科研之友
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摘要
To study physical properties of the natal filament gas around the cloud core harboring an exceptionally young low-mass protostar GF 9-2, we carried out J = 1-0 line observations of (CO)-C-12, (CO)-C-13, and (CO)-O-18 molecules using the Nobeyama 45 m telescope. The mapping area covers similar to one-fifth of the whole filament. Our (CO)-C-13 and (CO)-O-18 maps clearly demonstrate that the core formed at the local density maxima of the filament, and the internal motions of the filament gas are totally governed by turbulence with Mach number of similar to 2. We estimated the scale height of the filament to be H = 0.3-0.7 pc, yielding the central density of n(c) = 800-4200 cm(-3). Our analysis adopting an isothermal cylinder model shows that the filament is supported by the turbulent and magnetic pressures against the radial and axial collapse due to self-gravity. Since both the dissipation timescales of the turbulence and the transverse magnetic fields can be comparable to the free-fall time of the filament gas of 10(6) yr, we conclude that the local decay of the supersonic turbulence and magnetic fields made the filament gas locally unstable, hence making the core collapse. Furthermore, we newly detected a gas condensation with velocity width enhancement to similar to 0.3 pc southwest of the GF 9-2 core. The condensation has a radius of similar to 0.15 pc and an LTE mass of similar to 5M(circle dot). Its internal motion is turbulent with Mach number of similar to 3, suggesting a gravitationally unbound state. Considering the uncertainties in our estimates, however, we propose that the condensation is a precursor of a cloud core, which would have been produced by the collision of the two gas components identified in the filament.
- 出版日期2014-10-1
- 单位中国科学院国家天文台
