2000A&A...358..547K

We present the results of the search for variable stars in the central region of rather poorly studied globular cluster M53. We have obtained good quality light curves of the 23 previously known RR Lyrae stars in this cluster. Periods of four of them have been determined for the first time. One RR Lyrae variable till now classified as a Bailey type RRc, turned out to be type RRab. We have also confirmed the variability of ten RR Lyrae candidates discovered by Kravtsov (1990ATsir1544...21K) and derived their periods. Moreover, we have found four new variables of this type in the core of the cluster. Altogether, the light curves have been obtained for 37 RR Lyrae stars. The total number of known RR Lyrae stars in M53 equals now to 59, 29 of them being of type RRab and remaining 30 of RRc. The mean period of all known RRab variables in M53 amounts to 0.65±0.07d, and the average period for RRc variables is equal to 0.36±0.04d. Mean V magnitudes and ranges of variations have been derived for 19 RR Lyrae stars. We also report the discovery of variations in six cluster bright giants. For these stars, however, our observations are not sufficient to state whether the variability is periodic or not.