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Astron. Astrophys. 317, 164-170 (1997)

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Brown dwarfs in the Pleiades cluster: a CCD-based R, I survey *

M.R. Zapatero Osorio , R. Rebolo and E.L. Martín

Instituto de Astrofísica de Canarias, Vía Láctea s/n, E-38200 La Laguna, Tenerife, Spain

Received 20 March 1996 / Accepted 15 April 1996

Abstract

We have obtained deep CCD R and I mosaic imaging of 578 arcmin2 within 1[FORMULA].5 of the Pleiades' center - reaching a completeness magnitude I = 19.5 - with the aim of finding free-floating brown dwarfs. Teide 1, the best bona fide brown dwarf discovered so far in the cluster (Rebolo, Zapatero Osorio & Martín 1995), arose as a result of a combined photometric and astrometric study of [FORMULA] 1/4 of our covered area. The extension of our two-colour survey provides eight new additional brown dwarf candidates whose photometry is rather similar to that of Teide 1. Several of them are even fainter. Follow up low-resolution spectroscopy (Martín, Rebolo & Zapatero Osorio 1996) shows that one of them is indeed a Pleiades brown dwarf. Most of the remaining candidates are background late-M dwarfs which are contaminating our survey, possibly due to a small (previously unknown) cloud towards the cluster which affects some of our CCD fields. We did not expect any foreground M8-M9 field dwarf in our surveyed volume and surprisingly we have found one, suggesting that its number could be larger than inferred from recent luminosity function studies in the solar neighbourhood.

Key words: stars: pre-main sequence — stars: late-type — stars: low-mass, brown-dwarfs — open clusters: Pleiades

* Based on observations made with the Jacobus Kapteyn Telescope, operated on the island of La Palma by the Royal Greenwich Observatory in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias (IAC); on observations made with the IAC80 telescope operated by the IAC at its Observatorio del Teide; on observations made with the Nordic Optical Telescope in the Observatorio del Roque de los Muchachos; and on observations made with the 2.2 m telescope at the Spanish-German Astronomical Center, Calar Alto, Almería, Spain.

Send offprint requests to: M.R. Zapatero Osorio, e-mail: mosorio@iac.es

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