K2-265 b: a transiting rocky super-Earth

¹ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
e-mail: w.f.lam@warwick.ac.uk
² Aix Marseille University, CNRS, CNES, LAM, Marseille, France
³ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁴ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁵ Observatoire Astronomique de l’Université de Genève, 51 Chemin des Maillettes, 1290 Versoix, Switzerland
⁶ Departamento de Astrofísica, Centro de Astrobiología (CSIC-INTA), ESAC campus 28692 Villanueva de la Cañada (Madrid), Spain
⁷ INAF – Osservatorio Astrofisico di Torino, Strada Osservatorio 20, 10025, Pino Torinese (TO), Italy
⁸ Caltech/IPAC-NASA Exoplanet Science Institute, 770 S. Wilson Ave, Pasadena, CA 91106, USA
⁹ INAF – Osservatorio Astrofisica di Catania, Via S. Sofia 78, 95123, Catania Italy
¹⁰ European Southern Observatory (ESO), Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
¹¹ Departamento de Física e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, Portugal

Received: 12 August 2018
Accepted: 21 September 2018

Abstract

We report the discovery of the super-Earth K2-265 b detected with K2 photometry. The planet orbits a bright (V_mag = 11.1) star of spectral type G8V with a period of 2.37 days. We obtained high-precision follow-up radial velocity measurements from HARPS, and the joint Bayesian analysis showed that K2-265 b has a radius of 1.71 ± 0.11 R_⊕ and a mass of 6.54 ± 0.84 M_⊕, corresponding to a bulk density of 7.1 ± 1.8 g cm⁻³. Composition analysis of the planet reveals an Earth-like, rocky interior; this object has a rock mass fraction of ~80%. The short orbital period and small radius of the planet puts it below the lower limit of the photoevaporation gap, where the envelope of the planet could have eroded owing to strong stellar irradiation, leaving behind an exposed core. Knowledge of the planet core composition allows us to infer the possible formation and evolution mechanism responsible for its current physical parameters.