2025AJ....169..184S

We present a MIRI-MRS spectrum of the high-inclination protoplanetary disk around the solar-mass (K0) star MY Lup, obtained as part of the JWST Disk Infrared Spectral Chemistry Survey (JDISCS). The spectrum shows an unusually weak water emission spectrum for a disk around a star of its spectral type, but strong emission from CO₂, HCN, and isotopologues of both molecules. This includes the first ever detection of C¹⁸O¹⁶O and H¹³CN in an inner disk, as well as tentative detections of C¹⁷O¹⁶O and HC¹⁵N. Slab modeling provides the molecular temperatures, column densities, and emitting areas of the detected molecules. The emitting molecular gas is cold compared to that of other observed protoplanetary disk spectra. We estimate the isotopologue ratios of CO₂ and HCN, albeit with significant uncertainty. We suggest that the unusual spectrum of MY Lup arises from a combination of inner-disk clearing, which removes emission from warm water, and its nearly edge-on inclination, which enhances line-of-sight column densities, although unusual chemistry may also be required. MY Lup's spectrum highlights the potential to detect and measure trace isotopologues to study isotopic fractionation in protoplanetary disks; observations at higher spectral resolving power are needed to constrain the isotopologue ratios to greater precision.