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Session 25 - Stars in the Ultraviolet.
Display session, Tuesday, June 10
South Main Hall,

[25.04] Weighing Blue Stragglers in Globular Cluster Cores

R. A. Saffer (Villanova U.), M. M. Shara, M. Livio (STScI)

Hot, young blue straggler stars are observed by the Hubble Space Telescope to exist in the cores of very old globular clusters. Theory maintains that these stars must be more massive than hydrogen-burning cluster members as old as the clusters themselves. We have, for the first time, verified this theoretical claim by directly measuring the mass of a globular cluster core blue straggler. The derived mass, M = 1.7 \pm 0.4 M_ødot, is almost twice that of the oldest primordial hydrogen-burning cluster star. Furthermore, the star is found to be rotating rapidly, with a derived projected rotation velocity of v \sin i = 155 \pm 55 km s^-1. This large value for the rotation velocity tends to support the binary mass-transfer/merger hypothesis for blue straggler formation, rather than the physical stellar collision/merger hypothesis.

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Program listing for Tuesday