HR 8257: A Three-Dimensional Orbit And Basic Properties

Abstract

We have used interferometric and spectroscopic observations of HR 8257 to determine a three-dimensional orbit of the system. The orbit has a period of 12.21345 days and an eccentricity of 0.2895. The masses of the F0 and F2 dwarf components are 1.56 and 1.38M(circle dot), respectively, with fractional errors of 1.4%. Our orbital parallax of 13.632 +/- 0.095 mas, corresponding to a distance of 73.4 +/- 0.6 pc, differs from the Hipparcos result by just 2% and has a significantly smaller uncertainty. From our spectroscopic observations and spectral energy distribution modeling we determine the component effective temperatures and luminosities to be T(eff)(A) = 7030 +/- 200K and T(eff)(B) = 6560 +/- 200K and L(A) = 9.4 +/- 0.3 L(circle dot) and L(B) = 4.7 +/- 0.2 L(circle dot). The primary rotates pseudosynchronously, while the secondary is not far from its pseudosynchronous rotational velocity. Although both early-F stars are slowly rotating, neither component of this close binary is an Am star. A comparison with evolutionary tracks indicates that the stars are slightly metal poor, and although the components have evolved away from the zero-age main sequence, they are both still dwarfs.