Observational constraints of light element nucleosynthesis

Abstract

Enhanced deuterium was not detected in the metal-poor halo stars HD 140283, the protoplanetary nebula AFGL 2688, or the Orion nebula. The Galactic Center (GC) deuterium abundance in the 50 km/s molecular cloud is (2.0–10)×10 −6 and less than the local ISM D H = (0.9–1.7)×10 −5 . Thus the GC D results from infall of primordial halo matter combined with astration. The GC has not had an extended period (> 1Gyr) AGN activity, a large cosmic-ray luminosity (< 10 38 W), or a large γ-ray flux luminosity (< 10 35 W). Because there are no Galactic sources of D, the primordial D H ∼ 10 −4 . Therefore big-bang nucleosynthesis models predict a baryon density less than the critical density necessary to close the Universe in a flat Einstein de-Sitter Universe with < four neutrino families. Li and B (ISM Li H = 2×10 −9 and B H = 2.5 × 10 −10 ) are produced via cosmic-ray spallation reactions and possibly ν reactions in supernova envelopes. Li is also produced via mass loss from super-Li-rich red giants ( Li H = 3×10 −6 ) but LiCl and LiNC were not detected in the circumstellar envelope of the super-Li-rich C star IY Hya nor in the molecular envelope of the protoplanetary nebula AFGL 2688. These results can be explained if the circumstellar cloud formed prior to the SLR phase and the PN formed after the SLR phase. Enhanced Li and B abundances (expected from stellar activity) were not detected in the Galactic Center with Li H ⩽ 3.9 × 10 −8 and B H ⩽ 2.7 × 10 −6 so that the time-integrated cosmic-ray p flux is not enhanced by more than 100 times over the Galactic disk value.