Forbidden and intercombination lines of RR Telescopii: wavelength   measurements and energy levels
  Ultraviolet and visible spectra of the symbiotic nova RR Telescopii are used to derive reference wavelengths for many forbidden and intercombination transitions of ions +1 to +6 of elements C, N, O, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K and Ca. The wavelengths are then used to determine new energy values for the levels within the ions' ground configurations or first excited configuration. The spectra were measured by the Space Telescope Imaging Spectrograph of the Hubble Space Telescope and the UltraViolet Echelle Spectrograph of the European Southern Observatory in 2000 and 1999, respectively, and cover 1140 to 6915 A. Particular care was taken to assess the accuracy of the wavelength scale between the two instruments. An investigation of the profiles of the emission lines reveals that the nebula consists of at least two plasma components at different velocities. The components have different densities, and a simple model of the lines' emissions demonstrates that most of the lines principally arise from the high density component. Only these lines were used for the wavelength study. 
P.R. Young, U. Feldman, A. Lobel
astro-ph.SR