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Published September 10, 2013 | Submitted + Published
Journal Article Open

A MegaCam Survey of Outer Halo Satellites. II. Blue Stragglers in the Lowest Stellar Density Systems

Abstract

We present a homogeneous study of blue straggler stars across 10 outer halo globular clusters, 3 classical dwarf spheroidal galaxies, and 9 ultra-faint galaxies based on deep and wide-field photometric data taken with MegaCam on the Canada–France–Hawaii Telescope. We find blue straggler stars to be ubiquitous among these Milky Way satellites. Based on these data, we can test the importance of primordial binaries or multiple systems on blue straggler star formation in low-density environments. For the outer halo globular clusters, we find an anti-correlation between the specific frequency of blue stragglers and absolute magnitude, similar to that previously observed for inner halo clusters. When plotted against density and encounter rate, the frequency of blue stragglers is well fit by a single trend with a smooth transition between dwarf galaxies and globular clusters; this result points to a common origin for these satellites' blue stragglers. The fraction of blue stragglers stays constant and high in the low encounter rate regime spanned by our dwarf galaxies, and decreases with density and encounter rate in the range spanned by our globular clusters. We find that young stars can mimic blue stragglers in dwarf galaxies only if their ages are 2.5 ± 0.5 Gyr and they represent ~1%–7% of the total number of stars, which we deem highly unlikely. These results point to mass-transfer or mergers of primordial binaries or multiple systems as the dominant blue straggler formation mechanism in low-density systems.

Additional Information

© 2013 The American Astronomical Society. Received 2013 February 6; accepted 2013 July 8; published 2013 August 21. Based on observations obtained at the Canada–France–Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. We thank the referee for very useful comments that helped improve this paper significantly. F.A.S. thanks Andrés Guzmán for useful discussions. F.A.S. acknowledges support from CONICYT-PCHA/Doctorado Nacional/2010-21100133. R.R.M. acknowledges partial support from CONICYT Anillo project ACT-1122 and project BASAL PFB-06 as well as from the FONDECYT project N◦1120013. M.G. acknowledges support from the National Science Foundation under award number AST-0908752 and the Alfred P. Sloan Foundation. S.G.D. was supported in part by the NSF grant AST-0909182 and by the Ajax Foundation. This work was supported in part by the facilities and staff of the Yale University Faculty of Arts and Sciences High Performance Computing Center.

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Published - Santana_2013p106.pdf

Submitted - 1307.2236v1.pdf

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Created:
August 19, 2023
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October 24, 2023