Characterising the physical and chemical properties of a young Class 0 protostellar core embedded in the Orion B9 filament

Oskari Miettinen

doi:10.1007/s10509-016-2834-9

paper

Characterising the physical and chemical properties of a young Class 0 protostellar core embedded in the Orion B9 filament

arXiv:1606.08771 · doi:10.1007/s10509-016-2834-9

Abstract

The present study aims to characterise the physical and chemical properties of the protostellar core Orion B9-SMM3. The APEX telescope was used to perform a follow-up molecular line survey of SMM3. The following species were identified from the frequency range 218.2-222.2 GHz: $^{13}$ CO, C $^{18}$ O, SO, para-H $_{2}$ CO, and E $_{1}$ -type CH $_{3}$ OH. The on-the-fly mapping observations at 215.1-219.1 GHz revealed that SMM3 is associated with a dense gas core as traced by DCO $^{+}$ and p-H $_{2}$ CO. Altogether three different p-H $_{2}$ CO transitions were detected with clearly broadened linewidths (8.2-11 km s $^{- 1}$ in FWHM). The derived p-H $_{2}$ CO rotational temperature, $64 \pm 15$ K, indicates the presence of warm gas. We also detected a narrow p-H $_{2}$ CO line (FWHM=0.42 km s $^{- 1}$ ) at the systemic velocity. The p-H $_{2}$ CO abundance for the broad component appears to be enhanced by two orders of magnitude with respect to the narrow line value ( $\sim 3 \times 1 0^{- 9}$ versus $\sim 2 \times 1 0^{- 11}$ ). The detected methanol line shows a linewidth similar to those of the broad p-H $_{2}$ CO lines, which indicates their coexistence. The CO isotopologue data suggest that the CO depletion factor decreases from $\sim 27 \pm 2$ towards the core centre to a value of $\sim 8 \pm 1$ towards the core edge. In the latter position, the N $_{2}$ D $^{+}$ /N $_{2}$ H $^{+}$ ratio is revised down to $0.14 \pm 0.06$ . The origin of the subfragments inside the SMM3 core we found previously can be understood in terms of the Jeans instability if non-thermal motions are taken into account. The estimated fragmentation timescale, and the derived chemical abundances suggest that SMM3 is a few times $1 0^{5}$ yr old, in good agreement with its Class 0 classification inferred from the spectral energy distribution analysis. The broad p-H $_{2}$ CO and CH $_{3}$ OH lines, and the associated warm gas provide the first clear evidence of a molecular outflow driven by SMM3.

25 pages, 6 figures, 4 tables; accepted for publication in Astrophysics and Space Science

Characterising the physical and chemical properties of a young Class 0 protostellar core embedded in the Orion B9 filament

Abstract

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