Dynamical mass determination for the very low mass stars LHS 1070 B and C

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
² Astronomisches Rechen-Institut, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
³ Wise Observatory, Tel Aviv University, Tel Aviv 69978, Israel
⁴ Physikalisches Institut der Universität Köln, Germany

Corresponding author: Ch. Leinert, leinert@mpia-hd.mpg.de

Received: 12 October 2000
Accepted: 29 November 2000

Abstract

We followed the relative orbit of the close pair of very late-type stars in the nearby triple system LHS 1070 during the past seven years. These observations are used to derive the astrometric elements of the orbit. Using the period of years and assuming the distance of 7.39 pc given by van Altena ([CITE]) to be exactly correct, the combined mass of components B and C is 0.138 ± 0.003 . Otherwise, this mass scales with the third power of the distance, which presently is not known to better than 9% . The dynamical mass would equal the combined mass of derived from the theoretical mass-luminosity relation of Baraffe et al. ([CITE]) and Chabrier et al. ([CITE]) for a 5% larger distance of 7.78 pc. A critical comparison with the theoretical relations therefore has to await more precise parallax determinations for this comparatively faint system with visual magnitude . The wide orbit of component A around the center of mass of components B and C cannot yet be determined from our measurements. However, we can show that it is probably co-planar with the close pair orbit and should have a period in the range 60-1000 years.