Zodiacal exoplanets in time (ZEIT) - II. A 'super-Earth' orbiting a young K dwarf in the Pleiades Neighbourhood

• We describe a 'super-Earth'-size (2.30 +/- 0.16 R-circle plus)planet transiting an early K-type dwarf star in the Campaign 4 field observed by the K2 mission. The host star, EPIC 210363145, was identified as a candidate member of the approximately 120 Myr-old Pleiades cluster based on its kinematics and photometric distance. It is rotationally variable and exhibits near-ultraviolet emission consistent with a Pleiades age, but its rotational period is approximate to 20 d and its spectrum contains no H alpha emission nor the Li I absorption expected of Pleiades K dwarfs. Instead, the star is probably an interloper that is unaffiliated with the cluster, but younger (less than or similar to 1.3 Gyr) than the typical field dwarf. We ruled out a false positive transit signal produced by confusion with a background eclipsing binary by adaptive optics imaging and a statistical calculation. Doppler radial velocity measurements limit the companion mass to <2 times that of Jupiter. Screening of the light curves of 1014 potential Pleiades candidate stars uncovered no additional planets. An injection-and-recovery experiment using the K2 Pleiades light curves with simulated planets, assuming a planet population like that in the Kepler prime field, predicts only 0.8-1.8 detections (versus similar to 20 in an equivalent Kepler sample). The absence of Pleiades planet detections can be attributed to the much shorter monitoring time of K2 (80 d versus 4 yr), increased measurement noise due to spacecraft motion, and the intrinsic noisiness of the stars.

Ämnesord

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Nyckelord

planets and satellites:general

stars:low-mass

planetary systems

open clusters and associations:individual:Pleiades

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