Origin of the wide-orbit circumbinary giant planet HD 106906: A dynamical scenario and its impact on the disk

Abstract : A giant planet has been recently resolved at a projected distance of 730 au from the tight pair of young ($\sim$ 13 Myr) intermediate-mass stars HD 106906AB in the Lower Centaurus Crux (LCC) group. The stars are surrounded by a debris disk which displays a ring-like morphology and strong asymmetries at multiple scales. We aim at studying the likelihood of a scenario where the planet formed closer to the stars in the disk, underwent inward disk-induced migration, and got scattered away by the binary star before being stabilized by a close encounter (fly-by). We performed semi-analytical calculations and numerical simulations (Swift_HJS package) to model the interactions between the planet and the two stars. We accounted for the migration as a simple force. We studied the LCC kinematics to set constraints on the local density of stars, and therefore on the fly-by likelihood. We performed N-body simulations to determine the effects of the planet trajectories (ejection and secular effects) onto the disk morphology. The combination of the migration and mean-motion resonances with the binary star (often 1:6) can eject the planet. Nonetheless, we estimate that the fly-by hypothesis decreases the scenario probability to less than $10^{-7}$ for a derived local density of stars of 0.11 stars/pc$^{3}$. We show that the concomitant effect of the planet and stars trajectories induce spiral-features in the disk which may correspond to the observed asymmetries. Moreover, the present disk shape suggests that the planet is on an eccentric orbit. The scenario we explored is a natural hypothesis if the planet formed within a disk. Conversely, its low probability of occurrence and the fact that HD 106906 b shares some characteristics with other systems in Sco-Cen (e.g. HIP 78530, in terms of mass ratio and separation) may indicate an alternative formation pathway for those objects.
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Contributor : Marie-Paule Pomies <>
Submitted on : Wednesday, March 8, 2017 - 9:23:10 AM
Last modification on : Friday, April 5, 2019 - 8:24:05 PM

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Laetitia Rodet, H. Beust, M. Bonnefoy, A.-M. Lagrange, P. A. B. Galli, et al.. Origin of the wide-orbit circumbinary giant planet HD 106906: A dynamical scenario and its impact on the disk. Astronomy and Astrophysics - A&A, EDP Sciences, 2017, 602, pp.id.A12. ⟨10.1051/0004-6361/201630269⟩. ⟨hal-01484948⟩



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