<i>Herschel</i>images of NGC 6720: H<sub>2</sub>formation on dust grains

Hoof, P. A. M. van; Steene, G. C. Van de; Barlow, M. J.; Exter, Katrina; Sibthorpe, B.; Ueta, Toshiya; Peris, V.; Groenewegen, M. A. T.; Blommaert, J. A. D. L.; Cohen, Martin; Meester, W. De; Ferland, Gary J.; Gear, Walter Kieran; Gomez, Haley Louise; Hargrave, Peter Charles; Huygen, E.; Ivison, R. J.; Jean, C.; Leeks, S. J.; Lim, T.; Olofsson, G.; Polehampton, E. T.; Regibo, S.; Royer, P.; Swinyard, Bruce; Vandenbussche, B.; Winckel, H. Van; Waelkens, Christoffel; Walker, H. J.; Wesson, R.

doi:10.1051/0004-6361/201014590

Cited by 32 publications

(33 citation statements)

References 37 publications

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“…Molecular hydrogen formation in the knots is expected to be substantial after the central star entered the cooling track and underwent a strong drop in luminosity, and may still be ongoing at this moment, depending on the density of the knots and the properties of the grains in the knots and assuming the knots formed quickly. Especially in the latter case we expect a tight correlation between the dust emission and the H 2 emission (van Hoof et al 2010) as is observed in the Helix nebula.…”

Section: Comparison With H 2 Imagesupporting

confidence: 66%

“…Goldsmith (2001) found that for gas densities higher than 10 4.5 cm −3 the dust and gas temperatures will be closely coupled, also for temperatures as found in the Helix. It is another indication that, as is the case in the Ring Nebula (van Hoof et al 2010) andNGC 650 (van Hoof et al 2013), also in NGC 7293 H 2 and dust co-exist in these knots. This close correlation could be an indication of the formation of H 2 on dust grains.…”

Section: Comparison With H 2 Imagementioning

confidence: 82%

“…These knots may be density enhancements formed during the AGB phase in the shell and survived the ionization of the nebula (Matsuura et al 2009;Aleman et al 2011), or they may have formed because of instabilities and fragmentation at the ionization front when the nebula got ionized (García-Segura et al 2006;Huggins & Frank 2006). As knots are observed in older PNe having central stars well evolved on the cooling track, it has been suggested that they formed because of hydrodynamical instabilities when the nebular gas is going through recombination (O'Dell et al 2007;van Hoof et al 2010). The formation of H 2 most effectively takes place on the surface of dust grains, also at grain temperatures as found here for the Helix nebula (Cazaux & Tielens 2002.…”

Section: Comparison With H 2 Imagementioning

confidence: 99%

“…The high density in the knots makes it possible to shield the H 2 from the stellar radiation field. The high densities and low dust temperatures observed allow H 2 molecules to be reformed on dust grains on a reasonable timescale (van Hoof et al 2010). Molecular hydrogen formation in the knots is expected to be substantial after the central star entered the cooling track and underwent a strong drop in luminosity, and may still be ongoing at this moment, depending on the density of the knots and the properties of the grains in the knots and assuming the knots formed quickly.…”

Section: Comparison With H 2 Imagementioning

confidence: 99%

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Herschelimaging of the dust in the Helix nebula (NGC 7293)

Steene

Hoof

Exter

et al. 2015

A&A

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Aims. In our series of papers presenting the Herschel imaging of evolved planetary nebulae, we present images of the dust distribution in the Helix nebula (NGC 7293). Methods. Images at 70, 160, 250, 350, and 500 µm were obtained with the PACS and SPIRE instruments on board the Herschel satellite.Results. The broadband maps show the dust distribution over the main Helix nebula to be clumpy and predominantly present in the barrel wall. We determined the spectral energy distribution of the main nebula in a consistent way using Herschel, IRAS, and Planck flux values. The emissivity index of β = 0.99 ± 0.09, in combination with the carbon rich molecular chemistry of the nebula, indicates that the dust consists mainly of amorphous carbon. The dust excess emission from the central star disk is detected at 70 µm and the flux measurement agrees with previous measurement. We present the temperature and dust column density maps. The total dust mass across the Helix nebula (without its halo) is determined to be 3.5 × 10 −3 M at a distance of 216 pc. The temperature map shows dust temperatures between 22 K and 42 K, which is similar to the kinetic temperature of the molecular gas, confirming that the dust and gas co-exist in high density clumps. Archived images are used to compare the location of the dust emission in the far infrared (Herschel) with the ionized (GALEX and Hβ) and molecular (H 2 ) component. The different emission components are consistent with the Helix consisting of a thick walled barrel-like structure inclined to the line of sight. The radiation field decreases rapidly through the barrel wall.

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Section: Comparison With H 2 Imagesupporting

confidence: 66%

Section: Comparison With H 2 Imagementioning

confidence: 82%

Section: Comparison With H 2 Imagementioning

confidence: 99%

Section: Comparison With H 2 Imagementioning

confidence: 99%

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Herschelimaging of the dust in the Helix nebula (NGC 7293)

Steene

Hoof

Exter

et al. 2015

A&A

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“…To further test the emission mechanisms contributing to the VVV bands, we made use of the published photo-ionisation model of van Hoof et al (2010) for NGC 6720, the Ring nebula. This is the archetypal planetary nebula; the nebula is bipolar, seen almost pole-on, optically thick to ionizing radiation except towards the poles.…”

Section: Sources Of 08−21 μM Emission In Planetary Nebulae In the Vmentioning

confidence: 99%

Near-infrared photometry of Galactic planetary nebulae with the VVV Survey

Weidmann

Gamen

Hoof

et al. 2013

A&A

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Context. Planetary nebulae (PNe) are powerful tracers of evolved stellar populations. Among the 3000 known PNe in the Galaxy, about 600 are located within the 520 square-degree area covered by the VVV survey. The VVV photometric catalogue provides an important new dataset for the study of PNe, with high-resolution imaging in five near-infrared bands. Aims. There are various colour-colour diagrams that can be obtained from the VVV filters. We investigate the location of PNe in these diagrams and the separation from other types of objects. This includes the new Y−J vs. Z−Y diagram. Methods. Aperture photometry of known PNe in the VVV area was retrieved from source catalogues. Care was taken to minimise any confusion with field stars. The colours of the PNe we are determined for (H−K s ), (J−H), (Z−Y), and (Y−J), and compared to stars and to other types of emission line objects. Cloudy photo-ionisation models were used to predict colours for typical PNe.Results. We present near-infrared photometry for 353 known PNe. The best separation from other objects is obtained in the (H−K s ) vs. (J−H) diagram. We calculated the emission-line contribution to the in-band flux based on a model for NGC 6720: we find that this is highest in the Z and Y bands at over 50%, lower in the J band at 40%, and lowest in the H and K s bands at 20%. A new view of PNe in the wavelength domain of the Z and Y bands is shown. Photo-ionisation models are used to explore the observed colours in these bands. The Y band is shown to be dominated by He i 1.083 μm and He ii 1.012 μm, and colours involving this band are very sensitive to the temperature of the ionizing star. Conclusions. The VVV survey represents a unique dataset for studying crowded and obscured regions in the Galactic plane. The diagnostic diagrams presented here allow one to study the properties of known PNe and to uncover objects not previously classified.

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Division Xii / Commission 14 / Working Group Solids and Their Surfaces

Vidali¹

2011

Proc. IAU

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The ISO and Spitzer space observatories yielded a treasure trove of data on dust and ices covering dust grains. Now Herschel, and soon SOFIA and ALMA, will provide unprecedented views of the molecular world of the interstellar medium (ISM). It is on dust grains that key ISM molecules, such as hydrogen, formaldehyde, methanol, and water are formed. As a result of these new observations, there is a great need to know more about the interaction processes of atoms and molecules with dust grains. (The Proceedings of the 2010 NASA Laboratory Astrophysics Workshop () give a good view of recent accomplishments in the study of atom/molecule - solid interactions as well as other aspects of laboratory astrophysics.)

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Herschelimages of NGC 6720: H₂formation on dust grains

Cited by 32 publications

References 37 publications

Herschelimaging of the dust in the Helix nebula (NGC 7293)

Herschelimaging of the dust in the Helix nebula (NGC 7293)

Near-infrared photometry of Galactic planetary nebulae with the VVV Survey

Division Xii / Commission 14 / Working Group Solids and Their Surfaces

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Herschelimages of NGC 6720: H2formation on dust grains

Cited by 32 publications

References 37 publications

Herschelimaging of the dust in the Helix nebula (NGC 7293)

Herschelimaging of the dust in the Helix nebula (NGC 7293)

Near-infrared photometry of Galactic planetary nebulae with the VVV Survey

Division Xii / Commission 14 / Working Group Solids and Their Surfaces

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Herschelimages of NGC 6720: H₂formation on dust grains