A DYNAMICALLY COLLAPSING CORE AND A PRECURSOR OF A CORE IN A FILAMENT SUPPORTED BY TURBULENT AND MAGNETIC PRESSURES
A DYNAMICALLY COLLAPSING CORE AND A PRECURSOR OF A CORE IN A FILAMENT SUPPORTED BY TURBULENT AND MAGNETIC PRESSURES
复制标题
DOI：
10.1088/0004-637x/793/2/94
复制
发表时间：
2014-07
期刊：
影响因子：
--
通讯作者：
R. Furuya;Y. Kitamura;H. Shinnaga
中科院分区：
文献类型：
--
作者：
R. Furuya;Y. Kitamura;H. Shinnaga
为了研究云核周围孕育着极其年轻的低质量原恒星 GF 9-2 的原生丝状气体的物理特性，我们使用 Nobeyama 45 m 望远镜对 12CO、13CO 和 C18O 分子进行了 J = 1-0 线观测。映射区域覆盖整个灯丝的五分之一。我们的 13CO 和 C18O 图清楚地表明，核心在灯丝的局部密度最大值处形成，并且灯丝气体的内部运动完全由马赫数~2 的湍流控制。我们估计灯丝的尺度高度为 H = 0.3–0.7 pc，产生 nc = 800–4200 cm−3 的中心密度。我们采用等温圆柱模型的分析表明，细丝受到湍流和磁压力的支撑，以抵抗由于自重力而导致的径向和轴向塌陷。由于湍流和横向磁场的耗散时间尺度都可以与106年灯丝气体的自由落体时间相媲美，因此我们得出结论，超音速湍流和磁场的局部衰减使灯丝气体局部不稳定，从而导致核心塌陷。此外，我们新检测到气体凝结，其速度宽度增强至 GF 9-2 核心西南约 0.3 pc。凝结物的半径为 ∼0.15 pc，LTE 质量为 ∼5 M☉。它的内部运动是湍流，马赫数约为 3，表明其处于不受重力束缚的状态。然而，考虑到我们估计的不确定性，我们认为凝结是云核的前兆，云核是由灯丝中确定的两种气体成分碰撞产生的。
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 12CO, 13CO, and C18O molecules using the Nobeyama 45 m telescope. The mapping area covers ∼ one-fifth of the whole filament. Our 13CO and C18O 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 ∼2. We estimated the scale height of the filament to be H = 0.3–0.7 pc, yielding the central density of nc = 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 106 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 ∼0.3 pc southwest of the GF 9-2 core. The condensation has a radius of ∼0.15 pc and an LTE mass of ∼5 M☉. Its internal motion is turbulent with Mach number of ∼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.