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arXiv 1303.2841astro-ph.GA
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红矩形旋转圆盘中的暖气体:分子谱线发射的精确模型

Warm gas in the rotating disk of the Red Rectangle: accurate models of molecular line emission

V. Bujarrabal, J. Alcolea

摘要:

我们的目标是研究红矩形旋转圆盘中分子气体的激发条件,红矩形是唯一一个证明存在赤道旋转圆盘的后渐近巨枝天体。为了这个目的,我们开发了一个复杂的数值代码,准确地处理辐射转移在2-D,适应于研究分子线从旋转磁盘。本文介绍了红矩形中12 CO和13 CO J=6-5、J=10-9和J=16-15跃迁的远红外Herschel/HIFI观测结果。我们还详细介绍了我们的代码,并讨论了其预测的准确性,从比较测试良好的代码。通过模型拟合,将理论谱线轮廓与经验数据进行比较,从而推断出盘内的物理条件。我们的结论是,我们的代码是非常有效的,并产生可靠的结果。理论预测与我们的观测结果的比较表明,红色矩形盘的温度通常为~ 100-150 K,大约是以前从低J线的毫米波观测中推断的温度的两倍。我们讨论了这些新的温度估计的相关性,以了解这个原型对象的热力学和动力学,以及解释其他很少研究后AGB磁盘的观测。尽管我们先进的处理线的形成,我们的模型不能解释相对较强的线翼发射中间J过渡。我们认为,一个模型,包括一个旋转的磁盘只不能重现这些数据,并建议有一个额外的扩展(可能是双极)的结构,扩大约7- 15公里/秒。

英文摘要:

We aim to study the excitation conditions of the molecular gas in the rotating disk of the Red Rectangle, the only post-Asymptotic-Giant-Branch object in which the existence of an equatorial rotating disk has been demonstrated. For this purpose, we developed a complex numerical code that accurately treats radiative transfer in 2-D, adapted to the study of molecular lines from rotating disks. We present far-infrared Herschel/HIFI observations of the 12CO and 13CO J=6-5, J=10-9, and J=16-15 transitions in the Red Rectangle. We also present our code in detail and discuss the accuracy of its predictions, from comparison with well-tested codes. Theoretical line profiles are compared with the empirical data to deduce the physical conditions in the disk by means of model fitting. We conclude that our code is very efficient and produces reliable results. The comparison of the theoretical predictions with our observations reveals that the temperature of the Red Rectangle disk is typically ~ 100-150 K, about twice as high as previously deduced from mm-wave observations of lower-J lines. We discuss the relevance of these new temperature estimates for understanding the thermodynamics and dynamics of this prototype object, as well as for interpreting observations of other rarely studied post-AGB disks. Despite our sophisticated treatment of the line formation, our model cannot explain the relatively strong line-wing emission for intermediate-J transitions. We argue that a model including a rotating disk only cannot reproduce these data and suggest that there is an additional extended (probably bipolar) structure expanding at about 7--15 km/s.

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