MINDS. The detection of ${}^{13}$CO${}_2$ with JWST-MIRI indicates abundant CO${}_2$ in a protoplanetary disk

Abstract

We present JWST-MIRI MRS spectra of the protoplanetary disk around the low-mass T Tauri star GW Lup from the MIRI mid-INfrared Disk Survey (MINDS) GTO program. Emission from ${}^{12}$CO${}_2$, ${}^{13}$CO${}_2$, H${}_2$O, HCN, C${}_2$H${}_2$, and OH is identified with ${}^{13}$CO${}_2$ being detected for the first time in a protoplanetary disk. We characterize the chemical and physical conditions in the inner few au of the GW Lup disk using these molecules as probes. The spectral resolution of JWST-MIRI MRS paired with high signal-to-noise data is essential to identify these species and determine their column densities and temperatures. The $Q$-branches of these molecules, including those of hot-bands, are particularly sensitive to temperature and column density. We find that the ${}^{12}$CO${}_2$ emission in the GW Lup disk is coming from optically thick emission at a temperature of $\sim$400 K. ${}^{13}$CO${}_2$ is optically thinner and based on a lower temperature of $\sim$325 K, may be tracing deeper into the disk and/or a larger emitting radius than ${}^{12}$CO${}_2$. The derived $N_{\mathrm{C}{\mathrm{O}}_2}$/$N_{{\mathrm{H}}_2\mathrm{O}}$ ratio is orders of magnitude higher than previously derived for GW Lup and other targets based on \textit{Spitzer}-IRS data. This high column density ratio may be due to an inner cavity with a radius in between the H${}_2$O and CO${}_2$ snowlines and/or an overall lower disk temperature. This paper demonstrates the unique ability of JWST to probe inner disk structures and chemistry through weak, previously unseen molecular features.

15 pages, 10 figures. Accepted to ApJL