Tangential Motions and Spectroscopy within NGC 6720, the Ring Nebula

Abstract

We have combined recent Hubble Space Telescope WFPC2 images in the [O III] 5007 and [N II] 6583 lines with similar images made 9.557 years earlier to determine the motion of the Ring Nebula within the plane of the sky. Scaled ratio images argue for homologous expansion, that is, larger velocities scale with increasing distance from the central star. The rather noisy pattern of motion of individual features argues for the same conclusion and that the silhouetted knots move at the same rate as the surrounding gas. These tangential velocities are combined with information from a recent high resolution radial velocity study to determine a dynamic distance, which is in basic agreement with the distance determined from the parallax of the central star. We have also obtained very high signal to noise ratio moderate resolution spectra (9.4 Angstrom) along the major and minor axes of the nebula and from this determined the electron temperatures and density in the multiple ionization zones present. These results confirm the status of the Ring Nebula as one of the older planetary nebulae, with a central star transitioning to the white dwarf cooling curve. (Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA Contract No. NAS 5-26555 and the San Pedro Martir Observatory operated by the Universidad Nacional Autonoma de Mexico.)

Astronomical Journal, in press

References in corpus (10)

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• Unraveling the Helix Nebula: Its Structure and Knots
• Spatially-Resolved O II Recombination Line Observations of the Ring Nebula, NGC 6720
• On expansion parallax distances for planetary nebulae
• Determination of the Physical Conditions of the Knots in the Helix Nebula from Optical and Infrared Observations
• Merged ionization/dissociation fronts in planetary nebulae
• Hydrodynamical Velocity Fields in Planetary Nebulae
• The structure of Planetary Nebulae: theory vs. practice
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• Herschel images of NGC 6720: H2 formation on dust grains
• Studies of NGC 6720 with Calibrated HST WFC3 Emission-Line Filter Images--I: Structure and Evolution
• Polycyclic aromatic hydrocarbons and molecular hydrogen in oxygen-rich planetary nebulae: the case of NGC6720
• Studies of NGC 6720 with Calibrated HST WFC3 Emission-Line Filter Images--II:Physical Conditions
• Studies of NGC 6720 with Calibrated HST WFC3 Emission-Line Filter Images--III:Tangential Motions using AstroDrizzle Images
• The five axes of the Turtle: symmetry and asymmetry in NGC 6210
• Criss-cross mapping BD+30 3639: a new kinematic analysis technique