The unusually large population of Blazhko variables in the globular
  cluster NGC 5024 (M53)
  We report the discovery of amplitude and phase modulations typical of the
Blazhko effect in 22 RRc and 9 RRab type RR Lyrae stars in NGC 5024 (M53). This
brings the confirmed Blazhko variables in this cluster to 23 RRc and 11 RRab,
that represent 66% and 37% of the total population of RRc and RRab stars in the
cluster respectively, making NGC 5024 the globular cluster with the largest
presently known population of Blazhko RRc stars. We place a lower limit on the
overall incidence rate of the Blazhko effect among the RR Lyrae population in
this cluster of 52%. New data have allowed us to refine the pulsation periods.
The limitations imposed by the time span and sampling of our data prevents
reliable estimations of the modulation periods. The amplitudes of the
modulations range between 0.02 and 0.39 mag. The RRab and RRc are neatly
separated in the CMD, and the RRc Blazhko variables are on averge redder than
their stable couterparts; these two facts may support the hypothesis that the
HB evolution in this cluster is towards the red and that the Blazhko
modulations in the RRc stars are connected with the pulsation mode switch.
