蛇夫座无星核的内在形状
The intrinsic shapes of starless cores in Ophiuchus
摘要：
利用岩心的观测结果来推断其内在性质需要解决几个约束条件较差的逆问题。在这里，我们解决这些问题之一，即推断从预测的纵横比的核心蛇夫座的内在三维形状。四个模型提出，所有的基础上的标准假设，核心是随机取向的椭球体，并进一步假设，核心的形状是不相关的，其绝对大小。第一个也是最简单的模型，M1，有一个自由参数，并假设一个核心的相对轴是从一个对数正态分布中随机抽取的，平均值和标准差为零。第二个模型M2 a有两个自由参数，并假设对数正态分布（具有标准差σo）具有有限平均值μo，定义为μo<0意味着细长（扁长）核心更受欢迎，而μo>0意味着扁平（扁圆）核心更受欢迎。文中给出了第三模型（M2 b，两个自由参数）和第四模型（M4，四个自由参数）的细节。利用马尔可夫链蒙特卡罗抽样和贝叶斯分析方法，得到了模型参数的后验概率密度函数，并利用贝叶斯因子对模型的优劣进行了比较。我们表明，M1提供了一个可接受的拟合蛇夫座的数据与σ 0 ~ 0.57+/-0.06;而且，虽然其他模型有时提供了一个改进的拟合，有没有强有力的理由引入他们的额外参数。
英文摘要：
Using observations of cores to infer their intrinsic properties requires the solution of several poorly constrained inverse problems. Here we address one of these problems, namely to deduce from the projected aspect ratios of the cores in Ophiuchus their intrinsic three-dimensional shapes. Four models are proposed, all based on the standard assumption that cores are randomly orientated ellipsoids, and on the further assumption that a core's shape is not correlated with its absolute size. The first and simplest model, M1, has a single free parameter, and assumes that the relative axes of a core are drawn randomly from a log-normal distribution with zero mean and standard deviation σo. The second model, M2a, has two free parameters, and assumes that the log-normal distribution (with standard deviation σo) has a finite mean, μo, defined so that μo<0 means elongated (prolate) cores are favoured, whereas μo>0 means flattened (oblate) cores are favoured. Details of the third model (M2b, two free parameters) and the fourth model (M4, four free parameters) are given in the text. Markov chain Monte Carlo sampling and Bayesian analysis are used to map out the posterior probability density functions of the model parameters, and the relative merits of the models are compared using Bayes factors. We show that M1 provides an acceptable fit to the Ophiuchus data with σo ~ 0.57+/-0.06; and that, although the other models sometimes provide an improved fit, there is no strong justification for the introduction of their additional parameters.
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