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

Abstract

This paper reports updated results on our systematic mining of the DENIS database for nearby very cool M-dwarfs (M6V-M8V, 2.0<I-J<3.0, photometric distance within 30 pc), We calibrate the DENIS (M_I, I-J) colour-luminosity relationship from M dwarfs with well measured parallaxes (HIP, GCTP,...), obtaining distance errors for single dwarfs of 25%. Using proper motions measured on archive Schmidt plates for stars that meet the photometric selection criteria, we eliminate the giants by a Reduced Proper Motion cutoff, which is significantly more selective than a simple proper motion cutoff. 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 12.0<M_I<14.0 of 2.2(+-0.4)E-3 stars/pc^3/mag. 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.