Analysis of the Hipparcos measurements of HD 10697: A mass determination of a brown dwarf secondary

HD 10697 is a nearby main-sequence sitar around which a planet candidate has recently been discovered by means of radial velocity measurements (Vogt et ail.). The stellar orbit has a period of about 3 yr, the secondary minimum mass is 6.35 Jupiter masses (M-J), and the minimum semimajor axis is 0.36 mas. Using the Hipparcos data of HD 10697 together with the spectroscopic elements of Vogt et al., we found a semimajor axis of 2.1 +/- 0.7 mas, implying a mass of 38 +/- 13 M-J for the unseen companion. We therefore suggest that the secondary of HD 10697 is probably a brown dwarf, orbiting around its parent star at a distance of 2 AU.