Examinando por Autor "Tabernero, H. M."

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Acceso Abierto
ESPRESSO mass determination of TOI-263b: an extreme inhabitant of the brown dwarf desert
(EDP Sciences, 2021-06-04) Pallé, E.; Luque, R.; Zapatero Osorio, M. R.; Parviainen, H.; Ikoma, M.; Tabernero, H. M.; Zechmeister, M.; Mustill, A. J.; Béjar, V. J. S.; Narita, N.; Agencia Estatal de Investigación (AEI), European Research Council; Fundacao para a Ciencia e a Tecnologia (FCT); National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); Japan Society for the Promotion of Science (KAKENHI)
The TESS mission has reported a wealth of new planetary systems around bright and nearby stars amenable for detailed characterizations of planet properties and atmospheres. However, not all interesting TESS planets orbit around bright host stars. TOI-263 b is a validated ultra-short-period substellar object in a 0.56-day orbit around a faint (V = 18.97) M 3.5 dwarf star. The substellar nature of TOI-263 b was explored using multicolor photometry: a true radius of 0.87 ± 0.21 RJ was determined, establishing TOI-263 b ’s nature as somewhere between an inflated Neptune and a brown dwarf. The orbital period-radius parameter space occupied by TOI-263 b is quite unique, which prompted a further characterization of its true nature. Here, we report radial velocity measurements of TOI-263 obtained with three VLT units and the ESPRESSO spectrograph to retrieve the mass of TOI-263 b. We find that TOI-263 b is a brown dwarf with a mass of 61.6 ± 4.0 MJup. Additionally, the orbital period of the brown dwarf is found to be synchronized with the rotation period of the host star, and the system is found to be relatively active, possibly revealing a star–brown dwarf interaction. All these findings suggest that the system’s formation history might be explained via disk fragmentation and a later migration to close-in orbits. If the system is found to be unstable, TOI-263 will be an excellent target to test the migration mechanisms before the brown dwarf becomes “engulfed” by its parent star.
Acceso Abierto
The CARMENES search for exoplanets around M dwarfs: Rubidium abundances in nearby cool stars
(EDP Sciences, 2020-10-23) Abia, C.; Tabernero, H. M.; Korotin, S. A.; Montes, D.; Marfil, E.; Caballero, J. A.; Straniero, O.; Prantzos, N.; Ribas, I.; Reiners, A.; Quirrenbach, A.; Amado, P. J.; Béjar, V. J. S.; Cortés Contreras, M.; Dreizler, S.; Henning, T.; Jeffers, S. V.; Kaminski, A.; Kürster, M.; Lafarga, M.; López Gallifa, A.; Morales, J. C.; Nagel, E.; Passegger, V. M.; Pedraz, S.; Rodríguez López, C.; Schweitzer, A.; Zechmeister, M.; Fundacao para a Ciencia e a Tecnologia (FCT); Generalitat de Catalunya; National Aeronautics and Space Administration (NASA); Agencia Estatal de Investigación (AEI); López Gallifa, A. [0000-0001-6049-9366]; Tabernero, H. [0000-0002-8087-4298]; Montes, D. [0000-0002-7779-238X]; Korotin, S. [0000-0002-4058-8780]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737; Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFISICA DE ANDALUCIA (IAA), SEV-2017-0709; Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFÍSICA DE CANARIAS (IAC), SEV-2015-0548; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Due to their ubiquity and very long main-sequence lifetimes, abundance determinations in M dwarfs provide a powerful and alternative tool to GK dwarfs to study the formation and chemical enrichment history of our Galaxy. In this study, abundances of the neutron-capture elements Rb, Sr, and Zr are derived, for the first time, in a sample of nearby M dwarfs. We focus on stars in the metallicity range − 0.5 ≲ [Fe/H] ≲ +0.3, an interval poorly explored for Rb abundances in previous analyses. To do this we use high-resolution, high-signal-to-noise-ratio, optical and near-infrared spectra of 57 M dwarfs observed with CARMENES. The resulting [Sr/Fe] and [Zr/Fe] ratios for most M dwarfs are almost constant at about the solar value, and are identical to those found in GK dwarfs of the same metallicity. However, for Rb we find systematic underabundances ([Rb/Fe] < 0.0) by a factor two on average. Furthermore, a tendency is found for Rb – but not for other heavy elements (Sr, Zr) – to increase with increasing metallicity such that [Rb/Fe] ≳ 0.0 is attained at metallicities higher than solar. These are surprising results, never seen for any other heavy element, and are difficult to understand within the formulation of the s- and r-processes, both contributing sources to the Galactic Rb abundance. We discuss the reliability of these findings for Rb in terms of non-LTE (local thermodynamic equilibrium) effects, stellar activity, or an anomalous Rb abundance in the Solar System, but no explanation is found. We then interpret the full observed [Rb/Fe] versus [Fe/H] trend within the framework of theoretical predictions from state-of-the-art chemical evolution models for heavy elements, but a simple interpretation is not found either. In particular, the possible secondary behaviour of the [Rb/Fe] ratio at super-solar metallicities would require a much larger production of Rb than currently predicted in AGB stars through the s-process without overproducing Sr and Zr.