# JWST/MIRI Spectroscopy of the Disk of the Young Eruptive Star EX Lup in Quiescence

**Authors:** Ágnes Kóspál, Péter Ábrahám, Lindsey Diehl, Andrea Banzatti, Jeroen Bouwman, Lei Chen, Fernando Cruz-Sáenz de Miera, Joel D. Green, Thomas Henning, Christian Rab  
**arXiv:** [2301.08770](https://arxiv.org/abs/2301.08770)  
**Date:** 2023-01-20  
**Summary page:** https://www.summarizepaper.com/en/paper/2301.08770v1/

## Key points

- EX Lup is a low-mass pre-main sequence star that experiences accretion-related outbursts
- JWST/MIRI medium resolution spectroscopy was conducted on EX Lup 14 years after its powerful outburst
- The spectrum showed a forest of emission lines from organic molecules previously identified in infrared spectra of classical T Tauri disks, including H2O, OH, H2, HCN, C2H2 and CO2
- Spectral lines from water and OH were de-blended for the first time and provided an improved characterization of their distribution and density in the inner disk
- The spectrum also revealed broad emission bands from warm sub-micron size amorphous silicate grains at 10 and 18 um
- Crystalline forsterite grains were annealed in the inner disk within 1 au during the outburst in 2008 but later disappeared from their spectral signatures in the 10 um silicate band. However, JWST re-discovered these crystals via their 19.0, 20.0 and 23.5 um emission strength implying that these particles are now located at ~3 au from the star where they may be incorporated into planetesimals approaching the water snowline.
- This new information provides insight into how variable luminosity affects planet-forming material while explaining observed high crystalline fractions found in solar system comets - making EX Lup an ideal laboratory to study planet formation around young stars like itself as well as providing clues to our own solar system's history and evolution over time.

## Summary

EX Lup is a low-mass pre-main sequence star that occasionally experiences accretion-related outbursts. Recently, JWST/MIRI medium resolution spectroscopy was conducted on EX Lup fourteen years after its powerful outburst, during which it displayed a Class II spectrum. The results showed a forest of emission lines from molecules previously identified in infrared spectra of classical T Tauri disks, including H2O, OH, H2, HCN, C2H2 and CO2. The detection of these organic molecules demonstrates that they have returned after disappearing during the large outburst. Spectral lines from water and OH were de-blended for the first time and provided an improved characterization of their distribution and density in the inner disk. The spectrum also revealed broad emission bands from warm sub-micron size amorphous silicate grains at 10 and 18 um. During the outburst in 2008, crystalline forsterite grains were annealed in the inner disk within 1 au but later disappeared from their spectral signatures in the 10 um silicate band. However, with JWST re-discovering these crystals via their 19.0, 20.0 and 23.5 um emission strength implies that these particles are now located at ~3 au from the star where they may be incorporated into planetesimals approaching the water snowline. This new information provides insight into how variable luminosity affects planet-forming material while explaining observed high crystalline fractions found in solar system comets - making EX Lup an ideal laboratory to study planet formation around young stars like itself as well as providing clues to our own solar system's history and evolution over time.