Title:Blue Stragglers Stars in Ultra-Faint Dwarf Galaxies and Other Galactic Satellites

Abstract:
We have studied Blue Straggler Stars (BSSs) in different types of Galactic satellites in the outer halo: 
globular clusters, classical dwarf spheroidal galaxies and the recently discovered ultra-faint dwarfs (UFDs). 
The main goal is to characterize the BSS population in the most diffuse halo systems, where collisions are 
highly unlikely, thus, enabling us to test the BSS formation mechanism via mass-transfer in close binaries. 
Using new, deep and wide-field photometric data taken with MegaCam at the Canada-France-Hawaii 
Telescope we are able to assess and analyze various aspects on the nature of BSS, in both dark 
matter-dominated (galaxies) and dark matter-free (clusters) systems, which include specific frequencies of 
BSSs, correlations between these frequencies and the structural parameters of the Galactic satellites, and 
dominating BSS formation mechanism. 
Very interestingly, we find BSSs to be ubiquitous among all different satellites.
For globular clusters, we observe an anti-correlation between BSS frequency and absolute magnitude MV, 
supporting the binary origin of their BSSs.
For dwarf galaxies, we obtain a surprisingly flat BSS frequency distribution, with an overall value as high as 
the highest found for our clusters. This distribution further supports the binary origin for BSSs, but unlike 
globular clusters, it corresponds to a density regime where primordial binaries are unlikely to be unbound 
even in the brightest objects.
Besides a few exceptions, no spatial concentration of BSSs is observed in our systems, as expected from 
mass-transfer BSSs.  This suggests that mass-segregation processes have not played a significant role in 
forming or driving BSSs.