A kinematic determination of the structure of the double ring planetary nebula NGC 2392, the Eskimo

Slit spectra and existing "velocity cube" data have been used to determine the structure of the double ring planetary nebula NGC 2392. The inner shell is a stellar wind-sculpted prolate spheroid with a ratio of axes of 2:1 and the approaching end of the long axis pointed 20° from the line of sight in P.A. = 200°. The outer ring is caused by an outer disk with density dropping off with distance from the central star and with distance from its plane, which is the same as the equatorial band of high density in the inner shell. The outer disk contains a ring of higher density knots at a distance of 16″ and is losing material through free expansion, forming an outer envelope of increasing velocity. Within this outer envelope is a zone of density concentration caused by a shock front seen in [O III]. The tips of the inner shell have been blown away by the intense stellar wind from the central star. We use [S II] spectra to determine the densities in all of the major regions of the nebula. There is general agreement of the forms derived for the inner shell with the models put forward by Balick and his collaborators. The outer disk is evidence for highly concentrated equatorial mass loss from the precursor star. We have combined angular expansion rates with our derived tangential velocity of the inner shell to determine the distance to be 880 pc. We argue that the filamentary cores at the centers of the knots seen in the outer ring originate in the sublimation of bodies formed at the same time as the parent star. These would be comet-type bodies located in a region very much like the solar system's Oort cloud.