Examinando por Autor "Lodieu, N."

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Acceso Abierto
Spectral library of age-benchmark low-mass stars and brown dwarfs
(Oxford Academics: Oxford University Press, 2020-12-27) Manjavacas, E.; Lodieu, N.; Béjar, V. J. S.; Zapatero Osorio, M. R.; Boudreault, S.; Bonnefoy, M.; Ministerio de Economía y Competitividad (MINECO); Agencia Estatal de Investigación (AEI); Manjavacas, E. [0000-0003-0192-6887]; Zapatero Osorio, M. R. [0000-0001-5664-2852]
In recent years, some extremely red brown dwarfs have been discovered. They were believed to have a low surface gravity, but many of their spectral characteristics are similar to those of high-surface-gravity brown dwarfs, showing that the spectral characteristics of young brown dwarfs are poorly understood. We aim to test surface-gravity indicators in late-M and early-L brown dwarf spectra using data obtained with the X-shooter spectrograph at the Very Large Telescope. We select a benchmark sample of brown dwarf members of Chamaeleon I (∼2 Myr), Upper Scorpius (5−10 Myr), the Pleiades (132 ± 27 Myr) and Praesepe (590−790 Myr) with well-constrained ages and similar metallicities. We provide a consistent spectral classification of the sample in the optical and in the near-infrared. We measure the equivalent widths of their alkali lines, finding that they have a moderate correlation with age, especially for objects with spectral types M8 and later. We use spectral indices defined in the literature to estimate surface gravity, finding that their gravity assignment is accurate for 75 per cent of our sample. We investigate the correlation between red colour and age, finding that after ∼10 Myr, the colour does not change significantly for our sample with spectral types M6.0–L3.0. In this case, the red colours might be associated with circumstellar discs, ring structures, extinction, or viewing angle. Finally, we calculate the bolometric luminosity, and J and K bolometric corrections for our sample. We find that six objects are overluminous compared with other members of the same association. These objects are flagged as binary candidates by the Gaia survey.
Acceso Abierto
Strong H alpha emission in the young planetary mass companion 2MASS J0249-0557 c
(EDP Sciences, 2021-01-15) Chinchilla, P.; Béjar, V. J. S.; Lodieu, N.; Zapatero Osorio, M. R.; Gauza, B.; European Southern Observatory (ESO); Agencia Estatal de Investigación (AEI); European Space Agency (ESA); Chinchilla, P. [0000-0002-3031-4911]; Lodieu, N. [0000-0002-3612-8968]; Gauza, B. [0000-0001-5452-2056]
Aims. Our objective is the optical and near-infrared spectroscopic characterisation of 2MASS J0249−0557 c, a recently discovered young planetary mass companion to the β Pictoris (~25 Myr) member 2MASS J0249−0557. Methods. Using the Visible and Infrared Survey Telescope for Astronomy Hemisphere Survey and the Two Micron All Sky Survey (2MASS) data, we independently identified the companion 2MASS J0249−0557 c. We also obtained low-resolution optical spectroscopy of this object using the Optical System for Imaging and low-intermediate-Resolution Integrated Spectroscopy spectrograph at the Gran Telescopio Canarias, and near-infrared spectroscopy using the Son of Isaac spectrograph on the New Technology Telescope. Results. We classified 2MASS J0249−0557 c with a spectral type of L2.5 ± 0.5 in the optical and L3 ± 1 in the near-infrared. We identified several spectroscopic indicators of youth both in the optical and in the near-infrared that are compatible with the age of the β Pictoris moving group: strong absorption due to oxides, weak alkaline atomic lines, and a triangular shape of the H-band pseudo-continuum. We also detect a strong Hα emission, with a pseudo-equivalent width (pEW) of −90−40+20 Å, which seems persistent at timescales from several days to a few years. This indicates strong chromospheric activity or disk accretion. Although many M-type brown dwarfs have strong Hα emission, this target is one of the very few L-type planetary mass objects in which this strong Hα emission has been detected. Lithium absorption at 6708 Å is observed with pEW ≲5 Å. We also computed the binding energy of 2MASS J0249−0557 c and obtained an (absolute) upper limit of U = (−8.8 ± 4.4) × 1032 J. Conclusions. Similarly to other young brown dwarfs and isolated planetary mass objects, strong Hα emission due to accretion or chromospheric activity is also present in young planetary mass companions at ages of some dozen million years. We also found that 2MASS J0249−0557 c is one of the wide substellar companions with the lowest binding energy known to date.
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%.