417 research outputs found
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, m 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{}. 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%
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
Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs
We present medium resolution optical and NIR spectral data for components of
the newly discovered WISE J104915.57-531906.1AB (Luhman 16AB) brown dwarf
binary. The optical spectra reveal strong 6708 A Li I absorption in both Luhman
16A (8.0+/-0.4 A) and Luhman 16B (3.8+/-0.4 A). Interestingly, this is the
first detection of Li I absorption in a T dwarf. Combined with the lack of
surface gravity features, the Li I detection constrains the system age to 0.1 -
3 Gyr. In the NIR data, we find strong KI absorption at 1.168, 1.177, 1.243,
and 1.254 {\mu}m in both components. Compared to the strength of KI line
absorption in equivalent spectral subtype brown dwarfs, Luhman 16A is weaker
while Luhman 16B is stronger. Analyzing the spectral region around each doublet
in distance scaled flux units and comparing the two sources, we confirm the J
band flux reversal and find that Luhman 16B has a brighter continuum in the
1.17 {\mu}m and 1.25 {\mu}m regions than Luhman 16A. Converting flux units to a
brightness temperature we interpret this to mean that the secondary is ~ 50 K
warmer than the primary in regions dominated by condensate grain scattering.
One plausible explanation for this difference is that Luhman 16B has thinner
clouds or patchy holes in its atmosphere allowing us to see to deeper, hotter
regions. We also detect comparably strong FeH in the 0.9896 {\mu}m Wing-Ford
band for both components. Traditionally, a signpost of changing atmosphere
conditions from late-type L to early T dwarfs, the persistence and similarity
of FeH at 0.9896 {\mu}m in both Luhman 16A and Luhman 16B is an indication of
homogenous atmosphere conditions. We calculate bolometric luminosities from
observed data supplemented with best fit models for longer wavelengths and find
the components are consistent within 1{\sigma} with resultant Teffs of
1310+/-30 K and 1280+/-75 K for Luhman 16AB respectively.Comment: 17 pages, 11 figures, 4 tables. Submitted to ApJ and revised after
referee repor
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