Issue |
A&A
Volume 690, October 2024
|
|
---|---|---|
Article Number | A79 | |
Number of page(s) | 36 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/202451311 | |
Published online | 01 October 2024 |
A sub-Earth-mass planet orbiting Barnard’s star★
1
Instituto de Astrofísica de Canarias,
38205
La Laguna, Tenerife,
Spain
2
Departamento de Astrofísica, Universidad de La Laguna,
38206
La Laguna, Tenerife,
Spain
3
Consejo Superior de Investigaciones Científicas,
Spain
4
Observatoire de Genève, Département d’Astronomie, Université de Genève,
Chemin Pegasi 51b,
1290
Versoix,
Switzerland
5
Instituto de Astrofísica e Ciências do Espaco, CAUP, Universidade do Porto, Rua das Estrelas,
4150-762
Porto,
Portugal
6
Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre,
4169-007
Porto,
Portugal
7
Centro de Astrofísica da Universidade do Porto, Rua das Estrelas,
4150-762
Porto,
Portugal
8
Centro de Astrobiología (CAB), CSIC-INTA, ESAC campus,
Camino Bajo del Castillo s/n,
28692
Villanueva de la Cañada (Madrid),
Spain
9
INAF - Osservatorio Astronomico di Trieste,
via G. B. Tiepolo 11,
34143
Trieste,
Italy
10
IFPU–Institute for Fundamental Physics of the Universe,
via Beirut 2,
34151
Trieste,
Italy
11
INAF - Osservatorio Astrofisico di Torino,
Strada Osservatorio 20,
10025,
Pino Torinese (TO),
Italy
12
ESO - European Southern Observatory,
Av. Alonso de Cordova 3107, Vitacura,
Santiago,
Chile
13
Département de Physique, Institut Trottier de Recherche sur les Exoplanètes, Université de Montréal, Montréal,
Québec,
H3T 1J4,
Canada
14
INAF - Osservatorio Astronomico di Palermo,
Piazza del Parlamento 1,
90134
Palermo,
Italy
15
Instituto de Astrofísica e Ciências do EspaÇo, Faculdade de Ciências da Universidade de Lisboa, Campo Grande,
1749-016
Lisboa,
Portugal
16
Light Bridges S. L.,
Avda. Alcalde Ramírez Bethencourt, 17,
35004
Las Palmas de Gran Canaria, Canarias,
Spain
17
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
18
Center for Space and Habitability, University of Bern,
Gesellschaftsstrasse 6,
3012
Bern,
Switzerland
19
Weltraumforschung und Planetologie, Physikalisches Institut, University of Bern,
Gesellschaftsstrasse 6,
3012
Bern,
Switzerland
20
Subaru Telescope, National Astronomical Observatory of Japan,
650 N Aohoku Place,
Hilo,
HI
96720,
USA
21
Hamburger Sternwarte,
Gojenbergsweg 112,
21029
Hamburg,
Germany
★★ Corresponding author; e-mail: jonay.gonzalez@iac.es
Received:
29
June
2024
Accepted:
26
August
2024
Context. ESPRESSO guaranteed time observations (GTOs) at the 8.2m VLT telescope were performed to look for Earth-like exoplanets in the habitable zone of nearby stars. Barnard’s star is a primary target within the ESPRESSO GTO as it is the second closest neighbour to our Sun after the α Centauri stellar system.
Aims. We present here a large set of 156 ESPRESSO observations of Barnard’s star carried out over four years with the goal of exploring periods of shorter than 50 days, thus including the habitable zone (HZ).
Methods. Our analysis of ESPRESSO data using Gaussian process (GP) to model stellar activity suggests a long-term activity cycle at 3200 d and confirms stellar activity due to rotation at 140 d as the dominant source of radial velocity (RV) variations. These results are in agreement with findings based on publicly available HARPS, HARPS-N, and CARMENES data. ESPRESSO RVs do not support the existence of the previously reported candidate planet at 233 d.
Results. After subtracting the GP model, ESPRESSO RVs reveal several short-period candidate planet signals at periods of 3.15 d, 4.12 d, 2.34 d, and 6.74 d. We confirm the 3.15 d signal as a sub-Earth mass planet, with a semi-amplitude of 55 ± 7 cm s−1, leading to a planet minimum mass mp sin i of 0.37 ± 0.05 M⊕, which is about three times the mass of Mars. ESPRESSO RVs suggest the possible existence of a candidate system with four sub-Earth mass planets in circular orbits with semi-amplitudes from 20 to 47 cm s−1, thus corresponding to minimum masses in the range of 0.17–0.32 M⊕.
Conclusions. The sub-Earth mass planet at 3.1533 ± 0.0006 d is in a close-to circular orbit with a semi-major axis of 0.0229 ± 0.0003 AU, thus located inwards from the HZ of Barnard’s star, with an equilibrium temperature of 400 K. Additional ESPRESSO observations would be required to confirm that the other three candidate signals originate from a compact short-period planet system orbiting Barnard’s star inwards from its HZ.
Key words: techniques: radial velocities / techniques: spectroscopic / planets and satellites: terrestrial planets / stars: activity / stars: low-mass / stars: individual: GJ 699
Based [in part] on Guaranteed Time Observations collected at the European Southern Observatory under ESO programmes 1102.C-0744, 1104.C-0350, 106.21M2.001, 106.21M2.004, 106.21M2.006, 108.22GM.001, 108.2254.001, 108.2254.003, 108.2254.004, 108.2254.006, 110.24CD.001, 110.24CD.003 by the ESPRESSO Consortium.
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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