The CARMENES search for exoplanets around M dwarfs

A long-period planet around GJ 1151 measured with CARMENES and HARPS-N data^★

¹ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Bellaterra, Spain
e-mail: blanco@ice.csic.es
² Institut d’Estudis Espacials de Catalunya (IEEC), C/ Gran Capita 2–4, 08034 Barcelona, Spain
³ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
⁴ Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁵ Max Planck Institut für Sonnensystemforschung (MPS), Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁶ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁷ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁸ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁹ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁰ Thüringen Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹¹ Kimmel Fellow, Department of Earth & Planetary Sciences, Weizmann Institute of Science, Herzl St 234, 7610001 Rehovot, Israel
¹² Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹³ School of Sciences, European University Cyprus, Diogenes street, Engomi, 1516 Nicosia, Cyprus
¹⁴ Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
¹⁵ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy
¹⁶ Instituto de Astrofísica de Canarias (IAC), C/ Vía Láctea, 38205 La Laguna, Tenerife, Spain
¹⁷ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
¹⁸ Centre for Astrophysics, 499-565 West Street, Toowoomba, QLD, 4350, Australia
¹⁹ INAF – Osservatorio Astrofisico di Catania, Via Santa Sofia 78, 95123 Catania, Italy
²⁰ Centro Astronómico Hispano en Andalucía (CAHA), Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Spain
²¹ Max Planck Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germany
²² INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, Italy
²³ Departamento de Física de la Tierra y Astrofísica & IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, Pl. de las Ciencias, 1, 28040 Madrid, Spain
²⁴ Centro de Astrobiología (CAB), CSIC-INTA, Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain

Received: 24 September 2022
Accepted: 24 December 2022

Abstract

Context. Detecting a planetary companion in a short-period orbit through radio emission from the interaction with its host star is a new prospect in exoplanet science. Recently, a tantalising signal was found close to the low-mass stellar system GJ 1151 using LOFAR observations.

Aims. We studied spectroscopic time-series data of GJ 1151 in order to search for planetary companions, investigate possible signatures of stellar magnetic activity, and to find possible explanations for the radio signal.

Methods. We used the combined radial velocities measured from spectra acquired with the CARMENES, HARPS-N, and HPF instruments, extracted activity indices from those spectra in order to mitigate the impact of stellar magnetic activity on the data, and performed a detailed analysis of Gaia astrometry and all available photometric time series coming from the MEarth and ASAS-SN surveys.

Results. We found a M > 10.6 M_⊕ companion to GJ 1151 in a 390d orbit at a separation of 0.57 au. Evidence for a second modulation is also present; this could be due to long-term magnetic variability or a second (substellar) companion. The star shows episodes of elevated magnetic activity, one of which could be linked to the observed LOFAR radio emission. We show that it is highly unlikely that the detected GJ 1151 c, or any additional outer companion is the source of the detected signal. We cannot firmly rule out the suggested explanation of an undetected short-period planet that could be related to the radio emission, as we establish an upper limit of 1.2 M_⊕ for the minimum mass.