The impact of shocks on the chemistry of molecular clouds High resolution images of chemical differentiation along the NGC 1333-IRAS 2A outflow
The impact of shocks on the chemistry of molecular clouds High resolution images of chemical differentiation along the NGC 1333-IRAS 2A outflow
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DOI：
10.1051/0004-6361:20034216
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发表时间：
2003-11
影响因子：
6.5
通讯作者：
J. Jørgensen;M. Hogerheijde;G. Blake;E. F. Dishoeck;L. Mundy;F. L. L. Observatory-F.-L.-L.-Observatory-102503052;Steward Observatory;C. I. O. Technology.;U. Maryland;S. Observatory
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文献类型：
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作者：
J. Jørgensen;M. Hogerheijde;G. Blake;E. F. Dishoeck;L. Mundy;F. L. L. Observatory-F.-L.-L.-Observatory-102503052;Steward Observatory;C. I. O. Technology.;U. Maryland;S. Observatory
本文详细研究了低质量原恒星NGC 1333-IRAS 2A低至3”（650 AU）尺度的流出物的化学成分。介绍了欧文斯谷和伯克利-伊利诺伊州-马里兰州协会干涉仪的毫米波孔径合成观测结果，以及Onsala空间天文台20米望远镜和加州理工学院亚毫米波天文台的（亚）毫米单碟观测结果。高度准直的原恒星流出物与中央原恒星的分子缩合~15000 AU之间的相互作用被HCN、SiO、SO、CS和CH_(3)OH等分子物质清楚地追踪到。特别是SiO在流出液和分子凝结之间的界面处追踪到一个狭窄的高速分量。用多跃迁单碟观测来区分激波的化学性质和分子凝聚的化学性质，并解决其中的物理条件。统计平衡计算表明，静态和激波组分的温度分别为20和70 K，密度接近10^6 cm^（-3）。低激发线和高激发线的线型非常相似，表明每个组分内部的物理性质相当均匀。在激波区，ch3 OH、SiO和含硫分子的丰度显著提高了2 ~ 4个数量级。HCO^+只出现在激波的余波中，与模型一致，在激波中，HCO^+通过从颗粒地幔释放H_(2)O而被破坏。N_(2)H^+显示出窄线，不受流出物的影响，而是探测周围的云。总体分子库存与其他流出区和原恒星环境进行了比较。不同流出区HCN、H_(2)CO和CS的丰度存在差异，这可能与原子碳丰度的差异有关。与原恒星包层的温暖内部相比，在流出部分发现了更高的CH_(3)OH和SiO丰度，特别是CH_(3)OH和SiO，这可能与区域之间的密度差异有关。
This paper presents a detailed study of the chemistry in the outflow associated with the low-mass protostar NGC 1333-IRAS 2A down to 3" (650 AU) scales. Millimeter-wavelength aperture-synthesis observations from the Owens Valley and Berkeley-Illinois-Maryland-Association interferometers and (sub)millimeter single-dish observations from the Onsala Space Observatory 20 m telescope and Caltech Submillimeter Observatory are presented. The interaction of the highly collimated protostellar outflow with a molecular condensation ~15000 AU from the central protostar is clearly traced by molecular species such as HCN, SiO, SO, CS, and CH_(3)OH. Especially SiO traces a narrow high velocity component at the interface between the outflow and the molecular condensation. Multi-transition single-dish observations are used to distinguish the chemistry of the shock from that of the molecular condensation and to address the physical conditions therein. Statistical equilibrium calculations reveal temperatures of 20 and 70 K for the quiescent and shocked components, respectively, and densities near 10^6 cm^(-3). The line-profiles of low- and high-excitation lines are remarkably similar, indicating that the physical properties are quite homogeneous within each component. Significant abundance enhancements of two to four orders of magnitude are found in the shocked region for molecules such as CH_(3)OH, SiO and the sulfur-bearing molecules. HCO^+ is seen only in the aftermath of the shock consistent with models where it is destroyed through release of H_(2)O from grain mantles in the shock. N_(2)H^+ shows narrow lines, not affected by the outflow but rather probing the ambient cloud. The overall molecular inventory is compared to other outflow regions and protostellar environments. Differences in abundances of HCN, H_(2)CO and CS are seen between different outflow regions and are suggested to be related to differences in the atomic carbon abundance. Compared to the warm inner parts of protostellar envelopes, higher abundances of in particular CH_(3)OH and SiO are found in the outflows, which may be related to density differences between the regions.