# Grain Growth and Dust Segregation Revealed by Multi-wavelength Analysis of the Class I Protostellar Disk WL 17

**Authors:** Ilseung Han, Woojin Kwon, Yusuke Aso, Jaehan Bae, Patrick Sheehan  
**arXiv:** [2309.06076](https://arxiv.org/abs/2309.06076)  
**Date:** 2023-09-12  
**Summary page:** https://www.summarizepaper.com/en/paper/2309.06076v1/

## Key points

- Study focuses on early stages of planet formation through grain growth
- Limited understanding of grain growth in early stages of Class 0/I protostellar disks
- Archival data from ALMA analyzed for Class I protostellar disk WL 17
- Distinct disk substructures observed in Band 3 and Band 7 wavelengths
- Asymmetric spectral index map indicates possible grain growth and dust segregation
- Radiative transfer modeling confirms symmetric distribution of large grains and asymmetrical distribution of smaller grains
- WL 17's disk expected to be massive and gravitationally unstable
- Single Jupiter-mass protoplanet proposed as responsible for observed structures and grain growth in WL 17
- Study provides insights into early-stage grain growth on the protostellar disk scale

## Summary

This study focuses on the early stages of planet formation by examining the process of grain growth from small micrometer-sized particles to larger millimeter/centimeter-sized grains. Previous observations have shown grain growth in Class II protoplanetary disks and Class 0/I protostellar envelopes, but there is limited understanding of this process in the early stages of Class 0/I protostellar disks. To address this gap in knowledge, archival data from the Atacama Large Millimeter/submillimeter Array (ALMA) was analyzed for the Class I protostellar disk WL 17 located in the $\rho$ Ophiuchus molecular cloud. The data included observations at two different wavelengths: Band 3 ($\lambda$ = 3.1 mm) and Band 7 ($\lambda$ = 0.87 mm). The analysis revealed distinct disk substructures in both bands, with a central hole and symmetric ring observed in Band 3 and an off-center hole and asymmetric ring seen in Band 7. An asymmetric spectral index map also indicated possible grain growth and dust segregation on the protostellar disk scale with a low mean value of $\alpha$ = 2.28 $\pm$ 0.02. To further investigate these features, radiative transfer modeling was conducted which confirmed that large grains (around 10 cm) were symmetrically distributed throughout the disk while smaller grains (around 10 $\mu$m) exhibited asymmetrical distribution patterns. Additionally, the analysis suggested that WL 17's disk is expected to be massive and gravitationally unstable. The authors propose that a single Jupiter-mass protoplanet formed through gravitational instability could be responsible for generating the observed ring-like structure, grain growth, and dust segregation in WL 17. In summary, this study provides valuable insights into early-stage grain growth occurring on the protostellar disk scale and highlights the potential role of gravitational instability in shaping protoplanetary disks.