AAS 199th meeting, Washington, DC, January 2002
Session 6. Binary Stars
Display, Monday, January 7, 2002, 9:20am-6:30pm, Exhibit Hall

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[6.07] Blue Straggler Binaries and Mass Transfer

B. W. Carney (UNC), D. W. Latham (CfA), J. B. Laird (Bowling Green State Univ.), C. E. Grant (MIT ), J. A. Morse (CASA)

We have monitored the radial velocities of ten candidate field blue stragglers for time spans ranging from 15.9 to 19.0 years, or until a binary orbital solution was obtained. Three of the candidate blue stragglers show no signs of velocity variation, one appears to be a very long-period binary, and the remaining six are single-lined spectroscopic binaries, with periods ranging from 167 to 844 days. The orbital eccentricities are all low, e < 0.30, and = 0.11. Five of the six binary orbits have very low eccentricities, with = 0.07. We have re-analyzed the velocity data from Preston & Sneden (2000) and have derived orbital solutions similar to theirs for ten of the spectroscopic binaries among their ``blue metal-poor'' stars with [Fe/H]~\leq -0.6. Our orbital solutions for their seven binaries with periods longer than 20 days all have low eccentricities, with e \leq 0.26 and = 0.11. Of the five binary stars in our program with published abundances of lithium, all have been found to be deficient. In contrast, two of the three apparently single stars have published lithium abundances and show no deficiency. The mass functions for the thirteen binaries in our program and that of Preston & Sneden (2000) are consistent with the unseen companions all being white dwarfs with M \approx 0.55~M\odot and random orbital inclinations. {\em Our results are consistent with all field blue stragglers being binary systems with long periods and low eccentricities, the primary stars being deficient in lithium and the secondary stars being normal-mass white dwarfs, indicating mass transfer is the cause of the phenomenon.}

We thank the NSF for support of this work at UNC and BGSU.

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