Interstellar Sulfur Isotopes and Stellar Oxygen Burning

line survey has been made to study interstellar 32 S= 34 S and 34 S= 33 S ratios from the galactic disk. The four CS isotopomers were detected in 20 star forming regions with galactocentric distances between 3 and 9 kpc. From a comparison of line velocities, the C 33 S J=2{1 rest frequency is 250 kHz below the value given in the Lovas (1992) catalog. Taking 12 C= 13 C ratios from Wilson & Rood (1994) and assuming equal 12 C 32 S and 13 C 32 S excitation temperatures and beam lling factors, 12 C 32 S opacities are in the range 3 to 15; average 32 S= 34 S and 34 S= 33 S isotope ratios are 24.4 5.0 and 6.27 1.01, respectively. While no systematic variation in the 34 S= 33 S isotope ratio is found, the 32 S= 34 S ratio increases with galactocentric distance when accounting for the 12 C= 13 C gradient of the galactic disk. A t to the unweighted data yields 32 S= 34 S= 3.3 0.5(D GC /kpc) + 4.1 3.1 with a correlation coeecient of 0.84. Since the interstellar sulfur (S) isotopes are synthesized by oxygen burning in massive stars, consequences for nucleosynthesis and models of chemical evolution are brieey discussed.