Structure and Dynamics of the Globular Cluster Palomar 13
  We present Keck/DEIMOS spectroscopy and CFHT/MegaCam photometry for the Milky
Way globular cluster Palomar 13. We triple the number of spectroscopically
confirmed members, including many repeat velocity measurements. Palomar 13 is
the only known globular cluster with possible evidence for dark matter, based
on a Keck/HIRES 21 star velocity dispersion of sigma=2.2+/-0.4 km/s. We
reproduce this measurement, but demonstrate that it is inflated by unresolved
binary stars. For our sample of 61 stars, the velocity dispersion is
sigma=0.7(+0.6/-0.5) km/s. Combining our DEIMOS data with literature values,
our final velocity dispersion is sigma=0.4(+0.4/-0.3) km/s. We determine a
spectroscopic metallicity of [Fe/H]=-1.6+/-0.1 dex, placing a 1-sigma upper
limit of sigma_[Fe/H]~0.2 dex on any internal metallicity spread. We determine
Palomar 13's total luminosity to be M_V=-2.8+/-0.4, making it among the least
luminous known globular clusters. The photometric isophotes are regular out to
the half-light radius and mildly irregular outside this radius. The outer
surface brightness profile slope is shallower than typical globular clusters
(eta=-2.8+/-0.3). Thus at large radius, tidal debris is likely affecting the
appearance of Palomar 13. Combining our luminosity with the intrinsic velocity
dispersion, we find a dynamical mass of of M_1/2=1.3(+2.7/-1.3)x10^3 M_sun and
a mass-to-light ratio of M/L_V=2.4(+5.0/-2.4) M_sun/L_sun. Within our
measurement errors, the mass-to-light ratio agrees with the theoretical
predictions for a single stellar population. We conclude that, while there is
some evidence for tidal stripping at large radius, the dynamical mass of
Palomar 13 is consistent with its stellar mass and neither significant dark
matter, nor extreme tidal heating, is required to explain the cluster dynamics.
