Formation and Evolution of Blue Stragglers in 47 Tucanae

Publication Type
Journal Article
Year of Publication
Harvey Richer
Jeremy Heyl
Jason Kalirai
Ryan Goldsbury
Name of Publication
The Astrophysical Journal
Date Published
October 1, 2016
ISBN Number
blue stragglers; globular clusters: individual: 47 Tucanae; Hertzsprung–Russell and C–M diagrams; stars: evolution; stars: kinematics and dynamics
Blue stragglers (BSS) are stars whose position in thecolor-magnitude diagram (CMD) places them above the main sequence(MS) turn-off (TO) point of a star cluster. Using data from the core of47 Tuc in the ultraviolet (UV), we have identified various stellarpopulations in the CMD, and used their radial distributions to study theevolution and origin of BSS, and obtain a dynamical estimate of the massof BSS systems. When we separate the BSS into two samples by theirmagnitude, we find that the bright BSS show a much more centrallyconcentrated radial distribution and thus higher mass estimate (overtwice the TO mass for these BSS systems), suggesting an origin involvingtriple or multiple stellar systems. In contrast, the faint BSS are lessconcentrated, with a radial distribution similar to the MS binaries,pointing to the MS binaries as the likely progenitors of these BSS.Putting our data together with available photometric data in the visibleand using MESA evolutionary models, we calculate the expected number ofstars in each evolutionary stage for the normal evolution of stars andthe number of stars coming from the evolution of BSS. The resultsindicate that BSS have a post-MS evolution comparable to that of anormal star of the same mass and a MS BSS lifetime of about200-300 Myr. We also find that the excess population of asymptoticgiant branch stars in 47 Tuc is due to evolved BSS.