Parallaxes and physical properties of 11 mid-to-late T dwarfs

¹ INAF/Osservatorio Astronomico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy
e-mail: fmarocco@libero.it, smart@oato.inaf.it
² Università degli Studi di Torino, Facoltà di Scienze MFN – Dipartimento di Fisica, via Pietro Giuria 1, 10126 Torino, Italy
³ Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK
⁴ Gemini Observatory, Northern Operations Center, 670 N. Aohoku Place, Hilo, HI 96720, USA
⁵ Anglo-Australian Observatory, PO Box 296, Epping, NSW1710, Australia
⁶ Joint Astronomy Centre, 660 North Aohoku Place, Hilo, HI 96720, USA
⁷ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
⁸ Instituto de Astrofísica de Canarias, vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁹ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38205 La Laguna, Tenerife, Spain
¹⁰ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

Received: 14 July 2010
Accepted: 20 August 2010

Abstract

Aims. We present parallaxes of 11 mid-to-late T dwarfs observed in the UKIRT Infrared Deep Sky Survey. We use these results to test the reliability of model predictions in magnitude–color space, determine a magnitude-spectral type calibration, and, estimate a bolometric luminosity and effective temperature range for the targets.

Methods. We used observations from the UKIRT WFCAM instrument pipeline processed at the Cambridge Astronomical Survey Unit. The parallaxes and proper motions of the sample were calculated using standard procedures. The bolometric luminosity was estimated using near- and mid-infrared observations with two different methods. The corresponding effective temperature ranges were found adopting a large age-radius range.

Results. We show the models are unable to predict the colors of the latest T dwarfs indicating the incompleteness of model opacities for NH₃, CH₄ and H₂ as the temperature declines. We report the effective temperature ranges obtained.