Spectroscopic classification of red high proper motion objects in the Southern Sky

¹ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
² Department of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK e-mail: nl41@star.le.ac.uk
³ School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁴ Observatoire de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France
⁵ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK

Received: 30 November 2004
Accepted: 6 June 2005

Abstract

We present the results of spectroscopic follow-up observations for a sample of 71 red objects with high proper motions in the range 0.08-1.14 arcsec yr^-1 as detected using APM and SSS measurements of multi-epoch photographic Schmidt plates. Red objects were selected by combining the photographic B_JRI magnitudes with 2MASS near-infrared JHK_s magnitudes. Some 50 of the 71 spectroscopically classified objects turn out to be late-type (>M6) dwarfs and in more detail, the sample includes 35 ultracool dwarfs with spectral types between M8 and L2, some previously reported, as well as five M-type subdwarfs, including a cool esdM6 object, SSSPM J0500-5406. Distance estimates based on the spectral types and 2MASS J magnitudes place almost all of the late-type (>M6) dwarfs within 50 pc, with 25 objects located inside the 25 pc limit of the catalogue of nearby stars. Most of the early-type M dwarfs are located at larger distances of 100-200 pc, suggesting halo kinematics for some of them. All objects with Hα equivalent widths larger than 10 Å have relatively small tangential velocities (<50 km s^-1). Finally, some late-type but blue objects are candidate binaries.