坍塌的热分子核：G31 .41+0.31热核尘埃谱和氨谱线发射的模型
Collapsing Hot Molecular Cores: A Model for the Dust Spectrum and Ammonia Line Emission of the G31.41+0.31 Hot Core
摘要：
我们提出了一个模型，旨在重现观测到的光谱能量分布（SED）以及氨线发射的G31.41+0.31热核。核心被模拟为一个大质量恒星上正在经历激烈的吸积阶段的下落信封。我们假设一个信封的密度和速度结构的动力学崩溃的奇异对数吸球。恒星和包层的物理性质通过拟合SED确定。根据这些物理条件，计算了氨谱线的发射，并与（4，4）跃迁的亚弧秒分辨率VLA数据进行了比较。在该线拟合中唯一的自由参数是氨丰度。NH3（4，4）谱线的观测性质及其空间分布可以很好地再现，只要考虑到在较热（> 100 K）的地核内部区域中，由于氨分子被捕获的冰幔升华而产生的丰度的急剧增加。模型对（2，2）、（4，4）和（5，5）跃迁的预测也与文献中的单碟光谱相当一致。最好的拟合是一个25 Msun的恒星，质量吸积率为0.003 Msun/yr，总光度为200，000 Lsun的模型。气相氨的丰度范围从外部区域的2 \times 10^{-8}到内部区域的3 \times 10^{-6}。据我们所知，这是第一次，尘埃和分子线数据的热分子核心，包括亚弧秒分辨率的数据，空间解决核心的结构，已同时解释了物理自洽模型。这个模型表明，大质量的原恒星能够激发高激发氨跃迁到大尺度包层的外缘（30，000 AU）。
英文摘要：
We present a model aimed to reproduce the observed spectral energy distribution (SED) as well as the ammonia line emission of the G31.41+0.31 hot core. The core is modeled as an infalling envelope onto a massive star that is undergoing an intense accretion phase. We assume an envelope with a density and velocity structure resulting from the dynamical collapse of a singular logatropic sphere. The stellar and envelope physical properties are determined by fitting the SED. From these physical conditions, the ammonia line emission is calculated and compared with subarcsecond resolution VLA data of the (4,4) transition. The only free parameter in this line fitting is the ammonia abundance. The observed properties of the NH3(4,4) lines and their spatial distribution can be well reproduced provided it is taken into account the steep increase of the abundance in the hotter (> 100 K), inner regions of the core produced by the sublimation of icy mantles where ammonia molecules are trapped. The model predictions for the (2,2), (4,4), and (5,5) transitions are also in reasonably agreement with the single-dish spectra available in the literature. The best fit is obtained for a model with a star of 25 Msun, a mass accretion rate of 0.003 Msun/yr, and a total luminosity of 200,000 Lsun. The gas-phase ammonia abundance ranges from 2 \times 10^{-8} in the outer region to 3 \times 10^{-6} in the inner region. To our knowledge, this is the first time that the dust and molecular line data of a hot molecular core, including subarcsecond resolution data that spatially resolve the structure of the core, have been simultaneously explained by a physically self-consistent model. This modeling shows that massive protostars are able to excite high excitation ammonia transitions up to the outer edge (30,000 AU) of the large scale envelope.
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