Mixing, Metallicity, and Binaries on the Blue Horizontal Branch

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"Mixing, Metallicity, and Binaries on the Blue Horizontal Branch"AST-0098725Many changes happen to a star in the late stages of its evolution. With this award, the PI seeks to unravel the effects of deep interior mixing, mass loss, mass exchange and diffusion on the atmospheric abundances of blue horizontal branch stars. It has long been known that the blue horizontal branch can take on a very different appearance in globular clusters which seem at first sight to be very similar chemically. Strongest emphasis in the forthcoming work will be given to investigating the role of deep helium mixing and its causes. Work to date shows evidence that it does occur in two cases, in NGC6752 blue horizontal branch star which are cool enough for their atmospheres not to be influenced by diffusion, and in single extended horizontal branch stars which show C,N,O abundances that are correlated in the same way as in giant stars and are thus expected to have resulted from deep mixing. However, to reinforce this case, blue stars covering a much larger range of temperature are to be observed.