EPISODE. IV. Ice Inventory in the Envelope of EC 53

Abstract We present the 1.6–28 μ m spectra of the young protostar EC 53, obtained with the James Webb Space Telescope (JWST) Near Infrared Spectograph Integral Field Unit and MIRI Medium Resolution Spectroscopy during the quiescent and burst phases of its periodic brightness variations. To isolate ice absorption features, we modeled and removed the mid-infrared silicate dust absorption using a dedicated continuum-fitting procedure. In the optical depth spectrum, we first fit the broad H 2 O ice features and then decomposed the major ice components, including NH 3 , CO 2 , CH 3 OH, CO, and CH 4 , by matching laboratory profiles for both pure and H 2 O-mixed ices. The 4.62 μ m and 6.85 μ m bands are attributed to OCN – and NH 4 + ions, respectively. Minor or tentative contributions from complex species (HCOOH, H 2 CO, CH 3 COOH, CH 3 CHO, CH 3 CH 2 OH, and NH 2 CHO) are also considered for our global ice analysis. The silicate-corrected spectra reveal no measurable change in any ice absorption band between the two phases, indicating that moderate and short-period accretion bursts in EC 53 do not significantly alter the physical or chemical state of the ices within its envelope. The derived abundances of these major species relative to H 2 O significantly exceed the values typically observed toward other embedded protostars. Finally, we place the ice inventory of EC 53 in the context of other protostellar systems observed with JWST, highlighting that its chemically rich, thermally quiescent ice reservoir provides a benchmark for studying ice evolution under episodic accretion.