Study of widely separated binary systems based on Gaia data

Gaia is an ESA space mission primarily designed to perform high precision astrometric observations of stars, but it also observes more than 350,000 small bodies in the Solar System. Its measurements have revealed signatures of binarity such as in the (4337) Arecibo system, demonstrating Gaia's ability to detect binary motion [1]. Furthermore, under certain assumptions, these data allow us to derive the mass ratio and flux ratio of these close-by systems (unresolved systems) [2].

In this study, we explore Gaia data for widely separated binary systems where Gaia can partially or fully resolve the components. We combine Gaia astrometry with complementary observational datasets to derive the relative orbits and physical properties of a set of seven binary systems: (22) Kalliope and Linus; (317) Roxane and Olympias; (1509) Esclangona and S/2003 (1509) 1; (617) Patroclus and Menoetius; (90482) Orcus and Vanth; (174567) Varda and Ilmarë; and (136199) Eris and Dysnomia.

Our methodology consists of two steps. First, we determine the heliocentric orbit of each system using Gaia astrometry, which corresponds to the motion of the system’s center of mass. We then analyze the residuals from this solution, which reveal the motion of the photocentre of the most massive component. The offset between the center-of-mass orbit and the photocentre directly imposes constraints on the mass ratio of the binary system. Thanks to the Gaia data, our results demonstrate that, for the first time using this astrometric approach, we can directly infer, with good precision, the mass ratio and thus determine the individual masses and densities of the components.

We will present the derived orbital solutions, total masses, mass ratios, and individual component masses of our test objects, in addition with the future observation events (stellar occultations and mutual events) for constraining the size of the bodies, and hence their densities. 

1. Tanga, P., Pauwels, T., Mignard, F., et al. 2023, A&A, 674, A12

2. Liu, Z., Hestroffer, D., Desmars, J., and David, P. 2024, A&A, 688, L23.

Acknowledgements. This work has received support from France 2030 through the project named Académie Spatiale d'Île-de-France (https://academiespatiale.fr/) managed by the National Research Agency under bearing the reference ANR-23-CMAS-0041