SIMBAD references

In this paper, we show how Hipparcos parallaxes of distant visual binaries (π_Hip≲ 10 mas) can be refined. This is accomplished by using relevant orbital and spectral data. To this end, we study the pair of K0 giants, A 1808. A revised orbit of this system is presented that was calculated by taking into account a set of interferometric and visual measurements covering almost one orbital revolution. In addition, by analyzing its spectrum obtained with the 2.6 m telescope of the Byurakan Astrophysical Observatory (Armenia), we confirm the MK spectral type, K0III. On the basis of B - V photometric data, we derived the extinction A_V= 0.23±0.08 mag as well as obtained a spectroscopic parallax (π_sp= 3.19±0.21 mas) with a much smaller relative uncertainty of 6.6% compared with that of Hipparcos (42.1%; π_Hip = 2.43±1.00 mas). Accordingly, this system is now placed at 313±21 pc. With the obtained spectroscopic parallax, a dynamical mass of is obtained, which agrees well with that expected from standard calibrations.