Mathematics – Logic
Scientific paper
May 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aps..may..e504k&link_type=abstract
American Physical Society, APS/AAPT Joint Meeting, May 2-5, 1996, abstract #E5.04
Mathematics
Logic
Scientific paper
The primordial isotopic abundances of hydrogen, helium, and lithium provide an important test of big-bang nucleosynthesis (BBN) theory and constraints on the baryonic density of the universe. Recent advances in astronomical instrumentation, including the advent of the Keck 10m telescope and the Hubble Space Telescope (HST), have provided tighter measurements of these abundances and stimulated a re-examination of the standard BBN model in the light of these new data. This talk will review recent measurements of the cosmic abundances of D, ^4He, ^3He, and ^7Li and their implications for the cosmological baryon density and BBN. Recent observations of deuterium in the local interstellar medium with HST and in high-redshift intergalactic clouds with Keck have substantially reduced the uncertainty in the D/H value and provide better estimates of the effects of stellar processing on the measured abundance. Progress has also been made in the empirical determination of the primordial He and Li abundances, as measured from metal-poor ionized gas clouds and stars, respectively. Most of the remaining errors in these measurements are systematic in nature, involving uncertainties in line blending (D), atomic emissivities and ionization corrections (^4He), and in the effects of stellar processing on the observed abundance ratios (all species). Recent disagreements in the literature over the validity of the standard BBN model rest critically on how these systematic errors are estimated and propagated. A conservative assessment of the uncertainties suggests that the measured abundances are consistent with the standard model (N_ν = 3) for a reasonable range of baryonic densities. Future improvements in the measurement of D/H and ^4He/H should provide an incisive test of the standard model and definitive limits on the cosmological nucleon-to-photon ratio and baryon density.
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