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The intrinsic shapes of starless cores in Ophiuchus

Lomax, Oliver David ORCID:, Whitworth, Anthony Peter ORCID: and Cartwright, Annabel 2013. The intrinsic shapes of starless cores in Ophiuchus. Monthly Notices of the Royal Astronomical Society 436 (3) , pp. 2680-2688. 10.1093/mnras/stt1764

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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.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Last Modified: 15 Mar 2023 16:09

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