Photometric brown-dwarf classification. II. A homogeneous sample of 1361 L and T dwarfs brighter than J = 17.5 with accurate spectral types

We present a homogeneous sample of 1361 L and T dwarfs brighter than J = 17.5 (of which 998 are new), from an effective area of 3070 deg2, classified by the photo-type method to an accuracy of one spectral sub-type using izYJHKW1W2 photometry from SDSS+UKIDSS+WISE. Other than a small bias in the early L types, the sample is shown to be effectively complete to the magnitude limit, for all spectral types L0 to T8. The nature of the bias is an incompleteness estimated at 3% because peculiar blue L dwarfs of type L4 and earlier are classified late M. There is a corresponding overcompleteness because peculiar red (likely young) late M dwarfs are classified early L. Contamination of the sample is confirmed to be small: so far spectroscopy has been obtained for 19 sources in the catalogue and all are confirmed to be ultracool dwarfs. We provide coordinates and izYJHKW1W2 photometry of all sources. We identify an apparent discontinuity, $\Delta$m $\sim$ 0.4 mag., in the Y-K colour between spectral types L7 and L8. We present near-infrared spectra of nine sources identified by photo-type as peculiar, including a new low-gravity source ULAS J005505.68+013436.0, with spectroscopic classification L2{$\gamma$}. We provide revised izYJHKW1W2 template colours for late M dwarfs, types M7 to M9.Comment: Accepted for publication in A & A, 17 pages, 14 figures, catalogue of L and T dwarfs supplied here in source files (anc/ directory), and available on CD

Low-mass Tertiary Companions to Spectroscopic Binaries. I. Common Proper Motion Survey for Wide Companions Using 2MASS

We report the first results of a multi-epoch search for wide (separations greater than a few tens of AU), low-mass tertiary companions of a volume-limited sample of 118 known spectroscopic binaries within 30 pc of the Sun, using the Two Micron All Sky Survey Point Source Catalog and follow-up observations with the KPNO and CTIO 4 m telescopes. Note that this sample is not volume complete but volume limited, and, thus, there is incompleteness in our reported companion rates. We are sensitive to common proper motion companions with separations from roughly 200 AU to 10,000 AU (~10ˮ → ~ 10'). From 77 sources followed-up to date, we recover 11 previously known tertiaries, 3 previously known candidate tertiaries, of which 2 are spectroscopically confirmed and 1 rejected, and 3 new candidates, of which 2 are confirmed and 1 rejected. This yields an estimated wide tertiary fraction of 19.5^(+5.2)_(–3.7)%. This observed fraction is consistent with predictions set out in star formation simulations where the fraction of wide, low-mass companions to spectroscopic binaries is >10%

Discovery of a Possible Early-T Thick-Disk Subdwarf from the AllWISE2 Motion Survey

We have discovered a potential T0 $\pm$ 1 subdwarf from a search for sources in the AllWISE2 Motion Survey that do not have counterparts in surveys at shorter wavelengths. With a tangential velocity of $\sim$170 kms, this object - WISE J071121.36-573634.2 - has kinematics that are consistent with the thick-disk population of the Milky Way. Spectral fits suggest a low-metallicity for this object but also allow for the possibility of unresolved multiplicity. If WISE J0711-5736 is indeed an sdT0 dwarf, it would be only the second early-T subdwarf discovered to date.Comment: 11 pages, 6 figures, accepted to A

2MASS J06164006-6407194: The First Outer Halo L Subdwarf

We present the serendipitous discovery of an L subdwarf, 2MASS J06164006-6407194, in a search of the Two Micron All Sky Survey for T dwarfs. Its spectrum exhibits features indicative of both a cool and metal poor atmosphere including a heavily pressured-broadened K I resonant doublet, Cs I and Rb I lines, molecular bands of CaH, TiO, CrH, FeH, and H2O, and enhanced collision induced absorption of H2. We assign 2MASS 0616-6407 a spectral type of sdL5 based on a comparison of its red optical spectrum to that of near solar-metallicity L dwarfs. Its high proper motion (mu =1.405+-0.008 arcsec yr-1), large radial velocity (Vrad = 454+-15 km s-1), estimated uvw velocities (94, -573, 125) km s-1 and Galactic orbit with an apogalacticon at ~29 kpc are indicative of membership in the outer halo making 2MASS 0616-6407 the first ultracool member of this population.Comment: Accepted for publication in Ap

Discovery of a Companion at the L/T Transition with the Wide-field Infrared Survey Explorer

We report the discovery of a substellar companion to the nearby solar-type star HD 46588 (F7V, 17.9 pc, ~3 Gyr). HD 46588 B was found through a survey for common proper motion companions to nearby stars using data from the Wide-field Infrared Survey Explorer and the Two-Micron All-Sky Survey. It has an angular separation of 79.2" from its primary, which corresponds to a projected physical separation of 1420 AU. We have measured a spectral type of L9 for this object based on near-infrared spectroscopy performed with TripleSpec at Palomar Observatory. We estimate a mass of 0.064+0.008/-0.019 Msun from a comparison of its luminosity to the values predicted by theoretical evolutionary models for the age of the primary. Because of its companionship to a well-studied star, HD 46588 B is one of the few known brown dwarfs at the L/T transition for which both age and distance estimates are available. Thus, it offers new constraints on the properties of brown dwarfs during this brief evolutionary phase. The discovery of HD 46588 B also illustrates the value of the Wide-field Infrared Survey Explorer for identifying brown dwarfs in the solar neighborhood via their proper motions.Comment: Astrophysical Journal, in pres