We have identified a new early T dwarf only 3.6 pc from the Sun , as a common proper motion companion ( separation 1459 AU ) to the K5V star \varepsilon Indi ( HD 209100 ) .
As such , \varepsilon Indi B is one of the highest proper motion sources outside the solar system ( \sim 4.7 arcsec/yr ) , part of one of the twenty nearest stellar systems , and the nearest brown dwarf to the Sun .
Optical photometry obtained from the SuperCOSMOS Sky Survey was combined with approximate infrared photometry from the 2MASS Quicklook survey data release , yielding colours for the source typical of early T dwarfs .
Follow-up infrared spectroscopy using the ESO NTT and SOFI confirmed its spectral type to be T2.5 \pm 0.5 .
With K _ { s } = \mbox { 11 } ^ { \mbox { \tiny m } } . \mbox { 2 } , \varepsilon Indi B is 1.7 magnitudes brighter than any previously known T dwarf and 4 magnitudes brighter than the typical object in its class , making it highly amenable to detailed study .
Also , as a companion to a bright nearby star , it has a precisely known distance ( 3.626 pc ) and relatively well-known age ( 0.8–2 Gyr ) , allowing us to estimate its luminosity as log L/ L _ { \odot } = -4.67 , its effective temperature as 1260 K , and its mass as \sim 40–60 M _ { Jup } . \varepsilon Indi B represents an important addition to the census of the Solar neighbourhood and , equally importantly , a new benchmark object in our understanding of substellar objects .