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Hot and dense water in the inner 25 au of SVS13-A

Abstract : In the context of the ASAI (Astrochemical Surveys At IRAM) project, we carried out an unbiased spectral survey in the millimetre window towards the well known low-mass Class I source SVS13-A. The high sensitivity reached (3-12 mK) allowed us to detect at least six HDO broad (full width at half-maximum ∼4-5 km s-1) emission lines with upper level energies up to Eu = 837 K. A non-local thermodynamic equilibrium Large Velocity Gradient (LVG) analysis implies the presence of very hot (150-260 K) and dense (≥3 × 107 cm-3) gas inside a small radius (∼25 au) around the star, supporting, for the first time, the occurrence of a hot corino around a Class I protostar. The temperature is higher than expected for water molecules are sublimated from the icy dust mantles (∼100 K). Although we cannot exclude we are observing the effects of shocks and/or winds at such small scales, this could imply that the observed HDO emission is tracing the water abundance jump expected at temperatures ∼220-250 K, when the activation barrier of the gas phase reactions leading to the formation of water can be overcome. We derive X(HDO) ∼ 3 × 10-6, and a H2O deuteration ≥1.5 × 10-2, suggesting that water deuteration does not decrease as the protostar evolves from the Class 0 to the Class I stage.
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Submitted on : Thursday, June 9, 2022 - 5:11:32 PM
Last modification on : Saturday, June 25, 2022 - 3:06:35 AM

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C. Codella, C. Ceccarelli, E. Bianchi, L. Podio, R. Bachiller, et al.. Hot and dense water in the inner 25 au of SVS13-A. Monthly Notices of the Royal Astronomical Society: Letters, 2016, 462, pp.L75-L79. ⟨10.1093/mnrasl/slw127⟩. ⟨insu-03691492⟩

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