# New constraints on the millimetre emission of six debris disks

## TL;DR

This study used 9-mm observations to constrain dust grain size distributions in six debris disks, revealing values consistent with rubble-pile planetesimals and challenging some steady-state models.

## Contribution

First 9-mm observations of six debris disks providing new constraints on dust size distributions and planetesimal properties.

## Key findings

- Detected three debris disks at ~3-sigma significance.
- Derived dust size distribution slopes smaller than 3.5, within theoretical expectations.
- Results support rubble-pile planetesimal models over steady-state collisional cascades.

## Abstract

The presence of dusty debris around main sequence stars denotes the existence of planetary systems. Such debris disks are often identified by the presence of excess continuum emission at infrared and (sub-)millimetre wavelengths, with measurements at longer wavelengths tracing larger and cooler dust grains. The exponent of the slope of the disk emission at sub-millimetre wavelengths, `q', defines the size distribution of dust grains in the disk. This size distribution is a function of the rigid strength of the dust producing parent planetesimals. As part of the survey `PLAnetesimals around TYpical Pre-main seqUence Stars' (PLATYPUS) we observed six debris disks at 9-mm using the Australian Telescope Compact Array. We obtain marginal (~3-\sigma) detections of three targets: HD 105, HD 61005, and HD 131835. Upper limits for the three remaining disks, HD20807, HD109573, and HD109085, provide further constraint of the (sub-)millimetre slope of their spectral energy distributions. The values of q (or their limits) derived from our observations are all smaller than the oft-assumed steady state collisional cascade model (q = 3.5), but lie well within the theoretically expected range for debris disks q ~ 3 to 4. The measured q values for our targets are all < 3.3, consistent with both collisional modelling results and theoretical predictions for parent planetesimal bodies being `rubble piles' held together loosely by their self-gravity.