A quarter century of spectroscopic monitoring of the nearby M dwarf Gl 514

A super-Earth on an eccentric orbit moving in and out of the habitable zone^★,★★

¹ INAF - Osservatorio Astrofísico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
e-mail: [email protected]
² Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Bellaterra, Spain
³ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
⁴ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁵ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
⁶ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁷ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomia s/n, 18008 Granada, Spain
⁸ Observatoire Astronomique de l’Université de Genève, 51 Chemin des Pegasi, 1290 Versoix, Switzerland
⁹ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹⁰ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
¹¹ Departamento de Matemática y Física Aplicadas, Universidad Católica de la Santísíma Concepción, Concepción, Chile
¹² Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹³ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
¹⁴ Centro de Astrobiología (CAB, CSIC-INTA), Depto. de Astrofísica, ESAC campus, 28692 Villanueva de la Canada (Madrid), Spain
¹⁵ Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
¹⁶ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
¹⁷ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁸ Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almería, Spain
¹⁹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
²⁰ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²¹ 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
²² Institut für Astrophysik, Georg-August-Universität, Friedrich-HundPlatz 1, 37077 Göttingen, Germany
²³ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

Received: 10 March 2022
Accepted: 13 April 2022

Abstract

Context. Statistical analyses based on Kepler data show that most of the early-type M dwarfs host multi-planet systems consisting of Earth- to sub-Neptune-sized planets with orbital periods of up to ~250 days, and that at least one such planet is likely located within the habitable zone. M dwarfs are therefore primary targets to search for potentially habitable planets in the solar neighbourhood.

Aims. We investigated the presence of planetary companions around the nearby (7.6 pc) and bright (V = 9 mag) early-type M dwarf Gl 514, analysing 540 radial velocities collected over nearly 25 yr with the HIRES, HARPS, and CARMENES spectrographs.

Methods. The data are affected by time-correlated signals at the level of 2–3 m s⁻¹ due to stellar activity, which we filtered out, testing three different models based on Gaussian process regression. As a sanity cross-check, we repeated the analyses using HARPS radial velocities extracted with three different algorithms. We used HIRES radial velocities and Hipparcos-Gaia astrometry to put constraints on the presence of long-period companions, and we analysed TESS photometric data.

Results. We find strong evidence that Gl 514 hosts a super-Earth on a likely eccentric orbit, residing in the conservative habitable zone for nearly 34% of its orbital period. The planet Gl 514b has minimum mass m_b sin i_b = 5.2 ± 0.9 M_⊕, orbital period P_b = 140.43 ± 0.41 days, and eccentricity e_b = 0.45_−0.14^+0.15. No evidence for transits is found in the TESS light curve. There is no evidence for a longer period companion in the radial velocities and, based on astrometry, we can rule out a ~0.2 M_Jup planet at a distance of ~3–10 astronomical units, and massive giant planets and brown dwarfs out to several tens of astronomical units. We discuss the possible presence of a second low-mass companion at a shorter distance from the host than Gl 514 b.

Conclusions. Gl 514 b represents an interesting science case for studying the habitability of planets on eccentric orbits. We advocate for additional spectroscopic follow-up to get more accurate and precise planetary parameters. Further follow-up is also needed to investigate the presence of additional planetary signals of less than 1 m s⁻¹.