Characterization of the planetary system Kepler-101 with HARPS-N^⋆,⋆⋆

A hot super-Neptune with an Earth-sized low-mass companion

¹ INAF − Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
e-mail: bonomo@oato.inaf.it
² Observatoire Astronomique de l’Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
³ Dipartimento di Fisica e Astronomia “Galileo Galilei", Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁴ INAF − Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁵ SUPA, Institute for Astronomy, Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH93 HJ, UK
⁶ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
⁷ Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, 1350 Copenhagen, Denmark
⁸ SUPA, School of Physics & Astronomy, University of St. Andrews, North Haugh, St. Andrews Fife, KY16 9SS, UK
⁹ INAF − Fundación Galileo Galilei, Rambla Jos Ana Fernandez Prez 7, 38712 Brea Baja, Spain
¹⁰ INAF − IASF Milano, via Bassini 15, 20133 Milano, Italy
¹¹ INAF − Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90124 Palermo, Italy
¹² Centro de Astrofìsica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹³ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹⁴ Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK
¹⁵ Astrophysics Research Centre, School of Mathematics and Physics, Queens University, Belfast, UK

Received: 16 July 2014
Accepted: 12 September 2014

Abstract

We characterize the planetary system Kepler-101 by performing a combined differential evolution Markov chain Monte Carlo analysis of Kepler data and forty radial velocities obtained with the HARPS-N spectrograph. This system was previously validated and is composed of a hot super-Neptune, Kepler-101b, and an Earth-sized planet, Kepler-101c. These two planets orbit the slightly evolved and metal-rich G-type star in 3.49 and 6.03 days, respectively. With mass M_p = 51.1_-4.7^{+ 5.1} M_⊕, radius R_p = 5.77_-0.79^{+ 0.85} R_⊕, and density ρ_p = 1.45_-0.48^{+ 0.83} g cm^-3, Kepler-101b is the first fully characterized super-Neptune, and its density suggests that heavy elements make up a significant fraction of its interior; more than 60% of its total mass. Kepler-101c has a radius of 1.25_-0.17^{+ 0.19} R_⊕, which implies the absence of any H/He envelope, but its mass could not be determined because of the relative faintness of the parent star for highly precise radial-velocity measurements (K_p = 13.8) and the limited number of radial velocities. The 1σ upper limit, M_p< 3.8 M_⊕, excludes a pure iron composition with a probability of 68.3%. The architecture of the planetary system Kepler-101 − containing a close-in giant planet and an outer Earth-sized planet with a period ratio slightly larger than the 3:2 resonance − is certainly of interest for scenarios of planet formation and evolution. This system does not follow thepreviously reported trend that the larger planet has the longer period in the majority of Kepler systems of planet pairs with at least one Neptune-sized or larger planet.