Exploring the Stellar Content of the Galactic Halo

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In the past decade there has been a revolution in our ability to carry out detailed abundance analyses of stars in the Galactic halo, distant Milky Way globular clusters, and the satellite galaxies of the Milky Way, because, prior to the current generation of large telescopes and efficient spectrographs, these stars were too faint for high dispersion spectroscopy. Under this award, Dr. Judith Cohen (California Institute of Technology) will carry out a study of the chemical evolution of the halo of the Milky Way galaxy in detail, taking advantage of this tremendous advance in technology as well as leveraging off her previous, NSF-supported efforts, in which large samples of extremely metal-poor stars were identified. The elemental abundance patterns in these halo stars, both in the field and in the globular clusters, have direct implications for the early epochs of our Galaxy, the onset of chemical evolution of the Galaxy, the possible stellar sources which produced many elements at very early epochs (very massive stars and Type II supernovae), the age of the Galaxy, the relationship between the halo field stars and the galactic globular clusters, and the composition of the interstellar medium and the intergalactic medium. Such stars provide a chance to study the general chemical abundances in local material representing the high redshift Universe. Through this research, new insight will be gained into the relationship between the Galactic stellar halo and the satellite galaxies around the Milky Way, both as seen now and in the distant past.Under this award Dr. Cohen will also continue to be dedicated to the development of young scientists, particularly women and minorities, by providing valuable research experiences for undergraduates. In addition, lectures, both for the general public and at primarily undergraduate institutions, will continue. Dr. Cohen also will produce an exhibit intended for the general public in the lobby of the Cahill Center for Astronomy and Astrophysics, located on the campus of Caltech.