Very deep spectroscopy of the bright Saturn Nebula NGC 7009 -- I. Observations and plasma diagnostics

TL;DR

This paper presents a comprehensive deep spectroscopic analysis of the planetary nebula NGC 7009, identifying about 1200 emission lines, performing plasma diagnostics, and deriving physical conditions from optical spectra.

Contribution

It provides a detailed emission line catalog and plasma diagnostics for NGC 7009, utilizing advanced line identification and deblending techniques with a broad wavelength coverage.

Findings

Identification of ~1200 emission features including faint lines

Derivation of electron temperatures and densities from recombination lines

Comprehensive spectral data and plasma diagnostics for NGC 7009

Abstract

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.