- Crossfield, IJM
- Ciardi, DR
- Petigura, EA
- Sinukoff, E
- Schlieder, JE
- Howard, AW
- Beichman, CA
- Isaacson, H
- Dressing, CD
- Christiansen, JL
- Fulton, BJ
- Lépine, S
- Weiss, L
- Hirsch, L
- Livingston, J
- Baranec, C
- Law, NM
- Riddle, R
- Ziegler, C
- Howell, SB
- Horch, E
- Everett, M
- Teske, J
- Martinez, AO
- Obermeier, C
- Benneke, B
- Scott, N
- Deacon, N
- Aller, KM
- Hansen, BMS
- Mancini, L
- Ciceri, S
- Brahm, R
- Jordán, A
- Knutson, HA
- Henning, T
- Bonnefoy, M
- Liu, MC
- Crepp, JR
- Lothringer, J
- Hinz, P
- Bailey, V
- Skemer, A
- Defrere, D
- et al.
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), false positives, and 63 remaining candidates. Our validated systems span a range of properties, with median values of R = 2.3 R⊕, P = 8.6 days, T = 5300 K, and Kp = 12.7mag. 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 R⊕, Kp = 9-13 mag). Of particular interest are planets smaller than 2 R , orbiting stars brighter than Kp = 11.5 mag, 5 receiving Earth-like irradiation levels, and several multi-planet systems - including 4 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 >8 R⊕ and/or with P<3 days. Extrapolation of the current planetary yield suggests that K2 will discover between 500 and 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, are essential for maximizing the efficacy of planet-validation efforts for K2, TESS, and future large-scale surveys. P eff ⊕