Combining Astrometry and Spectroscopy

Orbital solutions for binary or multiple stellar systems that combine astrometry (e.g., position angles and angular separations) with spectroscopy (radial velocities) have important advantages over astrometric-only or spectroscopic-only solutions. In many cases they allow the determination of the absolute masses of the components, as well as the distance. Yet, these kinds of combined solutions that use different types of observations in a global least-squares fit are still not very common in the literature. An outline of the procedure is presented, along with examples to illustrate the sort of results that can be obtained. The same method can easily be extended to include other types of measurements (times of eclipse, Hipparcos observations, interferometric visibilities and closure phases, parallaxes, lunar occultations, etc.), which often complement each other and strengthen the solution.