimento di Astronomia, Universitá di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
⁵ Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead L41 1LD, UK

Corresponding author: S. Degl'Innocenti, scilla@astr18pi.difi.unipi.it

Received: 27 June 2000
Accepted: 9 November 2000

Abstract

In this paper we investigate the level of agreement between observations and "new" Asymptotic Giant Branch (AGB) models, as produced by updating the physical inputs adopted in previous stellar computations. One finds that the new physics increases the predicted luminosity of Horizontal Branch (HB) and AGB stellar structures by a similar amount, keeping unchanged the predictions about the difference in luminosity between these two evolutionary phases. The best fit of selected globular clusters appears rather satisfactory, disclosing the relevance of the assumption on the mass of the Red Giant Branch (RGB) progenitor in assessing the distance modulus of moderately metal rich clusters. The still existing uncertainties related either to the input physics or to the efficiency of some macroscopic mechanisms, like convection or microscopic diffusion, are critically discussed, ruling out the occurrence of the so called "breathing pulses" during the central He exhaustion, in agreement with earlier suggestions.