arXiv 0908.17192009-08-12astro-ph.SR

中等质量原恒星OMC2-FIR4的物理结构和水线谱预测

Physical structure and water line spectrum predictions of the Intermediate Mass protostar OMC2-FIR4

N. Crimier, C. Ceccarelli, B. Lefloch, A. Faure

备注：: 14 pages and 14 figures. A&A, accepted
DOI：: 10.1051/0004-6361/200911651

摘要：

目标。中等质量（IM）恒星是银河系的重要组成部分，因为它们对星际FUV场有重要贡献，因此在ISM的能量平衡中发挥重要作用。尽管它们的重要性，很少有人知道他们的形成过程，只有少数研究已经致力于描述中等质量原恒星演化的第一阶段。在这里，我们考虑在非常详细的情况下，最明亮和最近的已知年轻IM原恒星：FIR4在OMC 2组成的猎户座分子云复合体。方法.我们通过一维尘埃辐射转移计算分析了可用的连续辐射（地图和SED）。我们运行了大量的模型网格，以找到最适合数据的包络模型。导出的粉尘密度和温度分布，然后被用来计算气体温度分布，相等的气体冷却和加热方面的信封。最后，我们计算了各种可能的水丰度值的水线谱。结果FIR 4的光度被重新评估为1000 Lo，使FIR 4成为一颗中等质量的原恒星。FIR4周围的包络具有相对较浅的密度幂律指数，约为0.6。最令人惊讶的结果是，气体和尘埃在包层内部热解耦，尘埃冰在100 K升华。这对线路数据的解释有重要影响。我们提供了水的光谱的预测，并详细讨论了线，这将被观察到的赫歇尔空间天文台。

英文摘要：

Aims. Intermediate Mass (IM) stars are an important component of our Galaxy, as they significantly contribute to the interstellar FUV field and, consequently, play an important role in the energy balance of the ISM. Despite their importance, very little is known about their formation process and only a few studies have been devoted to characterize the first phases in the evolution of intermediate mass protostars. Here we consider in great detail the case of the brightest and closest known young IM protostar: FIR4 in the OMC2 component of the Orion molecular cloud complex. Methods. We analyzed the available continuum emission (maps and SED) through one-dimensional dust radiative transfer calculations. We ran large grids of models to find the envelope model that best fits the data. The derived dust density and temperature profiles have been then used to compute the gas temperature profile, equating gas cooling and heating terms across the envelope. Last, we computed the water line spectrum for various possible values of water abundance. Results. The luminosity of FIR4 has been reevaluated to 1000 Lo, making FIR4 definitively an Intermediate Mass protostar. The envelope surrounding FIR4 has a relatively shallow density power law index, ~ 0.6. The most surprising result is that the gas and dust are thermally decoupled in the interior of the envelope, where the dust ices sublimate at 100 K. This has important consequences in the interpretation of the line data. We provide the predictions for the water spectrum, and discuss in detail the lines which will be observed by the Herschel Space Observatory .

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