Cluster AgeS Experiment (CASE): Detection of a dwarf nova in the   globular cluster M55
  We report the detection of a dwarf nova (DN) in the core region of the globular cluster M55. Six outbursts were observed during 8 observing seasons spanning the period 1997-2004. The variable has an X-ray counterpart detected on images taken with the ROSAT telescope. Although we cannot offer proof of cluster membership, one can see that both the position on the H-R diagram and the X-ray flux are consistent with a bright DN at the cluster distance. According to our outburst statistics, no more than one similar DN could remain undetected in our field of view, centred at the cluster core. 
J. Kaluzny, P. Pietrukowicz, I.B. Thompson, W. Krzeminski, A.   Schwarzenberg-Czerny, W. Pych, G. Stachowski