The wide-field synoptic sky surveys , known as the Palomar Transient Factory ( PTF ) and the intermediate Palomar Transient Factory ( iPTF ) , will accumulate a large number of known and new RR Lyrae .
These RR Lyrae are good tracers to study the substructure of the Galactic halo if their distance , metallicity , and galactocentric velocity can be measured .
Candidates of halo RR Lyrae can be identified from their distance and metallicity before requesting spectroscopic observations for confirmation .
This is because both quantities can be obtained via their photometric light curves , because the absolute V -band magnitude for RR Lyrae is correlated with metallicity , and the metallicity can be estimated using a metallicity-light curve relation .
To fully utilize the PTF and iPTF light-curve data in related future work , it is necessary to derive the metallicity-light curve relation in the native PTF/iPTF R -band photometric system .
In this work , we derived such a relation using the known ab-type RR Lyrae located in the Kepler field , and it is found to be [ Fe / H ] _ { PTF } = -4.089 - 7.346 P + 1.280 \phi _ { 31 } ( where P is pulsational period and \phi _ { 31 } is one of the Fourier parameters describing the shape of the light curve ) , with a dispersion of 0.118 dex .
We tested our metallicity-light curve relation with new spectroscopic observations of a few RR Lyrae in the Kepler field , as well as several data sets available in the literature .
Our tests demonstrated that the derived metallicity-light curve relation could be used to estimate metallicities for the majority of the RR Lyrae , which are in agreement with the published values .