On Grain Dynamics in Debris Discs: Continuous Outward Flows and Embedded Planets

TL;DR

This paper uses grain dynamic models to explore how debris discs maintain steady outward flows and how embedded planets influence their signatures, highlighting the importance of grain generation rates and composition.

Contribution

It introduces a detailed model showing how grain generation frequency and composition affect steady out-moving flows in debris discs, and analyzes planetary signatures in different grain regimes.

Findings

Frequent grain generation (every 100 years) supports 1/R density profiles.

Long-lived grains show clear planetary signatures, unlike steady out-moving flows.

Smaller maximum grain sizes and specific compositions favor steady outflows.

Abstract

This study employed grain dynamic models to examine the density distribution of debris discs, and discussed the effects of the collisional time-intervals of asteroidal bodies, the maximum grain sizes, and the chemical compositions of the dust grains of the models, in order to find out whether a steady out-moving flow with an 1/R profile could be formed. The results showed that a model with new grains every 100 years, a smaller maximum grain size, and a composition C400 has the best fit to the 1/R profile because: (1) the grains have larger values of beta on average,therefore, they can be blown out easily; (2) the new grains are generated frequently enough to replace those have been blown out. With the above two conditions, some other models can have a steady out-moving flow with an approximate 1/R profile. However, those models in which new grains are generated every 1000 years have density distributions far from the profile of a continuous out-moving flow. Moreover, the analysis on the signatures of planets in debris discs showed that there are no indications when a planet is in a continuous out-moving flow, however, the signatures are obvious in a debris disc with long-lived grains.