A large spectroscopic sample of L and T dwarfs from UKIDSS LAS: peculiar objects, binaries, and space density
Date Issued
2015
Author(s)
Marocco, F.
•
Jones, H. R. A.
•
Day-Jones, A. C.
•
Pinfield, D. J.
•
Lucas, P. W.
•
Burningham, B.
•
Zhang, Z. H.
•
•
Gomes, J. I.
•
Smith, L.
Description
We thank the referee, John Gizis, for comments that have significantly improved the quality of this paper. FM would like to thank Antonio Chrysostomou and Philippe Delorme for the useful discussions and their valuable suggestions. This research is based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile programs 086.C-0450, 087.C-0639, 088.C-0048, and 091.C-0452. The authors would like to acknowledge the Marie Curie 7th European Community Framework Programme grant no. 247593 Interpretation and Parametrization of Extremely Red COOL dwarfs (IPERCOOL) International Research Staff Exchange Scheme. FM would like to acknowledge the support received from the European Science Foundation (ESF) within the framework of the ESF activity entitled ‘Gaia Research for European Astronomy Training’, Exchange Grant number 4641. This research has made use of: the SIMBAD data base operated at CDS France; the SpeX Prism Spectral Libraries, maintained by Adam Burgasser at http://pono.ucsd.edu/∼adam/browndwarfs/spexprism ; and, the M, L, and T dwarf compendium housed at dwarfArchives.org and maintained by Chris Gelino, Davy Kirkpatrick, and Adam Burgasser.
Abstract
We present the spectroscopic analysis of a large sample of late-M, L, and T dwarfs from the United Kingdom Deep Infrared Sky Survey. Using the YJHK photometry from the Large Area Survey and the red-optical photometry from the Sloan Digital Sky Survey we selected a sample of 262 brown dwarf candidates and we have followed-up 196 of them using the echelle spectrograph X-shooter on the Very Large Telescope. The large wavelength coverage (0.30-2.48 μm) and moderate resolution (R ̃ 5000-9000) of X-shooter allowed us to identify peculiar objects including 22 blue L dwarfs, 2 blue T dwarfs, and 2 low-gravity M dwarfs. Using a spectral indices-based technique, we identified 27 unresolved binary candidates, for which we have determined the spectral type of the potential components via spectral deconvolution. The spectra allowed us to measure the equivalent width of the prominent absorption features and to compare them to atmospheric models. Cross-correlating the spectra with a radial velocity standard, we measured the radial velocity of our targets, and we determined the distribution of the sample, which is centred at -1.7 ± 1.2 km s-1 with a dispersion of 31.5 km s-1. Using our results, we estimated the space density of field brown dwarfs and compared it with the results of numerical simulations. Depending on the binary fraction, we found that there are (0.85 ± 0.55) × 10-3 to (1.00 ± 0.64) × 10-3 objects per cubic parsec in the L4-L6.5 range, (0.73 ± 0.47) × 10-3 to (0.85 ± 0.55) × 10-3 objects per cubic parsec in the L7-T0.5 range, and (0.74 ± 0.48) × 10-3 to (0.88 ± 0.56) × 10-3 objects per cubic parsec in the T1-T4.5 range. We notice that there seems to be an excess of objects in the L-T transition with respect to the late-T dwarfs, a discrepancy that could be explained assuming a higher binary fraction than expected for the L-T transition, or that objects in the high-mass end and low-mass end of this regime form in different environments, i.e. following different initial mass functions.
Volume
449
Issue
4
Start page
3651
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.449.3651M
Rights
open.access
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