Volume 579, July 2015
|Number of page(s)||9|
|Section||Stellar structure and evolution|
|Published online||26 June 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
2 Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
3 Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093, USA
4 Main Astronomical Observatory of the National Academy of Sciences of Ukraine, 03680 Kyiv, Ukraine
5 Center for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK
6 Consejo Superior de Investigaciones Científicas, CSIC, Spain
Received: 19 December 2014
Accepted: 25 May 2015
Aims. The aim of the project is to search for lithium in absorption at 6707.8 Å to constrain the nature and mass of the brightest low-metallicity L-type dwarfs (referred to as L subdwarfs) identified in large-scale surveys.
Methods. We obtained low- to intermediate-resolution (R ~ 2500–9000) optical (~560–770 nm) spectra of two mid-L subdwarfs, SDSS J125637.13−022452.4 (SDSS1256; sdL3.5) and 2MASS J162620.14+392519.5 (2MASS1626; sdL4) with spectrographs on the European Southern Observatory Very Large Telescope and the Gran Telescopio de Canarias.
Results. We report the presence of a feature at the nominal position of the lithium absorption doublet at 6707.8 Å in the spectrum of SDSS1256, with an equivalent width of 66 ± 27 Å at 2.4σ, which we identify as arising from a CaH molecular transition based on atmosphere models. We do not see any feature at the position of the lithium feature in the spectrum of 2MASS1626. The existence of overlapping molecular absorption sets a confusion detection limit of [Li/H] = −3 for equivalently typed L subdwarfs. We provided improved radial velocity measurements of −126±10 km s-1 and −239±12 km s-1 for SDSS1256 and 2MASS1626, respectively, as well as revised Galactic orbits. We implemented adjusting factors for the CaH molecule in combination with the NextGen atmosphere models to fit the optical spectrum of SDSS1256 in the 6200–7300 Å range. We also estimate the expected Li abundance from interstellar accretion ([Li/H] = −5), place limits on circumstellar accretion (109 g/yr), and discuss the prospects of Li searches in cooler L and T subdwarfs.
Key words: techniques: spectroscopic / brown dwarfs / subdwarfs
Optical spectra of SDSS1256 and 2MASS 1626 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/579/A58
Based on observations collected at the European Southern Observatory, Chile, under programmes 089.C-0883 and 091.C-0594A.
Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma (programmes GTC64_10B and GTC38_11A).
© ESO, 2015
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