VLT / Infrared Integral Field Spectrometer Observations of Molecular Hydrogen Lines in the Knots in the Planetary Nebula NGC 7293 (the Helix Nebula)

Abstract

Knots are commonly found in nearby planetary nebulae (PNe) and star forming regions. Within PNe, knots are often found to be associated with the brightest parts of the nebulae and understanding the physics involved in knots may reveal the processes dominating in PNe. As one of the closest PNe, the Helix Nebula (NGC 7293) is an ideal target to study such small-scale (~300 AU) structures. We have obtained infrared integral spectroscopy of a comet-shaped knot in the Helix Nebula using SINFONI on the Very Large Telescope at high spatial resolution (50-125 mas). With spatially resolved 2 micron spectra, we find that the H2 rotational temperature within the cometary knots is uniform. The rotational-vibrational temperature of the cometary knot (situated in the innermost region of the nebula, 2.5 arcmin away from the central star), is 1800 K, higher than the temperature seen in the outer regions (5-6 arcmin from the central star) of the nebula (900 K), showing that the excitation temperature varies across the nebula. The obtained intensities are reasonably well fitted with 27 km s-1 C-type shock model. This ambient gas velocity is slightly higher than the observed [HeII] wind velocity of 13 km s-1. The gas excitation can also be reproduced with a PDR (photo dominant region) model, but this requires an order of magnitude higher UV radiation. Both models have limitations, highlighting the need for models that treats both hydrodynamical physics and the PDR.

Accepted for publication in MNRAS; A pdf file with full resolution images is available from http://optik2.mtk.nao.ac.jp/~mikako/abstract/helix.pdf

References in corpus (21)

• SINFONI - Integral Field Spectroscopy at 50 milli-arcsecond resolution with the ESO VLT
• A PDR-Code Comparison Study
• Nonlinear Instabilities in Shock-Bounded Slabs
• A Debris Disk around the Central Star of the Helix Nebula?
• Investigating the Near-Infrared Properties of Planetary Nebula II. Medium Resolution Spectra
• Trigonometric Parallaxes of Central Stars of Planetary Nebulae
• Dynamical and Pressure Structures in Winds with Multiple Embedded Evaporating Clumps I. 2D Numerical Simulations
• Unraveling the Helix Nebula: Its Structure and Knots
• Magnetic fields in planetary nebulae and post-AGB nebulae
• High Resolution CO and H2 Molecular Line Imaging of a Cometary Globule in the Helix Nebula
• The creation of the Helix planetary nebula (NGC 7293) by multiple events
• Infrared Observations of The Helix Planetary Nebula
• Chemistry and clumpiness in planetary nebulae
• The OMC-1 molecular hydrogen outflow as a fragmented stellar wind bubble
• The Dynamical Evolution of Planetary Nebulae After the Fast Wind
• A Multi-Instrument Study of the Helix Nebula Knots with the Hubble Space Telescope
• The Multitude of Molecular Hydrogen Knots in the Helix Nebula
• Determination of the Physical Conditions of the Knots in the Helix Nebula from Optical and Infrared Observations
• Kinematics, turbulence and evolution of planetary nebulae
• The tails in the Helix Nebula NGC 7293
• Filaments as Possible Signatures of Magnetic Field Structure in Planetary Nebulae

Cited by in corpus (19)

• Knots in the Helix Nebula found in H2
• The turbulent destruction of clouds - I. A k-epsilon treatment of turbulence in 2D models of adiabatic shock-cloud interactions
• Synthetic observations of simulated pillars of creation
• Numerical simulations of shocks encountering clumpy regions
• Observations of the Planetary Nebula SMP LMC 058 with the JWST MIRI Medium Resolution Spectrometer
• An Imaging Spectroscopic Survey of the Planetary Nebula NGC 7009 with MUSE
• H2 infrared line emission from the ionized region of planetary nebulae
• H${}_2$ emission in the low-ionisation structures of the Planetary Nebulae NGC 7009 and NGC 6543
• Spitzer mid-infrared spectroscopic observations of planetary nebulae
• CO in the C1 globule of the Helix nebula with ALMA
• Herschel spectral-mapping of the Helix Nebula (NGC 7293): Extended CO photodissociation and OH+ emission
• A comparison of shock-cloud and wind-cloud interactions: effect of increased cloud density contrast on cloud evolution
• VLT observations of the asymmetric Etched Hourglass Nebula, MyCn 18
• Modelling the Warm H2 Infrared Emission of the Helix Nebula Cometary Knots
• JWST observations of the Ring Nebula (NGC 6720) -- II. PAH emission
• OH${}^{+}$ emission from cometary knots in planetary nebulae
• The Effect of the Slit Configuration on the H${}_2$ 1-0~S(1) to Br$\gamma$ Line Ratio of Spatially Resolved Planetary Nebulae
• H${}_2$ molecular gas in the old planetary nebula NGC 3587
• Low-ionization structures in planetary nebulae -- IV. The molecular hydrogen counterpart