EPISODE IV: Ice Inventory in the Envelope of EC 53

TL;DR

This study analyzes JWST spectra of protostar EC 53 to characterize its ice composition, finding no significant change during brightness variations and highlighting its rich, stable ice reservoir as a benchmark for protostellar ice evolution.

Contribution

First detailed JWST-based ice inventory of EC 53, revealing stable ice features across phases and providing a benchmark for episodic accretion studies.

Findings

No measurable change in ice absorption bands between quiescent and burst phases.

Major ice species' abundances exceed typical values in other protostars.

EC 53's ice reservoir is chemically rich and thermally quiescent.

Abstract

We present the 1.6$-$28 $\mu$m spectra of the young protostar EC 53, obtained with JWST NIRSpec IFU and MIRI MRS 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 $\mu$m and 6.85 $\mu$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 to 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.