CO isotope studies and mass of the Sagittarius B2 molecular cloud

(C-13)O and (C-18)O observations of the central region of Sagittarius B2 are presented. A (C-13)O to (C-18)O abundance ratio of 9.0 + or - 1.9, consistent with the average ratio in the disk and other Galactic center sources, is obtained. Comparison of the (C-13)O column density based on the present data with H2 column density based on 1300 micron continuum data gives an upper limit of 10 to the -6th for the (C-13)O fractional abundance, a factor of two lower than the local value. The (C-12)O/H2 abundance ratio is a factor of six lower than the local value due to the lower (C-12)O to (C-13)O ratio. It is concluded that abundances of many molecular species in addition to the CO isotopes may be lower than in local clouds. The observations suggest a two-component structure for the cloud, with a constant density component and a component with density having a power-law dependence on the distance from cloud center. Values for the outer radius, total mass, and virial mass of the cloud are derived.