Disentangling the dust and gas contributions of the JWST/MIRI spectrum of Sz28

Abstract

Recent spectra of protoplanetary disks around very low-mass stars (VLMS), captured by the Mid-InfraRed Instrument (MIRI) on board the James Webb Space Telescope (JWST), reveal a rich carbon chemistry. Current interpretations of these spectra are based on 0D slab models and provide valuable estimates for molecular emission temperatures and column densities in the innermost disk. However, the established fitting procedures and simplified models are challenged by the many overlapping gas features. We aim to simultaneously determine the molecular and the dust composition of the disk around the VLMS Sz28 in a Bayesian way. We model the JWST/MIRI spectrum of Sz28 up to $17\mu \mathrm{m}$ using the Dust Continuum Kit with Line emission from Gas (DuCKLinG). Systematically excluding different molecules from the Bayesian analysis allows for an evidence determination of all investigated molecules and isotopologues. We continue by examining the emission conditions and locations of all molecules, analysing the differences to previous 0D slab fitting, and analysing the dust composition. We find very strong Bayesian evidence for the presence of C2H2, HCN, C6H6, CO2, HC3N, C2H6, C3H4, C4H2, and CH4 in the JWST/MIRI spectrum of Sz28. Additionally, we identify CH3 and find tentative indications for NH3. There is no evidence for water in the spectrum. However, we show that column densities of up to $2\times 10^{17}\mathrm{c}{\mathrm{m}}^{-2}$ could be hidden in the observational noise if assuming similar emission conditions of water as the detected hydrocarbons. Contrary to previous 0D slab results, a C4H2 quasi-continuum is robustly identified. We expect some of the stated differences to previous 0D slab fitting results to arise from an updated data reduction of the spectrum, but also due to the different modelling process. The latter reason underpins the need for more advanced models and fitting procedures.

accepted by Astronomy & Astrophysics

References in corpus (13)

• Bayes in the sky: Bayesian inference and model selection in cosmology
• A statistical test for Nested Sampling algorithms
• VIP: Vortex Image Processing package for high-contrast direct imaging
• The shape and composition of interstellar silicate grains
• The CARMENES search for exoplanets around M dwarfs -- Planet occurrence rates from a subsample of 71 stars
• MINDS. The detection of ${}^{13}$CO${}_2$ with JWST-MIRI indicates abundant CO${}_2$ in a protoplanetary disk
• Abundant hydrocarbons in the disk around a very-low-mass star
• The Occurrence Rate of Terrestrial Planets Orbiting Nearby Mid-to-late M Dwarfs from TESS Sectors 1-42
• MINDS. Abundant water and varying C/O across the disk of Sz 98 as seen by JWST/MIRI
• MINDS. Hydrocarbons detected by JWST/MIRI in the inner disk of Sz28 consistent with a high C/O gas-phase chemistry
• Herbig Stars: A Quarter Century of Progress
• Bayesian Analysis of Molecular Emission and Dust Continuum of Protoplanetary Disks
• Spatial distribution of crystalline silicates in protoplanetary disks: How to interpret mid-infrared observations

Cited by in corpus (3)

• MINDS: The very low-mass star and brown dwarf sample -- Hidden water in carbon-dominated protoplanetary disks
• MINDS survey of silicates in T Tauri disks: Correlation between dust and gas
• MINDS: The very low-mass star and brown dwarf sample II. Probing disk settling, dust properties, and dust-gas interplay with JWST/MIRI