Binary system dynamics and physical property analysis using Gaia astrometry

Gaia provides an exceptional opportunity to explore high-precision astrometric data for a large number of solar system objects. Thanks to its unprecedented precision, Gaia data can reveal the astrometric signatures of binary asteroids. This is the case of the binary system (4337) Arecibo, discovered by occultation. Using Gaia DR3 data [1], an astrometric wobble was clearly detected over several transits over a two days window.In this study, we investigated the Arecibo system, combining all Gaia FPR observations. We first fit the heliocentric orbit, where the residuals contain the binary signal. This signal is proportional to the relative orbit, and a scaling factor related to the flux ratio and mass ratio of the components (see [2], [3] for the analytical formula). We then adjust the relative orbit to derive the key parameters, including full orbital parameters, flux and mass ratio. Based on estimated volumes, we obtain overall densities of around ρ₁ ≈ 1.2 and ρ₂ ≈ 1.6 for the primary and secondary, respectively. These results indicate that this system is composed of ice-rich bodies in the outer main belt [4].Moreover, we are applying this method to other asteroid systems whose orbits are poorly known. Using Gaia observations combined with ground-based data, we have been able to refine their orbits. Furthermore, for trans-Neptunian objects, where the separation between the components is large enough for only the primary body to be observed by Gaia, the astrometric wobble can indicate the mass ratio. In such cases, Gaia data can be crucial in determining individual masses and, hence, density.For binary candidates identified in previous studies [5], it is possible to solely use Gaia data or adding it with primary-only occultation data to perform mutual orbit determination. This can help estimate the position of a potential satellite, guiding future occultation observations for detection and confirmation.Gaia's high-precision astrometric measurements enable us to estimate the individual masses and densities of solar system bodies. This provides valuable insights into the formation and evolution of the solar system. Additionally, by looking at orbital parameters, we can predict future mutual events and stellar occultations, which will provide further constraints on density. We aim to present preliminary results on main belt asteroid systems, TNBs and a few potential binaries, demonstrating how Gaia data contribute to our understanding of these objects and to future observation. [1] Tanga, P., Pauwels, T., Mignard, F., et al. 2023, A&A, 674, A12[2] Pravec, P. & Scheirich, P. 2012, Planet. Space Sci., 73, 56[3] Lindegren, L. 2022[4] Liu, Z., Hestroffer, D., Desmars, J., and David, P. 2024, A&A, 688, L23. [5] Liberato, L., Tanga, P., Mary, D., et al. 2024, A&A, 688, A5