;
• Penzias, A. A.
;
• Wannier, P. G.
;
• Linke, R. A.

Abstract

Results are reported for measurements of the relative isotopic abundances of carbon and sulfur in interstellar carbon monosulfide, which were made by observing the 2-mm rotational-line emission from (C-13)(S-32) and (C-12)(S-34) in five dense interstellar clouds: Sgr B, W51, Orion A, M17, and NGC 2264. For each cloud, the (C-13)(S-32)/(C-12)(S-34) intensity ratio is derived at the 3-sigma level by integrating over the velocity range where the (C-12)(S-34) intensity is greater than half its peak value. All the intensity ratios are found to be larger than the terrestrial abundance ratio, but measurements of the (C-12)(S-33)/(C-12)(S-34) intensity ratio in Sgr B and Orion A are not found to be significantly different from the terrestrial value. It is concluded that the data seem to indicate a source-to-source variation of the relative isotopic abundance in CS, and that the results are consistent with an approximately terrestrial value for the interstellar sulfur isotopic abundance ratios and a greater than terrestrial, although variable, abundance of C-13 relative to C-12.