A Transition From H2O To C2H2 Dominated Spectra With Decreasing Stellar Luminosity
The chemical composition of the inner regions of disks around young stars will determine the properties of planets forming there.
Many disk physical processes drive the chemical evolution, some of which depend on/correlate with the stellar properties. We aim to explore the connection between stellar properties and inner disk chemistry, using mid-infrared spectroscopy.
We use JWST-MIRI observations of a large, diverse sample of sources to explore trends between C2H2 and H2O. Additionally, we calculate the average spectrum for the T Tauri (M∗>0.2 M⊙) and very low-mass star (VLMS, M∗≤0.2 M⊙) samples and use slab models to determine the properties. We find a significant anti-correlation between the flux ratio of C2H2/H2O and the stellar luminosity. Disks around VLMS have significantly higher FC2H2/FH2O flux ratios than their higher-mass counterparts.
We also explore trends with the strength of the 10 μm silicate feature, stellar accretion rate, and disk dust mass, all of which show correlations with the flux ratio, which may be related to processes driving the carbon-enrichment in disks around VLMS, but also have degeneracies with system properties.
Slab model fits to the average spectra show that the VLMS H2O emission is quite similar in temperature and column density to a warm (∼600 K) H2O component in the T Tauri spectrum, indicating that the high C/O gas phase ratio in these disks is not due to oxygen depletion alone. Instead, the presence of many hydrocarbons, including some with high column densities, points to carbon enhancement in the disks around VLMS.
The observed differences in the inner disk chemistry as a function of host properties are likely to be accounted for by differences in the disk temperatures, stellar radiation field, and the evolution of dust grains.
Sierra L. Grant, Milou Temmink, Ewine F. van Dishoeck, Danny Gasman, Aditya M. Arabhavi, Benoît Tabone, Thomas Henning, Inga Kamp, Alessio Caratti o Garatti, Valentin Christiaens, Pacôme Esteve, Manuel Güdel, Hyerin Jang, Till Kaeufer, Nicolas T. Kurtovic, Maria Morales-Calderón, Giulia Perotti, Kamber Schwarz, Andrew D. Sellek, Lucas M. Stapper, Marissa Vlasblom, L.B.F.M. Waters
Comments: Accepted for publication in A&A. 15 pages, 9 figures. ArXiv abstract is shortened
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2508.04692 [astro-ph.EP] (or arXiv:2508.04692v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2508.04692
Focus to learn more
Submission history
From: Sierra Grant
[v1] Wed, 6 Aug 2025 17:56:05 UTC (797 KB)
https://arxiv.org/abs/2508.04692
Astrobiology, Astrochemistry,
