275 Candidates and 149 Validated Planets Orbiting Bright Stars in K2 Campaigns 0–10

Abstract

Since 2014, NASA's K2 mission has observed large portions of the ecliptic plane in search of transiting planets and has detected hundreds of planet candidates. With observations planned until at least early 2018, K2 will continue to identify more planet candidates. We present here 275 planet candidates observed during Campaigns 0-10 of the K2 mission that are orbiting stars brighter than 13 mag (in Kepler band) and for which we have obtained highresolution spectra (R = 44,000). These candidates are analyzed using the vespa package in order to calculate their false-positive probabilities (FPP). We find that 149 candidates are validated with an FPP lower than 0.1%, 39 of which were previously only candidates and 56 of which were previously undetected. The processes of data reduction, candidate identification, and statistical validation are described, and the demographics of the candidates and newly validated planets are explored. We show tentative evidence of a gap in the planet radius distribution of our candidate sample. Comparing our sample to the Kepler candidate sample investigated by Fulton et al., we conclude that more planets are required to quantitatively confirm the gap with K2 candidates or validated planets. This work, in addition to increasing the population of validated K2 planets by nearly 50% and providing new targets for follow-up observations, will also serve as a framework for validating candidates from upcoming K2 campaigns and the Transiting Exoplanet Survey Satellite, expected to launch in 2018.

Scaling K2. II. Assembly of a Fully Automated C5 Planet Candidate Catalog Using EDI-Vetter

“…One system of known planets was completely lost by our pipeline, EPIC 212157262. This system was detected and also confirmed by Mayo et al (2018), who used the K2SFF (Vanderburg & Johnson 2014) processed light curves. Some of the planets in this system produce signals near the detection threshold, and were not detected in our pipeline TCE search.…”

“…We limit our pipeline to a range of 0.5 days to 38 days. Previous surveys have found two systems that have multiple transiting planets with periods less than 0.5 days (EPIC 211305568; Dressing et al 2017a and EPIC 211562654;Mayo et al 2018). Upon visual inspection of the light curve, it appears these candidates were found with our TCE search, but then rejected by our ≥ 0.5 days vetting requirement.…”

“…By stitching the data from multiple campaigns together, the available data span can be extended to potentially find periods beyond our 38 day limit. An example of this is EPIC 211611158, which has a known planet at a period of 52.71 days (Mayo et al 2018). It should be noted that this planet was not found by stitching, but rather by relaxing the three transit requirement.…”

Evolution of the Radius Valley around Low-mass Stars from Kepler and K2

“…The inclusion of K2 PCs therefore requires that we account for sample contamination by false positives probabilistically. We do so by considering a number of studies from the literature that perform a transiting planet search in K2from any subset of its campaigns-and attempt to validate their uncovered PCs statistically based on follow-up observations (Montet et al 2015;Crossfield et al 2016;Dressing et al 2017;Hirano et al 2018;Livingston et al 2018;Mayo et al 2018). Each of these studies utilized some combination of ground-based photometry to validate planet ephemerides, reconnaissance spectroscopy to identify spectroscopic binaries, and speckle or AOassisted imaging to search for nearby stellar companions.…”

“…a These studies do not detect any FPs such that the reported FP rate upper limit is represented by its 95% confidence interval. b Mayo et al (2018) did not explicitly classify their non-validated planets as FPs so we define FPs within their sample as any PC whose false positive probability exceeds 10%.…”