GENERIC EVOLUTION OF DEUTERIUM AND HE-3

The primordial abundances of deuterium and of He-3, produced during bi g bang nucleosynthesis, depend sensitively on the baryon density. Thus , the observed abundances of D and He-3 may provide useful ''baryomete rs'' provided the evolution from primordial to present (or, presolar n ebula) abundances is understood. Inevitably, the derivation of primord ial from observed abundances requires the intervention of a model for galactic evolution and, so, the inferred primordial abundances are, ne cessarily, model-dependent. Here, an analytic framework for the evolut ion of D and He-3 is presented which is ''generic'' in the sense that it should describe the results of any specific galactic evolution mode l. The ''effective He-3 survival fraction'' Gamma(3), is the one free parameter which is model-specific. Solar system and interstellar data are used to infer upper and lower bounds to the primordial deuterium m ass fraction (X(2P)) as a function of Gamma(3), and these bounds are u sed to constrain the present baryon-to-photon ratio (eta) and baryon d ensity (Omega(R)). For Gamma(3) greater than or equal to 1/4 it is fou nd that (from D and He-3 alone): 3.1 less than or equal to eta(10)less than or equal to 9.0; 0.045 less than or equal to Omega(R)h(50)(2) le ss than or equal to 0.133(where H-0 = 50h(50) km s(-1) Mpc(-1)).