Poster abstract details

We have carried out new {it ab~initio} calculations of the effective recombination coefficients for the N~{sc ii} recombination spectrum. The new calculations are valid for temperatures down to an unprecedentedly low level (approximately $100$~K). We present very deep CCD spectrum of the bright, medium-excitation planetary nebula NGC,7009, with a wavelength coverage from 3040 to 11,000,{AA}. Emission line identification is carried out to identify all the emission features in the spectra, based on the available laboratory atomic transition data. Since the spectra are of medium resolution, we use multi-Gaussian line profile fitting to deblend faint blended lines, most of which are optical recombination lines (ORLs) emitted by singly ionized ions of abundant second-row elements such as C, N, O and Ne. In total about 1200 emission features are identified, with the faintest ones down to fluxes 10$^{-4}$ of H$eta$. Plasma diagnostics using optical forbidden line ratios are carried out. Also derived are electron temperatures and densities from the H~{sc i}, He~{sc i} and He~{sc ii} recombination spectrum. The most significant multiplets in optical emitted by C~{sc ii}, N~{sc ii}, O~{sc ii} and Ne~{sc ii} are analyzed against theoretical predictions. General agreement is found between observations and theoretical calculations. Ionic and elemental abundances are derived for C, N, O and Ne from both ORLs and collisionally excited lines (CELs). Elemental abundances of C, N, O and Ne from ORLs are higher than those from CELs by a factor of 5 -- 7.