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 × 107cm-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.
CODELLA, C., Ceccarelli, C., Bianchi, E., PODIO, L., Bachiller, R., Lefloch, B., et al. (2016). Hot and dense water in the inner 25 au of SVS13-A. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 462(1), 75-79 [10.1093/mnrasl/slw127].
Hot and dense water in the inner 25 au of SVS13-A
Testi, L.
2016
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 × 107cm-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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
