On the Evoution of the Light Elements I. D, He-3, and He-4

Abstract

The light elements D, \he3, \he4, and \li7 are produced in big bang nucleosynthesis and undergo changes in their abundances due to galactic processing. Since one may observe most of these elements only in contemporary environments, knowledge of the intervening evolution is necessary for determining the observational constraints on primordial nucleosynthesis. Chemical and stellar evolution model dependences in light element evolution are systematically investigated via a comparison of 1460 possible chemical evolution scenarios and of stellar nucleosynthesis yields, all of which have been selected to fit solar neighborhood C, N, O, and Fe abundances as well as the observed local gas density and gas mass fraction. The light element evolution and solar system yields in these models are found to span a wide range, explicitly demonstrating the model dependence. The range of model dependence for D, \he3, and \he4 solar abundances is calculated, and its sensitivity to the heavy element constraints is noted. The chemical evolution contribution to the uncertainty in the observed primordial light element abundances is estimated, and the effects of this uncertainty on big bang nucleosynthesis results are discussed. The predictions for the light elements are found to be correlated; the extent and physical origin of these correlations is discussed. D and \he3 evolution is found to have significant model dependence, however, the dominant factor determining their solar and interstellar abundances is their primordial abundance. In addition, \he3 is found to be very sensitive to the details of processing in low mass stars. \he4 yields are shown to be very model dependent; in particular, both the introduction of mass loss and the possibly very high \he4 stellar yields in the