Evolution of deuterium, He and He in the Galaxy

¹ Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italia
² Dipartimento di Astronomia, Universita' degli Studi di Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italia

Corresponding author: C. Chiappini, chiappini@ts.astro.it

Received: 8 July 2002
Accepted: 5 September 2002

Abstract

In this work we present the predictions of the “two-infall model” concerning the evolution of D, ³He and ⁴He in the solar vicinity, as well as their distribution along the Galactic disk. Our results show that, when adopting detailed yields taking into account the extra-mixing process in low and intermediate mass stars, the problem of the overproduction of ³He by the chemical evolution models is solved. The predicted distribution of ³He along the disk is also in agreement with the observations. We also predict the distributions of D/H, D/O and D/N along the disk, in particular D abundances close to the primordial value are predicted in the outer regions of the Galaxy. The predicted D/H, D/O and D/N abundances in the local interstellar medium are in agreement with the mean values observed by the Far Ultraviolet Spectroscopic Explorer mission, although a large spread in the D abundance is present in the data. Finally, by means of our chemical evolution model, we can constrain the primordial value of the deuterium abundance, and we find a value of (D/H) which implies 0.017, in agreement with the values from the Cosmic Microwave Background radiation analysis. This value in turn implies a primordial ⁴He abundance 0.244.