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Arxiv: JWST observations of ^{13}CO_{2} ice: Tracing the chemical environment and thermal history of ices in protostellar envelopes Published: 2/6/2024 9:00:15 PM Updated: 3/7/2024 1:24:08 PM

Paper abstract: The structure and composition of simple ices can be modified during stellarevolution by protostellar heating. Key to understanding the involved processesare thermal and chemical tracers that can diagnose the history and environmentof the ice. The 15.2 \mum bending mode of ^{12}CO_2 has proven to be avaluable tracer of ice heating events but suffers from grain shape and sizeeffects. A viable alternative tracer is the weaker ^{13}CO_2 isotopologueband at 4.39 \mum which has now become accessible at high S/N with the\textit{James Webb} Space Telescope (JWST). We present JWST NIRSpecobservations of ^{13}CO_2 ice in five deeply embedded Class 0 sourcesspanning a wide range in luminosities (0.2 - 10^4 L_{\odot} ) taken as partof the Investigating Protostellar Accretion Across the Mass Spectrum (IPA)program. The band profiles vary significantly, with the most luminous sourcesshowing a distinct narrow peak at 4.38 \mum. We first apply aphenomenological approach and show that a minimum of 3-4 Gaussian profiles areneeded to fit the ^{13}CO_2 absorption feature. We then combine thesefindings with laboratory data and show that a 15.2 \mum ^{12}CO_2 bandinspired five-component decomposition can be applied for the isotopologue bandwhere each component is representative of CO_2 ice in a specific molecularenvironment. The final solution consists of cold mixtures of CO_2 withCH_3OH, H_2O and CO as well as segregated heated pure CO_2 ice. Ourresults are in agreement with previous studies of the ^{12}CO_2 ice band,further confirming that ^{13}CO_{2} is a useful alternative tracer ofprotostellar heating events. We also propose an alternative solution consistingonly of heated CO_2:CH_3OH and CO_2:H_2O ices and warm pure CO_2 icefor decomposing the ice profiles of the two most luminous sources in oursample.