Interstellar CH - Excitation temperatures and abundance relative to H2CO

Details Interstellar CH - Excitation temperatures and abundance relative to H2CO Interstellar CH - Excitation temperatures and abundance relative to H2CO

Mar 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979a%26a....73..253g&link_type=abstract

Astronomy and Astrophysics, vol. 73, no. 3, Mar. 1979, p. 253-259.

Astronomy and Astrophysics

Astrophysics

32

Absorption Spectra, Abundance, Formaldehyde, Hydrocarbons, Interstellar Matter, Molecular Excitation, Cosmic Dust, H Ii Regions, Hydrogen Ions, Interstellar Chemistry, Interstellar Extinction, Molecular Absorption, Temperature Effects

Scientific paper

Observations of CH lines at 3264, 3335, and 3349 MHz have been made with the Effelsberg 100-m telescope toward the sources W3, 3C 123, NGC 2024, Sgr A, Sgr B2, W33, W43, W51, and K3-50. New absorption lines at 3335 MHz have been found toward W3, NGC 2024, W33, and W51. Five-point maps show that in nearly all cases the CH clouds are extended with respect to the 4 arcmin beam. Comparison of the CH spectra with H2CO absorption profiles at 4830 MHz provides information on the location of molecular clouds relative to the continuum sources. A determination of the excitation temperature in the dust cloud L1500, toward 3C 23, indicates that all three CH lines have only a weak (about 0.2%) inversion. Toward H II regions, however, the lower satellite line at 3264 MHz is inverted by more than 1%. On the basis of the derived excitation temperatures, the CH column densities are nearly the same for all of the sources observed, while the H2CO column density varies by three orders of magnitude. This result supports previous suggestions that CH is depleted in higher-density clouds.

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