Abstract
A (CS)-C-12-S-32, (CS)-C-13-S-32, (CS)-C-12-S-34, and (CS)-C-12-S-33 J=2-1 line survey has been made to study interstellar S-32/S-34 and S-34/S-33 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 (CS)-S-33 J=2-1 rest frequency is similar to 250 kHz below the value given in the Lovas (1992) catalog. Taking C-12/C-13 ratios from Wilson & Rood (1994) and assuming equal (CS)-C-12-S-32 and (CS)-C-13-S-32 excitation temperatures and beam filling factors, (CS)-C-12-S-32 opacities are in the range 3 to 15; average S-32/S-34 and S-34/S-33 isotope ratios are-24.4 +/- 5.0 and 6.27 +/- 1.01, respectively. While no systematic variation in the S-34/S-33 isotope ratio is found, the S-32/S-34 ratio increases with galactocentric distance when accounting for the C-12/C-13 gradient of the galactic disk. A fit to the unweighted data yields S-32/S-34 = 3.3 +/- 0.5 (D-GC/kpc) + 4.1 +/- 3.1 with a correlation coefficient 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 briefly discussed(1).