Correcting Velocity Dispersions of Dwarf Spheroidal Galaxies for Binary Orbital Motion
Abstract
We show that the measured velocity dispersions of dwarf spheroidal galaxies from about 4 to 10 km s-1 are unlikely to be inflated by more than 30% due to the orbital motion of binary stars and demonstrate that the intrinsic velocity dispersions can be determined to within a few percent accuracy using two-epoch observations with 1-2 yr as the optimal time interval. The crucial observable is the threshold fraction—the fraction of stars that show velocity changes larger than a given threshold between measurements. The threshold fraction is tightly correlated with the dispersion introduced by binaries, independent of the underlying binary fraction and distribution of orbital parameters. We outline a simple procedure to correct the velocity dispersion to within a few percent accuracy by using the threshold fraction and provide fitting functions for this method. We also develop a methodology for constraining properties of binary populations from both single- and two-epoch velocity measurements by including the binary velocity distribution in a Bayesian analysis.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2010
- DOI:
- 10.1088/0004-637X/721/2/1142
- arXiv:
- arXiv:1001.1160
- Bibcode:
- 2010ApJ...721.1142M
- Keywords:
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- binaries: spectroscopic;
- galaxies: kinematics and dynamics;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- doi:10.1088/0004-637X/721/2/1142