高质量恒星形成区II的化学分异。选定天体的分子多谱线和尘埃连续谱研究
Chemical differentiation in regions of high mass star formation II. Molecular multiline and dust continuum studies of selected objects
摘要：
本研究的目的是调查系统的化学分化的分子在高质量恒星形成的区域。我们观察到五个突出的网站的高质量恒星形成HCN，HNC，HCO+，它们的同位素，C18 O，C34 S和其他一些分子线，在3和1.3毫米和连续在1.3毫米的一些来源。考虑到早期获得的数据N2 H+，我们推导出分子丰度和物理参数的来源（质量，密度，电离分数等）。根据CH 3C 2 H的观测结果估计了动力学温度。然后，我们分析了分子丰度和物理参数之间的相关性，并讨论了适用于这些物种的化学模型。在我们的样本中，这些源的典型物理参数如下：动力学温度在~ 30-50 K之间（它系统地高于氨观测得到的温度，并且相当接近尘埃温度），质量从几十到几百个太阳质量，气体密度~ 10 ^5 cm^{-3}，电离分数~ 10^{-7}。在大多数情况下，电离分数朝向嵌入的YSO略微增加（几倍）。观察到的团块接近重力平衡。各种分子的分布存在系统差异。CO、CS和HCN的丰度基本不变。没有CO和/或CS耗尽的迹象，如在冷芯中。同时，HCO+，HNC，特别是N2 H+的丰度在这些对象中变化很大。它们与电离分数反相关，因此朝向嵌入的YSO降低。对于N2 H+，这可以解释为解离重组是占主导地位的破坏过程。N2 H+、HCO+和HNC是大质量原恒星的重要指示物。
英文摘要：
The aim of this study is to investigate systematic chemical differentiation of molecules in regions of high mass star formation. We observed five prominent sites of high mass star formation in HCN, HNC, HCO+, their isotopes, C18O, C34S and some other molecular lines, for some sources both at 3 and 1.3 mm and in continuum at 1.3 mm. Taking into account earlier obtained data for N2H+ we derive molecular abundances and physical parameters of the sources (mass, density, ionization fraction, etc.). The kinetic temperature is estimated from CH3C2H observations. Then we analyze correlations between molecular abundances and physical parameters and discuss chemical models applicable to these species. The typical physical parameters for the sources in our sample are the following: kinetic temperature in the range ~ 30-50 K (it is systematically higher than that obtained from ammonia observations and is rather close to dust temperature), masses from tens to hundreds solar masses, gas densities ~ 10^5 cm^{-3}, ionization fraction ~ 10^{-7}. In most cases the ionization fraction slightly (a few times) increases towards the embedded YSOs. The observed clumps are close to gravitational equilibrium. There are systematic differences in distributions of various molecules. The abundances of CO, CS and HCN are more or less constant. There is no sign of CO and/or CS depletion as in cold cores. At the same time the abundances of HCO+, HNC and especially N2H+ strongly vary in these objects. They anti-correlate with the ionization fraction and as a result decrease towards the embedded YSOs. For N2H+ this can be explained by dissociative recombination to be the dominant destroying process. N2H+, HCO+, and HNC are valuable indicators of massive protostars.
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