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We present a new search for variable stars in the Galactic globular clusterM28 (NGC 6626). The search is based on a series of BVI images obtained with theSMARTS Consortium's 1.3m telescope at Cerro Tololo Inter-American Observatory,Chile. The search was carried out using the ISIS v2.2 image subtractionpackage. We find a total of 25 variable stars in the field of the cluster, 9being new discoveries. Of the newly found variables, 1 is an ab-type RR Lyraestar, 6 are c-type RR Lyrae, and 2 are long-period/semi-regular variables. V22,previously classified as a type II Cepheid, appears as a bona-fide RRc in ourdata. In turn, V20, previously classified as an ab-type RR Lyrae, could not beproperly phased with any reasonable period. The properties of the ab-type RRLyrae stars in M28 appear most consistent with an Oosterhoff-intermediateclassification, which is unusual for bona-fide Galactic globulars clusters.However, the cluster's c-type variables do not clearly support such anOosterhoff type, and a hybrid Oosterhoff I/II system is accordingly anotherpossibility, thus raising the intriguing possibility of multiple populationsbeing present in M28. Coordinates, periods, and light curves in differentialfluxes are provided for all the detected variables.

Variable stars in the globular cluster M28 (NGC 6626)