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Thirteen transitions within the ground 3d^2 configuration of Fe VII areidentified in ultraviolet and optical spectra of the symbiotic star RRTelescopii obtained with the STIS instrument of the Hubble Space Telescope. Theline fluxes are compared with theoretical data computed with the recent atomicdata of K.A. Berrington et al., and high resolution optical spectra fromVLT/UVES are used to identify blends. Seven branching ratios are measured, withthree in good agreement with theory and one affected by blending. Thelambda5277/lambda4943 branching ratio is discrepant by > 3 sigma, indicatingerrors in the atomic data for the lambda5277 line. A least-squares minimizationscheme is used to simultaneously derive the temperature, T, and density, N_e,of the RR Tel nebula, and the interstellar extinction, E(B-V), towards RR Telfrom the complete set of emission lines. The derived values are: log T/K = 4.50+/- 0.23, log N_e/cm^-3=7.25 +/- 0.05, and E(B-V)<0.27. The extinction is notwell-constrained by the Fe VII lines, but is consistent with the more accuratevalue E(B-V)=0.109^{+0.052}_{-0.059} derived here from the Ne Vlambda2974/lambda1574 ratio in the STIS spectrum. Large differences between theK.A. Berrington et al. electron excitation data and the earlier F.P. Keenan &P.H. Norrington data-set are demonstrated, and the latter is shown to giveworse agreement with observations.Comment: To be published in Astronomy & Astrophysics; 7 pages, 4 figure

Fe VII lines in the spectrum of RR Telescopii