Ultraviolet observations of planetary nebulae. IV. The C IV lines at lambda 1550 Å.

Summary. We present measurements and upper limits to the flux of the C iv lines at A = 1550 A originating from planetary nebulae. We compare the measured line fluxes with theoretical predictions and discuss the possible effects of dust absorption on the fluxes. We conclude that line fluxes can be used to determine carbon abundances in these nebulae. The resultant abundances vary between the solar abundance to an order of magnitude lower than this. Key words: planetary nebulae - ultraviolet observations - abundances of carbon