SMA OBSERVATIONS OF C2H IN HIGH-MASS STAR-FORMING REGIONS

C2H is a representative hydrocarbon that is abundant and ubiquitous in the interstellar medium. To study its chemical properties, we present Submillimeter Array observations of the C2H N = 3-2 and. HC3N J = 30-29 transitions. and the 1.1 mm continuum emission toward four OB cluster-forming regions, AFGL 490, ON 1, W33 Main, and G10.6-0.4, which cover a bolometric luminosity range of similar to 10(3)-10(6) L-circle dot. We found that on large scales, the C2H emission traces the dense molecular envelope. However, for all observed sources, the peaks of C2H emission are offset by several times. 104 AU from the peaks of 1.1 mm continuum emission, where the most luminous stars are located. By comparing the distribution and profiles of C2H hyperfine lines and the 1.1 mm continuum emission, we find that the C2H column density (and abundance) around the 1.1 mm continuum peaks is lower than those in the ambient gas envelope. Chemical models suggest that C2H might be transformed to other species owing to increased temperature and density;. thus, its reduced abundance could be the signpost of the heated molecular gas in the similar to 10(4) AU vicinity around the embedded high-mass stars. Our results support such theoretical prediction for centrally embedded similar to 10(3)-10(6) L-circle dot OB star-forming cores, while future higher-resolution observations are required to examine the C2H transformation around the localized sites of high-mass star formation.