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RCW 120: a possible case of hit and run, elucidated by multitemperature dust mapping

Marsh, K A and Whitworth, A P 2018. RCW 120: a possible case of hit and run, elucidated by multitemperature dust mapping. Monthly Notices of the Royal Astronomical Society 483 (1) , pp. 352-358. 10.1093/mnras/sty3186

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Abstract

We present resolution-enhanced images of warm dust at multiple temperatures and opacity index values in the star-forming bubble/H ii region, RCW 120. The image set, representing a four-dimensional hypercube of differential column density, was obtained using our Bayesian procedure, ppmap. The cool peripheral material (∼16–22 K) exhibits ragged clumpy structure as noted previously by others. However, at higher temperatures (≲26 K) the geometry changes dramatically, showing a bubble boundary which is accurately circular in projection, except for the previously reported opening in the north. Comparison with Spitzer 8 μ μ m data suggests that the ∼26–30 K dust seen by Herschel resides in the photodissociation region (PDR) surrounding the H ii region. Its projected radial profile is consistent with that of a spherical shell, thus arguing against previous suggestions of cylindrical or planar geometry. The inferred geometry is, in fact, consistent with previous interpretations of the H ii region as a classical Strömgren sphere, except for the fact that the ionizing star (CD −38 ∘ . .∘ 11636; O8V) is displaced by more than half a radius from its geometric centre. None of the previously published models has satisfactorily accounted for that displacement. It could, however, be explained by proper motion of the O star at ∼2–4 km s−1 since its formation, possibly due to a cloud–cloud collision. We suggest that the current spherical bubble constitutes the fossilized remnant of the initial expansion of the H ii region following the formation of the star, which now continues to flee its formation site.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 9 January 2019
Date of Acceptance: 19 November 2018
Last Modified: 10 Jan 2019 12:45
URI: http://orca.cf.ac.uk/id/eprint/118256

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