Letter to the Editor
ε Indi B: A new benchmark T dwarf *
1
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
2
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
Corresponding author: R.-D. Scholz, rdscholz@aip.de
Received:
26
November
2002
Accepted:
15
December
2002
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
ε Indi (HD 209100). As such, ε Indi B is one of the highest proper
motion sources outside the solar system (~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 ± 0.5. With 
, ε Indi B is 1.7 mag brighter than any previously
known T dwarf and 4 mag 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 (
pc) and
relatively well-known age (0.8–2 Gyr), allowing us to estimate its
luminosity as 
/ 
, its effective temperature as 1260 K,
and its mass as ~ 40–60 MJup . ε 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.
Key words: astrometry and celestial mechanics: astrometry / astronomical data base: surveys / stars: late-type / stars: low mass, brown dwarfs
© ESO, 2003