Abstract
We present the Kepler Object of Interest (KOI) catalog of transiting exoplanets based on searching four years of Kepler time series photometry (Data Release 25, Q1-Q17). The catalog contains 8054 KOIs of which 4034 are planet candidates with periods between 0.25 and 632 days. Of these candidates, 219 are new in this catalog and include two new candidates in multi-planet systems (KOI-82.06 and KOI-2926.05), and ten new high-reliability, terrestrial-size, habitable zone candidates. This catalog was created using a tool called the Robovetter which automatically vets the DR25 Threshold Crossing Events (TCEs) found by the Kepler Pipeline (Twicken et al. 2016). Because of this automation, we were also able to vet simulated data sets and therefore measure how well the Robovetter separates those TCEs caused by noise from those caused by low signal-to-noise transits. Because of these measurements we fully expect that this catalog can be used to accurately calculate the frequency of planets out to Kepler's detection limit, which includes temperate, super-Earth size planets around GK dwarf stars in our Galaxy. This paper discusses the Robovetter and the metrics it uses to decide which TCEs are called planet candidates in the DR25 KOI catalog. We also discuss the simulated transits, simulated systematic noise, and simulated astrophysical false positives created in order to characterize the properties of the final catalog. For orbital periods less than 100 d the Robovetter completeness (the fraction of simulated transits that are determined to be planet candidates) across all observed stars is greater than 85%. For the same period range, the catalog reliability (the fraction of candidates that are not due to instrumental or stellar noise) is greater than 98%. However, for low signal-to-noise candidates found between 200 and 500 days, our measurements indicate that the Robovetter is 73.5% complete and 37.2% reliable across all searched stars (or 76.7% complete and 50.5% reliable when considering just the FGK dwarf stars). We describe how the measured completeness and reliability varies with period, signal-to-noise, number of transits, and stellar type. Also, we discuss a value called the disposition score which provides an easy way to select a more reliable, albeit less complete, sample of candidates. The entire KOI catalog, the transit fits using Markov chain Monte Carlo methods, and all of the simulated data used to characterize this catalog are available at the NASA Exoplanet Archive.
Highlights
Kepler’s mission to measure the frequency of Earth-size planets in the Galaxy is an important step toward understanding the Earth’s place in the universe
The Data Release 25 (DR25) Kepler Object of Interest (KOI) catalog has been characterized so that it can serve as the basis for occurrence rate studies of exoplanets with periods as long as 500 days
Https://exoplanetarchive.ipac.caltech.edu/cgi-bin/TblView/nph-tblView? app=ExoTbls&config=koifpp https://exoplanetarchive.ipac.caltech.edu/cgi-bin/TblView/nph-tblView? app=ExoTbls&config=koiapp missed. For this DR25 KOI catalog, the vetting completeness has been balanced against the catalog reliability, i.e., how often false alarms are mistakenly classified as PCs
Summary
Kepler’s mission to measure the frequency of Earth-size planets in the Galaxy is an important step toward understanding the Earth’s place in the universe. To confirm the validity and further characterize identified planet candidates, the Kepler mission benefited from an active, funded, follow-up observing program This program used ground-based radial velocity measurements to determine the mass of exoplanets (e.g., Marcy et al 2014) when possible and ruled out other astrophysical phenomena, like background eclipsing binaries, that can mimic a transit signal. Both funded and unfunded high-resolution imaging studies have covered ≈90% of known KOIs (see, e.g., Law et al 2014; Baranec et al 2016; Furlan et al 2017; Ziegler et al 2017) to identify close companions (bound or unbound) that would be included in Kepler’s rather large 3 98 pixels. Using planet candidates discovered with Kepler, several papers have measured the frequency of small planets in the habitable zone of Sun-like stars (see, e.g., Petigura et al 2013; Burke et al 2015; Foreman-Mackey et al 2016) using various methods. Burke et al (2015) used the Q1–Q16 KOI catalog (Mullally et al 2015) to look at G and K stars and concluded that 10% (with an allowed range of 1%–200%) of solar-type stars host planets with radii and orbital periods within 20% of that of the Earth. Burke et al (2015) considered various systematic effects and showed that they dominate the uncertainties, and he concluded that improved measurements of the stellar properties, the detection efficiency of the search, and the reliability of the catalog will have the most impact in narrowing the uncertainties in such studies
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