The case of HD 106906 debris disc: A binary's revenge

TL;DR

This study investigates how the gravitational influences of a binary star system and a distant planetary companion shape the structure and observable features of the debris disc around HD 106906, providing insights into planetary system dynamics.

Contribution

It offers a detailed dynamical model of the HD 106906 debris disc considering both the binary and planetary perturbers, highlighting the binary's dominant role in disc morphology.

Findings

Binary dominates disc dynamics within uncertainties

Disc's eccentricity depends on planetary orbit parameters

Constraints on planetary orbit from observed disc symmetry

Abstract

Debris disc architecture presents [exo-]planetary scientists with precious clues for processes of planet formation and evolution, including constraints on planetary mass perturbers. This is particularly true of the disc in HD 106906, which in early HST, then follow up polarimetric observations, presented asymmetries and needle-like features that have been attributed to perturbations by a massive, and unusually distant external planetary companion. Here, we revisit the long-term secular dynamical evolution of the HD 106906 disc allowing for the combined gravitational action of the planetary companion and the inner stellar binary which holds the system together. We argue that the binary is strong enough to impose a dynamical break at the disc's location, resulting in distinctive observational signatures which we render via simulated surface density maps and vertical structure profiles. Within uncertainties on the planet's orbit, we show that the disc can go from being fully dominated by the inner binary to significantly so, and is hardly ever outside its reach. The extent of binary dominance impacts the disc's mean eccentricity, a metric which we map as a function of the planet's semi-major axis and orbital eccentricity, with and without radiation pressure. We can thus constrain the planet's orbit to ease the tension between evident axisymmetry in the millimeter, and apparent asymmetry in scattered light. We discuss phase space structure, then inclination distribution, arguing for the relevance of our results to a variety of hierarchical systems, as we set the stage for generalizations that allow for disc self-gravity and collisional evolution.