17,105 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
Stellar Velocity Dispersion of the Leo A Dwarf Galaxy
We measure the first stellar velocity dispersion of the Leo A dwarf galaxy,
\sigma = 9.3 +- 1.3 km/s. We derive the velocity dispersion from the radial
velocities of ten young B supergiants and two HII regions in the central region
of Leo A. We estimate a projected mass of 8 +- 2.7 x10^7 solar masses within a
radius of 2 arcmin, and a mass to light ratio of at least 20 +- 6 M_sun/L_sun.
These results imply Leo A is at least ~80% dark matter by mass.Comment: 6 pages, accepted to Ap
Local Magnetic Inhomogeneities in Lightly Doped BaFeAs
We report As NMR measurements in BaFeAs doped with Ni. Like
Co, Ni doping suppresses the antiferromagnetic and structural phase transitions
and gives rise to superconductivity for sufficiently large Ni doping. The spin
lattice relaxation rate diverges at , with a critical exponent consistent
with 3D ordering of local moments. In the ordered state the spectra quickly
broaden inhomogeneously with doping. We extract the average size of the ordered
moment as a function of doping, and show that a model in which the order
remains commensurate but with local amplitude variations in the vicinity of the
dopant fully explains our observations.Comment: 4 pages, 4 figure
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