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Water abundance variations around high-mass protostars: HIFI observations of the DR21 region

机译：高质量原恒星周围的水丰度变化：DR21地区的HIFI观测

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Context. Water is a key molecule in the star formation process, but its spatial distribution in star-forming regions is not well known. Aims. We study the distribution of dust continuum and H2O and 13COline emission in DR21, a luminous star-forming region with a powerful outflow and a compact H II region. Methods. Herschel-HIFI spectra near 1100GHz show narrow 13CO 10-9emission and H2O 111-000 absorption from the dense core and broad emission from the outflow in both lines. The H2Oline also shows absorption by a foreground cloud known from ground-based observations of low-J COlines. Results. The dust continuum emission is extended over 36'' FWHM, while the 13CO and H2Olines are confined to 24''or less. The foreground absorption appears to peak further North thanthe other components. Radiative transfer models indicate very lowabundances of for H2O and for 13CO in the dense core, and higher H2O abundances of in the foreground cloud and in the outflow. Conclusions. The high H2O abundance in the warm outflow is probably due to the evaporation of water-rich icy grain mantles, while the H2Oabundance is kept down by freeze-out in the dense core and by photodissociation in the foreground cloud. Key words: ISM: molecules - stars: formation - astrochemistry - ISM: individual objects: DR21
机译：上下文。水是恒星形成过程中的关键分子，但是在恒星形成区域中水的空间分布尚不清楚。目的我们研究了DR21中的粉尘连续体，H2O和13COline排放的分布，DR21是一个具有强大外流和紧凑的H II区的发光恒星形成区。方法。 1100 GHz附近的Herschel-HIFI光谱显示，密集的岩心吸收13CO 10-9的辐射较窄，H2O 111-000吸收，两条管线的出口均吸收较宽的辐射。 H2Oline还显示出前景云的吸收，该前景云是从低J COline的地面观测得知的。结果。连续粉尘排放范围扩大到36''FWHM，而13CO和H2Oline限制在24''或更小。前景吸收似乎比其他成分更向北倾斜。辐射转移模型表明，致密核中H2O和13CO的丰度非常低，而前景云和流出物中H2O的丰度较高。结论。在温暖的流出中，高的H2O丰度可能是由于富水冰冷的地幔蒸发所致，而H2O丰度则通过致密岩心中的冻结和前景云中的光解离作用而得以降低。关键词：ISM：分子-恒星：形成-天体化学-ISM：单个物体：DR21

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