An analysis of the blue straggler population in the Sgr dSph globular
  cluster Arp 2
  We present and discuss new BVI CCD photometry in the field of the globular
cluster Arp~2, which is considered a member of the Sagittarius Dwarf Spheroidal
Galaxy. The main goal of this investigation is to study of the statistics and
spatial distribution of blue straggler stars in the cluster. Blue stragglers
are stars observed to be hotter and bluer than other stars with the same
luminosity in their environment. As such, they appear to be much younger than
the rest of the stellar population. Two main channels have been suggested to
produce such stars: (1) collisions between stars in clusters or (2) mass
transfer between, or merger of, the components of primordial short-period
binaries. The spatial distribution of these stars inside a star cluster,
compared with the distribution of stars in different evolutionary stages, can
cast light on the most efficient production mechanism at work. In the case of
Arp~2, we found that blue straggler stars are significantly more concentrated
than main sequence stars, while they show the same degree of concentration as
evolved stars (either red giants or horizontal branch stars). Since Arp~2 is
not a very concentrated cluster, we suggest that this high central
concentration is an indication that blue stragglers are mostly primordial
binary stars.
