Observations of sulfur dioxide in the Kleinmann-low Nebula

Abstract

Observations of SO2 toward the Orion KL Nebula revealed 14 transitions of SO2 and S-34(O2), which span an excitation range up to 365 K above the ground state. The data suggest the partial saturation of the strongest SO2 lines and increased rotational temperature from 90 K to about 150 K for energy levels over 300 K. This seems to indicate the kinetic temperature of the plateau source. The size of the SO2 emitting region in Orion is estimated to be less than or equal to 25 arcsec. This value is consistent with estimates of the plateau source size from 50 SO and other molecules. The S-34(O2) lines are about 30 percent stronger than predicted by the terrestrial S/34-S ratio, suggesting that the isotope ratio is not terrestrial. New detections of the strongest SO2 lines toward the sources W51 and DR21(OH) confirm the earlier possible detection of SO2 in W3(OH).