INTERSTELLAR C-12/C-13 RATIO REVISITED

Observations of the molecular ion CH+ at 4232 angstrom in the direction of zeta-Oph have determined the (CH+)-C-12/(CH+)-C-13 abundance ratio to be 67.6 +/- 4.5. The equivalent widths of (CH+)-C-12 and (CH+)-C-13 lines used for this determination were 23.246 +/- 0.068 m angstrom and 0.410 +/- 0.022 m angstrom, 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 C-12/C-13 abundance ratio in the direction of zeta-Oph is close to 70.