# Hot exozodiacal dust: an exocometary origin?

**Authors:** Élie Sezestre, Jean-Charles Augereau, Philippe Thébault  
**arXiv:** [1903.06130](https://arxiv.org/abs/1903.06130)  
**Date:** 2019-03-14  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/1903.06130v1/

## Key points

- The study investigates two mechanisms for the production of exozodiacal dust: Poynting-Robertson drag pile-up scenario and exocometary dust delivery scenario.
- A new numerical model was developed to calculate dust dynamics, including non-orbit-averaged equations for grains close to the star, dust sublimation, and a radiative transfer code for direct comparison with observations.
- Four stellar types and three dust compositions were considered, assuming a parent belt at 50 au.
- The Poynting-Robertson drag pile-up scenario cannot produce long-lived submicron-sized grains close to the star. Inward drifting grains fill in the region between the parent belt and sublimation distance, producing an unrealistically strong mid-infrared excess compared to near-infrared excess.
- Exocometary dust delivery scenario can form a narrow ring close to the sublimation zone populated with large grains several tens to several hundred micrometers in radius. This scenario provides a better match with observations if carbon-rich grains are present.
- The required number of active exocomets needed to sustain observed dust level is reasonable.
- Hot exozodiacal dust detected by near-infrared interferometry is unlikely due to inward grain migration by Poynting-Robertson drag from distant parent belt but could instead have an exocometary origin.

## Summary

The study aims to investigate two mechanisms for the production of exozodiacal dust: the Poynting-Robertson drag pile-up scenario and the exocometary dust delivery scenario. The authors developed a new numerical model that calculates dust dynamics, including non-orbit-averaged equations for grains close to the star, dust sublimation, and a radiative transfer code for direct comparison with observations. They considered four stellar types, three dust compositions, and assumed a parent belt at 50 au. The results show that it is impossible to produce long-lived submicron-sized grains close to the star in the Poynting-Robertson drag pile-up scenario. Inward drifting grains fill in the region between the parent belt and sublimation distance, producing an unrealistically strong mid-infrared excess compared to near-infrared excess. The dust pile-up at the sublimation radius is insufficient to boost near-IR flux of exozodi enough to dominate over mid-infrared excess. However, in the case of exocometary dust delivery scenario, a narrow ring can form close to sublimation zone populated with large grains several tens to several hundred micrometers in radius. Although not perfect, this scenario provides a better match with observations if carbon-rich grains are present. The required number of active exocomets needed to sustain observed dust level is reasonable. Therefore, hot exozodiacal dust detected by near-infrared interferometry is unlikely due to inward grain migration by Poynting-Robertson drag from distant parent belt but could instead have an exocometary origin.