M75, A Globular Cluster with a Trimodal Horizontal Branch. II. BV photometry of the RR Lyrae Variables

We present new BV CCD photometry, light curves, and ephemerides for nine previously known, 29 newly detected RR Lyrae variables, and one newly detected variable of an unknown type in the globular cluster M75. The photometry used for the detection of the additional variables was obtained with the image subtraction package ISIS. The data were acquired on an observing run in 1999 July and range over seven observing nights. Estimates of fundamental photometric parameters are presented including intensity- and magnitude-averaged B and V magnitudes, magnitude-averaged colors, pulsation periods, and pulsation amplitudes. The mean period of the RRab variables, ⟨P_ab⟩ = 0.5868 days, and the number fraction of RRc stars, N_c/N_RR = 0.342, are both large for an Oosterhoff type I (OoI) globular cluster, suggesting that M75 may be Oosterhoff-intermediate. Possible conflicts between Oosterhoff-type determination based on the A_V–log P and A_B–log P diagrams are discussed. The physical parameters of the RRc and RRab variables, as obtained from Fourier decomposition of their light curves, do not show any clear deviation from normal OoI behavior.