We present MMT/Megacam imaging in Sloan g and r of the extremely low luminosity Boötes II Milky Way companion .
We use a bootstrap approach to perform robust measurements of , and uncertainties on , Boötes II ’ s distance , luminosity , size , and morphology .
Comparisons with theoretical isochrones and empirical globular cluster fiducials show that Boötes II ’ s stellar population is old and metal-poor ( [ Fe/H ] \mathrel { \hbox to 0.0 pt { \lower 3.0 pt \hbox { $ \sim$ } \hss } \raise 2.0 pt \hbox { $ < $ } } -2 ) .
Assuming a stellar population like that of M92 , Boötes II is at a distance of 42 \pm 2 kpc , closer than the initial published estimate of 60 \pm 10 kpc .
This distance revision , combined with a more robust measurement of Boötes II ’ s structure with a Plummer model ( exponential model ) results in a more compact inferred physical half-light size of r _ { h } \simeq 36 ( 33 ) \pm 9 ( 10 ) pc and lower inferred luminosity of M _ { V } \simeq - 2.4 ( -2.2 ) \pm 0.7 ( 0.7 ) mag .
The revised size and luminosity we calculate move Boötes II into a region of size-luminosity space not previously known to be occupied by old stellar populations , but also occupied by the recently discovered Milky Way satellites Willman 1 and SEGUE 1 .
We show that the apparently distorted morphology of Boötes II is not statistically significant given the present data .
We use a tidal argument to support a scenario where Boötes II is a dwarf galaxy ( dark matter dominated ) rather than a globular cluster ( not dark matter dominated ) , although the uncertainty on the M / L we infer for Boötes II is substantial .
Moreover , we can not rule out that Boötes II is a star cluster on the verge of disruption , such as Palomar 5 .