A HARPS view on K2-3^⋆,⋆⋆

¹ Univ. Grenoble Alpes, IPAG, 38000 Grenoble, France
e-mail: jose-manuel.almenara-villa@obs.ujf-grenoble.fr
² CNRS, IPAG, 38000 Grenoble, France
³ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁴ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
⁵ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁶ Observatoire Astronomique de l’Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland
⁷ Observatoire de Haute Provence, 04670 Saint-Michel l’Observatoire, France
⁸ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁹ Departamento de Física, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, RN, Brazil
¹⁰ Departamento de Astronomía, Universidad de Chile, 1058 Santiago, Chile
¹¹ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal

Received: 18 February 2015
Accepted: 27 August 2015

Abstract

K2 space observations recently found that three super-Earths transit the nearby M dwarf K2-3. The apparent brightness and the small physical radius of their host star rank these planets amongst the most favourable for follow-up characterisations. The outer planet orbits close to the inner edge of the habitable zone and might become one of the first exoplanets searched for biomarkers using transmission spectroscopy. We used the HARPS velocimeter to measure the mass of the planets. The mass of planet b is 8.4 ± 2.1 M_⊕, while our determination of those planets c and d are affected by the stellar activity. With a density of 4.32^+2.0_-0.76 g cm^-3, planet b is probably mostly rocky, but it could contain up to 50% water.