Kepler Bonus: Light Curves of Kepler Background Sources

Abstract

NASA’s Kepler primary mission observed about 116 deg2 in the sky for 3.5 consecutive years to discover Earth-like exoplanets. This mission recorded pixel cutouts, known as target pixel files (TPFs), of over 200,000 targets that were selected to maximize the scientific yield. The Kepler pipeline performed aperture photometry for these primary targets to create light curves. However, hundreds of thousands of background sources were recorded in the TPFs and have never been systematically analyzed. This work uses the linearized field deblending (LFD) method, a point-spread function (PSF) photometry algorithm, to extract light curves. We use Gaia Data Release 3 as the input catalog to extract 606,900 light curves from long-cadence TPFs; 406,548 are new light curves of background sources, while the rest are Kepler’s targets. These light curves have comparable quality to those computed by the Kepler pipeline, with combined differential photometric precision values <100 ppm for sources G < 16. The light-curve files are available as high-level science products at the Mikulski Archive for Space Telescopes. Files include PSF and aperture photometry as well as extraction metrics. Additionally, we improve the background and PSF modeling in the LFD method. The LFD method is implemented in the Python library psfmachine. We demonstrate the advantages of this new data set with two examples: deblending of contaminated false-positive Kepler objects of interest identifying the origin of the transit signal and the changes in estimated transit depth of planets using PSF photometry, which improves dilution when compared with aperture photometry. This new nearly unbiased catalog enables further studies in planet search, occurrence rates, and other time-domain studies.