paper

Molecular Similarity and Water Diversity in Coeval Binary Disks: JWST/MIRI Observations of Sz 65 and Sz 66

arXiv:2605.28043 · doi:10.3847/1538-4357/ae736e

Abstract

We present JWST/MIRI Medium Resolution Spectrometer spectra of the wide-separation (projected separation $= 980$ au) binary protoplanetary disks Sz 65 (K7; $0.68 M_{⊙}$ ) and Sz 66 (M3; $0.30 M_{⊙}$ ), reduced using the uniform pipeline of the JWST Disk Infrared Spectral Chemistry Survey. Both disks show rich molecular emission, including H $_{2}$ O, CO $_{2}$ , HCN, C $_{2}$ H $_{2}$ , and OH. The scaled spectra of the two disks exhibit remarkably similar H $_{2}$ O, CO $_{2}$ , and HCN line emission in the 13--18 $I^¼$ m region, with the only notable difference being stronger C $_{2}$ H $_{2}$ emission in the primary (Sz 65). Beyond 18 $I^¼$ m, the difference in H $_{2}$ O line emission between the two disks increases. Both the flux ratios and the slab-model-derived mass ratios of cold to hot H $_{2}$ O ( $\sim$ 200 K to $\sim$ 750 K) and warm to hot H $_{2}$ O ( $\sim$ 450 K to $\sim$ 750 K) are significantly higher in the secondary (Sz 66). Because binary stars share nearly the same age and metallicity, and as both disks appear compact in millimeter emission ( $< 30$ au), we suggest that the excess cold H $_{2}$ O in the secondary is best explained by its unstructured dust disk, in contrast to the primary, which shows gaps at 6 and 20 au. The enhanced cold water in the secondary is consistent with efficient pebble drift across the water snow line and increased H $_{2}$ O vapor from the sublimation of icy mantles. Our results demonstrate that wide-separation binaries can serve as powerful control samples for isolating the impact of individual disk properties on inner-disk chemistry and evolution.

Published in The Astrophysical Journal; 23 figures, 4 tables