Rotation and Oxygen Abundances of Horizontal Branch Stars

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Peterson, Ruth AST 96-18502 Dr. Peterson will explore the influence stellar internal rotation and oxygen abundance have on a star's properties during the core-He burning phase of evolution (the Horizontal Branch phase). Although overall metallicity is a primary factor controlling the location of a star on the Horizontal Branch, it is clear there is a 'second' parameter that also influences its position. Many physical variables have been proposed for the second parameter - age, helium, oxygen, and carbon abundances, rotation, and other parameters that control the amount of mass loss - but no single 'second' parameter has been clearly identified. Dr. Peterson proposes to continue investigations into the effects of oxygen abundance and rotation in a larger sample of stars and globular clusters to map the influence of these parameters. New observations and the analysis of observations in hand will delineate trends in stellar rotation and oxygen abundances across a wide range of cluster metallicity, HB morphology and concentration, as well as provide more extensive samples within selected clusters. ***