Abstract
The systems V819 Her, V2388 Oph, and V1031 Ori are triples comprised of an eclipsing binary orbiting with a distant visual component on a longer orbit. A detailed analysis of these interesting systems, combining the two observational techniques: interferometry and apparent period variation, was performed.
The interferometric data for these three systems obtained during the last century determine the visual orbits of the distant components in the systems. The combined analysis of the positional measurements together with the analysis of apparent period changes of the eclipsing binary (using the minima timings) can be used to study these systems in a combined approach, resulting in a set of parameters otherwise unobtainable without the radial velocities.
The main advantage of the technique presented here is the fact that one needs no spectroscopic monitoring of the visual orbits, which have rather long periods: 5.5 yr for V819 Her, 9.0 yr for V2388 Oph, and 31.3 yr for V1031 Ori, respectively. The eccentricities of the outer orbits are 0.69, 0.33, and 0.92, respectively.
Moreover, the use of minima timings of the eclipsing pairs helps us to derive the orientation of the orbit in space with no ambiguity around the celestial plane. And finally, the combined analysis yielded also an independent determination of the distance of V819 Her ( 68.7 +/- 1.8 pc), and V2388 Oph (70.6 +/- 8.9 pc).
We also present a list of similar systems, which would be suitable for a combined analysis like this one.