We present the results of formaldehyde and methanol deuteration measurements towards the Class I low-mass protostar SVS13-A in the framework of the IRAM 30-m ASAI (Astrochemical Surveys at IRAM) project. We detected emission lines of formaldehyde, methanol and their deuterated forms (HDCO, D2CO, CHD2OH, CH3OD) with Eupup to 276 K. The formaldehyde analysis indicates Tkin∼ 15-30 K, n_H_2 \ge 106cm-3and a size of about 1200 au suggesting an origin in the protostellar envelope. For methanol, we find two components: (I) a high temperature (Tkin∼ 80 K) and very dense (>108cm-3) gas from a hot corino (radius ≃ 35 au), and (II) a colder (Tkin≤ 70 K) and more extended (radius ≃ 350 au) region. The deuterium fractionation is 9 × 10-2for HDCO, 4 × 10-3for D2CO and 2-7 × 10-3for CH2DOH, up to two orders of magnitude lower than the values measured in Class 0 sources. We also derive formaldehyde deuteration in the outflow: 4 × 10-3, in agreement with what found in the L1157-B1 protostellar shock. Finally, we estimate [CH2DOH]/[CH3OD] ≃ 2. The decrease of deuteration in the Class I source SVS13-A with respect to Class 0 sources can be explained by gas-phase processes. Alternatively, a lower deuteration could be the effect of a gradual collapse of less deuterated external shells of the protostellar envelope. The present measurements fill in the gap between pre-stellar cores and protoplanetary discs in the context of organic deuteration measurements.
Bianchi, E., CODELLA, C., Ceccarelli, C., FONTANI, F., Testi, L., Bachiller, R., et al. (2017). Decrease of the organic deuteration during the evolution of Sun-like protostars: the case of SVS13-A. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 467(3), 3011-3023 [10.1093/mnras/stx252].
Decrease of the organic deuteration during the evolution of Sun-like protostars: the case of SVS13-A
Testi, L.;
2017
Abstract
We present the results of formaldehyde and methanol deuteration measurements towards the Class I low-mass protostar SVS13-A in the framework of the IRAM 30-m ASAI (Astrochemical Surveys at IRAM) project. We detected emission lines of formaldehyde, methanol and their deuterated forms (HDCO, D2CO, CHD2OH, CH3OD) with Eupup to 276 K. The formaldehyde analysis indicates Tkin∼ 15-30 K, n_H_2 \ge 106cm-3and a size of about 1200 au suggesting an origin in the protostellar envelope. For methanol, we find two components: (I) a high temperature (Tkin∼ 80 K) and very dense (>108cm-3) gas from a hot corino (radius ≃ 35 au), and (II) a colder (Tkin≤ 70 K) and more extended (radius ≃ 350 au) region. The deuterium fractionation is 9 × 10-2for HDCO, 4 × 10-3for D2CO and 2-7 × 10-3for CH2DOH, up to two orders of magnitude lower than the values measured in Class 0 sources. We also derive formaldehyde deuteration in the outflow: 4 × 10-3, in agreement with what found in the L1157-B1 protostellar shock. Finally, we estimate [CH2DOH]/[CH3OD] ≃ 2. The decrease of deuteration in the Class I source SVS13-A with respect to Class 0 sources can be explained by gas-phase processes. Alternatively, a lower deuteration could be the effect of a gradual collapse of less deuterated external shells of the protostellar envelope. The present measurements fill in the gap between pre-stellar cores and protoplanetary discs in the context of organic deuteration measurements.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
