Surface Abundances of NGC 188 Blue Stragglers as a Clue to Formation History
American Astronomical Society, AAS Meeting #222, #214.05
Published in Jun 2013
Studies of the old open cluster NGC 188 have discovered a blue straggler binary frequency nearly three times the binary fraction of main-sequence stars, and a secondary mass distribution peaking at 0.5 solar masses for long-period blue stragglers. These features suggest that asymptotic giant branch mass transfer in binary stars dominates the production of blue stragglers in open clusters. However, sophisticated N-body simulations point toward stellar collisions being the dominant formation process. These two mechanisms are expected to result in measurably different blue straggler surface abundances. Blue stragglers resulting from stellar collisions of main-sequence stars are predicted to retain roughly the same surface abundance as the more massive star in the collision. On the other hand, blue stragglers formed by mass transfer from an evolved companion will have a surface abundance altered by the nucleosynthesis that occurred within the evolved donor star. We present first results of a surface abundance study of 21 blue stragglers in NGC 188 using the Hydra multi-object spectrograph on the WIYN 3.5 m telescope. These results include measurements of barium, oxygen, and carbon and offer a clue to the formation history of blue stragglers in open clusters. We gratefully acknowledge funding from the National Science Foundation under grant AST-0908082.
(c) 2013: American Astronomical Society