Herschel低质量恒星形成区中的水（WISH-LM）：用HIFI观测到的L1448-MM中的高速H2O子弹
Water in low-mass star-forming regions with Herschel (WISH-LM): High-velocity H2O bullets in L1448-MM observed with HIFI
摘要：
介绍了在“Herschel恒星形成区中的水”（WISH）关键方案范围内获得的Herschel-HIFI对低质量恒星形成天体L1448-MM中的水的观测，该天体以其突出的外流而闻名。在548 GHz下，探测到6条H2- 16 O谱线（Eup/kB ~ 50-250 K），COJ = 10-9（Eup/kB ~ 305 K），H2- 18 O谱线110-101。除了宽的中心分量和窄的吸收外，所有谱线都显示出在距离源速度|v| > 50 km/s的“子弹”中的强发射。在H $_2$ O中，相对于中心组分，子弹状结构比CO中的突出得多，并且在H2O轮廓形状中随着激发几乎没有变化。从CO谱线得到的子弹中的激发条件意味着温度>150 K，密度>10^5 cm^-3，与宽谱分量的激发条件相似。H2O/CO丰度比在“子弹”和宽组分中是相似的，~ 0.05-1.0，尽管它们在分子喷流中的不同起源以及流出物和包层之间的相互作用。高H2O丰度表明子弹富含H2。“子弹”和宽部件中的H2O冷却相似，并且高于相同部件中的CO冷却。这些数据说明了Herschel-HIFI在低质量恒星形成物体中解开不同动力学成分并确定其激发和化学条件的能力。
英文摘要：
Herschel-HIFI observations of water in the low-mass star-forming object L1448-MM, known for its prominent outflow, are presented, as obtained within the `Water in star-forming regions with Herschel' (WISH) key programme. Six H2-16O lines are targeted and detected (E_up/k_B ~ 50-250 K), as is CO J= 10-9 (E_up/k_B ~ 305 K), and tentatively H2-18O 110-101 at 548 GHz. All lines show strong emission in the "bullets" at |v| > 50 km/s from the source velocity, in addition to a broad, central component and narrow absorption. The bullets are seen much more prominently in H$_2$O than in CO with respect to the central component, and show little variation with excitation in H2O profile shape. Excitation conditions in the bullets derived from CO lines imply a temperature >150 K and density >10^5 cm^-3, similar to that of the broad component. The H2O/CO abundance ratio is similar in the "bullets" and the broad component, ~ 0.05-1.0, in spite of their different origins in the molecular jet and the interaction between the outflow and the envelope. The high H2O abundance indicates that the bullets are H2 rich. The H2O cooling in the "bullets" and the broad component is similar and higher than the CO cooling in the same components. These data illustrate the power of Herschel-HIFI to disentangle different dynamical components in low-mass star-forming objects and determine their excitation and chemical conditions.
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