Serendipity and the Sloan Digital Sky Survey: Discovery of the Largest Known Planetary Nebula on the Sky

Investigation of spectra from the Sloan Digital Sky Survey reveals the presence of a region of ionized gas of greater than 2° diameter centered approximately at α = 10^h37^m, δ = -00^°18' (J2000.0) (Galactic coordinates l = 248^°, b = +48^°). [O III] λλ4959, 5007 emission is particularly strong, and emission from Hα and [N II] λλ6548, 6583 is also detectable over a substantial area on the sky. The combination of emission-line ratios, the close to zero heliocentric radial velocity, and the morphology of the structure is consistent with an identification as a very nearby planetary nebula. The proximity of the hot, DO white dwarf PG 1034+001 further strengthens this interpretation. The object is (1) the largest planetary nebula on the sky, (2) certainly closer than any planetary nebula other than Sh 2-216, and (3) the first to be unambiguously associated with a DO white dwarf. A parallax distance for PG 1034+001 would establish whether the structure is in fact the closest, and one of the physically largest, planetary nebulae known.