Detalles de publicación
PP 024104
A sub-Earth-mass planet orbiting Barnard's star
(1) Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife,
Spain
(2) Departamento de Astrofísica, Universidad de La Laguna, E-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 Espac̃o, CAUP, Universidade
do Porto, Rua das Estrelas, 4150-762, Porto, Portugal
(6) Departamento de Física e Astronomia, Faculdade de Ciências, Uni-
versidade do Porto, Rua do Campo Alegre, 4169-007, Porto, Portu-
gal
(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, E-28692, Villanueva de la Cañada
(Madrid), Spain
(9) INAF - Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11,
I-34143, Trieste, Italy
(10) IFPU–Institute for Fundamental Physics of the Universe, via Beirut
2, I-34151 Trieste, Italy
(11) INAF - Osservatorio Astrofisico di Torino, Strada Osservatorio 20,
I-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 Parla-
mento 1, I-90134 Palermo, Italy
(15) Instituto de Astrofísica e Ciências do EspaÇo, Faculdade de Ciên-
cias da Universidade de Lisboa, Campo Grande, 1749-016, Lisboa,
Portugal
(16) Light Bridges S. L., Avda. Alcalde Ramírez Bethencourt, 17, E-
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,
E-28040 Madrid, Spain
(18) Center for Space and Habitability, University of Bern,
Gesellschaftsstrasse 6, 3012 Bern, Switzerland
(19) Weltraumforschung und Planetologie, Physikalisches Institut, Uni-
versity 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, Ger-
many
Barnard's star is a primary target within the ESPRESSO guaranteed time observations (GTO) as it is the second closest neighbour to our Sun after the $\alpha$ Centauri stellar system. 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). Our analysis of ESPRESSO data using Gaussian process (GP) to model stellar activity suggests a long-term activity cycle at 3200d and confirms stellar activity due to rotation at 140d 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 233d. After subtracting the GP model, ESPRESSO RVs reveal several short-period candidate planet signals at periods of 3.15d, 4.12d, 2.34d, and 6.74d. We confirm the 3.15d signal as a sub-Earth mass planet, with a semi-amplitude of $55 \pm 7$cm/s, leading to a planet minimum mass $m_p \sin i$ of $0.37 \pm 0.05$Mearth, 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 47cm/s, thus corresponding to minimum masses in the range of 0.17-0.32Mearth. The sub-Earth mass planet at $3.1533 \pm 0.0006$d is in a close-to circular orbit with a semi-major axis of $0.0229 \pm 0.0003$AU, thus located inwards from the HZ of Barnard's star, with an equilibrium temperature of 400K. 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.