Dust Spreading in Debris Discs: Do Small Grains Cling on to Their Birth Environment?

Abstract

Debris discs are dusty belts of planetesimals around main-sequence stars, similar to the asteroid and Kuiper belts in our solar system. The planetesimals cannot be observed directly, yet they produce detectable dust in mutual collisions. Observing the dust, we can try to infer properties of invisible planetesimals. Here we address the question of what is the best way to measure the location of outer planetesimal belts that encompass extrasolar planetary systems. A standard method is using resolved images at mm-wavelengths, which reveal dust grains with sizes comparable to the observational wavelength. Smaller grains seen in the infrared (IR) are subject to several non-gravitational forces that drag them away from their birth rings, and so may not closely trace the parent bodies. In this study, we examine whether imaging of debris discs at shorter wavelengths might enable determining the spatial location of the exo-Kuiper belts with sufficient accuracy. We find that around M-type stars the dust best visible in the mid-IR is efficiently displaced inward from their birth location by stellar winds, causing the discs to look more compact in mid-IR images than they actually are. However, around earlier-type stars where the majority of debris discs is found, discs are still the brightest at the birth ring location in the mid-IR regime. Thus, sensitive IR facilities with good angular resolution, such as MIRI on JWST, will enable tracing exo-Kuiper belts in nearby debris disc systems.

16 pages

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Cited by in corpus (9)

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• Solar System Physics for Exoplanet Research
• A $75\%$ Occurrence Rate of Debris Discs around F stars in the $\beta$ Pic Moving Group
• Constraining planetesimal stirring: how sharp are debris disc edges?
• A Layered Debris Disk around M Star TWA 7 in Scattered Light
• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) II. The radial structure of debris discs
• Inner edges of planetesimal belts: collisionally eroded or truncated?
• The big sibling of AU Mic: a cold dust-rich debris disk around CP-72 2713 in the $\beta$ Pic moving group
• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) V: Comparison between scattered light and thermal emission