Molecular Hydrogen in the Ionized Region of Planetary Nebulae

Aleman, Isabel; Gruenwald, R.

doi:10.1086/383562

Cited by 32 publications

(52 citation statements)

References 71 publications

(58 reference statements)

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“…An independent study by Guerrero et al (2000) found definite H 2 detections in 13/15 bipolar PNe. These encouraging results are supported theoretically by Aleman & Gruenwald (2004) who modelled the physical conditions responsible for the presence of H 2 in PNe. They found higher H 2 mass fractions are associated with higher central star temperatures, which is consistent with the higher than average temperatures amongst bipolar PNe (Corradi & Schwarz 1995), thereby providing a simple physical explanation of Gatley's rule.…”

Section: Gatley's Rule and Mid-infrared Imagingsupporting

confidence: 55%

Binary planetary nebulae nuclei towards the Galactic bulge

Miszalski

Acker

Parker

et al. 2009

A&A

146

218

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Considerable effort has been applied towards understanding the precise shaping mechanisms responsible for the diverse range of morphologies exhibited by planetary nebulae (PNe). A binary companion is increasingly gaining support as a dominant shaping mechanism, however morphological studies of the few PNe that we know for certain were shaped by binary evolution are scarce or biased. Newly discovered binary central stars (CSPN) from the OGLE-III photometric variability survey have significantly increased the sample of post common-envelope (CE) nebulae available for morphological analysis. We present Gemini South narrow-band images for most of the new sample to complement existing data in a qualitative morphological study of 30 post-CE nebulae. Nearly 30% of nebulae have canonical bipolar morphologies, however this rises to 60% once inclination effects are incorporated with the aid of geometric models. This is the strongest observational evidence yet linking CE evolution to bipolar morphologies. A higher than average proportion of the sample shows low-ionisation knots, filaments or jets suggestive of a binary origin. These features are also common around emission-line nuclei which may be explained by speculative binary formation scenarios for H-deficient CSPN.

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Section: Gatley's Rule and Mid-infrared Imagingsupporting

confidence: 55%

Binary planetary nebulae nuclei towards the Galactic bulge

Miszalski

Acker

Parker

et al. 2009

A&A

146

218

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“…H À + h followed by the H + H À ! H 2 + e À mechanism (see Aleman & Gruenwald 2004;Natta & Hollenbach 1998). We note that our total column density for the neutral carbon, N C i; tot ¼ 2:2 ; 10 14 cm À2 , is $2 orders of magnitude higher than what is expected for N C i; tot in typical H ii regions, as discussed in Appendix A of Jenkins & Shaya (1979).…”

Section: I Fine-structure Pressure Diagnosticmentioning

confidence: 57%

Molecular and Atomic Excitation Stratification in the Outflow of the Planetary Nebula M27

McCandliss¹,

France²,

Lupu³

et al. 2007

ApJ

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High-resolution spectroscopy with FUSE and HST STIS of atomic and molecular velocity stratification in the nebular outflow of M27 challenge models of the abundance kinematics in planetary nebulae. The simple picture of a very high speed ($1000 km s À1 ), high-ionization, radiation-driven stellar wind surrounded by a slower ($10 km s À1 ) mostly molecular outflow, with low-ionization and neutral atomic species residing at the wind interaction interface, is not supported. Instead, we find vibrationally excited H 2 intermixed with mostly neutral atomic species at a transition velocity (33 km s À1 ) between a fast (33Y65 km s À1 ) low-ionization zone and a slow (P33 km s À1 ) high-ionization zone. Ly fluorescence of H 2 has been detected, but far-UV continuum fluorescence has not. The diffuse nebular medium is inhospitable to molecules and dust. Maintaining a modest equilibrium abundance of H 2 [N (H 2 )/N (H i)T1] in the diffuse nebular medium requires a source of H 2 , mostly likely the clumpy nebular medium. The stellar SED shows no sign of reddening [E(B À V ) < 0:01], but paradoxically H /H indicates E(B À V ) $ 0:1. The enhancement of H /H in the absence of dust may result from a two-step process of H 2 ionization by Lyman continuum photons followed by dissociative recombination [ H 2 + ! H þ 2 + e À ! H(1s) + H(nl )], which ultimately produces fluorescence of H and Ly . In the optically thin limit at the inferred radius of the velocity transition, we find that dissociation of H 2 by stellar Lyman continuum photons is an order of magnitude more efficient than spontaneous dissociation by far-UV photons. The importance of this H 2 destruction process in H ii regions has been overlooked.

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“…The transition from fully ionized gas to neutral gas will be gradual and the transition layer will have a considerable thickness. Aleman & Gruenwald (2004) stopped their calculations when n(H + )/n H = 10 −4 was reached 1 . Cloudy by default stops when the electron temperature drops below 4000 K, based on the notion that at lower temperatures the forbidden optical emission lines will no longer be excited effectively and the stopping radius will coincide with the outer radius in optical images of the nebula.…”

Section: Can H 2 Survive In the Ionized Region?mentioning

confidence: 99%

Herschelimages of NGC 6720: H₂formation on dust grains

Hoof

Steene

Barlow

et al. 2010

A&A

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Herschel PACS and SPIRE images have been obtained of NGC 6720 (the Ring nebula). This is an evolved planetary nebula with a central star that is currently on the cooling track, due to which the outer parts of the nebula are recombining. From the PACS and SPIRE images we conclude that there is a striking resemblance between the dust distribution and the H 2 emission, which appears to be observational evidence that H 2 forms on grain surfaces. We have developed a photoionization model of the nebula with the Cloudy code which we used to determine the physical conditions of the dust and investigate possible formation scenarios for the H 2 . We conclude that the most plausible scenario is that the H 2 resides in high density knots which were formed after the recombination of the gas started when the central star entered the cooling track. Hydrodynamical instabilities due to the unusually low temperature of the recombining gas are proposed as a mechanism for forming the knots. H 2 formation in the knots is expected to be substantial after the central star underwent a strong drop in luminosity about one to two thousand years ago, and may still be ongoing at this moment, depending on the density of the knots and the properties of the grains in the knots.

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Molecular Hydrogen in the Ionized Region of Planetary Nebulae

Cited by 32 publications

References 71 publications

Binary planetary nebulae nuclei towards the Galactic bulge

Binary planetary nebulae nuclei towards the Galactic bulge

Molecular and Atomic Excitation Stratification in the Outflow of the Planetary Nebula M27

Herschelimages of NGC 6720: H₂formation on dust grains

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Molecular Hydrogen in the Ionized Region of Planetary Nebulae

Cited by 32 publications

References 71 publications

Binary planetary nebulae nuclei towards the Galactic bulge

Binary planetary nebulae nuclei towards the Galactic bulge

Molecular and Atomic Excitation Stratification in the Outflow of the Planetary Nebula M27

Herschelimages of NGC 6720: H2formation on dust grains

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Herschelimages of NGC 6720: H₂formation on dust grains