M75, a Globular Cluster with a Trimodal Horizontal Branch. Ii. Bv Photometry of the Rr Lyrae Variables
نویسنده
چکیده
We present new BV CCD photometry, light curves, and ephemerides for 9 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 July 1999 and range over 7 observing nights. Estimates of fundamental photometric parameters are presented including intensityand magnitude-averaged B and V magnitudes, magnitude-averaged colors, pulsation periods, and pulsation amplitudes. The mean period of the RRab variables, 〈Pab〉 = 0.5868 d, and the number fraction of RRc stars, Nc/NRR = 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 AV − log P and AB − 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. Subject headings: Galaxy: globular clusters: individual: M75 (NGC 6864) – Stars: horizontal-branch – Stars: variables: RR Lyr
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M75, a Globular Cluster with a Trimodal Horizontal Branch. I. Color-magnitude Diagram
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