Physics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt.........7f&link_type=abstract
PhD Dissertation, Chicago Univ. Chicago, IL United States
Physics
1
Helium Isotopes, Light Elements, Nuclear Fusion, Chemical Evolution, Lithium Isotopes, Abundance, Solar Neighborhood, Metallicity
Scientific paper
The light elements D, He-3, He-4, and Li-7 are produced in big bang nucleosynthesis (BBN) 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, He-3 and He-4 solar abundances is calculated, and the sensitivity of this range to the heavy element constraints is noted. The predictions for the light elements are found to be correlated; the extent and physical origin of these correlations is discussed. D and He-3 evolution is found to have significant model dependence, however, the dominant factor determining their solar and interstellar abundances is their primordial abundance. In addition, He-3 is found to be very sensitive to the details of processing in low mass stars. He-4 yields are shown to be very model dependent; in particular, both the introduction of mass loss and the possibly very high He-4 stellar yields in the poorly understood mass range of approximately 8-12 solar mass can lead to large enhancement of He-4 production and can lead to large slopes of (Delta Y)/(Delta N) and (Delta Y)/(Delta O). It is found that the inclusion of secondary nitrogen leads to only a small distortion in the low metallicity Y - N relation if there is also a significant contribution of primary N, as demanded by observations.
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