Abstract
The highly excited regions of the planetary nebula NGC 6302 are visualized with an image taken in the light of [Ne V] 3426 Å. When compared with the Hβ image taken by Bohigas (1994), the highly excited plasma is seen to extend ~ 45'' at both sides of a central lane bisecting the nebula, in a manner reminiscent of a jet nozzle. Excitation initially lessens away from the equatorial plane, but the gas is then ``re-excited" in four well delineated arches defining a bipolar structure. Temperature maps derived from the O+2 and N+ lines were also produced, and it was found that T[O III] is always larger than T[N II], as expected since I(He II λ4686)/I(Hβ) ≥ 0.25. Temperatures are smaller in high density regions. There is no correlation between the temperature or the temperature ratio with the excitation mechanism (photons or shocks). A surprisingly tight correlation exists between T[N II] and T[O III]/T[N II], with the latter increasing as T[N II] decreases. Comparing spectroscopic observations of regions with different degree of excitation, it is found that ``standard'' ionization correction factors underestimate the abundance of higher ionization stages. Better results are obtained when using the scheme recommended for regions where most of helium is doubly ionized, though this circumstance fails to occur in NGC 6302.
