Liu, X-W; Barlow, MJ; Zhang, Y; Bastin, RJ; Storey, PJ; (2006) Chemical abundances for Hf 2-2, a planetary nebula with the strongest-known heavy-element recombination lines. Monthly Notices of the Royal Astronomical Society , 368 (4) pp. 1959-1970. 10.1111/j.1365-2966.2006.10283.x.