Examinando por Autor "Marfil, E."

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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.