JWST observations of 13CO_2 ice: Tracing the chemical environment and thermal history of ices in protostellarenvelopes

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Titel: JWST observations of 13CO_2 ice: Tracing the chemical environment and thermal history of ices in protostellarenvelopes

Beteiligte: Brunken, Nashanty G.C.; Rocha, Will R.M.; van Dishoeck, Ewine F.; Gutermuth, Robert; Tyagi, Himanshu; Slavicinska, Katerina; Nazari, Pooneh; Megeath, Thomas S.; Evans II, Neal J.; Narang, Mayank; Manoj, P.; Rubinstein, Adam E.; Watson, Dan M.; Looney, Leslie W.; Linnartz, Harold; Caratti o Garatti, Alessio; Beuther, Henrik; Linz, Hendrik; Klaassen, Pamela; Poteet, Charles A.; Federman, Samuel; Anglada, Guillem; Atnagulov, Prabhani; Bourke, Tyler L.; [...]

Erschienen: EDP Sciences, 2024

Sprache: Nicht zu entscheiden

DOI: 10.1051/0004-6361/202348718

ISSN: 0004-6361; 1432-0746

Schlagwörter: Space and Planetary Science ; Astronomy and Astrophysics

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Beschreibung: The structure and composition of simple ices can be severely modified during stellar evolution by protostellar heating. Key to understanding the involved processes are thermal and chemical tracers that can be used to diagnose the history and environment of the ice. The 15.2 mu m bending mode of CO_2 in particular has proven to be a valuable tracer of ice heating events but suffers from grain shape and size effects. A viable alternative tracer is the weaker CO_2 isotopologue band at 4.39 mu m, which has now become accessible at high S/N with the James Webb Space Telescope (JWST). In this study we present JWST NIRSpec observations of CO_2 ice in five deeply embedded Class 0 sources that span a wide range in masses and luminosities (0.2 - $L_ ) taken as part of the Investigating Protostellar Accretion Across the Mass Spectrum (IPA) program. The band profiles vary significantly depending on the source, with the most luminous sources showing a distinct narrow peak at 4.38 mu m. We first applied a phenomenological approach with which we demonstrate that a minimum of three to four Gaussian profiles are needed to fit the absorption feature of CO_2 . We then combined these findings with laboratory data and show that a 15.2 mu m CO_2 bending-mode-inspired five-component decomposition can be applied to the isotopologue band, with each component representative of CO_2 ice in a specific molecular environment. The final solution consists of cold mixtures of CO_2 with CH_3OH H_2O and CO as well as segregated heated pure CO_2 ice at 80 K. Our results are in agreement with previous studies of the CO_2 ice band, further confirming that CO_2 is a useful alternative tracer of protostellar heating and ice composition. We also propose an alternative solution consisting only of heated mixtures of CO_2 CH_3OH and CO_2 H_2O ices and warm pure CO_2 ice at 80 K (i.e., no cold CO_2 ices) for decomposing the ice profiles of HOPS 370 and IRAS 20126, the two most luminous sources in our sample that show strong evidence of ice heating resulting in ice segregation.

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