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Eccentricity of wide binary stars

Presentation #105.02 in the session Binary Stars.

Published onApr 25, 2022
Eccentricity of wide binary stars

Eccentricity is one of the fundamental orbital parameters in orbital dynamics. It not only provides critical constraints on binary formation mechanisms, but also plays a key role in the formation of hot Jupiters and close binaries via the secular three-body interaction. However, eccentricity is challenging to measure for wide binaries due to their extremely long orbital periods. In this talk, I will show that we can infer the eccentricity distribution of wide binaries even when we only have a snapshot of their orbits. In particular, with Gaia data, we use the “v-r angle”, the angle between the separation vector and the relative velocity vector in a wide binary, to infer binary eccentricities. I will present that the eccentricity distribution strongly depends on binary separations, and it becomes a mysterious super-thermal distribution at >1000 AU. I will further discuss how eccentricities change among subsamples of wide binaries, especially equal-mass wide binaries. This v-r angle method provides a new technique for measuring eccentricities for long-period systems, critical for understanding binary formation, evolution, and stellar orbits in the Galactic center and globular clusters.

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