An imaging spectroscopic survey of the planetary nebula NGC 7009 with MUSE^★,★★

¹ European Southern Observatory, Karl-Schwarzschild Strasse 2, 85748 Garching, Germany
e-mail: jwalsh@eso.org
² Instituto de Astrofísica de Canarias (IAC), 38025 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁴ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁵ Department of Physics and Astronomy, University of Denver, 2112 E. Wesley Ave., Denver, CO, 80210, USA
⁶ Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Manchester M13 9PL, UK
⁷ Laboratory for Space Research, University of Hong Kong, Pokfulam Road, Hong Kong
⁸ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile
⁹ Institut für Astro- und Teilchenphysik, Leopold–Franzens Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
¹⁰ Leiden Observatory, University of Leiden, Leiden, the Netherlands
¹¹ Oberkasseler Straße 130, 40545 Düsseldorf, Germany
¹² Okayama Observatory, Kyoto University Honjo, Kamogata, Asakuchi, Okayama, 719-0232, Japan

Received: 17 May 2018
Accepted: 14 September 2018

Abstract

Aims. The spatial structure of the emission lines and continuum over the 50″ extent of the nearby, O-rich, PN NGC 7009 (Saturn Nebula) have been observed with the MUSE integral field spectrograph on the ESO Very Large Telescope. This study concentrates on maps of line emission and their interpretation in terms of physical conditions.

Methods. MUSE Science Verification data, in <0.6″ seeing, have been reduced and analysed as maps of emission lines and continuum over the wavelength range 4750–9350 Å. The dust extinction, the electron densities and temperatures of various phases of the ionized gas, abundances of species from low to high ionization and some total abundances are determined using standard techniques.

Results. 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 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 t² between a CEL and ORL temperature, showing considerable detail. Total abundances of only 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. An integrated spectrum over an area of 2340 arcsec² was also formed and compared to 1D photoionization models.

Conclusions. 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 hundreds of lines over areas of hundreds of arcsec² and follow-on studies are outlined.