Rocket-ultraviolet spectrum and models of the planetary nebula NGC 7662

An ultraviolet spectrum of NGC 7662 was obtained with a rocket-borne telescope in a 130 s exposure by using a microchannel plate detector and film. The observed fluxes are given for both the lines and the continuum on an absolute basis. The correction for interstellar extinction with E(B-V) = 0.22 was determined on the basis of the observed and calculated line ratios for the hydrogenic recombination line of He II at 1640 A to Hβ. A detailed set of models of the thermal and ionization structure of NGC 7662 was constructed for the purpose of interpreting the rocket observations. Predictions of three models are presented and compared with the ultraviolet as well as the existing visible, infrared, and radio observations. The spectral energy distribution of the central star for the models was specified so that the observed emission lines could be fitted. The resulting flux distribution is within 50% of a 100,000 K blackbody with some features which resemble recent spherical, non-LTE models but with a smaller discontinuity at 228 A. The observed C III] intercombination line at 1909 A and the C IV line at 1549 are best fitted with a solar carbon abundance and C/O ratio equal to unity. In order to obtain this fit, dielectronic recombination and charge exchange between neutral hydrogen and C IV were included, both of which increased the concentration of C III. The observed continuum consists of light from the central star and from the nebula, which contributes primarily by means of the two-photon process in H0 and the Balmer continuum. 4 figures, 4 tables