Astrometric-spectroscopy binary star orbits. IV - Beta Coronae Borealis

From a combination of speckle interferometric and visual measurements with recent radial velocities, an improved current orbit was derived for beta Coronae Borealis with a period of 10.55 yr, an eccentricity of 0.538, periastron at 1980.472, and a semimajor axis of 0.2032 arcsec and have combined this with a long Allegheny parallax series to obtain a new parallax estimate of + 0.026 + or - 0.004 arcsec and a system mass of 4.3 + or - 2.0 solar masses, for which the error is due almost entirely to the uncertainty in the parallax. With this parallax, the system absolute magnitude becomes M(v) = + 0.7 and the absolute magnitude of the F0p primary becomes + 0.9 + or - 0.3. The orbital elements differ significantly from those derived from the Lick radial velocities of a half century ago, which also indicated the presence of a third body in the system. The recent velocities do not show this variation. The Lick radial- velocity evidence for a third body in the system was reexamined and it was found that its existence is statistically likely. It is possible that it cannot now be detected because perturbations have brought its orbit plane presently into the plane of the sky. (Author)