DENIS J081730.0-615520: An overlooked mid-T dwarf in the solar neighborhood

TL;DR

This paper reports the discovery and characterization of DENIS J081730.0-615520, a bright mid-T dwarf in the solar neighborhood, highlighting the incompleteness of current brown dwarf surveys and providing detailed follow-up data.

Contribution

It identifies a previously overlooked bright mid-T dwarf in the solar neighborhood and provides its astrometry and spectroscopy, emphasizing the importance of nearby brown dwarf census completeness.

Findings

DENIS J081730.0-615520 is the brightest mid-T dwarf in the sky.

Located at 4.9 ± 0.3 pc, it is among the three closest brown dwarfs to the Sun.

The object has a spectral type of T6.

Abstract

Recent wide-field near-infrared surveys have uncovered a large number of cool brown dwarfs, extending the temperature sequence down to less than 500 K and constraining the faint end of the luminosity function. One interesting implication of the derived luminosity function is that the brown dwarf census in the immediate (<10 pc) solar neighborhood is still largely incomplete, and some bright (J<16) brown dwarfs remain to be identified in existing surveys. These objects are especially interesting as they are the ones that can be studied in most detail, especially with techniques that require large fluxes (e.g. time-variability, polarimetry, high-resolution spectroscopy) that cannot realistically be applied to objects uncovered by deep surveys. By cross-matching the DENIS and the 2MASS point-source catalogs, we have identified an overlooked brown dwarf -DENIS J081730.0-615520- that is the brightest field mid-T dwarf in the sky (J = 13.6). We present astrometry and spectroscopy follow-up observations of this brown dwarf. Our data indicate a spectral type T6 and a distance -from parallax measurement- of 4.9\pm0.3 pc, placing this mid-T dwarf among the 3 closest isolated brown dwarfs to the Sun.