Star count density profiles and structural parameters of 26 Galactic
  globular clusters
  We used a proper combination of high-resolution HST observations and
wide-field ground based data to derive the radial star density profile of 26
Galactic globular clusters from resolved star counts (which can be all freely
downloaded on-line). With respect to surface brightness (SB) profiles (which
can be biased by the presence of sparse, bright stars), star counts are
considered to be the most robust and reliable tool to derive cluster structural
parameters. For each system a detailed comparison with both King and Wilson
models has been performed and the most relevant best-fit parameters have been
obtained. This is the largest homogeneous catalog collected so far of star
count profiles and structural parameters derived therefrom. The analysis of the
data of our catalog has shown that: (1) the presence of the central cusps
previously detected in the SB profiles of NGC 1851, M13 and M62 is not
confirmed; (2) the majority of clusters in our sample are fitted equally well
by the King and the Wilson models; (3) we confirm the known relationship
between cluster size (as measured by the effective radius) and galactocentric
distances; (4) the ratio between the core and the effective radii shows a
bimodal distribution, with a peak at ~ 0.3 for about 80% of the clusters, and a
secondary peak at ~ 0.6 for the remaining 20%. Interestingly, the main peak
turns out to be in agreement with what expected from simulations of cluster
dynamical evolution and the ratio between these two radii well correlates with
an empirical dynamical age indicator recently defined from the observed shape
of blue straggler star radial distribution, thus suggesting that no exotic
mechanisms of energy generation are needed in the cores of the analyzed
clusters.
