NE V and NE VI Lines in the Ultraviolet Spectrum of the Symbiotic Star RR Telescopii

Abstract

New theoretical Ne VI] electron density-sensitive ratios are presented for the intercombination transitions R₁ = I(1006.1 Å)/I(999.6 Å) and R₂ = 1(1010.6 Å)/I(999.6 Å). Temperature-sensitive ratios are also given for the Ne V] ratio R = 1(1137.0 Å)/I(1574.8 Å). 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 ≃ 18,000 K and N_e ≃ 10⁶ 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 Å)/I(1644 Å) and Ne IV] I(1602 Å)/I(2423 Å). 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.