Ultra-high-resolution observations of the intrinsic line profiles of interstellar CH, CH+ and CN

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Abstract
Ultra-high-resolution (0.3 km s–1 FWHM) observations of interstellar CH and CH+ are presented for five southern stars (HD 110432, 152234, 152235, 152236 and 152270); CN spectra were also obtained for HD 152236 and 152270, and Ca K and K I spectra for HD 110432. These observations have enabled us to resolve the intrinsic line profiles towards these stars for the first time, and have made possible the accurate measurement of the velocity dispersions (b-values) of the various atomic and molecular velocity components. The line profiles are found to be inconsistent with shock theories for the production of CH+ in diffuse molecular clouds, and favour the view that this molecule is produced in warm (T ≳ 2000 K) gas at the interfaces between cool dense clouds and the hot interior of the Sco-Cen bubble. In the case of one star (HD 152270) the b-value measurements conclusively demonstrate an onion-shell-like structure for the absorbing cloud, with CN occurring in the coolest/least turbulent region (presumably the deep interior), CH in a somewhat hotter/more turbulent region (presumably the outer regions), and CH+ in the warmest/most turbulent region of all (as expected for an interface with a hot inter cloud medium.

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