Astrometric study of the triple star ADS 9173

An approximate orbit of the wide visual binary star ADS 9173 A(Bb) with a period of ～6000 yr has been determined for the first time by the method of apparent motion parameters. The orbit was computed using a short (1982–2004) arc of photographic observations obtained with the 26-inch Pulkovo Observatory refractor and the Hipparcos parallax. Agreement of the new orbit with the observations from the WDS catalog beginning in 1832 serves as a check. The errors in the orbital elements are large, but the orientation elements of the orbital plane (i and Ω) were estimated reliably. Component B has an invisible spectroscopic companion with a period of 4.9 yr. An astrometric orbit of Bb consistent with radial velocity measurements was determined from the residuals to the relative orbital motion of A(Bb). The orbital planes are nearly coplanar. If the mass of component B is taken in accordance with the mass—luminosity relation, 1.5 M _⊙, and the parallax is 0.″021, then the mass of the secondary component is no less than 0.5M _⊙. Component A may also be a long-period binary system.