The Blue Stragglers: At the Interface of Stellar Evolution and Stellar Dynamics

Type Conference Paper
Names Robert D. Mathieu
Proceedings Title AIP Conference Proceedings
Conference Name International Conference on Binaries: In Celebration of Ron Webbink's 65th Birthday
Place Melville, NY
Publisher American Institute of Physics
Volume 1314
Pages 95-104
Series 95-104
Date December 1, 2010
Short Title The Blue Stragglers
Library Catalog NASA ADS
Abstract Recent extensive radial-velocity surveys of old open clusters have revealed rich spectroscopic binary populations among the blue stragglers. The WIYN Open Cluster Survey of NGC 188 in particular has shown among the blue stragglers: i) a high binary frequency of 76+/-19% (as compared to 23+/-3% for the solar-type main sequence stars) ii) a concentration of orbital periods around P~1000 days, with a range of eccentricities that includes e~0 iii) at least 40% rotating faster (vsin i~10-50 km/s) than old main-sequence stars of similar surface temperature; iv) a bi-modal spatial distribution with distinct core and halo populations; v) underluminosity for their masses. The very high binary frequency points definitively to an origin in multiple-star systems for most of the NGC188 blue stragglers. In fact, triple systems may play a crucial role in the formation of blue stragglers, perhaps through Kozai processes or through enhancing the rates of dynamical encounters for very hard binaries Finally, if the internal structure, magnetic fields and winds of blue stragglers mimic normal main-sequence stars, with commensurate spin-down times, then our finding that some blue stragglers have not yet spun down can place upper limits on their ages.
Tags BINARY STARS, BRIGHTNESS, Black holes, ECLIPSING BINARY STARS, Eclipsing binaries, Luminosities, STELLAR EVOLUTION, Spectroscopic binaries, and spectral classification, close binaries, colors, effective temperatures, magnitudes
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