The discovery of a T6.5 subdwarf

Authors :: Ben Burningham
P. W. Lucas
Leigh C. Smith
Hugh R. A. Jones
Adam J. Burgasser
C. V. Cardoso
Richard L. Smart
Source :: Monthly Notices of the Royal Astronomical Society. 440:359-364
Publication Year :: 2014
Publisher :: Oxford University Press (OUP), 2014.
Abstract: We report the discovery of ULAS J131610.28+075553.0, a sdT6.5 dwarf in the UKIDSS Large Area Survey 2 epoch proper motion catalogue. This object displays significant spectral peculiarity, with the largest yet seen deviations from T6 and T7 templates in the Y and K bands for this subtype. Its large, ~1 arcsec/yr, proper motion suggests a large tangential velocity of Vtan = 240 - 340km/s, if we assume its MJ lies within the typical range for T6.5 dwarfs. This makes it a candidate for membership of the Galactic halo population. However, other metal poor T dwarfs exhibit significant under luminosity both in specific bands and bolometrically. As a result, it is likely that its velocity is somewhat smaller, and we conclude it is a likely thick disc or halo member. This object represents the only T dwarf earlier than T8 to be classified as a subdwarf, and is a significant addition to the currently small number of known unambiguously substellar subdwarfs.<br />Comment: 8 pages, 5 figures. MNRAS accepted