Dr. Sneden and his team study the chemical compositions of stars in the Milky Way's disk and halo, which hold clues to the birth and evolution of our Galaxy. This work combines medium to high resolution spectroscopic observations, careful abundance analyses, and improved laboratory atomic physics data to determine accurate abundance data for large samples of halo and disk field and cluster stars that provide insights on the chemical evolution of our Galaxy.
The analysis of large samples will provide more statistically robust samples to understand what really has happened to build the Milky Way's heavy element content from virtually zero to the present metal-rich solar chemical composition. The study of Galactic chemical evolution is done through four different but connected tasks here.
First, a new large-sample of neutron-capture elemental abundances in very metal-poor halo population field stars is studied. This greatly expands the analyzed stellar sample, while limiting the abundance set to four key elements that can be detected in the spectra of very low metallicity stars. This is used to track the range of element production that can occur in rapid-blast neutron-capture nucleosynthetic environments.
Second, the metallicity and elemental abundance ratios of hundreds to thousands individual globular cluster stars are surveyed to obtain spectra over an extremely large evolution and luminosity range, from the cluster main sequences to the tips of their red giant branches. In one approach, multi-object spectra with limited wavelength coverage of hundreds-thousands of stars in a few globular clusters will be taken to check whether consistent metallicities and abundance ratios of iron-group elements can be obtained from all stars of a cluster. Any luminosity dependent variations could call into question the underlying assumptions in standard chemical composition analyses. In another approach, multi-object spectra of large wavelength coverage of stars over large luminosity ranges in many more globular clusters are used to test the theories of production of the light volatile elements in these self-contained stellar systems.
Third, a new survey of metallicities, CNO abundances, and carbon isotope (12C/13C) ratios is undertaken for evolved stars of Galactic open clusters. The approach here combines for the first time coverage of spectral features in both the visible and infrared spectral regions , in order to obtain accurate abundances of H-burning products in stars up and down the red giant branches of individual clusters. These in turn provide more complete descriptions of evolution and mixing in metal-rich disk stellar systems.
Fourth, continued laboratory and stellar studies of iron-group element transitions in the Sun and in metal-poor stars are conducted to bring heightened accuracy to basic stellar abundance analyses.
There is continued development and free dissemination of computer codes and atomic line data to the world-wide community of stellar spectroscopists. Emphasis is placed on significant changes to the computer codes to perform chemical composition analyses automatically. As part of this project, an ongoing program involving a secondary-school educator group will be expanded, with new emphasis on remote observing opportunities for the educators.
