The [TSUP]3[/TSUP]H[CLC]e[/CLC] Abundance in the Planetary Nebula NGC 3242

Using the NRAO 140 Foot Telescope, we have confirmed our earlier detection of 3He in the planetary nebula NGC 3242 made with the 100 m radio telescope of the Max-Planck-Institut für Radioastronomie. Both spectrometers show that the observed 3He+ 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 3He+ emission suggests an abundance by number of 3He/H = (2–5) × 10-4, which is more than an order of magnitude higher than typically found in Galactic H II regions.