The CARMENES search for exoplanets around M dwarfs

First visual-channel radial-velocity measurements and orbital parameter updates of seven M-dwarf planetary systems^⋆,⋆⋆

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: trifonov@mpia.de
² Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
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 Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁵ Zentrum für Astronomie der Universtät Heidelberg, Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany
⁶ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁷ Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB, c/ de Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain
⁸ Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
⁹ Instituto de Astrofśica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain, and Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna ; Spain
¹⁰ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹¹ Centro Astronómico Hispano-Alemán (CSIC-MPG), Observatorio Astronómico de Calar Alto, Sierra de los Filabres-04550 Gérgal, Almería, 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 Dipartimento di Fisica, Unversità di Roma, “Tor Vergata”, via della Ricerca Scientifica, 1 – 00133 Roma, Italy
²⁰ Weizmann Institute of Science, 234 Herzl Street, Rehovot 761001, Israel
²¹ University College Dublin, School of Physics, Belfield, Dublin 4, Ireland
²² European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
²³ The University of Chicago, Edward H. Levi Hall, 5801 South Ellis Avenue, Chicago, Illinois 60637, USA
²⁴ Universidad de Granada, Av. del Hospicio, s/n, 18010 Granada, Spain
²⁵ QUCAM Astronomical Detectors, http://www.qucam.com/  
²⁶ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
²⁷ 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
²⁸ Dpto de Física, Ingeniería de Sistemas y Teoría de la Señal, Escuela Politécnica Superior, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain

Received: 25 June 2017
Accepted: 20 September 2017

Abstract

Context. The main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS and either were reported to have one short period planetary companion (GJ 15 A, GJ 176, GJ 436, GJ 536 and GJ 1148) or are multiple planetary systems (GJ 581 and GJ 876).

Aims. We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES.

Methods. We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems were fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability.

Results. We confirm or provide supportive arguments for planets around all the investigated stars except for GJ 15 A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days. Although we cannot confirm the super-Earth planet GJ 15 Ab, we show evidence for a possible long-period (P_c = 7030_-630⁺⁹⁷⁰ d) Saturn-mass (m_csini = 51.8_-5.8^+5.5M_⊕) planet around GJ 15 A. In addition, based on our CARMENES and HIRES data we discover a second planet around GJ 1148, for which we estimate a period P_c = 532.6_-2.5^+4.1 days, eccentricity e_c = 0.342_-0.062^+0.050 and minimum mass m_csini = 68.1_-2.2^+4.9M_⊕.

Conclusions. The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars.