Transiting Planets Near the Snow Line from Kepler. I. Catalog

We present a comprehensive catalog of cool (period P ≳ 2 yr) transiting planet candidates in the 4 yr light curves from the prime Kepler mission. Most of the candidates show only one or two transits and have largely been missed in the original Kepler Object of Interest catalog. Our catalog is based on all known such candidates in the literature, as well as new candidates from the search in this paper, and provides a resource to explore the planet population near the snow line of Sun-like stars. We homogeneously performed pixel-level vetting, stellar characterization with Gaia parallax and archival/Subaru spectroscopy, and light-curve modeling to derive planet parameters and to eliminate stellar binaries. The resulting clean sample consists of 67 planet candidates whose radii are typically constrained to 5%, in which 23 are newly reported. The number of Jupiter-sized candidates (29 with radius r> 8 {R}_\oplus ) in the sample is consistent with the Doppler occurrence. The smaller candidates are more prevalent (23 with 4< r/{R}_\oplus < 8, 15 with r/{R}_\oplus < 4) and suggest that long-period Neptune-sized planets are at least as common as the Jupiter-sized ones, although our sample is yet to be corrected for detection completeness. If the sample is assumed to be complete, these numbers imply the occurrence rate of 0.39 ± 0.07 planets with 4< r/{R}_\oplus < 14 and 2< P/{yr}< 20 per FGK dwarf. The stars hosting candidates with r> 4 {R}_\oplus have systematically higher [Fe/H] than do the Kepler field stars, providing evidence that giant planet-metallicity correlation extends to P> 2 {yr}.

Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.