Abundance of interstellar carbon toward Zeta Ophiuchi

We report on the detection of the weak intersystem transition of semiforbidden C II 2325 A in the sight line toward Zeta Oph using the Ech-B mode of the Goddard High-Resolution Spectrograph. The measured equivalent width of the semiforbidden C II line is W(lambda) = 0.52 +/- 0.12 mA, implying a C II column density of 1.80 (+/- 0.42) x 10 exp 17 atoms/sq cm and (C/H) sub Zeta Oph = 1.32 (+/- 0.32) x 10 exp -4.