2006ApJ...640..360B

We used the VLA to search for ³He⁺ emission from two Galactic planetary nebulae (PNe): NGC 6572 and J320. Standard stellar models predict that the ³He/H abundance ratios for PNe should be 1-2 orders of magnitude higher than the primordial value (³He/H∼10^–5 by number) determined from Galactic H II region abundances and confirmed by WMAP cosmic microwave background results. Chemical evolution models suggest that fewer than 5% of all PNe enrich the interstellar medium (ISM) with ³He at the level of standard stellar models. Our target PNe are therefore anomalous in that they were selected from a sample deliberately biased to contain objects with properties that maximized the likelihood of a ³He detection by the VLA. We have detected the 8.665 GHz hyperfine ³He⁺ transition in J320 at the 4 σ level. The ³He/H abundance ratio is 1.9x10^–3 with roughly a factor of 2 uncertainty. For NGC 6572 we find an upper limit of ³He/H≲10^–3. This detection of ³He in J320 makes it the second PN known to have an anomalously high ³He abundance, confirming that at least some low-mass stars produce significant amounts of ³He that survives to the PN stage and enriches the ISM.