NEW MOLECULAR OPACITIES AND EFFECTIVE TEMPERATURE OF RGB STELLAR MODELS

Theroretical evolutionary sequences of low mass and metal poor stars h ave been computed by adopting the latest tabulations of molecular opac ity provided by Kurucz (1991), Neuforge (1993), Alexander & Ferguson ( 1994). The effects on the location of the theoretical Red Giant Branch due to different assumptions on the chemical composition and on the o uter boundary conditions, have been investigated. By comparing theoret ical RGBs and observational data (Frogel et al. 1983), an attempt has been made to obtain a calibration of the mixing length suitable for me tal poor low mass stars. Due to the inclusion of updated low temperatu re opacities, one finds that an evident correlation between mixing len gth and metallicity exists. Therefore, some evidence against the use o f the solar calibrated mixing length for non solar like stellar struct ures, is briefly discussed.