The Origin and Evolution of the Light Elements D and 3He

by Sean Thomas Scully

Under the supervision of Professor Keith Olive

ABSTRACT

The evolution of the light elements D and 3He are examined in the context of galactic chemical evolution models. Recent measurements of D in quasar absorption systems yield two conflicting primordial abundances of D including both a high and a low value. New chemical evolution models must therefore necessarily be developed which are able to reproduce the observed abundances of D in the context of these new measurements. Chemical evolution models are developed which are capable of destroying a large amount of D in order to be consistent with the solar and present day observed values. Overproduction of metals associated with the increased stellar processing is avoided by introducing an outflow mechanism based on supernova-driven winds. The well-known problem of the overproduction of 3He using yields from standard stellar evolutionary models is examined in terms of non-standard chemical evolution models and additionally by incorporating new stellar yields which include the effects of rotational mixing in stellar evolution models to test whether the problem is one of chemical evolution or stellar evolution. In all models tests, critical examination is made of how well each model can reproduce other observational parameters such as the age-metallicity relationship, local gas fraction, and especially the paucity of metal poor dwarf stars in the solar neighborhood or the "G-Dwarf problem".