Volume 581, September 2015
|Number of page(s)||11|
|Section||Stellar structure and evolution|
|Published online||07 September 2015|
1 Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38200 La Laguna, Tenerife, Spain
e-mail: email@example.com; firstname.lastname@example.org; email@example.com
2 Departamento de Astrofísica, Universidad de La Laguna (ULL), 38205 La Laguna, Tenerife, Spain
3 Centro de Astrobiología (CSIC-INTA), Ctra. Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
4 Consejo Superior de Investigaciones Científicas, CSIC, Spain
5 Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Ukraine
6 Center for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK
7 Universidad Politécnica de Cartagena, Campus Muralla del Mar, Cartagena, 30202 Murcia, Spain
Received: 5 September 2014
Accepted: 30 June 2015
Aims. The aim of the project is to characterise the two components of the brown dwarf system nearest to the Sun, WISE J104915.57−531906.1 (also called Luhman 16AB) at optical and near-infrared wavelengths.
Methods. We obtained high signal-to-noise intermediate-resolution (R ~ 6000−11 000) optical (600−1000 nm) and near-infrared (1000−2480 nm) spectra of each component of Luhman 16AB with the X-Shooter instrument on the Very Large Telescope.
Results. We classify the primary and secondary of the Luhman 16 system as L6−L7.5 and T0±1, respectively, in agreement with previous measurements published in the literature. We present measurements of the lithium pseudo-equivalent widths, which appear of similar strength in both components (8.2 ± 1.0 Å for the L and 8.4 ± 1.5 Å for the T component). The presence of lithium (7Li) in both components implies masses lower than 0.06 M⊙, while the comparison with models suggests lower limits of 0.04 M⊙. The detection of lithium in the T component is the first of its kind. Similarly, we assess the strength of other alkali lines (e.g. pseudo-equivalent widths of 6−7 Å for RbI and 4−7 Å for CsI) present in the optical and near-infrared regions and compare with estimates for L and T dwarfs. We also derive effective temperatures and luminosities of each component of the binary: −4.66 ± 0.08 dex and 1305+180-135 K for the L dwarf and −4.68 ± 0.13 dex and 1320+185-135 K for the T dwarf. According to our radial velocity determinations, the binary does not appear to belong to any of the well-known moving group. Our preliminary theoretical analysis of the optical and J-band spectra indicates that the L- and T-type spectra can be reproduced with a single temperature and gravity but different relative chemical abundances, which strongly affects the spectral energy distribution of L/T transition objects.
Key words: techniques: spectroscopic / brown dwarfs / binaries: general / stars: fundamental parameters
Based on observations collected at the European Southern Observatory, Chile, under DDT programme 290.C-5200(B) (PI Lodieu).
FITS files of the reduced spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/581/A73
© ESO, 2015
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.