The (C-12)O/(C-13)O ratio toward Zeta Ophiuchi

A tentative detection of the J = 1 - 0 emission line of (C-13)O has been obtained with SEST from a 24.4 hour integration. The velocity resolution used was 0.23 km/s and the FWHP beamwidth was 45 arcsec. If the (C-13)O line data are conservatively interpreted as an upper limit, the (C-12)O/(C-13)O ratio is not less than 60. Our result supports the previous determination of a large value of the isotope ratio in this cloud, made using radio emission lines with a 1.6-arcmin beam, and extends the ratio based on emission lines to a smaller region. When interpreted as a lower limit, our data is consistent with the ratio obtained from UV absorption line data for (C-12)O and (C-13)O.