K2 Discovers a Busy Bee: An Unusual Transiting Neptune Found in the Beehive Cluster

Abstract

Open clusters have been the focus of several exoplanet surveys, but only a few planets have so far been discovered. The Kepler spacecraft revealed an abundance of small planets around small cool stars, therefore, such cluster members are prime targets for exoplanet transit searches. Keplerʼs new mission, K2, is targeting several open clusters and star-forming regions around the ecliptic to search for transiting planets around their low-mass constituents. Here, we report the discovery of the first transiting planet in the intermediate-age ( and an orbital period of 10.134 days. We combined photometry, medium/high-resolution spectroscopy, adaptive optics/speckle imaging, and archival survey images to rule out any false-positive detection scenarios, validate the planet, and further characterize the system. The planet's radius is very unusual as M-dwarf field stars rarely have Neptune-sized transiting planets. The comparatively large radius of K2-95b is consistent with the other recently discovered cluster planets K2-25b (Hyades) and K2-33b (Upper Scorpius), indicating systematic differences in their evolutionary states or formation. These discoveries from K2 provide a snapshot of planet formation and evolution in cluster environments and thus make excellent laboratories to test differences between field-star and cluster planet populations.

Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. IV. Updated Properties for 86 Cool Dwarfs Observed during Campaigns 1–17

“…EPIC 211916756 (K2-95) is the only star fromMann et al (2017a) included in this paper. Our estimates of R = 0.42 ± 0.01 R , T eff = 3463 ± 76K agree well with the previously published estimates of R = 0.44 ± 0.02 R and T eff = 3410 ± 65K fromMann et al (2017a); R = 0.402 ± 0.050 R and T eff = 3471 ± 124K fromObermeier et al (2016); R = 0.44 ± 0.03 R and T eff = 3325 ± 100K fromPepper et al (2017); and R = 0.42 ± 0.09 R and T eff = 3704 ± 214K fromMartinez et al (2017).…”

Stellar and Planetary Parameters for K2's Late-type Dwarf Systems from C1 to C5

“…This indicates that there is an excellent agreement between our two methods and verifies the validity of our approach. Additionally, our stellar parameters are consistent with those from a number of previous publications Montet et al 2015;Petigura et al 2015;Mann et al 2016;Obermeier et al 2016;Schlieder et al 2016).…”

Precise Masses in the WASP-47 System

“…The Kepler era of discovery was instead expected to give way to a new era in which the K2 mission would largely find more of the same kinds of planets that had been previously discovered, just orbiting brighter stars or in different environments. While K2 has certainly delivered in that regard, finding small planets around nearby stars well-suited to detailed characterization (Vanderburg et al , 2016aSinukoff et al 2016;Crossfield et al 2017; Rodriguez et al 2017), temperate planets around M-dwarfs Petigura et al 2015;Dressing et al 2017aDressing et al , 2017bMartinez et al 2017), and planets in open clusters (David et al 2016;Libralato et al 2016;Mann et al 2016aMann et al , 2016bObermeier et al 2016;Mann et al 2017), K2 is still delivering new and unexpected discoveries, like the unique architecture of the WASP-47 system, that are yielding fundamental insights about the formation and evolution of planetary systems.…”