A&A 367, 183-188 (2001)

DOI: 10.1051/0004-6361:20000408

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

**Ch. Leinert**

^{1}, H. Jahreiß^{2}, J. Woitas^{1}, S. Zucker^{3}, T. Mazeh^{3}, A. Eckart^{4}and R. Köhler^{1}^{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

(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 (1995)
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. (1998) and Chabrier et al.
(2000) 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 *V* = 15.3.
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.

**Key words:**low-mass stars

**--**binaries

**--**mass-luminosity relation

Offprint request: Ch. Leinert, leinert@mpia-hd.mpg.de

SIMBAD Objects

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*ESO 2001*