The detection of 3He+ in a planetary nebula using the VLA

We used the VLA to search for He-3(+) emission from two Galactic planetary nebulae ( PNe): NGC 6572 and J320. Standard stellar models predict that the He-3/ H abundance ratios for PNe should be 1-2 orders of magnitude higher than the primordial value (He-3/H similar to 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 He-3 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 He-3 detection by the VLA. We have detected the 8.665 GHz hyperfine He-3(+) transition in J320 at the 4 sigma level. The 3He/H abundance ratio is 1.9; 10(-3) with roughly a factor of 2 uncertainty. For NGC 6572 we find an upper limit of 3He/ HP10(-3) . This detection of He-3 in J320 makes it the second PN known to have an anomalously high He-3 abundance, confirming that at least some low-mass stars produce significant amounts of He-3 that survives to the PN stage and enriches the ISM.