SIMBAD references

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=2-5x10^–4, which is more than an order of magnitude higher than typically found in Galactic H II regions.