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Radial distributions of various stellar populations and the evolution of the globular cluster 47 Tucanae

University of British Columbia

Blue stragglers (BSS) are stars whose position in the Color-Magnitude Diagram (CMD) places them above the main sequence turn-off point in a given cluster. Three possible origins have been proposed: stellar collisions, evolution of binary systems, and evolution of hierarchical triples. 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. When we separate the BSS in two samples divided by their magnitude, we find that the bright BSS show a much more centrally concentrated radial distribution and higher mass estimates, 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 this populations as their progenitors. A sample of evolved BSS was found on the UV CMD, this put together with available photometric data and MESA evolutionary models resulted in time scales and number of observed and expected stars agreeing nicely with the BSS having 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 extra population of the asymptotic giant branch (AGB) stars in 47 Tuc is due to evolved BSS, with the bulk of the contamination being in the red giant branch bump of the BSS that, according to our models, falls in the same magnitude and color range as the observed AGB bump.

Text

2016-01-06

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/56275

Astronomy

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/