Rapid Rotation of UltraLi-depleted Halo Stars and Their Association with Blue Stragglers

摘要

Observations of 18 halo main-sequence turnoff stars, four of which are extremely deficient in Li, show that three of the Li-poor ones have substantial line broadening. We attribute this to stellar rotation. Despite the great ages of halo stars, for G202-65, BD +51 deg 1817, and Wolf 550 we infer v sin i = 8.3 ± 0.4, 7.6 ± 0.3, and 5.5 ± 0.6 km s~-1, respectively. The stated errors are 3 α. For CD -31 deg 19466 we derive a 3 αupper limit v sin i < 2.2 km s~-1. The three rotating stars are known spectroscopic binaries. We explain the high rotation velocities in terms of mass and angular momentum transfer onto the surface of the turnoff star from an ini- tially more massive donor.