New neighbours

V. 35 DENIS late-M dwarfs between 10 and 30 parsecs

¹ Centre d'Analyse des Images, GEPI, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
² GEPI, Observatoire de Paris, 5 place J. Janssen, 92195 Meudon Cedex, France
³ Laboratoire d'Astrophysique de Grenoble, Université J. Fourier, BP 53, 38041 Grenoble, France
⁴ Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Highway, Kamuela, HI 96743, USA
⁵ SIO, Observatoire de Paris, 5 place J. Janssen, 92195 Meudon Cedex, France
⁶ Observatoire de la Côte d'Azur, Département Fresnel, BP 4229, 06304 Nice Cedex 4, France
⁷ LESIA, Observatoire de Paris, 5 place J. Janssen, 92195 Meudon Cedex, France
⁸ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁹ École Normale Supérieure de Cachan, 61 avenue du Président-Wilson, 94230 Cachan, France

Corresponding author: F. Crifo, francoise.crifo@obspm.fr

Received: 15 July 2002
Accepted: 31 January 2003

Abstract

This paper reports updated results on our systematic mining of the DENIS database for nearby very cool M-dwarfs (M 6V-M 8V, , photometric distance within 30 pc), initiated by Phan-Bao et al. (2001, hereafter Paper I). We use M dwarfs with well measured parallaxes (HIP, GCTP, ...) to calibrate the DENIS (M_I, ) colour-luminosity relationship. The resulting distance error for single dwarfs is about 25%. Proper motions, as well as B and R magnitudes, were measured on archive Schmidt plates for those stars in the DENIS database that meet the photometric selection criteria. We then eliminate the giants by a Reduced Proper Motion cutoff, which is significantly more selective than a simple proper motion cutoff. It greatly reduces the selection bias against low tangential velocity stars, and results in a nearly complete sample. Here we present new data for 62 red dwarf candidates selected over 5700 square degrees in the DENIS database. 26 of those originate in the 2100 square degrees analysed in Paper I, with improved parameters here, and 36 were found in 3600 additional square degrees. 25 of those are new nearby dwarfs. We determine from that sample of 62 stars a stellar density for of  stars pc^-3 mag^-1. This value is consistent with photometric luminosity functions measured from deeper and smaller-field observations, but not with the nearby star luminosity function. In addition we cross-identified the NLTT and DENIS catalogues to find 15 similar stars, in parts of the sky not yet covered by the colour-selected search. We present distance and luminosity estimates for these 15 stars, 10 of which are newly recognized nearby dwarfs. A similar search in Paper I produced 4 red dwarf candidates, and we have thus up to now identified a total of 35 new nearby late-M dwarfs.