Abstract:
The distribution of single ionized helium Y(+) in the Galactic H II region W3A has been determined using high-resolution observations of radio recombination lines in the 76, 92, and 110 alpha lines. The angular resolutions range from two to eight arcsec. In these lines, at frequencies between 14.7 to 4.9 GHz, the average Y(+) is found to vary from about 8 percent to about 12 percent. However, there are individual regions in W3A with Y(+) in excess of 20 percent. Enhancement of Y(+) due to underionization of hydrogen caused by the hardening of the radiation field is discussed. It is found that the high values of Y(+) cannot be due to variations in the ionization structure and thus must be due to a local enhancement of the helium abundance. A possible source of such enhancements might be an obscured evolved stellar object
