We combine precision radial velocity data from four different published works of the stars in the Leo II dwarf spheroidal galaxy .
This yields a dataset 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 dataset , 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 ^ { +0.09 } _ { -0.10 } 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 ( \sim 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 3 for binary fractions on the higher end of what has been seen in other dwarf spheroidals .