Letter to the Editor

The CARMENES search for exoplanets around M dwarfs

HD147379 b: A nearby Neptune in the temperate zone of an early-M dwarf^★

¹ Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
Ansgar.Reiners@phys.uni-goettingen.de
² Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB, c/ de Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain
³ Centro de Astrobiología (CSIC-INTA), Instituto Nacional de Técnica Aeroespacial, Ctra. de Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁴ Zentrum für Astronomie der Universtät Heidelberg, Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany
⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁶ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁷ Centro Astronómico Hispano-Alemán (CSIC-MPG), Observatorio Astronómico de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almería, Spain
⁸ Instituto de Astrofísica de Canarias, and Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Tenerife, Spain
⁹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁰ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹¹ Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹² Leiden Observatory, Leiden University, Postbus 9513, 2300 RA, Leiden, The Netherlands
¹³ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
¹⁴ School of Physics and Astronomy, Queen Mary, University of London, 327 Mile End Road, London E1 4NS, UK
¹⁵ Instituto Nacional de Astrofísica, óptica y Electrónica, Luis Enrique Erro 1, Sta. Ma. Tonantzintla, Puebla, Mexico
¹⁶ FRACTAL SLNE C/ Tulipán 2, P13-1A, 28231 Las Rozas de Madrid, Spain
¹⁷ Institut für Theoretische Physik und Astrophysik, Leibnizstraße 15, 24118 Kiel, Germany
¹⁸ Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
¹⁹ Dpto. de Teoría de la Señal y Comunicaciones, Universidad Carlos III de Madrid, Escuela Politécnica Superior, Avda. de la Universidad, 30, 28911 Leganés, Madrid, Spain
²⁰ Dipartimento di Fisica, Unversità di Roma, “Tor Vergata”, Via della Ricerca Scientifica, 1, 00133 Roma, Italy
²¹ INAF, Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
²² Weizmann Institute of Science, 234 Herzl Street, Rehovot 761001, Israel
²³ University College Dublin, School of Physics, Belfield, Dublin 4, Ireland
²⁴ Universidad de Granada, Av. del Hospicio, s/n, 18010 Granada, Spain
²⁵ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
²⁶ The University of Chicago, Edward H. Levi Hall, 5801 South Ellis Avenue, Chicago, Illinois 60637, USA
²⁷ Dpto. de Física, Ingeniería de Sistemas y Teoría de la Señal, Escuela Politécnica Superior, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
²⁸ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany

Received: 24 October 2017
Accepted: 30 November 2017

Abstract

We report on the first star discovered to host a planet detected by radial velocity (RV) observations obtained within the CARMENES survey for exoplanets around M dwarfs. HD 147379 (V = 8.9 mag, M = 0.58 ± 0.08 M_⊙), a bright M0.0 V star at a distance of 10.7 pc, is found to undergo periodic RV variations with a semi-amplitude of K = 5.1 ± 0.4 m s⁻¹ and a period of P = 86.54 ± 0.06 d. The RV signal is found in our CARMENES data, which were taken between 2016 and 2017, and is supported by HIRES/Keck observations that were obtained since 2000. The RV variations are interpreted as resulting from a planet of minimum mass m_P sin i = 25 ± 2 M_⊕, 1.5 times the mass of Neptune, with an orbital semi-major axis a = 0.32 au and low eccentricity (e < 0.13). HD 147379 b is orbiting inside the temperate zone around the star, where water could exist in liquid form. The RV time-series and various spectroscopic indicators show additional hints of variations at an approximate period of 21.1 d (and its first harmonic), which we attribute to the rotation period of the star.