CCD photometry of the globular cluster M15: RR Lyrae Fourier decomposition and physical parameters

Abstract

Results of CCD photometry using V and R filters are reported for 33 RR Lyrae stars in M15. The periodicities of some variables have been revised and new ephemerides are given. The Blazhko effect, previously reported in V12, was not detected. Applying the approach of Fourier decomposition of the light curves, the physical parameters of the type RRab and RRc variables were estimated. The cluster is Oosterhoff type II and the values for the iron content and distance are: [Fe/H]= -1.98 +/- 0.24 and d = 8.67 +/- 0.41 kpc, respectively. The mean values of the physical parameters determined for the RR Lyrae stars place the cluster precisely into the sequences Oosterhoff type -metallicity and metallicity-effective temperature, valid for globular clusters. Evidences of evolution from the ZAHB are found for the RRc but not for the RRab stars.