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Harvard ADS: JWST detections of amorphous and crystalline HDO ice toward massive protostars

Paper abstract: This work aims to utilize the increased sensitivity and resolution of the JWST to quantify the HDO/H_{2}O ratio in ices toward young stellar objects (YSOs) and to determine if the HDO/H_{2}O ratios measured in the gas phase toward massive YSOs (MYSOs) are representative of the ratios in their ice envelopes. Two protostars observed in the Investigating Protostellar Accretion (IPA) program using JWST NIRSpec were analyzed: HOPS 370, an intermediate-mass YSO (IMYSO), and IRAS 20126+4104, a MYSO. The HDO ice toward these sources was detected above the 3\sigma level and quantified via its 4.1 \mum band. The contributions from the CH_{3}OH combination modes to the observed optical depth in this spectral region were constrained via the CH_{3}OH 3.53 \mum band to ensure that the integrated optical depth of the HDO feature was not overestimated. H_{2}O ice was quantified via its 3 \mum band. From these fits, ice HDO/H_{2}O abundance ratios of 4.6\pm1.8\times10^{-3} and 2.6\pm1.2\times10^{-3} are obtained for HOPS 370 and IRAS 20126+4104, respectively. The simultaneous detections of both crystalline HDO and crystalline H_{2}O corroborate the assignment of the observed feature at 4.1 \mum to HDO ice. The ice HDO/H_{2}O ratios are similar to the highest reported gas HDO/H_{2}O ratios measured toward MYSOs as well as the hot inner regions of isolated low-mass protostars, suggesting that at least some of the gas HDO/H_{2}O ratios measured toward massive hot cores are representative of the HDO/H_{2}O ratios in ices. The need for an H_{2}O-rich CH_{3}OH component in the CH_{3}OH ice analysis supports recent experimental and observational results that indicate that some CH_{3}OH ice may form prior to the CO freeze-out stage in H_{2}O-rich ice layers.