Talk abstract details

The extraction of chemical abundances of ionised nebulae from a limited spectral range is usually hampered by the lack of emission lines corresponding to certain ionic stages. So far, the missing emission lines have been accounted for by the ionisation correction factors (ICFs), constructed under simplistic assumptions like spherical geometry by using 1-D photoionisation modelling.

In this talk I will discuss the first results of our ongoing project to find a new set of ICFs to determine total abundances of N, O, Ne, Ar, and S, with optical spectra, in the case of non-spherical PNe. These results are based on a grid of 3-D photoionisation modelling of round, elliptical and bipolar shaped PNe, spanning the typical PNe luminosities, effective temperatures and densities.

We show that the additional corrections --to the largely used Kingsburgh and Barlow (1994) ICFs-- are always higher for bipolars than for ellipticals. Moreover, these additional corrections are, for bipolars, up to: 15\% for oxygen, 30\% for nitrogen, 20\% for neon, 25\% for argon and 50\% for sulphur. Finally, on top of the fact that corrections change greatly with shape, they vary as greatly with the central star temperature.