The limitations of steady state models of interstellar clouds are explored by means of comparison with observational data corresponding to clouds in front of Zeta Per, Zeta Oph, Chi Oph, and... Show moreThe limitations of steady state models of interstellar clouds are explored by means of comparison with observational data corresponding to clouds in front of Zeta Per, Zeta Oph, Chi Oph, and Omicron Per. The improved cloud models were constructed to reproduce the observed H and H2(J) column densities for several lines of sight. The main difference from previous models is the treatment of self-shielding in the H2 lines. Other improvements over previous models are discussed as well. Show less
Observations of C2 in the (3,O) band around 7720 A toward Zeta Ophiuchi are presented and used to provide additional support for the suggestion of a low temperature in the center of the principal... Show moreObservations of C2 in the (3,O) band around 7720 A toward Zeta Ophiuchi are presented and used to provide additional support for the suggestion of a low temperature in the center of the principal cloud toward that star. Twelve absorption features belonging to the P, Q, and R branches and originating from levels up to J-double prime = 10 can be identified. Measured equivalent widths and the column densities obtained from them by assuming a linear relationship are presented. The column densities in the various rotational levels generally agree well with those found from observations of C2 in the (2,0) Phillips band around 8750 A. The observed C2 rotational distribution implies a low kinetic temperature of roughly 30 K and a relatively low but uncertain density of roughly 200/cm in the center of the cloud. Show less
