Palomar Transient Factory and RR Lyrae: Metallicity-Light Curve Relation Based on ab-Type RR Lyrae in Kepler Field

Abstract

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 $[Fe/H{]}_{PTF}=-4.089-7.346P+1.280{\varphi }_{31}$ (where $P$ is pulsational period and ${\varphi }_{31}$ 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.

arXiv commentApJS in-press, 19 pages, 4 tables and 19 figures

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• Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves: I. Period-Fourier-Metallicity Relations for Fundamental Mode RR Lyrae
• On the variation of light curve parameters of RR Lyrae variables at multiple wavelengths
• Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves: II. Period-Fourier-Metallicity Relations for First Overtone RR Lyrae
• Photometric-Metallicity and Distance Estimates for $\sim$70,000 RR Lyrae Stars from the Zwicky Transient Facility
• Leveraging Deep Learning for Time Series Extrinsic Regression in predicting photometric metallicity of Fundamental-mode RR Lyrae Stars
• A Study of Pulsation properties of 57 Non-Blazhko effect ab-type RR Lyrae stars with homogeneous metallicities from the LAMOST-Kepler/K2 survey
• Metallicity estimation of RR Lyrae stars from their I-band light curves
• Evaluating the V-band Photometric Metallicity with Fundamental Mode RR Lyrae in the Kepler Field
• rrlfe: Software for Generating and Applying Metallicity Calibrations for RR Lyrae Variable Stars Across a Wide Range of Phases and Temperatures