The Origins and Binary Properties of Subdwarf B Stars

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Green, Elizabeth" The Origins and Binary Properties of Subdwarf B Stars "AST- 0098699Subdwarf B stars are among the brightest of highly evolved stars. The suggested binary star origin for most of them becomes important in several diverse areas of contemporary astrophysics ranging from stellar population studies in external galaxies to the common envelope evolution in interacting binary stars. This award is for continuing work in obtaining the remaining observations necessary for determining the binary properties and for comparing these properties with theoretical expectations. An extensive spectroscopic program is planned using University of Arizona observing facilities. Most studies to date concern binary stars with the largest velocity amplitude. To fully understand the range of possible orbital parameters, the new observations will be directed towards a kinematically unbiased sample. Once the orbital ephemerides are known, precise photometric monitoring will be carried out in order to search for eclipses, reflection effects and ellipsoidal variations that will put additional constraints on the binary star parameters.