EDP Sciences
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Volume 367, Number 1, February III 2001
Page(s) 183 - 188
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20000408

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. Leinert1, H. Jahreiß2, J. Woitas1, S. Zucker3, T. Mazeh3, A. Eckart4 and R. Köhler1

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 )

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 $16.1 \pm 1.4$ 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 $\pm$ 0.003 $M_{\odot}$. 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 $0.161 \pm 0.002$ $M_{\odot}$ 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

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