Water in star-forming regions with Herschel (WISH)
Water in star-forming regions with Herschel (WISH)
复制标题
赫歇尔恒星形成区域的水（WISH）
DOI：
10.1051/0004-6361/201424267
复制
发表时间：
2014
影响因子：
6.5
通讯作者：
F. Wyrowski
中科院分区：
文献类型：
--
作者：
J. Mottram;L. Kristensen;E. V. Dishoeck;S. Bruderer;I. S. Jose;A. Karska;R. Visser;G. Santangelo;A. Benz;E. Bergin;P. Caselli;F. Herpin;M. Hogerheijde;D. Johnstone;T. V. Kempen;R. Liseau;B. Nisini;M. Tafalla;F. V. D. Tak;F. V. D. Tak;F. Wyrowski
上下文。流出是恒星形成过程的重要组成部分，既是持续活跃吸积的结果，也是小尺度机械反馈的主要来源之一。水是这些效应的理想示踪剂，因为在原恒星的不同部分，特别是流出的条件下，水的丰度很高。目标。对于0级和I级源，我们对流出喷射系统中的水探测到的物理条件进行了限制和量化。方法：研究方法。作为WIST保证时间键计划的一部分，我们给出了对29颗附近的0/I类原恒星观测到的多次水跃迁的速度分辨Herschel HiFi光谱。这些谱线被分解成不同的高斯分量，每个分量与原恒星系统的三个部分中的一个有关：静止的包络、空腔激波和喷流中以及流出底部的黑子激波。然后，我们使用非LTE radex模型来约束两个流出相关组件中存在的激发条件。结果。与CO相反，源位置的水排放在光学上很厚，但实际上很薄，线比不随速度变化。空穴激波和黑子激波的物理条件相似，激后H-2密度在10(5)-10(8)cm(-3)量级，H2O柱密度在10(16)-10(18)cm(-2)量级。H2O的发射起源于致密发射区：对于斑点激波，对应于半径为10-200AU的点源，而对于空腔激波，则来自沿流出腔壁的一层薄层，厚度为1-30AU。结论。在源头位置的水发射跟踪流出流中的两个不同的运动分量：流出流底部或喷流中的J激波，以及空腔壁上薄层中的C激波。物理条件的相似性与非来源测定形成对比，后者显示相似的密度但较低的柱密度和较大的填充因子。我们认为这是由于这些位置在激波性质和几何形状上的差异。I类信号源的激励条件与0类信号源相似，但线宽和发射区大小一般较小。我们认为，是风速驱动了外流，而不是包络密度或质量的降低，这是0级源和I级源之间H2O强度降低的原因。
Context. Outflows are an important part of the star formation process as both the result of ongoing active accretion and one of the main sources of mechanical feedback on small scales. Water is the ideal tracer of these effects because it is present in high abundance for the conditions expected in various parts of the protostar, particularly the outflow. Aims. We constrain and quantify the physical conditions probed by water in the outflow-jet system for Class 0 and I sources. Methods. We present velocity-resolved Herschel HIFI spectra of multiple water-transitions observed towards 29 nearby Class 0/I protostars as part of the WISH guaranteed time key programme. The lines are decomposed into different Gaussian components, with each component related to one of three parts of the protostellar system; quiescent envelope, cavity shock and spot shocks in the jet and at the base of the outflow. We then use non-LTE radex models to constrain the excitation conditions present in the two outflow-related components. Results. Water emission at the source position is optically thick but effectively thin, with line ratios that do not vary with velocity, in contrast to CO. The physical conditions of the cavity and spot shocks are similar, with post-shock H-2 densities of order 10(5) -10(8) cm(-3) and H2O column densities of order 10(16) -10(18) cm(-2). H2O emission originates in compact emitting regions: for the spot shocks these correspond to point sources with radii of order 10-200 AU, while for the cavity shocks these come from a thin layer along the outflow cavity wall with thickness of order 1-30 AU. Conclusions. Water emission at the source position traces two distinct kinematic components in the outflow; J shocks at the base of the outflow or in the jet, and C shocks in a thin layer in the cavity wall. The similarity of the physical conditions is in contrast to off-source determinations which show similar densities but lower column densities and larger filling factors. We propose that this is due to the differences in shock properties and geometry between these positions. Class I sources have similar excitation conditions to Class 0 sources, but generally smaller line-widths and emitting region sizes. We suggest that it is the velocity of the wind driving the outflow, rather than the decrease in envelope density or mass, that is the cause of the decrease in H2O intensity between Class 0 and I sources.