Spectroscopic distances of nearby ultracool dwarfs

¹ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, Taipei 106, Taiwan, R.O.C. e-mail: pbngoc@asiaa.sinica.edu.tw
² Research School of Astronomy and Astrophysics, Australian National University, Cotter Rd, Weston, ACT 2611, Australia

Received: 18 August 2005
Accepted: 29 September 2005

Abstract

We present updated results of spectroscopic follow-up observations of a sample of 45 M dwarf candidates identified by Phan-Bao et al. (2003, A&A, 401, 959) based on the DENIS photometry and proper motion measurements. Forty one of these are nearby late-M dwarfs ( pc) with spectral types ranging from M5.0 to M8.5 computed from the spectral indices. One contaminant is probably an F-G main sequence star reddened by intervening dust and three stars that were not observed have previous classifications as M dwarfs in the literature. In this paper, we identify three M7.5, five M8.0, one M8.5 dwarf and confirm two new M8.0 dwarf members of the 25 pc volume.