Strong RR Lyrae excess in the Hercules-Aquila Cloud
  We map the large-scale sub-structure in the Galactic stellar halo using
accurate 3D positions of ~14,000 RR Lyrae reported by the Catalina Sky Survey.
In the heliocentric distance range of 10-25 kpc, in the region of the sky
approximately bounded by 30{\deg} < l < 55{\deg} and -45{\deg} < b < -25{\deg},
there appears to be a strong excess of RRab stars. This overdensity, peaking at
18 kpc, is most likely associated with the so-called Hercules-Aquila Cloud,
previously detected using Main Sequence tracers at similar distances in the
Sloan Digital Sky Survey data. Our analysis of the period-amplitude
distribution of RR Lyrae in this region indicates that the HAC is dominated by
the Oosterhoff I type population. By comparing the measured RR Lyrae number
density to models of a smooth stellar halo, we estimate the significance of the
observed excess and provide an updated estimate of the total luminosity of the
Cloud's progenitor.
