Two T dwarfs from the UKIDSS early data release



T. R. Kendall; M. Tamura; C. G. Tinney; E. L. Martin; M. Ishii; D. J. Pinfield; P. W. Lucas; H. R. A. Jones; S. K. Leggett; S. Dye; P. C. Hewett; F. Allard; I. Baraffe; D. B. Y. Navascues; G. Carraro; S. L. Casewell; G. Chabrier; R. J. Chappelle; F. Clarke; A. Day-Jones; N. Deacon; P. D. Dobbie; S. Folkes; N. C. Hambly; S. T. Hodgkin; T. Nakajima; R. F. Jameson; N. Lodieu; A. Magazzu; M. J. McCaughrean; Y. V. Pavlenko; N. Tadashi;M. R. Z. Osorio


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Abbreviated Journal Title

Astron. Astrophys.


infrared : stars; stars : low-mass, brown dwarfs; stars : fundamental; parameters; DEEP SKY SURVEY; INITIAL MASS FUNCTION; ULTRACOOL DWARFS; BROWN DWARF; CLASSIFICATION; DISCOVERY; Astronomy & Astrophysics


Context. We report on the first ultracool dwarf discoveries from the UKIRT Infrared Deep Sky Survey ( UKIDSS) Large Area Survey Early Data Release ( LAS EDR), in particular the discovery of T dwarfs which are fainter and more distant than those found using the 2MASS and SDSS surveys. Aims. We aim to show that our methodologies for searching the similar to 27 deg(2) of the LAS EDR are successful for finding both L and T dwarfs via cross-correlation with the Sloan Digital Sky Survey ( SDSS) DR4 release. While the area searched so far is small, the numbers of objects found shows great promise for near-future releases of the LAS and great potential for finding large numbers of such dwarfs. Methods. Ultracool dwarfs are selected by combinations of their YJH(K) UKIDSS colours and SDSS DR4 z - J and i - z colours, or, lower limits on these red optical/infrared colours in the case of DR4 dropouts. After passing visual inspection tests, candidates have been followed up by methane imaging and spectroscopy at 4 m and 8m-class facilities. Results. Our main result is the discovery following CH(4) imaging and spectroscopy of a T4.5 dwarf, ULAS J 1452+0655, lying similar to 80 pc distant. A further T dwarf candidate, ULAS J 1301+0023, has very similar CH4 colours but has not yet been confirmed spectroscopically. We also report on the identification of a brighter L0 dwarf, and on the selection of a list of LAS objects designed to probe for T-like dwarfs to the survey J-band limit. Conclusions. Our findings indicate that the combination of the UKIDSS LAS and SDSS surveys provide an excellent tool for identifying L and T dwarfs down to much fainter limits than previously possible. Our discovery of one confirmed and one probable T dwarf in the EDR is consistent with expectations from the previously measured T dwarf density on the sky.

Journal Title

Astronomy & Astrophysics





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