Physics of accretion onto young stars .1. Parametric models

The article will present the influence of accreting material on the structure of young stars. We model accretion through a formalism based upon the Richardson criterion which relates the power of buoyancy forces to the kinetic energy of turbulence. In our models we assume that in radiative regions matter is close to marginal stability and we generalize this formalism to convective zones. We take into account the angular momentum as well as the thermal and chemical properties of the accreted matter. We present figures that depict the profile of mass deposition in the star. We study parametrically peculiar aspects of the accretion physics such as how energy is transported through the accretion process or what is the effect of chemical composition differences between the star and the accretion disk or what is the result of accreting more or less angular momentum. The models show that very rapidly the accreted matter can reach the convective zone and eventually can be dragged to the center of the star. This approach will be soon incorporated into evolutionary models of young stellar objects.