朝向无星核心的水汽：赫歇尔视角
摘要
SWAS和Odin对暗云中气相水丰度给出了严格的限制上限（x(H2O) < 7x10^-9）。我们利用赫歇尔望远镜大幅提高的角分辨率和灵敏度，研究超越先前上限的无星核心中水汽的化学性质，并测量恒星形成前演化阶段的水汽丰度。利用赫歇尔HIFI对两个无星核心——B68（一个博克球状体）和L1544（一个嵌入金牛座分子云复合体的前恒星核）——进行了基态邻位水（o-H2O）跃迁（557 GHz）的高光谱分辨率观测。在0.59 km s^-1的速度通道内，B68和L1544光谱的亮度温度均方根分别为2.0和2.2 mK。B68的连续谱水平为3.5+/-0.2 mK，L1544为11.4+/-0.4 mK。B68中未检测到显著特征，3 sigma上限与o-H2O柱密度N(o-H2O) < 2.5x10^13 cm^-2或丰度x(o-H2O) < 1.3x10^-9一致，比SWAS对该源的上限低一个数量级以上。L1544光谱在5 sigma水平显示一个吸收特征，由此我们获得了暗云中首次测量的o-H2O柱密度值：N(o-H2O) = (8+/-4)x10^12 cm^-2。相应的丰度在半径> 7000 AU处为x(o-H2O) ~ 5x10^-9，在中心附近约为2x10^-10。辐射传输分析表明，这与在距核心中心0.1 pc处（此处冻结和光解离均可忽略）峰值约为10^-8的x(o-H2O)分布一致。赫歇尔提供了暗区水汽的首次测量。前恒星核（如L1544，具有高中心密度、强连续谱和大包层）是最终揭示分子云中水固/气平衡的非常有前景的工具。
引用
@article{arxiv.1007.1248,
title = {Water vapor toward starless cores: the Herschel view},
author = {P. Caselli and E. Keto and L. Pagani and Y. Aikawa and U. A. Yildiz and F. F. S. van der Tak and M. Tafalla and E. A. Bergin and B. Nisini and C. Codella and E. F. van Dishoeck and R. Bachiller and A. Baudry and M. Benedettini and A. O. Benz and P. Bjerkeli and G. A. Blake and S. Bontemps and J. Braine and S. Bruderer and J. Cernicharo and F. Daniel and A. M. di Giorgio and C. Dominik and S. D. Doty and P. Encrenaz and M. Fich and A. Fuente and T. Gaier and T. Giannini and J. R. Goicoechea and Th. de Graauw and F. Helmich and G. J. Herczeg and F. Herpin and M. R. Hogerheijde and B. Jackson and T. Jacq and H. Javadi and D. Johnstone and J. K. Jorgensen and D. Kester and L. E. Kristensen and W. Laauwen and B. Larsson and D. Lis and R. Liseau and W. Luinge and M. Marseille and C. McCoey and A. Megej and G. Melnick and D. Neufeld and M. Olberg and B. Parise and J. C. Pearson and R. Plume and C. Risacher and J. Santiago-Garcia and P. Saraceno and R. Shipman and P. Siegel and T. A. van Kempen and R. Visser and S. F. Wampfler and F. Wyrowski},
journal= {arXiv preprint arXiv:1007.1248},
year = {2015}
}
备注
Accepted for publication in Astronomy and Astrophysics (HIFI first results issue)