Examinando por Autor "Rebolo, R."

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Restringido
Two close binaries across the hydrogen-burning limit in the Praesepe open cluster
(Oxford Academics: Oxford University Press, 2020-08-21) Lodieu, N.; Del Burgo, C.; Manjavacas, E.; Zapatero Osorio, M. R.; Álvarez, C.; Béjar, V. J. S.; Boudreault, S.; Lyke, J.; Rebolo, R.; Chinchilla, P.; Consejo Nacional de Ciencia y Tecnología (CONACYT); Ministerio de Economía y Competitividad (MINECO); Manjavacas, E. [0000-0003-0192-6887]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
We present Keck I/OSIRIS and Keck II/NIRC2 adaptive optics imaging of two member candidates of the Praesepe stellar cluster (d = 186.18 ± 0.11 pc; 590–790 Myr), UGCS J08451066+2148171 (L1.5 ± 0.5) and UGCS J08301935+2003293 (no spectroscopic classification). We resolved UGCS J08451066+2148171 into a binary system in the near-infrared, with a K-band wavelength flux ratio of 0.89 ± 0.04 and a projected separation of 60.3 ± 1.3 mas (11.2 ± 0.7 au; 1σ). We also resolved UGCS J08301935+2003293 into a binary system with a flux ratio of 0.46 ± 0.03 and a separation of 62.5 ± 0.9 mas. Assuming zero eccentricity, we estimate minimum orbital periods of ∼100 yr for both systems. According to theoretical evolutionary models, we derive masses in the range of 0.074–0.078 and 0.072–0.076 M⊙ for the primary and secondary of UGCS J08451066+2148171 for an age of 700 ± 100 Myr. In the case of UGCS J08301935+2003293, the primary is a low-mass star at the stellar/substellar boundary (0.070–0.078 M⊙), while the companion candidate might be a brown dwarf (0.051–0.065 M⊙). These are the first two binaries composed of L dwarfs in Praesepe. They are benchmark systems to derive the location of the substellar limit at the age and metallicity of Praesepe, determine the age of the cluster based on the lithium depletion boundary test, derive dynamical masses, and improve low-mass stellar and substellar evolutionary models at a well-known age and metallicity.
Acceso Abierto
USco1621 B and USco1556 B: Two wide companions at the deuterium-burning mass limit in Upper Scorpius
(EDP Sciences, 2020-01-24) Chinchilla, P.; Béjar, V. J. S.; Lodieu, N.; Gauza, B.; Zapatero Osorio, M. R.; Rebolo, R.; Pérez Garrido, A.; Álvarez, C.; Manjavacas, E.; European Southern Observatory (ESO); Agencia Estatal de Investigación (AEI); Ministerio de Economía y Competitividad (MINECO); Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT); Chinchilla, P. [0000-0002-3031-4911]; Béjar, V. J. S. [0000-0002-5086-4232]; Lodieu, N. [0000-0002-3612-8968]; Gauza, B. [0000-0001-5452-2056]; Zapatero Osorio, M. R. [0000-0001-5664-2852]; Rebolo, R. [0000-0003-3767-7085]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Aims. Our objective is to identify analogues of gas giant planets, but located as companions at wide separations of very young stars. The main purpose is to characterise the binarity frequency and the properties of these substellar objects, and to elucidate their early evolutionary stages. Methods. To identify these objects, we cross correlated the Visible and Infrared Survey Telescope for Astronomy Hemisphere Survey and the United Kingdom Infrared Telescope Infrared Deep Sky Survey Galactic Clusters Survey catalogues to search for common proper motion companions to 1195 already known members of Upper Scorpius (USco; age ~5–10 Myr, distance ~145 pc). We present the discovery and spectroscopic characterisation of two very wide substellar companions of two early-M stars in Upper Scorpius: USco1621 B and USco1556 B. We obtained optical and near-infrared low-resolution spectroscopy of the candidates to characterise their spectral energy distribution and confirm their youth and membership to the association. We also acquired adaptive optics images of the primaries and secondaries to search for signs of binarity and close companions. Results. By comparison with field dwarfs and other young members of USco, we determined a spectral type of M8.5 in the optical for both companions, along with L0 and L0.5 in the near-infrared for USco1621 B and USco1556 B, respectively. The spectra of the two companions show evident markers of youth, such as weak alkaline Na I and K I lines, along with the triangular shape of the H-band. The comparison with theoretical evolutionary models gives estimated masses of 0.015 ± 0.002 and 0.014 ± 0.002 M⊙, with temperatures of 2270 ± 90 and 2240 ± 100 K, respectively. The physical separations between the components of both systems are 2880 ± 20 and 3500 ± 40 AU for USco1621 and USco1556 systems, respectively. We did not find any additional close companion in the adaptive optics images. The probability that the two secondaries are physically bound to their respective primaries, and not chance alignments of USco members, is 86%, and the probability that none of them are physically related is 1.0%.