The CARMENES search for exoplanets around M dwarfs: two terrestrial planets orbiting G 264-012 and one terrestrial planet orbiting Gl 393

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We report the discovery of two planetary systems, namely G 264–012, an M 4.0 dwarf with two terrestrial planets (M_(b) sin i = 2.50^(+0.29)_(−0.30) Mꙩ and M_(c) sin i = 3.75^(+0.48)_(−0.47) Mꙩ), and Gl 393, a bright M 2.0 dwarf with one terrestrial planet (M_(b) sin i = 1.71 ± 0.24 Mꙩ). Although both stars were proposed to belong to young stellar kinematic groups, we estimate their ages to be older than about 700 Ma. The two planets around G 264–012 were discovered using only radial-velocity (RV) data from the CARMENES exoplanet survey, with estimated orbital periods of 2.30 d and 8.05 d, respectively. Photometric monitoring and analysis of activity indicators reveal a third signal present in the RV measurements, at about 100 d, caused by stellar rotation. The planet Gl 393 b was discovered in the RV data from the HARPS, CARMENES, and HIRES instruments. Its identification was only possible after modelling, with a Gaussian process (GP), the variability produced by the magnetic activity of the star. For the earliest observations, this variability produced a forest of peaks in the periodogram of the RVs at around the 34 d rotation period determined from Kepler data, which disappeared in the latest epochs. After correcting for them with this GP model, a significant signal showed at a period of 7.03 d. No significant signals in any of our spectral activity indicators or contemporaneous photometry were found at any of the planetary periods. Given the orbital and stellar properties, the equilibrium temperatures of the three planets are all higher than that for Earth. Current planet formation theories suggest that these two systems represent a common type of architecture. This is consistent with formation following the core accretion paradigm.
© ESO 2021. Artículo firmado por 55 autores. CARMENES is an instrument for the Centro Astronómico Hispano-Alemán (CAHA) at Calar Alto (Almería, Spain), operated jointly by the Junta de Andalucía and the Instituto de Astrofísica de Andalucía (CSIC). CARMENES was funded by the Max-Planck-Gesellschaft (MPG), the Consejo Superior de Investigaciones Científicas (CSIC), the Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through projects FICTS-2011-02, ICTS-2017-07-CAHA-4, and CAHA16-CE-3978, and the members of the CARMENES Consortium (Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Andalucía, Landessternwarte Königstuhl, Institut de Ciències de l’Espai, Institut für Astrophysik Göttingen, Universidad Complutense de Madrid, Thüringer Landessternwarte Tautenburg, Instituto de Astrofísica de Canarias, Hamburger Sternwarte, Centro de Astrobiología and Centro Astronómico Hispano-Alemán), with additional contributions by the MINECO, the Deutsche Forschungsgemeinschaft through the Major Research Instrumentation Programme and Research Unit FOR2544 “Blue Planets around Red Stars”, the Klaus Tschira Stiftung, the states of Baden-Württemberg and Niedersachsen, and by the Junta de Andalucía. We acknowledge financial support from the Agencia Estatal de Investigación of the Ministerio de Ciencia, Innovación y Universidades and the ERDF through projects PID2019-109522GB-C5[1:4]/AEI/10.13039/501100011033, PGC2018- 098153-B-C33, AYA2017-89637-R and the Centre of Excellence “Severo Ochoa” and “María de Maeztu” awards to the Instituto de Astrofísica de Canarias (SEV-2015-0548), Instituto de Astrofísica de Andalucía (SEV-2017-0709), and Centro de Astrobiología (MDM-2017-0737), the Fundação para a Ciência e a Tecnologia and the ERDF (COMPETE2020), the Programa Operacional Competitividade e Internacionalização (UID/FIS/04434/2019, UIDB/04434/2020, UIDP/04434/2020, PTDC/FIS-AST/[32113,28953,28987]/2017 and POCI-01- 0145-FEDER-[032113,028953,028987]), the Generalitat de Catalunya (CERCA programme), the European Research Council under the Horizon 2020 Framework programme (ERC Advanced Grant Origins 832428), FONDECYT (3180063), the Swiss National Science Foundation for supporting research with HARPS (SNSF 140649, 152721, 166227, and 184618), and NASA (NNX17AG24G). This publication made use of the SIMBAD database, the Aladin sky atlas, and the VizieR catalogue access tool developed at CDS, Strasbourg Observatory, France, the Python libraries Matplotlib, NumPy, and SciPy, the collection of software packages AstroPy and topfplotter, and data from the CARMENES data archive at CAB (CSIC-INTA), the ESO Science Archive Facility under request number vperdelw-552557, the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI), and the K2 mission.
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