Deuterium, lithium, and the Hubble Deep Field

This article presents a theoretical framework for the evolution of the ligh t-element nuclides in the Galactic disk. By understanding this evolution co rrectly, we can reliably obtain the primordial abundances of the nuclides D , He-4, and Li-7. We use two key assumptions, those of (1) infall of metal- poor gas to the disk at an increasing rate and (2) destruction, as well as production (except for D), of fragile nuclides in hot, relatively dense sup ergiant envelopes. Light nuclides are accelerated by supernova shocks, and many are confined to hot interstellar zones by magnetic fields. Their repea ted passage through the hot envelopes causes depletion, which peaked during the main star-forming phase of Galaxy evolution around z approximate to 1, as measured from the Hubble Deep Field. This mechanism has dominated stell ar depletion in reducing the D/H abundance from its primordial value of sim ilar or equal to 2 x 10(-4) to its solar system value of similar or equal t o 2.5 x 10(-5) and subsequently to the current interstellar medium value of 1.5 x 10-5 The model accounts well for the solar system and the current ra tios of Li-7/Li-6 and B-11/B-10. It fits extremely well a standard big bang nucleosynthesis model with baryon density similar or equal to 0.05.