K2 Mission Gold: EPIC 201912552b, a Moon Sized Exoplanet With Earth's Insolation (and 17 other systems!)

Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 18 Systems, Including a Planet Receiving Earth-like Insolation

Authors:

Montet et al

Abstract:

The extended Kepler mission, K2, is now providing photometry of new fields every three months in a search for transiting planets. In a recent study, Foreman-Mackey and collaborators presented a list of 36 planet candidates orbiting 31 stars in K2 Campaign 1. In this contribution, we present stellar and planetary properties for all systems. We combine ground-based seeing-limited survey data and adaptive optics imaging with an automated transit analysis scheme to validate 18 candidates as planets and identify 6 candidates as likely false positives. Of particular interest is EPIC 201912552, a bright (K=8.9) M2 dwarf hosting a 2.24 \pm 0.25 Earth radius planet with an equilibrium temperature of 271 \pm 16 K and an orbital period of 33 days. We also present two new open-source software packages that enabled this analysis: isochrones, a flexible tool for fitting theoretical stellar models to observational data to determine stellar properties, and vespa, a new general-purpose procedure to calculate false positive probabilities and statistically validate transiting exoplanets.

It would not let me put all the exoplanet names in the labels, so I am putting them here:

EPIC 201208431b, EPIC 201338508b, EPIC 201338508c, EPIC 201367065b, EPIC 201367065c, EPIC 201505350b, EPIC 201505350c, EPIC 201577035b, EPIC 20163023b, EPIC 201629650b, EPIC 201702477b, EPIC 201736247b, EPIC 201754305b, EPIC 201754305c, EPIC 20185537b, EPIC 20192552b, EPIC 201912552b