NEW RADIATIVE OPACITIES - THEIR INFLUENCE ON STELLAR MODELS

We investigate the influence of different assumptions about radiative opacity on the theoretical evolution of stellar structures in the rang e of low and intermediate mass stars. Selected evolutionary models wit h Z less-than-or-equal-to 0.02 have been evolved through H and He burn ing phases, in order to allow a comparison between models obtained on the basis of either the recent Livermore (OPAL) or the previous Los Al amos opacity tabulations (LAOL). Our main results are: (i) The use of OPAL produce appreciable variations of the evolutionary scenario only for stellar models having mass larger than 3M. (at Z = 0.02). (ii) In all cases, stellar properties depending on the physical structure of t he H or He burning cores are practically insensitive to the latest opa city computations. In particular, this is the case for lifetimes durin g both H and He burning phases. (iii) When a stellar model presents an extended radiative envelope (as for example during most of the centra l He burning of an intermediate mass stars) the use of the OPAL leads to significantly more faint models. This difference between models pro duced by means of new and old opacity decreases as the metallicity is decreased. (iv) Such differences can be largely eliminated by moderate ly increasing the true metallicity of LAOL models with respect to thei r nominal values.