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Blue not brown: UKIDSS T dwarfs with suppressed K-band flux | | D. N. Murray
; B. Burningham
; H. R. A Jones
; D. J. Pinfield
; P. W. Lucas
; S. K. Leggett
; C. G. Tinney
; A. C. Day-Jones
; D. J. Weights
; N. Lodieu
; J. A. Perez Prieto
; E. Nickson
; Z. H. Zhang
; J. R. A. Clarke
; J. S. Jenkins
; M. Tamura
; | | Date: |
25 Jan 2011 | | Abstract: | We have used blue near-infrared colours to select a group of 12
spectroscopically-confirmed UKIDSS T dwarfs later than T4. From amongst these
we identify the first two kinematic halo T-dwarf candidates. Blue near-infrared
colours have been attributed to collisionally-induced hydrogen absorption,
which is enhanced by either high surface gravity or low metallicity. Proper
motions are measured and distances estimated, allowing the determination of
tangential velocities. U and V components are estimated for our objects by
assuming radial velocity = 0 km/s. From this, ULAS J0926+0835 is found to have
U=62 km/s and V=-140km/s and ULAS J1319+1209 is found to have U=192 km/s and
V=-92 km/s. These values are consistent with potential halo membership.
However, these are not the bluest objects in our selection. The bluest is ULAS
J1233+1219, with J-K=-1.16 +/- 0.07, and surprisingly this object is found to
have young disc-like U and V. Our sample also contains Hip 73786B, companion to
the metal-poor K5 dwarf Hip 73786. Hip 73786 is a metal-poor star, with
[Fe/H]=-0.3 and is located at a distance of 19 pc. U, V, W space velocity
components are calculated for Hip 73786A and B, finding that U=-48 +/- 7 km/s,
V=-75 +/- 4 km/s and W=-44 +/- 8 km/s. From the properties of the primary, Hip
73786B is found to be at least 1.6 Gyr old. As a metal poor object, Hip 73786B
represents an important addition to the sample of known T dwarf benchmarks. | | Source: | arXiv, 1101.4881 | | Services: | Forum | Review | PDF | Favorites | |
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