We present very deep CCD spectrum of the bright, medium-excitation planetary
nebula NGC 7009, with a wavelength coverage from 3040 to 11000 A. Traditional
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. Computer-aided emission-line
identification, using the code EMILI developed by Sharpee et al., is then
employed to further identify all the emission lines thus obtained. In total
about 1200 emission features are identified, with the faintest ones down to
fluxes 10^{-4} of H_beta. The flux errors for all emission lines, estimated
from multi-Gaussian fitting, are presented. Plots of the whole optical
spectrum, identified emission lines labeled, are presented along with the
results of multi-Gaussian fits. Plasma diagnostics using optical forbidden line
ratios are carried out. Also derived are electron temperatures and densities
from the H I, He I and He II recombination spectrum.Comment: 66 pages, 16 figures, 7 tables, paper accepted by MNRAS in Marc
