PHYSICS OF ACCRETION ONTO YOUNG STARS .1. PARAMETRIC MODELS

The article will present the influence of accreting material on the st ructure of young stars. We model accretion through a formalism based u pon the Richardson criterion which relates the power of buoyancy force s to the kinetic energy of turbulence. In our models we assume that in radiative regions matter is close to marginal stability and we genera lize this formalism to convective zones. We take into account the angu lar momentum as well as the thermal and chemical properties of the acc reted matter. We present figures that depict the profile of mass depos ition in the star. We study parametrically peculiar aspects of the acc retion physics such as how energy is transported through the accretion process or what is the effect of chemical composition differences bet ween the star and the accretion disk or what is the result of accretin g more or less angular momentum. The models show that very rapidly the accreted matter can reach the convective zone and eventually can be d ragged to the center of the star. This approach will be soon incorpora ted into evolutionary models of young stellar objects.