Seventy six T dwarfs from the UKIDSS LAS: benchmarks, kinematics and an updated space density

TL;DR

This paper reports the discovery of 76 new T dwarfs from UKIDSS LAS, analyzes their properties, identifies benchmark systems, and updates the space density estimates of late-T dwarfs using new models and data.

Contribution

It provides the largest sample of T dwarfs from UKIDSS LAS, identifies new benchmark systems, and offers revised insights into their colors, metallicity effects, and space densities.

Findings

H - [4.5] and J - W2 colors are more sensitive to metallicity than previously thought.

The dominance of young objects in late-T dwarf samples is no longer supported.

Updated space densities for late-T dwarfs are provided and compared with models and WISE data.

Abstract

We report the discovery of 76 new T dwarfs from the UKIDSS Large Area Survey (LAS). Near-infrared broad and narrow-band photometry and spectroscopy are presented for the new objects, along with WISE and warm-Spitzer photometry. Proper motions for 128 UKIDSS T dwarfs are presented from a new two epoch LAS proper motion catalogue. We use these motions to identify two new benchmark systems: LHS 6176AB, a T8+M4 pair and HD118865AB, a T5.5+F8 pair. Using age constraints from the primaries and evolutionary models to constrain the radii we have estimated their physical properties from their bolometric luminosity. We compare the colours and properties of known benchmark T dwarfs to the latest model atmospheres and draw two principal conclusions. Firstly, it appears that the H - [4.5] and J - W2 colours are more sensitive to metallicity than has previously been recognised, such that differences in metallicity may dominate over differences in Teff when considering relative properties of cool objects using these colours. Secondly, the previously noted apparent dominance of young objects in the late-T dwarf sample is no longer apparent when using the new model grids and the expanded sample of late-T dwarfs and benchmarks. This is supported by the apparently similar distribution of late-T dwarfs and earlier-type T dwarfs on reduced proper motion diagrams that we present. Finally, we present updated space densities for the late-T dwarfs, and compare our values to simulation predictions and those from WISE.