Henry This project will study the origin of Nitrogen using damped Lyman-alpha systems (DLAs) as probes of chemical evolution in the early Universe. The basic uncertainty is whether the principal contribution comes from slower-evolving stars which eject material via planetary nebulae and end as white dwarfs, or more massive stars which evolve rapidly and spread elements heavier than hydrogen and helium by ending with a supernova explosion. The difference in speed of these two processes is the key to the investigation: the time it takes a lower-mass star to distribute elements is a significant fraction of the age of DLAs, which are absorption-line systems of low metallicity and high redshift. The researcher will numerically calculate detailed chemical evolution models and compare them to observations provided by colleagues. Some especially well-observed DLAs will be used to constrain star formation histories. This study will also test ideas relating the distribution of DLA properties either to characteristics of the initial stellar mass function, or to the effects of Population III nucleosynthesis.
A significant contribution to astronomy will continue to be the critical evaluation of published stellar yields based on their predictive success, an activity for which this investigator is particularly noted. This work will affect our understanding of an abundant and biologically important element. The research will result in one doctoral dissertation and will enhance collaborations both in the US and abroad. ***
