Blue not brown: UKIRT Infrared Deep Sky Survey T dwarfs with suppressed K-band flux

Abstract

The definitive version can be found at: http://onlinelibrary.wiley.com/ Copyright Royal Astronomical SocietyWe have used blue near-infrared colours to select a group of 12 spectroscopically confirmed United Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (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 V-rad = 0. From this, ULAS J0926+0835 is found to have U = 62 km s(-1) and V = -140 km s(-1), and ULAS J1319+1209 is found to have U = 192 km s(-1) and V = -92 km s(-1). 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 +/- 0.1 and is located at a distance of 19 +/- 0.7 pc. U, V, W space velocity components are calculated for Hip 73786A and B, finding that U = -48 +/- 7 km s(-1), V = -75 +/- 4 km s(-1) and W = -44 +/- 8 km s(-1). 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

Discovery of the benchmark metal-poor T8 dwarf BD +01° 2920B

“…(iv) WISEP J150457.58+053800.1 is a W1 + W2 detected candidate 63 arcsec from HIP 73786 (GJ 576), a K8V star at 18.6pc. This candidate is a known (discovered in UKIDSS) T6p companion to this somewhat metal poor star (Scholz 2010;Murray et al 2011). Fig.…”

“…With sensitivity to a growing field L, T and Y dwarf search space, it is becoming feasible to search for multiple systems (e.g. Burningham et al 2009aBurningham et al , 2010aBurningham et al , 2011aLeggett et al 2010c;Zhang et al 2010;Day-Jones et al 2011;Murray et al 2011) or moving group associations (e.g. Clarke et al 2010;Gálvez-Ortiz et al 2010).…”

A 1500 deg2 near infrared proper motion catalogue from the UKIDSS Large Area Survey

“…Comparison of our new measured proper motion for the halo T dwarf candidate ULAS J1319+1209 with that reported in Murray et al (2011) highlights a significant discrepancy. We measure a considerably lower proper motion, which suggests kinematics most consistent with membership of the Galactic disk, rather than the halo.…”

Spectroscopic Follow-up of Discoveries from the NEOWISE Proper Motion Survey

“…To date, only two early-type T subdwarfs are known: the sdT0 WISE 071121.36−573634.2 discovered by Kellogg et al (2018) as part of the follow-up for the AllWISE2 motion survey (Kirkpatrick et al 2016); and the sdT1.5 WISE 210529.08−623558.7, discovered by Luhman & Sheppard (2014) as part of an analysis of high proper motion objects from the WISE survey. In addition, there are three published late-type T subdwarfs: the sdT5.5 HIP73786B, a common proper motion companion to the metal-poor K-star HIP73786 discovered by Murray et al (2011) using data from the United Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS); the sdT6.5 ULAS J131610.28+075553.0 discovered by Burningham et al (2014) in the UKIDSS Large Area Survey; and the sdT8 WISE J200520.38+542433.9, a companion to the sdM1.5 Wolf 1130, discovered by Mace et al (2013) using photometry from 2MASS, WISE, and other telescopes. Although it was not initially designated as a T subdwarf, showed that the peculiar T6 dwarf 2MASS 0937+2931 has a sub solar metallicity and has a spectral morphology consistent with other T subdwarfs.…”