Ultraviolet spectra of planetary nebulae

High-dispersion IUE spectra of NGC 7662 have been obtained with exposure times optimized for measurement of the relative strengths of the components of: CIVlambdalambda1548, 1551; CIII] lambdalambda1907, 1909 and [Ne IV] lambdalambda 2422, 2424. The CIV ratio (lambda1548)/(lambda1551) is expected to be 2.00, the ratio of the statistical weights of the emitting levels, and the observed value is 1.92 +- 0.15. The CIII] and [NeIV] ratios depend upon the electron density, Nsub(e), and from the observations it is concluded that Nsub(e) for NGC7662 is in the range 1300 to 4000 cm-3. The presence of the dielectronic recombination line CIIIlambda 2297 is established beyond doubt. The absolute calibration of IUE high-dispersion spectra is also discussed. (author)