Waterfalls around protostars: Infall motions towards Class 0/I envelopes as probed by water
Waterfalls around protostars: Infall motions towards Class 0/I envelopes as probed by water
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DOI：
10.1051/0004-6361/201321828
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发表时间：
2013-08
期刊：
影响因子：
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通讯作者：
J. Mottram;E. Dishoeck;M. Schmalzl;L. Kristensen;R. Visser;M. Hogerheijde;S. Bruderer
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文献类型：
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作者：
J. Mottram;E. Dishoeck;M. Schmalzl;L. Kristensen;R. Visser;M. Hogerheijde;S. Bruderer
摘要：恒星要形成，物质必须从核心鳞片通过外壳向中央原恒星下落。原恒星周围的速度分布没有受到很好的约束。作为“Herschel星形成区中的水”（WISH）调查的一部分，在Herschel上用HIFI观测到的6颗0类原恒星和1颗I类原恒星显示了水线观测的下降特征。我们使用1-D非LTE RATRAN辐射传输模型的观测水线约束这些源的原恒星信封的下落速度和化学。我们假设一个自由落体的速度分布，并找到了最佳的拟合，不同的半径，在下降发生。在研究得很好的0类原恒星NGC 1333-IRAS 4A中，我们发现，在我们的观测敏感的整个包层（r>~1000 Au）上都发生了下沉。对于4个源，下沉发生在核心到外壳尺度（即~10000-3000 Au）。在2个源中，在基态线中看到的逆P-Cygni轮廓更可能是由于大尺度运动或前景云。模型，包括一个简单的考虑化学与观察是一致的，而使用步骤丰度配置文件不。在6/7原恒星的内部包层中没有检测到激发水，这进一步证明了在这些半径处，水必须从气相中严重耗尽。其中四个源的入流是超音速的，所有源的入流都必须发生在包层的外缘，这可能是坍缩是全球性的或由外而内而不是由内而外的证据。IRAS 4A的质量下降速率很大（>~10^-4 msol/yr），高于质量流出速率和预期的质量吸积速率，这表明任何小尺度的扁平盘状结构都将是引力不稳定的，可能导致旋转碎裂和/或幕式吸积。
Abridged abstract: For stars to form, material must fall inwards from core scales through the envelope towards the central protostar. The velocity profile around protostars is poorly constrained. 6 Class 0 protostars and one Class I protostars observed with HIFI on board Herschel as part of the "Water in star-forming regions with Herschel" (WISH) survey show infall signatures in water line observations. We use 1-D non-LTE RATRAN radiative transfer models of the observed water lines to constrain the infall velocity and chemistry in the protostellar envelopes of these sources. We assume a free-fall velocity profile and, having found the best fit, vary the radii over which infall takes place. In the well-studied Class 0 protostar NGC1333-IRAS4A we find that infall takes place over the whole envelope to which our observations are sensitive (r>~1000 AU). For 4 sources infall takes place on core to envelope scales (i.e. ~10000-3000 AU). In 2 sources the inverse P-Cygni profiles seen in the ground-state lines are more likely due to larger-scale motions or foreground clouds. Models including a simple consideration of the chemistry are consistent with the observations, while using step abundance profiles are not. The non-detection of excited water in the inner envelope in 6/7 protostars is further evidence that water must be heavily depleted from the gas-phase at these radii. Infall in four of the sources is supersonic and infall in all sources must take place at the outer edge of the envelope, which may be evidence that collapse is global or outside-in rather than inside-out. The mass infall rate in IRAS4A is large (>~10^-4 msol\yr), higher than the mass outflow rate and expected mass accretion rates onto the star, suggesting that any flattened disk-like structure on small scales will be gravitationally unstable, potentially leading to rotational fragmentation and/or episodic accretion.