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

Abstract

We describe a "super-Earth"-size (2.30 ± 0.16R ⊕ ) 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 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 ≈ 20 d and its spectrum contains no Hα 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 (< 1 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 lightcurves of 1014 potential Pleiades candidate stars uncovered no additional planets. An injection-and-recovery experiment using the K2 Pleiades lightcurves with simulated planets, assuming a planet population like that in the Kepler prime field, predicts only 0.8-1.8 detections (vs. ∼ 20 in an equivalent Kepler sample). The absence of Pleiades planet detections can be attributed to the much shorter monitoring time of K2 (80 days vs. 4 years), increased measurement noise due to spacecraft motion, and the intrinsic noisiness of the stars.

TESS Reveals that the Nearby Pisces–Eridanus Stellar Stream is only 120 Myr Old

“…If we are correct, this would mean that the stream provides an environment to its stars that is distinct from that of the Pleiades, and which might be representative of a more common star formation channel in the Galaxy than dense cluster formation (e.g., Clark et al 2005). That would make the Psc-Eri stream an excellent target for exoplanet searches, which have so far turned up nothing for the Pleiades (Gaidos et al 2017). et al (2019) discovered an exciting new stellar stream located relatively nearby (d ≃ 80-226 pc).…”

“…If true, the Psc-Eri stream could become a valuable benchmark system for comparing environmental impact relative to the Pleiades, and for examining how photoevaporation sculpts planet sizes. To date, no planets have been found in the Pleiades (Gaidos et al 2017). The stream thus presents a new opportunity to search for Pleiades-aged planets.…”

Planetesimals around stars with TESS (PAST) – I. Transient dimming of a binary solar analogue at the end of the planet accretion era

“…Other distant sources can be the source of faint signals, e.g. by "sticking" of charge from a bright variable star like an eclipsing binary (Gaidos et al 2017) but these effects are unlikely to produce a 10% signal in a bright star. We conclude that the binary system HD 240779+BD+10 714B is responsible for the signal, but which star of the two (or both?)…”

Three Small Planets Transiting the Bright Young Field Star K2-233

“…The mission has yielded all of the known transiting planets in young clusters and associations to date (see Rizzuto et al 2017, for a review), as well as a number of planets around active field stars that are likely to be moderately young (e.g. Gaidos et al 2017;Dai et al 2017;Barragán et al 2018). K2 is also responsible for contributing some of the brightest known transiting planet hosts, such as HIP 41378 (Vanderburg et al 2016a), HD 106315 (Crossfield et al 2017;Rodriguez et al 2017), HD 3167 (Vanderburg et al 2016b;Gandolfi et al 2017), and GJ 9827 (Rodriguez et al 2018;Niraula et al 2017).…”