ε Indi B: A new benchmark T dwarf

Free access article

Issue		A&A Volume 398, Number 3, February II 2003


Page(s)		L29 - L33
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20021847

A&A 398, L29-L33 (2003)
DOI: 10.1051/0004-6361:20021847

Letter

$\varepsilon$ Indi B: A new benchmark T dwarf

R.-D. Scholz¹, M. J. McCaughrean¹, N. Lodieu¹ and B. Kuhlbrodt²

¹ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
² Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

(Received 26 November 2002 / Accepted 15 December 2002 )

Abstract
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 (~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 $K_{\rm s}= {11}^{\rm m}.{2}$ , $\varepsilon$ 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 ( $3.626\pm 0.009$ 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 ~ 40-60 $M_{\rm Jup}$ . $\varepsilon$ 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.

Key words: astrometry and celestial mechanics: astrometry -- astronomical data base: surveys -- stars: late-type -- stars: low mass, brown dwarfs

Offprint request: R.-D. Scholz, rdscholz@aip.de

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