Letter to the Editor

The CARMENES search for exoplanets around M dwarfs

No evidence for a super-Earth in a 2-day orbit around GJ 1151^⋆

¹ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Bellaterra, Spain
e-mail: perger@ice.cat
² Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
³ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁴ Centro de Astrobiología (CSIC-INTA), ESAC, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁵ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁶ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁷ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁸ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁹ Centro Astronómico Hispano-Alemán (CAHA), Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Spain
¹⁰ Thüringen Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹² Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
¹³ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹⁴ 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, 28040 Madrid, Spain
¹⁵ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁶ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain

Received: 11 March 2021
Accepted: 22 April 2021

Abstract

Context. The interaction between Earth-like exoplanets and the magnetic field of low-mass host stars are considered to produce weak emission signals at radio frequencies. A study using LOFAR data announced the detection of radio emission from the mid M-type dwarf GJ 1151 that could potentially arise from a close-in terrestrial planet. Recently, the presence of a 2.5-M_⊕ planet orbiting GJ 1151 with a 2-day period has been claimed using 69 radial velocities (RVs) from the HARPS-N and HPF instruments.

Aims. We have obtained 70 new high-precision RV measurements in the framework of the CARMENES M-dwarf survey and use these data to confirm the presence of the claimed planet and to place limits on possible planetary companions in the GJ 1151 system.

Methods. We analysed the periodicities present in the combined RV data sets from all three instruments and calculated the detection limits for potential planets in short-period orbits.

Results. We cannot confirm the recently announced candidate planet and conclude that the 2-day signal in the HARPS-N and HPF data sets is most probably produced by a long-term RV variability, possibly arising from an outer planetary companion that has yet to be constrained. We calculate a 99.9% significance detection limit of 1.50 m s⁻¹ in the RV semi-amplitude, which places upper limits of 0.7 M_⊕ and 1.2 M_⊕ on the minimum masses of potential exoplanets with orbital periods of 1 and 5 days, respectively.