Radio observations of CH in three dark nebulae and the correlation of CH with optical extinction and molecular hydrogen

Details Radio observations of CH in three dark nebulae and the correlation of CH with optical extinction and molecular hydrogen Radio observations of CH in three dark nebulae and the correlation of CH with optical extinction and molecular hydrogen

May 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986a%26a...160..157m&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 160, no. 1, May 1986, p. 157-170.

Astronomy and Astrophysics

Astrophysics

91

Astronomical Spectroscopy, Hydrocarbons, Hydrogen, Interstellar Matter, Nebulae, Radio Observation, Abundance, Line Spectra, Star Distribution

Scientific paper

Observations of the 3335 MHz (9 cm) CH line have been carried out in the dark nebulae L134, L178O, and L159O using the 43-m radio telescope at Green Bank. CH column densities have been derived and are compared with optical extinctions derived from starcounts and convolved with a Gaussian response function corresponding to the beam of the radio telescope. The application of the starcount technique to clouds at high latitudes is discussed and errors introduced by usage of the van Rhijn (1929) lg N(m)-curves are pointed out. A good correlation is found between the CH column density and optical extinction in L 1590 and L 1780. In both these clouds the relation is very similar, the mean value being: N(CH)= 3.4 1O13(AB-0m.3) cm-2. A comparison of this relationship with model calculations shows that the current CH formation theories with gas phase reactions only are able to explain the observations. A comparison of lg N(CH) with lg N(H2) is presented for diffuse, dark and molecular cloud data. The diffuse and dark cloud data fit to the same linear relationship N(CH) ∝ N(H2), whereas the molecular clouds are underabundant in CH. This is predicted theoretically to happen for the large gas densities prevailing in the molecular cloud cores. Finally, the structure of the three nebulae is briefly discussed in light of the present CH and extinction data.

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