Analysis of RR Lyrae Stars in the Northern Sky Variability Survey

We use data from the Northern Sky Variability Survey (NSVS), obtained fromthe first generation Robotic Optical Transient Search Experiment (ROTSE-I), toidentify and study RR Lyrae variable stars in the solar neighborhood. Weinitially identified 1197 RRab (RR0) candidate stars brighter than the ROTSEmedian magnitude V = 14. Periods, amplitudes, and mean V magnitudes aredetermined for a subset of 1188 RRab stars with well defined light curves.Metallicities are determined for 589 stars by the Fourier parameter method andby the relationship between period, amplitude, and [Fe/H]. We comment upon thedifficulties of clearly classifying RRc (RR1) variables in the NSVS dataset.Distances to the RRab stars are calculated using an adoptedluminosity-metallicity relation with corrections for interstellar extinction.The 589 RRab stars in our final sample are used to study the properties of theRRab population within 5 kpc of the Sun. The Bailey diagram of period versusamplitude shows that the largest component of this sample belongs to Oosterhofftype I. Metal-rich ([Fe/H] > -1) RRab stars appear to be associated with theGalactic disk. Our metal-rich RRab sample may include a thin disk as well as athick disk population, although the uncertainties are too large to establishthis. There is some evidence among the metal-rich RRab stars for a decline inscale height with increasing [Fe/H], as was found by Layden (1995). Thedistribution of RRab stars with -1 < [Fe/H] < -1.25 indicates that within thismetallicity range the RRab stars are a mixture of stars belonging to halo anddisk populations.Comment: 68 pages, 26 figures, 9 tables, accepted to A