Formation and Evolution of Blue Stragglers in 47 Tucanae

Abstract

Blue stragglers (BSS) are stars whose position in the Color-Magnitude Diagram (CMD) places them above the main sequence turn-off (TO) point of a star cluster. Using data from the core of 47 Tuc in the ultraviolet (UV), we have identified various stellar populations in the CMD, and used their radial distributions to study the evolution and origin of BSS, and obtain a dynamical estimate of the mass of BSS systems. When we separate the BSS into two samples by their magnitude, we find that the bright BSS show a much more centrally concentrated radial distribution and thus higher mass estimate (over twice the TO mass for these BSS systems), suggesting an origin involving triple or multiple stellar systems. In contrast, the faint BSS are less concentrated, with a radial distribution similar to the main sequence (MS) binaries, pointing to the MS binaries as the likely progenitors of these BSS. Putting our data together with available photometric data in the visible and using MESA evolutionary models, we calculate the expected number of stars in each evolutionary stage for the normal evolution of stars and the number of stars coming from the evolution of BSS. The results indicate that BSS have a post-MS evolution comparable to that of a normal star of the same mass and a MS BSS lifetime of about 200-300 Myr. We also find that the excess population of asymptotic giant branch (AGB) stars in 47 Tuc is due to evolved BSS.

arXiv comment11 pages, 4 figures, 6 tables, accepted in ApJ

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• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters - XV. The dynamical clock: reading cluster dynamical evolution from the segregation level of blue straggler stars
• The Gaia-ESO survey: impact of extra-mixing on C- and N-abundances of giant stars
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• Deep HST Imaging in 47 Tucanae: A Global Dynamical Model
• Spectral Energy Distribution of Blue Stragglers in the core of 47 Tucanae
• UVIT-HST-GAIA view of NGC 288: A census of hot stellar population and their properties from UV
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• The Mass and Age Distribution of Halo White Dwarfs in the Canada-France Imaging Survey
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• Study of UV bright stellar populations in the globular cluster NGC 1261 using AstroSat
• The origin of ultramassive white dwarfs: hints from Gaia EDR3
• The fractions of post-binary-interaction stars and evolved blue straggler stars on the red giant branch of globular clusters
• Stellar populations of the globular cluster NGC 5053 investigated using AstroSat-Ultra Violet Imaging Telescope