Interstellar C-12/C-13 ratio revisited

Observations of the molecular ion CH + at 4232 A in the direction of ζ Oph have determined the 12 CH + / 13 CH + abundance ratio to be 67.6±4.5. The equivalent widths of 12 CH + and 13 CH + lines used for this determination were 23.246±0.068 mA and 0.410±0.022 mA, respectively. The line profiles show a very broad component with Gaussian velocity dispersion parameter b=9.9±1.3 km s −1 . These data provide strong evidence that the 12 C/ 13 C abundance ratio in the direction of ζ Oph is close to 70