Orbital Parameters for 65 Wide Binary Systems: no evidence for gravitational anomaly at low acceleration

Abstract

We use a Monte Carlo analysis to study whether wide binaries can be represented by bound Newtonian orbits, and, if this is the case, whether the distribution of the orbital parameters agrees with expectations. The potential orbits are classified according to the $χ^2$ probability of representing star coordinates, parallaxes, velocity components and masses. We apply this analysis to 44 systems previously published, to which we add 26 wide binaries, consisting of twin low-mass (M) stars. We find orbital solutions for 65 systems, and derive the distribution of their orbital parameters. For one system composed of M-type stars, no Newtonian bound solution can be found; however, this pair is a member of the young Argus association and therefore not a suitable target. The remaining four systems that cannot be fit were already identified as likely disrupted binaries. The uncertainty in the separation between the components, given by the parallax error, is by far the dominant error source, and the main limitation of the present analysis, affecting especially the determination of the orbits' inclination angle and phase. Newtonian dynamics describe well our sample. When dividing the sample into two subsamples, according to the mutual acceleration, the eccentricity and periastron distributions agree with theoretical expectations; inclination and phase are distorted by the parallax-limited separation, more strongly in the high-acceleration (37 systems) than in the low-acceleration ($A_N < 10^{-9} m s^{-2}$, 28 systems) subsample, which is opposite to what a gravitational signal would produce. In particular the ratio between observed velocity difference and circular velocity does not show any excess for the low acceleration sample. When parametrized as a boost $γ$ parameter to the velocity, $0.95 < γ<1.05 (1 σ)$, fully consistent with Newton also for the low acceleration sample.