CORINOS. II. JWST-MIRI detection of warm molecular gas from an embedded, disk-bearing protostar

We present James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI) observations of warm CO and H2O gas in emission toward the low-mass protostar IRAS 15398-3359, observed as part of the CORINOS program. The CO is detected via the rovibrational fundamental band and hot band near 5 μm, whereas the H2O is detected in the rovibrational bending mode at 6–8 μm. Rotational analysis indicates that the CO originates in a hot reservoir of 1551 ± 135 K, while the water is much cooler at 212 ± 2 K. Neither the CO nor the H2 O line images are significantly spatially extended, constraining the emission to within ∼40 au of the protostar. The compactness and high temperature of the CO are consistent with an origin in the embedded protostellar disk, or a compact disk wind. In contrast, the water must arise from a cooler region and requires a larger emitting area (compared to CO) to produce the observed fluxes. The water may arise from a more extended part of the disk, or from the inner portion of the outflow cavity.