We present a 3D photoionization model of the planetary nebula NGC 6302 , one of the most complex and enigmatic objects of its kind .
It ’ s highly bipolar geometry and dense massive disk , coupled with the very wide range of ions present , from neutral species up to Si ^ { 8 + } , makes it one of the ultimate challenges to nebular photoionization modelling .

Our mocassin model is composed of an extremely dense geometrically thin circumstellar disk and a large pair of diffuse bipolar lobes , a combination which was necessary to reproduce the observed emission-line spectrum .
The masses of these components , 2.2 M _ { \odot } and 2.5 M _ { \odot } respectively , gives a total nebular mass of 4.7 M _ { \odot } , of which 1.8 M _ { \odot } ( 39 % ) is ionized .
Discrepancies between our model fit and the observations are attributed to complex density inhomogeneities in the nebula .
The potential to resolve such discrepancies with more complex models is confirmed by exploring a range of models introducing small-scale structures .
Compared to solar abundances helium is enhanced by 50 % , carbon is slightly subsolar , oxygen is solar , and nitrogen is enhanced by a factor of 6 .
These all imply a significant 3rd dredge-up coupled with hot-bottom burning CN-cycle conversion of dredged-up carbon to nitrogen .
Aluminium is also depleted by a factor of 100 , consistent with depletion by dust grains .

The central star of NGC 6302 is partly obscured by the opaque circumstellar disk , which is seen almost edge-on , and as such its properties are not well constrained .
However , emission from a number of high-ionization ‘ coronal ’ lines provides a strong constraint on the form of the high-energy ionizing flux .
We model emission from the central star using a series of stellar model atmospheres , the properties of which are constrained from fits to the high-ionization nebular emission lines .
Using a solar abundance stellar atmosphere we are unable to fit all of the observed line fluxes , but a substantially better fit was obtained using a 220,000 K hydrogen-deficient stellar atmosphere with \log g = 7.0 and L _ { \star } = 14 , 300 L _ { \odot } .
The H-deficient nature of the central star atmosphere suggests that it has undergone some sort of late thermal pulse , and fits to evolutionary tracks imply a central star mass of 0.73–0.82 M _ { \odot } .
Timescales for these evolutionary tracks suggest the object left the top of the asymptotic giant branch \sim 2100 years ago , in good agreement with studies of the recent mass-loss event that formed one pair of the bipolar lobes .
Based on the modelled nebular mass and central star mass we estimate the initial mass of the central star to be 5.5 M _ { \odot } , in approximate agreement with that derived from evolutionary tracks .