The evolution of 3He, 4He and D in the galaxy

In this work we present the predictions of a modified version of the "two-infall model" (Chiappini et al. 1997 - CMG) for the evolution of He-3, He-4 and D in the solar vicinity, as well as their distributions along the Galactic disk. In particular, we show that when allowing for extra-mixing process in low mass stars (M < 2.5 M.), as predicted by Charbonnel and do Nascimento (1998), a long standing problem in chemical evolution is solved, namely: the overproduction of He-3 by the chemical evolution models as compared to the observed values in the sun and in the interstellar medium. Moreover, we show that chemical evolution models can constrain the primordial value of the deuterium abundance and that a value of (D/H)(p) < 3 x 10(-5) is suggested by the present model. Finally, adopting the primordial He-4 abundance suggested by Viegas et al. (1999), we obtain a value for DeltaY/DeltaZ similar or equal to 2 and a butter agreement with the solar He-4 abundance.