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We report the discovery of a new group of double-periodic RR Lyrae stars fromthe analysis of the OGLE-IV Galactic bulge photometry. In 11 stars identifiedin the OGLE catalog as first overtone pulsators (RRc stars) we detectadditional longer period variability of low amplitude, in the mmag regime. Oneadditional star of the same type is identified in a published analysis of theKepler space photometry. The period ratio between the shorter first overtoneperiod and a new, longer period lies in a narrow range around 0.686. Thus, theadditional period is longer than the expected period of the undetected radialfundamental mode. The obvious conclusion that addition periodicity correspondsto a gravity or a mixed mode faces difficulties, however.

Discovery of a new group of double-periodic RR Lyrae stars in the OGLE-IV photometry