197 Candidates and 104 Validated Planets in K2’s First Five Fields

September 2016 • 2016ApJS..226....7C

Authors • Crossfield, Ian J. M. • Ciardi, David R. • Petigura, Erik A. • Sinukoff, Evan • Schlieder, Joshua E. • Howard, Andrew W. • Beichman, Charles A. • Isaacson, Howard • Dressing, Courtney D. • Christiansen, Jessie L. • Fulton, Benjamin J. • Lépine, Sébastien • Weiss, Lauren • Hirsch, Lea • Livingston, John • Baranec, Christoph • Law, Nicholas M. • Riddle, Reed • Ziegler, Carl • Howell, Steve B. • Horch, Elliott • Everett, Mark • Teske, Johanna • Martinez, Arturo O. • Obermeier, Christian • Benneke, Björn • Scott, Nic • Deacon, Niall • Aller, Kimberly M. • Hansen, Brad M. S. • Mancini, Luigi • Ciceri, Simona • Brahm, Rafael • Jordán, Andrés • Knutson, Heather A. • Henning, Thomas • Bonnefoy, Michaël • Liu, Michael C. • Crepp, Justin R. • Lothringer, Joshua • Hinz, Phil • Bailey, Vanessa • Skemer, Andrew • Defrere, Denis

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}\oplus , P = 8.6 days, {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 76 planets smaller than 2 R , 15 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 (\lt 2{R}\oplus ) and larger for candidates with radii \gt 8{R}\oplus and/or with P\lt 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.


IPAC Authors


Jessie Christiansen

Associate Scientist


David Ciardi

Senior Scientist


Benjamin Fulton

Assistant Scientist