Clumps and Axisymmetric Features in Debris Discs

TL;DR

This study explains how debris discs with inner clumps can appear axisymmetric in their outer regions if small dust grains are below the blowout size, reaching a steady state quickly after collision events.

Contribution

It demonstrates that small dust grains below the blowout size lead to an axisymmetric outer debris disc in a quasi-steady state, resolving mass budget issues.

Findings

Axisymmetric outer debris discs form when small grains are below blowout size.

Steady state is achieved within a few thousand years after collision events.

This model addresses the mass budget problem of Vega's debris disc.

Abstract

This paper studied the structures of debris discs, focusing on the conditions that can form an axisymmetric-looking outer disc from systems with inner clumps. The main conclusion was that as long as the dominated dust grains are smaller than the blowout size, it is easy to form an axisymmetric-looking outer debris disc, which is part of a quasi-steady state of the whole system. This quasi-steady state is established through the balance between grain generations and a continuous out-going grain flow. Assuming there is an event that starts planetesimal collisions and the corresponding grain generations, this balance can be approached in a few thousand years. This result suggested that a quasi-steady-state picture could solve the possible mass budget problem of Vega's outer debris disc.