The 3He abundance in the planetary nebula NGC 3242

Using the NRAO 140 Foot Telescope, we have confirmed our earlier detection of He-3 in the planetary nebula NGC 3242 made with the 100 m radio telescope of the Max-Planck-Institut fur Radioastronomie. Both spectrometers show that the observed He-3(+) hyperfine line has a double-peaked structure. This line shape naturally arises if NGC 3242 is modeled as a dense core surrounded by a very low density expanding shell. The observed He-3(+) emission suggests an abundance by number of He-3/H = (2-5) x 10(-4), which is more than an order of magnitude higher than typically found in Galactic H II, regions.