HELIUM ENRICHMENT AND CARBON IONIZATION IN THE W3 CORE

We present high-sensitivity images of the H92 alpha, He92 alpha, and C 92 alpha recombination line emission from H II regions in the Galactic radio source W3. Our 8.3 GHz VLA observations have 4'' resolution and sufficient sensitivity to image the carbon recombination line in four of the eight H II regions in the complex. Portions of W3A, the larges t and probably most evolved of the H II regions, have a helium abundan ce as high as 20% by number (nearly twice the cosmic abundance) which confirms previous observations made with lower signal-to-noise ratios. W3A also shows large velocity gradients in the H92 alpha line; we con clude that the gradient is probably caused by the evaporation of the d ense molecular core associated with IRS 5. Near the edges of W3B and W 3C, strong C+ emission is found where no hydrogen or helium Line emiss ion is detected. This C+ emission comes from the interface zone betwee n the H II region and the surrouding molecular cloud. We show that the C+ velocity is more typical of the surrounding molecular cloud while the H+ and He+ velocities trace the ionized gas. A H92 alpha velocity gradient is used as a probe of the gasdynamics in W3B; a model is prop osed which explains the gradient. Despite the fact that W3C and W3D ar e separate H II regions, they apparently share a common C+ region; the C92 alpha line intensity is up to 70% that of the H92 alpha line. Thr ee independent methods provide an electron temperature in the range of T-e = 8000-9000 K for W3A; a wider range of values is derived for W3B and W3D. W3B shows signs (10 sigma) of a decreasing radial electron t emperature gradient.