The Neutral Shells of Planetary Nebulae

Natta, A.; Hollenbach, D. J.

doi:10.1007/978-94-011-5244-0_119

Cited by 31 publications

(73 citation statements)

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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: 56%

“…In the PN formation scenario suggested by Kwok et al (1978) a fast ($1000 km s À1 ), low-density, radiation-driven wind from the hot star shocks and ionizes the slow-moving ($10 km s À1 ), high-density, mostly molecular AGB wind, resulting in the expanding structures we see at later times. Natta & Hollenbach (1998) have computed detailed timedependent changes in the atomic and molecular emissions in a phenomenologically motivated interacting-winds model. Their model consists of an interior ionization region bounded by a shell propagating outward with a velocity of 25 km s À1 overrunning and shocking a mostly molecular AGB wind with a velocity of 8 km s À1 .…”

Section: Ionization Kinematicsmentioning

confidence: 99%

“…We note that the amplitude of the velocity structures for their 1Y2.5 M models are in the range of the outflow velocities exhibited by the line profiles in Figures 15Y17. Unfortunately they give no details on the ionization kinematics of the main and halo regions as a function of time, as Natta & Hollenbach (1998) have done. A model combining the detailed time-dependent calculation of the atomic and molecular emissions of Natta & Hollenbach (1998) with the radiative hydrodynamic rigor of Villaver et al (2002b) would be useful for interpreting these observations.…”

Section: Ionization Kinematicsmentioning

confidence: 99%

“…This result is considered somewhat surprising because the close presence of a hot star suggests that far-UV continuum excited fluorescence of the H 2 may be important. For instance, Natta & Hollenbach (1998) calculate that continuumpumped fluorescence processes dominate thermal processes in PNe evolutionary models at late times k5000 years. Herald & Bianchi (2002 and Dinerstein et al (2006) have reported excited H 2 absorption features in FUSE spectra of a handful of CSPNe located in the Galaxy and Large Magellanic Cloud.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: I Fine-structure Pressure Diagnosticmentioning

confidence: 56%

Section: Ionization Kinematicsmentioning

confidence: 99%

Section: Ionization Kinematicsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

McCandliss¹,

France²,

Lupu³

et al. 2007

ApJ

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“…However, previous models (Natta & Hollenbach 1998) have focused on stellar temperatures above 30 000 K, or even higher, such as the case of the Helix Nebula (Henney et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Photodissociation in proto-planetary nebulae

Garcı́a-Segura¹

2010

A&A

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Aims. We explore the effects of photodissociation at the stages of post-asymptotic giant branch stars to find a mechanism able to produce multi-polar shapes. Methods. We perform two-dimensional gasdynamical simulations to model the effects of photodissociation in proto-planetary nebulae. Results. We find that post-asymptotic giant branch stars with ∼7000 K or hotter are able to photodissociate a large amount of the circumstellar gas. We compute several solutions for nebulae with low-velocity multi-lobes. We find that the early expansion of a dissociation front is crucial to understand the number of lobes in proto-planetary nebulae. Conclusions.A dynamical instability appears when cooling is included in the swept-up molecular shell. This instability is similar to the one found in photoionization fronts, and it is associated with the thin-shell Vishniac instability. The dissociation front exacerbates the growth of the thin-shell instability, creating a fast fragmentation in shells expanding into media with power-law density distributions such as r −2 .

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Photochemistry and Molecular Formation in Planetary Nebulae

Hasegawa

2003

Symp. - Int. Astron. Union

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The Neutral Shells of Planetary Nebulae

Cited by 31 publications

References 0 publications

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

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

Photodissociation in proto-planetary nebulae

Photochemistry and Molecular Formation in Planetary Nebulae

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