Observational Tests of Mixing in Low Mass Stars

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9624680 Briley A program of research in stellar spectroscopy and photometry will be carried out. The research efforts are specifically targeted at providing observational constraints on the chemical abundance modifying mechanisms believed to be operating in evolving low mass stars. The objects to be observed will include galactic globular cluster stars. These stars are known to vary in their light-element abundances. Stars which are in evolving members of old open clusters of stars will also be observed. These types of stars are the among the brightest stars and are most often observed to obtain data for use in chemical abundance determinations. An understanding of the processes which alter the distribution of important elements, such as oxygen and lithium, from their primordial values is required before conclusions can be drawn regarding the chemical history of our galaxy. In collaboration with researchers at other institutions, a series of observational programs will be pursued which will use some of the most recent techniques in astronomical instrumentation. The programs include: 1) A study of isotopic carbon and other light element abundances in cluster stars as probes of deep mixing in the stars and to obtain the sensitivity of the mixing mechanism to stellar mass and composition. 2) The determination of the location of the onset of mixing in moderately metal-poor globular cluster stars. 3) Measurement and analysis of ultaviolet wavelength Nitrogen Hydride (NH) band strengths among bright globular cluster stars to directly determine nitrogen abundances (a crucial input required to assess the role of deep mixing). 4) Placing constraints on the limits of primordial oxygen variations in the globular clusters through the widths of their color-magnitude diagrams. The development of collaborative programs with scientists at other institutions to obtain data, with local reduction and analysis of the data, benefits not only the resident faculty (by stimulating profess ional growth), but also benefits the undergraduate students through early exposure to fundamental research. As a complement to the research projects, a course in basic astrophysics (stellar atmospheres and interiors) is being developed for the Physics/Astronomy Department. A series of animations of complex astrophysical processes will be developed, using current stellar model atmospheres, as a supplement to the course. The resulting animations will be developed in the Mpeg format and made available to other teachers over the Internet. ***