IMAGES OF LOW EXCITATION HC3N EMISSION FROM IRC-DEGREES-216(10)

Spatially and kinematically resolved images of emission in the ground state J = 1-->0 F = 2-->1 line of HC3N at lambda = 3.3cm are presented which illustrate the structure of the molecular shell surrounding the evolved carbon star IRC+10 degrees 216. This ground state line, which traces cool material, should provide a good probe of outlying materia l. The emission appears ringlike, peaking at a radial distance of 12'' , but with substantial contributions from the entire envelope, extendi ng to a radial distance of about 30'' from the star. The J = 1-->0 F = 2-->1 line emission in the vibrationally excited 2 nu(7)(2) state has not been detected. A model is developed which reproduces both the ima ges shown here, and also other images from lines in the millimeter wav elength region. The results show that the ringlike appearance of HC3N emission occurs because of the shell form of HC3N abundance distributi on, with a peak at radius 15'' falling off more slowly exterior to the peak than interior to it. A second model produces a better fit to the observations, but requires an interior region of unrealistically high HC3N abundance and a low mass loss rate.