Spectrophotometric Results from the Copernicus Satellite. V. Abundances of Molecules in Interstellar Clouds

Abstract

Scans were made at the absorption wavelengths of CO, CO+, CN+, CS, C2, OH, NO, NO+, NH+, SiO, MgH+, and H2O. Except for CO, no features were detected in the stars observed, with E(B - V) ranging up to 0.3. The greatest abundance of CO was found in the direction of Oph, where absorptions for several vibrational bands of the fourth-positive system were recorded by the low resolution detector and a column density of 4.6 X 1014 cm-2 was derived. The much stronger C X i + and E i + transitions at 1087.9 and 1076.1 A showed up in the high-resolution spectra of X Ori, Per, and a Cam, yielding column densities of 1.9 X 1013, 3.1 X 1013 and 3.5 X 1013 cm-2, respectively. Comparison of the R(1) and P(1) lines to R(0) in the C 1 + 1 + transition gave a rotational temperature of 5 K for CO toward these three stars. For a kinetic temperature of 20 -50 this excitation is consistent with a number density of neutrals ranging from 10 to 100 cm-3 according to Goldsmith. Subject headings: abundances - interstellar matter - molecules, interstellar - spectra, ultraviolet - spectrophotometry