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HD 106906
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Title: On the origin of the wide-orbit circumbinary giant planet HD 106906: A dynamical scenario and its impact on the disk
Author: L. Rodet, H. Beust, M. Bonnefoy, A.-M. Lagrange, P. A. B. Galli, C. Ducourant, R. Teixeira

A giant planet has been recently resolved at a projected distance of 730 au from the tight pair of young (~ 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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Posts: 131433
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TYC 8637-2434-1
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Title: HD 106906: A Case Study for External Perturbations of a Debris Disk
Author: Erika R. Nesvold, Smadar Naoz, Michael Fitzgerald

Models of debris disk morphology are often focused on the effects of a planet orbiting interior to or within the disk. Nonetheless, an exterior planetary-mass perturber can also excite eccentricities in a debris disk, via Laplace-Lagrange secular perturbations in the coplanar case or Kozai-Lidov perturbations for mutually inclined companions and disks. HD 106906 is an ideal example of such a system, as it harbours a confirmed exterior 11 M_Jup companion at a projected separation of 650 au outside a resolved, asymmetric disk. We use collisional and dynamical simulations to investigate the interactions between the disk and the companion, and to use the disk's observed morphology to place constraints on the companion's orbit. We conclude that the disk's observed morphology is consistent with perturbations from the observed interior companion. Generalizing this result, we suggest that exterior perturbers, as well as interior planets, should be considered when investigating the cause of observed asymmetries in a debris disk.

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HD 106906: Exiled exoplanet possibly kicked out of star's local neighbourhood

ASU scientists zoom in to study the dynamics that drive planet formation.
A planet discovered last year sitting at an unusually large distance from its star - 16 times farther than Pluto is from the sun - may have been kicked out of its birthplace close to the star in a process similar to what may have happened early in our own solar system's history.

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Posts: 131433
Date:
HD 106906 b
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UA Astronomers Discover Planet That Shouldn't Be There

An international team of astronomers, led by a University of Arizona graduate student, has discovered the most distantly orbiting planet found to date around a single, sun-like star. It is the first exoplanet - a planet outside of our solar system - discovered at the UA.
Weighing in at 11 times Jupiter's mass and orbiting its star at 650 times the average Earth-Sun distance, planet HD 106906 b is unlike anything in our own Solar System and throws a wrench in planet formation theories.

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