An Imaging Spectroscopic Survey of the Planetary Nebula NGC 7009 with MUSE

TL;DR

This study uses MUSE integral field spectroscopy to map the spatial structure, physical conditions, and chemical abundances of the planetary nebula NGC 7009, revealing detailed ionization and temperature variations.

Contribution

First detailed spatial maps of electron temperature, density, and abundance variations in NGC 7009 using MUSE data, including differences between CEL and ORL diagnostics.

Findings

Maps of electron temperature and density across the nebula.

Detection of spatial variations in He/H and O abundances.

Comparison of ionization correction methods showing non-uniform abundance maps.

Abstract

The spatial structure of the emission lines and continuum over the 50 arcsecond extent of the nearby, O-rich, planetary nebula NGC 7009 (Saturn Nebula) have been observed with the MUSE integral field spectrograph on the ESO Very Large Telescope. Science Verification data, in <0.6 arcsecond seeing, have been reduced and analysed as images over the wavelength range 4750-9350A. Emission line maps over the bright shells are presented, from neutral to the highest ionization available (He II and [Mn V]). For collisionally excited lines (CELs), maps of electron temperature (T_e from [N II] and [S III]) and electron density (N_e from [S II] and [Cl III]) are available and for optical recombination lines (ORLs) temperature (from the Paschen jump and ratio of He I lines) and density (from high Paschen lines). These estimates are compared: for the first time, maps of the differences in CEL and ORL T_e's have been derived, and correspondingly a map of t^2 between a CEL and ORL temperature, showing considerable detail. Total abundances of He and O were formed, the latter using three ionization correction factors. However the map of He/H is not flat, departing by ~2% from a constant value, with remnants corresponding to ionization structures. Ionization correction factor methods are compared for O abundance, but none delivers a flat map. An integrated spectrum over an area of 2340 square arcseconds was also formed and compared to 1D photoionization models. The spatial variation of a range of nebular parameters illustrates the complexity of the ionized media in NGC 7009. These MUSE data are very rich with detections of many lines over areas of hundreds of square arcseconds and follow-on studies are indicated. (Abridged)