标题： 关于冷低质量分子核中水丰度的敏感限制 显示英文标题

标题： Sensitive Limits on the Water Abundance in Cold Low Mass Molecular Cores

摘要： 我们展示了对两个冷的无星云团B68和ρ天蝎座Core D中水蒸气的SWAS观测。每个源都报告了对o-H2O的1(10)-1(01)跃迁的灵敏非检测。这两个分子核心之前已经被详细的观测表征了物理结构。利用这些相对明确的物理特性和蒙特卡洛辐射传递模型，我们从丰度计算中消除了一个最大的不确定性，并设定了到目前为止冷低质量分子核心中水的最低丰度限制。这些限制分别是< 3 x 10^{-8}（相对于H2）和< 8 x 10^{-9}在B68和ρ天蝎座D中。如此低的丰度证实了冷（T < 20 K）核心中正交水蒸气的一般缺乏。只要水的正交/顺式比不是接近零，这些限制远远低于理论预测，并似乎支持这样一个建议，即密集低质量核心中的大部分水被冻结到冷尘埃颗粒表面上。 显示英文摘要

摘要： We present SWAS observations of water vapor in two cold star-less clouds, B68 and Core D in rho Ophiuchus. Sensitive non-detections of the 1(10)-1(01) transition of o-H2O are reported for each source. Both molecular cores have been previously examined by detailed observations that have characterized the physical structure. Using these rather well defined physical properties and a Monte-Carlo radiation transfer model we have removed one of the largest uncertainties from the abundance calculation and set the lowest water abundance limit to date in cold low-mass molecular cores. These limits are < 3 x 10^{-8} (relative to H2) and < 8 x 10^{-9} in B68 and rho Oph D, respectively. Such low abundances confirm the general lack of ortho-water vapor in cold (T < 20 K) cores. Provided that the ortho/para ratio of water is not near zero, these limits are well below theoretical predictions and appear to support the suggestion that most of the water in dense low-mass cores is frozen onto the surfaces of cold dust grains.