Discerning the Origins of Blue Stragglers: Masses and Rotation Rates

Details Discerning the Origins of Blue Stragglers: Masses and Rotation Rates Discerning the Origins of Blue Stragglers: Masses and Rotation Rates

Jul 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999hst..prop.8226s&link_type=abstract

HST Proposal ID #8226

Physics

Hst Proposal Id #8226 Hot Stars

Scientific paper

Conventional wisdom holds that the masses of Blue Straggler Stars {BSS} in globular clusters {GCs} are significantly larger than the turnoff mass. We have, for the first time, supported this theoretical claim by directly measuring the mass of the blue straggler BSS-19 in the core of 47 Tuc to be M = 1.7 +/- 0.4 M{sun}, nearly twice that of the oldest core- hydrogen burning cluster star {Shara et al. 1997, ApJ, 489, L59}. Observations reveal that the BSS in Galactic open clusters have low rotation velocities. However, we also have found that BSS-19 is rotating rapidly, with a measured projected rotation velocity v sin i = 155 +/- 55 kms. We propose to obtain STIS spectroscopy of 20 BSS in each of the GCs 47 Tuc, M 3, and NGC 6752, in order to measure accurate masses and rotation rates. The mass distributions will test the most basic assumption about BSS, namely, that massive stars with lifetimes <= 10^9 yr are continuously forming {probably by coalescence} in the oldest {gta 10^10 yr} objects in the universe. Together, the mass and rotation velocity distributions will distinguish between collisional and close binary coalescence scenarios. Our proposed observations will definitively constrain theories of BSS formation in GCs.

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