Radiative Transfer of HCN: Interpreting observations of hyperfine anomalies
Radiative Transfer of HCN: Interpreting observations of hyperfine anomalies
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HCN 的辐射传输：解释超精细异常的观测结果
DOI：
10.1093/mnras/stw835
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发表时间：
2016
影响因子：
4.8
通讯作者：
Eric Keto
中科院分区：
文献类型：
--
作者：
A. Mullins;R. M. Loughnane;R. M. Loughnane;M. Redman;B. Wiles;N. Guegan;J. Barrett;Eric Keto;Eric Keto
分子的转动谱线具有超精细分裂，可以通过其超精细分量的相对谱线强度来探测分子的光学深度，超精细分裂在解释发射气体的物理条件方面特别有利，因为通过第二次转动跃迁，可以导出气体的密度和温度。然而，对于HCN，超精细线的相对强度是异常的。它们的比例在不同的源之间可能有很大的差异，并且与局部热力学平衡不一致。这是HCN超精细异常，并且它阻止使用HCN发射的简单LTE模型来导出可靠的光学深度。在本文中，我们演示了如何建模HCN超精细线发射，并获得准确的线比，光谱线的形状和光学深度。我们表明，通过单独进行辐射传输计算在每个超精细水平，而不是在每个旋转水平的总和，异常超精细发射自然出现。要做到这一点，不仅需要精确的超精细态之间的辐射率，而且还需要精确的碰撞率。我们调查的超精细碰撞率，通过“比例法”，并通过直接重新耦合计算得出的不同设置的影响。通过广泛的参数扫描典型的低质量星星的形成条件，我们表明HCN线比是高度可变的光学深度。我们还重现了观察到的效果，即红-蓝不对称的超精细线（一个下落签名）开关内的一个单一的旋转过渡的意义。
Molecules with hyperfine splitting of their rotational line spectra are useful probes of optical depth, via the relative line strengths of their hyperfine components.The hyperfine splitting is particularly advantageous in interpreting the physical conditions of the emitting gas because with a second rotational transition, both gas density and temperature can be derived. For HCN however, the relative strengths of the hyperfine lines are anomalous. They appear in ratios which can vary significantly from source to source, and are inconsistent with local thermodynamic equilibrium. This is the HCN hyperfine anomaly, and it prevents the use of simple LTE models of HCN emission to derive reliable optical depths. In this paper we demonstrate how to model HCN hyperfine line emission, and derive accurate line ratios, spectral line shapes and optical depths. We show that by carrying out radiative transfer calculations over each hyperfine level individually, as opposed to summing them over each rotational level, the anomalous hyperfine emission emerges naturally. To do this requires not only accurate radiative rates between hyperfine states, but also accurate collisional rates. We investigate the effects of different sets of hyperfine collisional rates, derived via the 'proportional method' and through direct recoupling calculations. Through an extensive parameter sweep over typical low mass star forming conditions, we show the HCN line ratios to be highly variable to optical depth. We also reproduce an observed effect whereby the red-blue asymmetry of the hyperfine lines (an infall signature) switches sense within a single rotational transition.
HCN、HNC、DCN 和 DNC 的电子轰击旋转和超精细激发
DOI：
10.1111/j.1365-2966.2007.12416.x
发表时间：
2007
影响因子：
4.8
作者：
Faure A
通讯作者：
Faure A