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
Interstellar absorption lines of the C2 (2-0) Phillips band at 8750 A have been searched for in the spectra of southern stars. Seventeen lines originating from the lowest eight rotational levels... Show moreInterstellar absorption lines of the C2 (2-0) Phillips band at 8750 A have been searched for in the spectra of southern stars. Seventeen lines originating from the lowest eight rotational levels have been detected toward Chi Oph, and eleven lines originating from the lowest five rotational levels toward HD 154368 and 147889. No C2 lines were seen toward HD 149404. A recently developed theory has been used to extract information about the density, temperature or strength of the radiation field in the line-forming interstellar regions from the observed rotational populations. The results are compared with those obtained from other molecular observations. Toward Chi Oph, the interstellar radiation field appears enhanced in the ultraviolet part of the spectrum relative to the infrared part. The C2 data suggest a higher kinetic temperature for the material in front of HD 147889 than is inferred from radio observations. Show less
