Expelled grains from an unseen parent body around AU Mic

TL;DR

This paper models the observed fast-moving structures in AU Mic's debris disk as expelled dust from an unseen parent body, constraining its possible location and dust properties through numerical simulations.

Contribution

It introduces a new dynamical model explaining the structures as dust expelled by a hidden source, fitting observed features with high-beta grains and specific parent body locations.

Findings

High beta values (~6) imply sub-micronic grains and active star conditions.

Parent body likely located around 8 or 28 au depending on its motion.

Sequential dust release scenario explains the radial structure evolution.

Abstract

Recent observations of the debris disk of AU Mic have revealed asymmetric, fast outward-moving arch-like structures above the disk midplane. No model can readily explain the characteristics of these features. We present a model aiming to reproduce the dynamics of these structures, more specifically their high projected speeds and their apparent position. We test the hypothesis of dust emitted by a point source and then expelled from the system by the strong stellar wind of this young, M-type star. In this model, we make the assumption that the dust grains follow the same dynamics as the structures. We perform numerical simulations of test particle trajectories to explore the available parameter space, in particular the radial location $R_{0}$ of the dust producing parent body and the size of the dust grains as parameterized by $\beta$ (ratio of stellar wind and radiation pressure forces over gravitation). We consider both the case of a static and an orbiting parent body. We find that, for all considered scenarii, there is always a set of ($R_0, \beta$) parameters able to fit the observed features. The common characteristics of these solutions is that they all require a high value of $\beta$, of around 6. This means that the star is probably very active and the grains composing the structures are sub-micronic, in order to reach such high $\beta$ values. As for the location of the hypothetical parent body, we constrain it to lie around 8 au (orbiting case) or 28 au (static case). We show that the scenario of sequential dust releases by an unseen, punctual parent body is able to explain the radial behaviour of the observed structures. We predict the evolution of the structures to help future observations to discriminate between the different parent body configurations that have been considered. We expect new structures to appear on the northwest side of the disk in the coming years.