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

This paper deals with theoretical predictions for He burning models in a ra nge of masses covering the so-called Red Giant Branch phase transition. Tak ing as a guideline the observational constraints given by Hipparcos paralla xes to the predicted luminosity of models originated from Red Giant progeni tors with He core undergoing electron degeneracy, we compare models by vari ous authors as recently appeared in the literature, disclosing sensitive di fferences in the predicted luminosity. The "solidity" of these theoretical predictions is investigated by exploring the effects of varying the assumpt ions about the efficiency of core overshooting or the amount of mass loss, giving quantitative estimates of the related uncertainties. However, one fi nds 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 aut hors convincingly demonstrates that the different luminosity predictions ar e the natural results of evolutionary codes with different - but all reason able-input physics. In this context observations suggests that stellar mode ls based on the "most updated" input physics are possibly overestimating th e luminosity of these structures, raising doubts on several current predict ions concerning the luminosity of HE stars in galactic globulars.