Bibcode
Lodieu, N.; Burgasser, A. J.; Pavlenko, Y.; Rebolo, R.
Bibliographical reference
Astronomy and Astrophysics, Volume 579, id.A58, 9 pp.
Advertised on:
7
2015
Journal
Citations
9
Refereed citations
8
Description
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.
Optical spectra of SDSS1256 and 2MASS 1626 are only available at the CDS
via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/579/A58Based
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).
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