ORFEUS OBSERVATIONS OF S-VI, O-VI AND P-V IN THE STELLAR WIND FROM THE NUCLEUS OF NGC-6543

During the ORFEUS-SPAS (Orbiting Retrievable Far and Extreme Ultraviol et Spectrometer on the Shuttle Pallet Satellite) mission STS-51, flown in September 1993, we observed, to our knowledge for the first time, the central star of the planetary nebula NGC 6543 in the far ultraviol et (90 nm 115 nm) wavelength region using the University of California , Berkeley spectrometer. The spectral resolution of the instrument dur ing the flight was about 0.03 nm. The observed stellar continuum energ y distribution can be approximated by a modelled stellar atmosphere fr om Clegg and Middlemass with a temperature of 50 000 K and a gravity o f log(g)=4.5, using an extinction of E(B - V)= 0.08. In addition to na rrow absorption lines of atomic species (e.g. HI, CI, NI, OI) the spec trum shows narrow absorption lines of molecular hydrogen and strong P- Cygni line profiles of the S VI (93.3 nm, 93.5 nm), O VI (103.2 nm, 10 3.8 nm) and P V (111.8 nm, 112.8 nm) resonance doublets. The analysis of these three P-Cygni line doublers using the escape probability meth od yields together with the consideration of the NV (123.9nm, 124.3nm) , Si IV (139.4nm, 140.3nm) and CIV (154.8 nm, 155.1 nm) P-Cygni line d oublers from IUE spectra as a mean value for the lower limit of the ce ntral star's mass loss rate 2.8 10(-9) M circle dot/yr. This value for the stellar mass loss rate of the nucleus of NGC 6543 is compatible w ithin a factor of two with the expected mass loss rate from the approx imate radiation driven wind theory for an evolved star with a mass of 0.62 M circle dot, a luminosity of 3030 L circle dot and an effective temperature of 50 000 K.