We report the discovery of a new ultra-faint globular cluster in the constellation of Ursa Minor , based on stellar photometry from the MegaCam imager at the Canada-France-Hawaii Telescope ( CFHT ) .
We find that this cluster , Muñoz 1 , is located at a distance of 45 \pm 5 kpc and at a projected distance of only 45 \arcmin from the center of the Ursa Minor dSph galaxy .
Using a Maximum Likelihood technique we measure a half-light radius of 0 \arcmin . 5 , or equivalently 7 pc and an ellipticity consistent with being zero .
We estimate its absolute magnitude to be M _ { V } = -0.4 \pm 0.9 , which corresponds to L _ { V } = 120 ^ { +160 } _ { -65 } L _ { \sun } and we measure a heliocentric radial velocity of -137 \pm 4 km s ^ { -1 } based on Keck/DEIMOS spectroscopy .
This new satellite is separate from Ursa Minor by \sim 30 kpc and 110 km s ^ { -1 } suggesting the cluster is not obviously associated with the dSph , despite the very close angular separation .
Based on its photometric properties and structural parameters we conclude that Muñoz 1 is a new ultra-faint stellar cluster .
Along with Segue 3 this is one of the faintest stellar clusters known to date .