On the nature of the brightest globular cluster in M81
  We analyse the photometric, chemical, star formation history and structural
properties of the brightest globular cluster (GC) in M81, referred as GC1 in
this work, with the intention of establishing its nature and origin. We find
that it is a metal-rich ([Fe/H]=-0.60+/-0.10), alpha-enhanced
([Alpha/Fe]=0.20+/0.05), core-collapsed (core radius r_c=1.2 pc, tidal radius
r_t = 76r_c), old (>13 Gyr) cluster. It has an ultraviolet excess equivalent of
~2500 blue horizontal branch stars. It is detected in X-rays indicative of the
presence of low-mass binaries. With a mass of 10 million solar masses, the
cluster is comparable in mass to M31-G1 and is four times more massive than
Omega Cen. The values of r_c, absolute magnitude and mean surface brightness of
GC1 suggest that it could be, like massive GCs in other giant galaxies, the
left-over nucleus of a dissolved dwarf galaxy.
