The Binary Fraction of Stars in Dwarf Galaxies: The Case of Leo II
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Author
Spencer, M.
Mateo, Mario
Walker, Matthew G.

Olszewski, Edward W.
McConnachie, Alan W.
Kirby, Evan N.

Koch, Andreas
Affiliation
Univ Arizona, Steward ObservIssue Date
2017-05-19Keywords
binaries: generalgalaxies: dwarf
galaxies: individual (Leo II)
galaxies: kinematics and dynamics
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Show full item recordPublisher
IOP PUBLISHING LTDCitation
The Binary Fraction of Stars in Dwarf Galaxies: The Case of Leo II 2017, 153 (6):254 The Astronomical JournalJournal
The Astronomical JournalRights
© 2017. The American Astronomical Society. All rights reserved.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
We combine precision radial velocity data from four different published works of the stars in the Leo II dwarf spheroidal galaxy. This yields a data set that spans 19 years, has 14 different epochs of observation, and contains 372 unique red giant branch stars, 196 of which have repeat observations. Using this multi-epoch data set, we constrain the binary fraction for Leo II. We generate a suite of Monte Carlo simulations that test different binary fractions using Bayesian analysis and determine that the binary fraction for Leo II ranges from 0.30(-0.10)(+0.09) to 0.34(-0.11)(+0.11), depending on the distributions of binary orbital parameters assumed. This value is smaller than what has been found for the solar neighborhood (similar to 0.4-0.6) but falls within the wide range of values that have been inferred for other dwarf spheroidals (0.14-0.69). The distribution of orbital periods has the greatest impact on the binary fraction results. If the fraction we find in Leo II is present in low-mass ultra-faints, it can artificially inflate the velocity dispersion of those systems and cause them to appear more dark matter rich than in actuality. For a galaxy with an intrinsic dispersion of 1 km s(-1) and an observational sample of 100 stars, the dispersion can be increased by a factor of 1.5-2 for Leo II-like binary fractions or by a factor of three. for binary fractions on the higher end of what has been seen in other dwarf spheroidals.ISSN
1538-3881Version
Final published versionSponsors
National Science Foundation Graduate Research Fellowship [DGE1256260]; NSF [AST1312997, AST1313045, AST1412999, AST1313006]Additional Links
http://stacks.iop.org/1538-3881/153/i=6/a=254?key=crossref.3e60c9d0148f2fe76a84f5230f9ada71ae974a485f413a2113503eed53cd6c53
10.3847/1538-3881/aa6d51