Search for Extra-Tidal RR Lyrae Stars in Milky Way Globular Clusters
  From Gaia DR2
  We used extra-tidal RR Lyrae stars to study the dynamics of Galactic globular
clusters and know how effects like dynamical friction and tidal disruption
affect these clusters. The Gaia DR2 catalog for RR Lyrae stars (Clementini et
al. 2018) is used along with the proper motions and tidal radii data for the
globular clusters compiled from literature. A sample of 56 Galactic globular
clusters is analyzed. Out of these 56 Galactic globular clusters, only 11 have
extra-tidal RR Lyrae stars. However, only two clusters, namely, NGC 3201 and
NGC 5024, have enough extra-tidal RR Lyrae stars to draw interesting
conclusions. NGC 3201 has 13 extra-tidal RR Lyrae stars which are
asymmetrically distributed around its center with more number of stars in its
trailing zone than its leading part. We conclude that these asymmetrical tidal
tails are due to the combined effect of tidal disruption and the stripped
debris from the cluster. On the other hand, NGC 5024 has 5 extra-tidal RR Lyrae
stars, four of them are concentrated in a region which is at a distance of
about 3 times the tidal radius from its center. These may be the stars that are
being ripped apart from the cluster due to tidal disruption. The presence of
these extra-tidal RR Lyrae stars in the clusters can be an indication that more
cluster stars are present outside their tidal radii which may be revealed by
deep wide field CMDs of the clusters.
