无星致密核FeSt 1-457的动力学状态：脉动球？
The Dynamical State of the Starless Dense Core FeSt 1-457: A Pulsating Globule?
摘要：
为了研究无星球FeSt 1-457的运动学和化学性质，对CS、HCO+、C18 O和N2 H+进行了高分辨分子谱线观测。的HCO+和CS光谱显示出清晰的自反转和不对称的配置文件在整个面对的小球。所观察到的不对称性的意义是指示全球存在的膨胀运动在外层的球。这些运动似乎是亚音速的，明显低于小球的逃逸速度。我们的观测结果与近红外消光数据的比较表明，球状体是引力束缚的。综上所述，我们认为，所观察到的膨胀起源于小球外层的振荡运动，而小球本身可能处于流体静力平衡附近的准稳定状态。CO和N2 H+的观测线宽的分析证实，热压力是云的内部支持的主要组成部分。一个简单的计算表明，脉动的主导模式将是一个l = 2模式，周期为0.3百万年。变形的球状体由于大振幅l = 2振荡可能是负责的双峰结构的核心检测到的高分辨率消光图。分子线观测和消光数据的详细比较提供了C18 O和HCO+显著耗尽的证据，而N2 H+可能未耗尽到约40个视消光量级的云深。
英文摘要：
High resolution molecular line observations of CS, HCO+, C18O and N2H+ were obtained toward the starless globule FeSt 1-457 in order to investigate its kinematics and chemistry. The HCO+ and CS spectra show clear self-reversed and asymmetric profiles across the face of the globule. The sense of the observed asymmetry is indicative of the global presence of expansion motions in the outer layers of the globule. These motions appear to be subsonic and significantly below the escape velocity of the globule. Comparison of our observations with near-infrared extinction data indicate that the globule is gravitationally bound. Taken together these considerations lead us to suggest that the observed expansion has its origin in an oscillatory motion of the outer layers of the globule which itself is likely in a quasi-stable state near hydrostatic equilibrium. Analysis of the observed linewidths of CO and N2H+ confirm that thermal pressure is the dominant component of the cloud's internal support. A simple calculation suggests that the dominant mode of pulsation would be an l = 2 mode with a period of 0.3 Myr. Deformation of the globule due to the large amplitude l = 2 oscillation may be responsible for the double-peaked structure of the core detected in high resolution extinction maps. Detailed comparison of the molecular-line observations and extinction data provides evidence for significant depletion of C18O and perhaps HCO+ while N2H+ may be undepleted to a cloud depth of about 40 magnitudes of visual extinction.
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