1997A&A...321..891Z

During the ORFEUS-SPAS (Orbiting Retrievable Far and Extreme Ultraviolet 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 ultraviolet (90nm-115nm) wavelength region using the University of California, Berkeley spectrometer. The spectral resolution of the instrument during the flight was about 0.03nm. The observed stellar continuum energy distribution can be approximated by a modelled stellar atmosphere from Clegg and Middlemass with a temperature of 50000K and a gravity of log(g)=4.5, using an extinction of E(B-V)=0.08. In addition to narrow absorption lines of atomic species (e.g. HI, CI, NI, OI) the spectrum shows narrow absorption lines of molecular hydrogen and strong P-Cygni line profiles of the SVI (93.3nm, 94.5nm), OVI (103.2nm, 103.8nm) and PV (111.8nm, 112.8nm) resonance doublets. The analysis of these three P-Cygni line doublets using the escape probability method yields together with the consideration of the NV (123.9nm, 124.3nm), SiIV (139.4nm, 140.3nm) and CIV (154.8nm, 155.1nm) P-Cygni line doublets from IUE spectra as a mean value for the lower limit of the central star's mass loss rate 2.8x10^–9M_☉/yr. This value for the stellar mass loss rate of the nucleus of NGC 6543 is compatible within a factor of two with the expected mass loss rate from the approximate radiation driven wind theory for an evolved star with a mass of 0.62M_☉, a luminosity of 3030L_☉ and an effective temperature of 50000K.