Exploring the substellar temperature regime down to ~550K
Abstract
We report the discovery of three very late T dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS) Third Data Release: ULAS J101721.40+011817.9 (ULAS1017), ULAS J123828.51+095351.3 (ULAS1238) and ULAS J133553.45+113005.2 (ULAS1335).We detail optical and near-infrared photometry for all three sources, and mid-infrared photometry for ULAS1335. We use near-infrared spectra of each source to assign spectral types T8p (ULAS1017), T8.5 (ULAS1228) and T9 (ULAS1335) to these objects. We estimate that ULAS1017 has 750 < Teff < 850K, and 5.0 < log g < 5.5, assuming solar metallicity, an age of 1.6-15 Gyr, a mass of 33-70 MJ and lies at a distance of 31-54 pc. We extend the unified scheme of Burgasser et al. (2006) to the type T9 and suggest the inclusion of the WJ index to replace the now saturated J-band indices. ULAS1335 is the same spectral type as ULAS J003402.77-005206.7 and CFBDS J005910.90-011401.3. Comparison of model spectra with that of ULAS1335 suggest a temperature below 600K. We find ULAS1335 to be extremely red in near to mid-infrared colours, with H-[4.49]=4.34+/-0.04. This is the reddest near to mid-infrared colour yet observed for a T dwarf, which supports Teff < 600K, and we estimate Teff ~550-600K for ULAS1335. We estimate that ULAS1335 has an age of 0.6-5.3 Gyr, a mass of 15-31 MJ and lies at a distance of 8-12 pc.
Cite
@article{arxiv.0806.0067,
title = {Exploring the substellar temperature regime down to ~550K},
author = {Ben Burningham and D. J. Pinfield and S. K. Leggett and M. Tamura and P. W. Lucas and D. Homeier and A. Day-Jones and H. R. A. Jones and J. R. A. Clarke and M. Ishii and M. Kuzuhara and N. Lodieu and M. R. Zapatero Osorio and B. P. Venemans and D. J. Mortlock and D. Barrado y Navascues and E. L. Martin and A. Magazzu},
journal= {arXiv preprint arXiv:0806.0067},
year = {2009}
}
Comments
MNRAS accepted. 17 pages, 15 figures. Abstract abridged. Revised to reflect referees comments. Revisions include: slightly revised Teff estimate for ULAS1335; additional figure demonstrating spectral type index degeneracy; revised discussion of NH3-H index; revised IRAC photometry based on re-reduction (small changes)