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Astron. Astrophys. 327, L25-L28 (1997)

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Letter to the Editor

Field brown dwarfs found by DENIS *

X. Delfosse 1, C.G. Tinney 2, T. Forveille 1, N. Epchtein 3, E. Bertin 4, 5, 6, J. Borsenberger 4, E. Copet 3, B. de Batz 3, P. Fouqué 3, 6, S. Kimeswenger 7, T. Le Bertre 3, F. Lacombe 3, D. Rouan 3 and D. Tiphène. 3

1 Observatoire de Grenoble, 414 rue de la Piscine, Domaine Universitaire de S [FORMULA] Martin d'Hères, F-38041 Grenoble, France
2 Anglo-Australian Observatory, PO Box 296, Epping. NSW 2121. Australia
3 Observatoire de Paris, 5, Place Jules Janssen, F-92195 Meudon Cedex, France
4 Institut d'Astrophysique de Paris, 98bis, Bd Arago, F-75014 Paris, France
5 Sterrewacht Leiden, University of Leiden, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
6 European Southern Observatory, Casilla 19001, Santiago 19, Chile
7 Institut für Astronomie der Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria

Received 21 July 1997 / Accepted 19 August 1997

Abstract

We present three candidate field brown dwarfs, identified by the DENIS survey. This on-going three colour survey of the southern sky has, as of July 1997, covered over 30% of the southern hemisphere in the I, J and Kshort passbands. The enormous sampled volume makes DENIS ideal for detecting brown dwarfs. The present results are based on preliminary processing of about 230 square degrees of DENIS data - a small fraction of the existing sky coverage. This reveals a sizeable population of very cold dwarfs, three of which are at least as cool as GD 165B. Infrared spectra confirm their dwarf status, and provide effective temperature information: one object (DENIS-P J1058.7-1548) is comparable in temperature to GD 165B and a second (DENIS-P J1228.2-1547) is slightly cooler, while a third (DENIS-P J0205.4-1159) is significantly so - though not as cold as Gl 229B. The infrared spectrum of DENIS-P J0205.4-1159 shows evidence for a methane absorption band, which implies an effective temperature much below the stellar limit. Lastly, recent detections of lithium in DENIS-P J1228.2-1547 have proven it to have a substellar mass. This makes it (together with the recently discovered object Kelu-1) the first bona-fide isolated field brown dwarf.

Key words: stars: late-type – low-mass – brown dwarfs

* Partly based on observations obtained at the European Southern Observatory

Send offprint requests to: Xavier Delfosse,
e-mail: Xavier.Delfosse@obs.ujf-grenoble.fr

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© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998
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