Ultraviolet spectra of planetary nebulae - III. Mass loss from the central star of NGC 6543

An ultraviolet spectrum of the central star of NGC 6543 has been obtained at low dispersion with the short wave camera of the IUE satellite. Prominent P Cygni lines are observed for C IV, N IV and V, O IV and V and Si IV. The terminal velocity is V(∞) = 2150 ± 100 kms⁻¹. The observations are analysed using the moments W₀ and W₁ of the line profiles, where W_i is proportional to $$\int(F_{\lambda} -F_\text c)(\lambda-\lambda_0)^i\enspace d\lambda$$. Using formulae of Castor, expressions are obtained for the moments in terms of the usual variables of Sobolev theory. For optically thin lines, W₁ is proportional to $$n(\text {level})\times\dot M$$, where n(level) is the fractional abundance of an element in the lower level for the line, and $$\dot M$$ the mass loss rate. Assuming that practically all the oxygen is O IV and O V, it is concluded that $$\dot M$$ is of order 1.0 × 10⁻⁷M_⊙yr⁻¹. The He II lines λ 4686 and λ 1640 are of stellar origin and their observed strengths and profiles are consistent with the adopted values of $$\dot M$$ and V(∞). The strong C IV and N V lines show that the electron temperature in the wind is comparable with the photospheric temperature. No evidence is found for abundance anomalies.