arXiv 1301.02532013-01-02astro-ph.GA

强反转脉泽中的非局域辐射转移

Non--local radiative transfer in strongly inverted masers

F. Daniel, J. Cernicharo

DOI：: 10.1051/0004-6361/201219588

摘要：

脉泽跃迁通常在密度和温度范围很大的介质中观察到。它们可用于获得关于观测区域的动力学和物理条件的信息。为了获得可靠的约束条件的物理条件普遍存在的激射区，它是必要的模型的能级的观察分子的激发机制。我们提出了一种数值方法，使我们能够获得自洽的解决方案的统计平衡和辐射转移方程。本文利用标准脉泽理论，将短特征线法推广到积分-微分辐射转移方程的解，使之适用于强脉泽谱线的情况。我们已经将我们的方法应用到水分子的脉泽线，我们与一个不太准确的方法得到的结果进行比较。在大的脉泽不透明度的制度，我们发现大的差异，可能高达几个数量级的脉泽线的强度。然而，这两种方法之间的比较表明，对热线的影响是适度的。最后，利用He、o-H2和p-H2的速率系数，讨论了速率系数对H2O激射线和不透明度的影响。我们发现，脉泽性质的线是不受选定的碰撞率。然而，从一组到另一组，建模的线不透明度和强度可以分别变化高达~2和~10倍。

英文摘要：

Maser transitions are commonly observed in media exhibiting a large range of densities and temperatures. They can be used to obtain information on the dynamics and physical conditions of the observed regions. In order to obtain reliable constraints on the physical conditions prevailing in the masing regions, it is necessary to model the excitation mechanisms of the energy levels of the observed molecules. We present a numerical method that enables us to obtain self-consistent solutions for both the statistical equilibrium and radiative transfer equations. Using the standard maser theory, the method of Short Characteristics is extended to obtain the solution of the integro-differential radiative transfer equation, appropriate to the case of intense masing lines. We have applied our method to the maser lines of the H2O molecule and we compare with the results obtained with a less accurate approach. In the regime of large maser opacities we find large differences in the intensity of the maser lines that could be as high as several orders of magnitude. The comparison between the two methods shows, however, that the effect on the thermal lines is modest. Finally, the effect introduced by rate coefficients on the prediction of H2O masing lines and opacities is discussed, making use of various sets of rate coefficients involving He, o-H2 and p-H2. We find that the masing nature of a line is not affected by the selected collisional rates. However, from one set to the other the modelled line opacities and intensities can vary by up to a factor ~2 and ~10 respectively.

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