Non-Keplerian effects in precision radial velocity measurements of double-line spectroscopic binary stars: numerical simulations

Abstract

Current precision in radial velocity (RV) measurements of binary stars reaches $\sim$2 ms$^{-1}$. This level of precision means that RV models have to take into account additional non-Keplerian effects such as tidal and rotational distortion of the components of a binary star, relativistic effects and orbital precession. We generate synthetic binaries using Yonsei-Yale stellar models. For typical representatives we investigate the impact of various orbital orientations and different non-Keplerian effects on the RV curves. To this end we simulate RV observations with an added white noise of different scale. Subsequently we try to reconstruct the input orbital parameters and their errors by fitting a model using a standard least-squares method. In particular we investigate the connection between the tidal distortion of the shape of the stars and the best-fit orbital eccentricity, the possibility of deriving orbital inclination of a non-eclipsing binary star by exploiting relativistic effects and the circumstances in which the orbital precession can be detected. We confirm that the method proposed by to obtain orbital inclination with use of the relativistic effect does work in favourable cases and that it can be used even for orbital configurations far from an edge-on orientation. We show that the RV variations imposed by tidally distorted stars can mimic non-zero eccentricity in some binaries. The scale of such an effect depends on the RV accuracy. Finally, we demonstrate that the apsidal precession can be easily detected with precision RVs. In particular we can detect orbital precession of $10^{-4}$ rad yr$^{-1}$, $10^{-3}$ rad yr$^{-1}$ for precision of RVs of 1 ms$^{-1}$ and 10 ms$^{-1}$ respectively.