Abundances and rotational temperatures of the C2 interstellar molecule towards six reddened early-type stars

Abstract

Using high-resolution (~85000) and high signal-to-noise ratio (~200) optical spectra acquired with the European Southern Observatory Ultraviolet and Visual Echelle Spectrograph, we have determined the interstellar column densities of C2 for six Galactic lines of sight with E(B- V) ranging from 0.33 to 1.03. For our purposes, we identified and measured absorption lines belonging to the (1, 0), (2, 0) and (3, 0) Phillips bands A1Πu-X1Σ+g. We report on the identification of a few lines of the C2 (4, 0) Phillips system towards HD 147889. The curve-of-growth method is applied to the equivalent widths to determine the column densities of the individual rotational levels of C2. The excitation temperature is extracted from the rotational diagrams. The physical parameters of the intervening molecular clouds (e.g. gas kinetic temperatures and densities of collision partners) were estimated by comparison with the theoretical model of excitation of C2.

11 pages, 3 figures, MNRAS 2010

References in corpus (3)

• A Catalog of Diffuse Interstellar Bands in the Spectrum of HD 204827
• Abundances and Behavior of 12CO, 13CO, and C2 in Translucent Sight Lines
• Excitation temperature of C2 and broadening of the 6196A diffuse interstellar band

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• Galactic extinction laws: II. Hidden in plain sight, a new interstellar absorption band at 7700 Å broader than any known DIB
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• The EDIBLES Survey. VII. A survey of C2 and C3 in interstellar clouds