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arXiv 1808.04802astro-ph.GAastro-ph.SR
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由观测值估算坍落原恒星核的角动量

On estimating angular momenta of infalling protostellar cores from observations

Shangjia Zhang, Lee Hartmann, Manuel Zamora, Aleksandra Kuznetsova

摘要:

我们使用碰撞流的情况下的分子云的形成的数值模拟研究的早期状态,低质量的原恒星核心的角动量的观测估计的可靠性。我们发现,适当的修正投影因子,分子线观测NH $_3$的速度梯度可以用来提供合理的估计核心角动量的一个因素内的两个到三个,有一些大的低估,由于不利的视角。我们的结果不同于以前的研究,这些研究表明,观测可能会高估真实的角动量多达一个数量级;这种差异可能是由于我们的模拟中小尺度上的速度场更加平滑,这是由于允许湍流衰减和引力下降占主导地位。这些结果强调了理解“湍流”速度的性质的重要性,并对核心坍缩过程中原恒星盘的形成产生了影响。

英文摘要:

We use numerical simulations of molecular cloud formation in the colliding flow scenario to investigate the reliability of observational estimates of the angular momenta of early-state, low-mass protostellar cores. We show that, with suitable corrections for projection factors, molecular line observations of velocity gradients in NH$_3$ can be used to provide reasonable estimates of core angular momenta within a factor of two to three, with a few large underestimates due to unfavorable viewing angles. Our results differ from previous investigations which suggested that observations might overestimate true angular momenta by as much as an order of magnitude; the difference is probably due to the much smoother velocity field on small scales in our simulations, which result from allowing turbulence to decay and gravitational infall to dominate. The results emphasize the importance of understanding the nature of 'turbulent' velocities, with implications for the formation of protostellar disks during core collapse.

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