Ne v and Ne vi lines in the ultraviolet spectrum of the symbiotic star RR Telescopii

New theoretical Ne VI] electron density-sensitive ratios are presented for the intercombination transitions R(1) = I(1006.1 Angstrom)/I(999.6 degrees) and R(2) = I(1010.6 Angstrom)/I(999.6 Angstrom). Temperature-sensitive ratios are also given for the Ne V] ratio R = I(1137.0 Angstrom)/I(1574.8 Angstrom). We discuss the potential usefulness of these line ratios for studying hot gas and apply them to the case of the symbiotic system RR Telescopii. Using far-UV data that has recently been acquired with the Hopkins Ultraviolet Telescope, we conclude that the Ne V and Ne VI emission in RR Tel is due to photoionization, with the temperature and density of the emitting region being approximately T-e similar or equal to 18,000 K and N-e similar or equal to 10(6) cm(-3), respectively. These results are similar to those estimated using other high ionization line diagnostics of the nebular material, such as O V I(1371 Angstrom)/I(1644 Angstrom) and Ne IV] I(1602 Angstrom)/I(2423 Angstrom). Although these Ne V] and Ne VI] lines have been used as diagnostics for solar physics, we believe that this is the first instance in which they have been applied to another astrophysical object.