The Binary Fraction of Stars in Dwarf Galaxies: The Case of Leo II
FInal Published Version
Walker, Matthew G.
Olszewski, Edward W.
McConnachie, Alan W.
Kirby, Evan N.
AffiliationUniv Arizona, Steward Observ
galaxies: individual (Leo II)
galaxies: kinematics and dynamics
MetadataShow full item record
PublisherIOP PUBLISHING LTD
CitationThe Binary Fraction of Stars in Dwarf Galaxies: The Case of Leo II 2017, 153 (6):254 The Astronomical Journal
JournalThe Astronomical Journal
Rights© 2017. The American Astronomical Society. All rights reserved.
Collection InformationThis 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 firstname.lastname@example.org.
AbstractWe 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.
VersionFinal published version
SponsorsNational Science Foundation Graduate Research Fellowship [DGE1256260]; NSF [AST1312997, AST1313045, AST1412999, AST1313006]