CFBDS J005910.90-011401.3: reaching the T-Y Brown Dwarf transition?

TL;DR

This paper reports the discovery of CFBDS J005910.90-011401.3, the coolest brown dwarf identified to date, with detailed spectral analysis suggesting it is at the T-Y transition, providing insights into ultra-cool substellar objects.

Contribution

The discovery and characterization of CFBDS0059 as the coolest brown dwarf, potentially marking the T-Y spectral transition, with detailed spectral and physical parameter estimation.

Findings

CFBDS0059 is approximately 50K cooler than the previous coolest brown dwarf.

Estimated temperature of CFBDS0059 is around 620K, with a mass of 15-30 Jupiter masses.

Spectral features suggest the onset of ammonia absorption, indicating a transition towards the Y spectral class.

Abstract

We report the discovery of CFBDS J005910.90-011401.3 (hereafter CFBDS0059), the coolest brown dwarf identified to date. We found CFBDS0059 using i' and z' images from the Canada-France-Hawaii Telescope (CFHT), and present optical and near-infrared photometry, Keck laser guide star adaptive optics imaging, and a complete near-infrared spectrum, from 1.0 to 2.2 $\mu$m. A side to side comparison of the near-infrared spectra of CFBDS0059 and ULAS J003402.77-005206.7 (hereafter ULAS0034), previously the coolest known brown dwarf, indicates that CFBDS0059 is ~50+/-15K cooler. We estimate a temperature of Teff ~ 620K and gravity of log g ~ 4.75. Evolutionary models translate these parameters into an age of 1-5 Gyr and a mass of 15-30 M_Jup. We estimate a photometric distance of ~13pc, which puts CFBDS0059 within easy reach of accurate parallax measurements. Its large proper motion suggests membership in the older population of the thin disk. The spectra of both CFBDS0059 and ULAS J0034 shows probable absorption by a wide ammonia band on the blue side of the $H$-band flux peak. If, as we expect, that feature deepens further for still lower effective temperatures, its appearance will become a natural breakpoint for the transition between the T spectral class and the new Y spectral type. CFBDS0059 and ULAS J0034 would then be the first Y0 dwarfs.