197 CANDIDATES AND 104 VALIDATED PLANETS IN K2's FIRST FIVE FIELDS

Abstract

We present 197 planet candidates discovered using data from the first year of the NASA K2 mission (Campaigns 0-4), along with the results of an intensive program of photometric analyses, stellar spectroscopy, high-resolution imaging, and statistical validation. We distill these candidates into sets of 104 validated planets (57 in multi-planet systems), 30 false positives, and 63 remaining candidates. Our validated systems span a range of properties, with median values of R P = 2.3 R ⊕ , P = 8.6 d, T eff = 5300 K, and Kp = 12.7 mag. Stellar spectroscopy provides precise stellar and planetary parameters for most of these systems. We show that K2 has increased by 30% the number of small planets known to orbit moderately bright stars (1-4 R ⊕ , Kp = 9-13 mag). Of particular interest are 37 planets smaller than 2 R ⊕ , 15 orbiting stars brighter than Kp = 11.5 mag, five receiving Earth-like irradiation levels, and several multi-planet systems -including four planets orbiting the M dwarf K2-72 near mean-motion resonances. By quantifying the likelihood that each candidate is a planet we demonstrate that our candidate sample has an overall false positive rate of 15 − 30%, with rates substantially lower for small candidates (< 2R ⊕ ) and larger for candidates with radii > 8R ⊕ and/or with P < 3 d. Extrapolation of the current planetary yield suggests that K2 will discover between 500 − 1000 planets in its planned four-year mission -assuming sufficient follow-up resources are available. Efficient observing and analysis, together with an organized and coherent follow-up strategy, is essential to maximize the efficacy of planet-validation efforts for K2 , TESS , and future large-scale surveys. 1 We distinguish "confirmed" systems (with measured masses) from "validated" systems (whose planetary nature has been statistically demonstrated, e.g. with false positive probability < 1% ).

K2-66b and K2-106b: Two Extremely Hot Sub-Neptune-size Planets with High Densities

“…K2-106 (EPIC 220674823) is a G star in K2 Campaign 8 (C8) with two transiting sub-Neptunes, including a USP subNeptune (K2-106b). We note that K2-66b was first reported as a planet candidate by Vanderburg et al (2015) and statistically validated by Crossfield et al (2016). Both K2-106 planets were first reported and statistically validated by Adams et al (2016b) as part of the Short-period Planets Group effort.…”

“…8 during the observations. Crossfield et al (2016) presented NIRC2 AO imaging of K2-66 obtained by our group, which we do not show here. The star was found to be single.…”

“…The same Gaussian process was used to model and subtract the spacecraft motion from K2 pixel data. We use the same K2-66 light curve presented in Crossfield et al (2016), so we do not display it in this work.…”

“…K2-106 was observed from 2016 January 04 to 2016 March 23 UT (80 days) as part of K2 Campaign 8. We generated stellar light curves from the respective target pixel files using the same procedures detailed in Sinukoff et al (2016) and Crossfield et al (2016). The same Gaussian process was used to model and subtract the spacecraft motion from K2 pixel data.…”

“…The Kepler spacecraft has been collecting precise photometry of numerous fields along the ecliptic plane, each for nearly three continuous months (Howell et al 2014). With 10,000-20,000 stars per campaign, hundreds of transiting planet candidates have been discovered Adams et al 2016a;Barros et al 2016;Pope et al 2016), many of which have been statistically validated or confirmed as planets (Crossfield et al 2016;Sinukoff et al 2016). This includes several USPs around bright stars amenable to Doppler spectroscopy, including WASP-47e Dai et al 2015;Sinukoff et al 2017) and HD 3167b (Vanderburg et al 2016).…”