Physics of accretion onto young stars - III. Comparisons with observations

We present new evolutionary sequences for long lasting accreting low-mass ( 0.1 M. less than or equal to M less than or equal to 2.5 M.) pre-main seque nce stars. The calculations, performed for two different mass accretion rat es, show that accretion accelerates the evolution of the star. The star has a smaller radius and goes down its convective track faster than in a stand ard scheme. Consequently, the age of a star, as given by its location on th e Hertzsprung-Russell diagram, is lower than that of a non-accreting star. We discuss H-2 and Li-7 burning and show how accretion affects the surface abundance of these elements. Notably, we point out that deuterium must be p resent at the surface of accreting intermediate-mass stars. Finally, we est imate the age, mass and radius of a sample of T Tauri stars located in the Taurus Auriga star forming region.