# Stellar winds can affect gas dynamics in debris disks and create observable belt winds

**Authors:** Quentin Kral, James Pringle, Luca Matrà, Philippe Thébault  
**arXiv:** [2211.04191](https://arxiv.org/abs/2211.04191)  
**Date:** 2022-11-08  
**Summary page:** https://www.summarizepaper.com/en/paper/2211.04191v1/

## Key points

- Gas is detected in extrasolar systems around mature stars with planetesimal belts
- This gas is believed to be released from planetesimals and has been modeled using a viscous disk approach
- At low densities, the gas may be blown out by the stellar wind instead of forming a disk
- An analytical model was developed for A to M stars that can follow the evolution of gas outflows and determine when the transition occurs between a disk or a wind
- Belts with gas densities $< 7 \, (\Delta R/50 {\rm \, au})^{-1}$ cm$^{-3}$ would create a wind rather than a disk
- Debris disks with low fractional luminosities $f$ are more likely to create gas winds, which could be observed with current facilities such as ALMA (CO and CO$^+$ could be good tracers)
- Systems containing low gas masses such as Fomalhaut or TWA 7 or more generally debris disks with fractional luminosities $f \lesssim 10^{-5} (L_\star/L_\odot)^{-0.37} $ or stellar luminosity $\gtrsim 20 \, L_\odot$ (A0V or earlier) are likely to generate gas outflows (or belt winds) rather than form disks
- The detection of these gas winds would allow for the measurement of otherwise difficult to measure stellar wind properties of main-sequence stars
- The study provides maps showing the gas density in X,Y and X,Z planes as well as mean velocity map in X,Z planes which can help further understand complex dynamics of debris disks and highlight importance of considering stellar wind effects when modeling these systems

## Summary

Gas is commonly detected in extrasolar systems around mature stars with planetesimal belts. This gas is believed to be released from planetesimals and has been modeled using a viscous disk approach. However, at low densities, the gas may be blown out by the stellar wind instead of forming a disk. To investigate this phenomenon, an analytical model was developed for A to M stars that can follow the evolution of gas outflows and determine when the transition occurs between a disk or a wind. The crucial criterion for determining whether a belt of radial width $\Delta R$ will create a wind or a disk is the gas density for which gas particles stop being protected from stellar wind protons impacting at high velocities on radial trajectories. The study found that belts with gas densities $< 7 \, (\Delta R/50 {\rm \, au})^{-1}$ cm$^{-3}$ would create a wind rather than a disk. This finding could explain recent observations of outflowing gas in NO Lup. Additionally, the properties of these belt winds can be used to measure stellar wind properties such as their densities and velocities. Debris disks with low fractional luminosities $f$ are more likely to create gas winds, which could be observed with current facilities such as ALMA (CO and CO$^+$ could be good tracers). The study concludes that systems containing low gas masses such as Fomalhaut or TWA 7 or more generally debris disks with fractional luminosities $f \lesssim 10^{-5} (L_\star/L_\odot)^{-0.37} $ or stellar luminosity $\gtrsim 20 \, L_\odot$ (A0V or earlier) are likely to generate gas outflows (or belt winds) rather than form disks. Gas observed to be outflowing at high velocity in young systems like NO Lup could potentially be examples of such belt winds. The detection of these gas winds would allow for the measurement of otherwise difficult to measure stellar wind properties of main-sequence stars. The study also provides maps showing the gas density in X,Y and X,Z planes as well as mean velocity map in X,Z planes which can help further understand complex dynamics of debris disks and highlight importance of considering stellar wind effects when modeling these systems. Overall this research sheds light on how different parameters affect formation and evolution of debris disks around mature stars and provides useful insights into their dynamics.