The Composition of Stars and Star Clusters in the Galaxy

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One of the most basic questions astronomers are asked by the layman is "where did the atoms composing the Earth and our bodies" come from?" Indeed during the last generation astronomers have put a great deal of work into answering this question by mapping the enrichment of interstellar gas by heavy element atoms from stellar explosions that occur after these atoms are formed from hydrogen by complex nucleosynthetic reactions in the deep interiors of highly evolved stars. Although earlier work concentrated on determining the chemical abundance of the iron group elements, recent investigations have shown that the iron-group abundance enhancements did not start until comparatively late in the history of the Galaxy. Better indicators of enrichment during the early era (including the first hour after the Big Bang) are provided by the elements oxygen, carbon, and beryllium. The oldest stars betray this history best, but they are faint and difficult to observe. Moreover, the absorption line leading to abundance determinations of beryllium is located in the ultraviolet part of the spectrum that is inaccessible to Earth-based astronomers except in high mountain, low-latitude observatories such as Mauna Kea in Hawaii. The Principal Investigator (PI) has been active in studying chemical evolution studies of old stars in the Galaxy for years and will extend her investigation to the faint halo stars in the Galaxy with this three year award. Recent advances in detector technology should also permit the PI to obtain not only more accurate abundances but also to sample the chemical evolution in stars that were formed during the original collapse of the Galaxy from a proto-galactic cloud. The abundance results for beryllium may also permit a more constrained model of the Big Bang to be developed.