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

McCandliss, Stephan R.; France, Kevin; Lupu, Roxana; Burgh, Eric B.; Sembach, Kenneth; Kruk, J. W.; Andersson, B. G.; Feldman, P. D.

doi:10.1086/512803

Cited by 15 publications

(21 citation statements)

References 87 publications

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“…The parameters of the hydrogen absorption models used are given in Table 4, along with our utilized E B − V values, determined by fitting the far‐UV and UV spectra. In some cases (NGC 1535, 2392 and 6543), the addition of a second component of hot molecular hydrogen (presumably circumstellar, rather than interstellar) better matches observations, as has been found for other CSPN (Herald & Bianchi 2004a,b, 2007; McCandliss et al 2007). We estimate the uncertainty in our H i column densities to be ±0.1 (log) and those of our E B − V determinations to be ±0.02 mag (although it is higher in the cases of NGC 7662 and 2448, due to low‐resolution UV spectra and nebular contamination, respectively).…”

Section: Modelingsupporting

confidence: 71%

“…We have also identified, from the high‐resolution UV data of some stars (NGC 1350, LSS 1362 and NGC 1535), the signature of nebular absorption lines. Such data sets may potentially be used to map the velocity structure of the nebular material and provide an important test the standard interacting wind model of PN evolution (McCandliss et al 2007; McCandliss & Kruk 2007).…”

Section: Discussionmentioning

confidence: 99%

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The winds of hydrogen-rich central stars of planetary nebulae

Herald¹,

Bianchi²

2011

Monthly Notices of the Royal Astronomical Society

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We have modelled far‐UV, UV and optical spectra of a sample of 10 hydrogen‐rich central stars of planetary nebulae (CSPN) using stellar atmosphere codes to derive their photospheric and wind parameters. The resulting stellar temperatures range from 40 to 120 kK, well spanning the CSPN evolutionary phase and allowing certain trends to be discerned. In particular, an inhomogeneous wind structure and X‐ray emission in the wind are required to match spectral diagnostic lines in many cases. For the majority of the sample, a wind clumping factor of 0.1 ≤f≤ 0.04 is derived (mainly from the P vλλ1118, 28 and O vλ1371 lines). Such factors correspond to clump densities of ∼10–25 times that of the smooth wind density, with resulting mass‐loss rates one‐third to one‐fifth the smooth wind values, which is of significant consequence to nebular dynamics, stellar and galactic evolution. Furthermore, we find clumping to begin at small radii (∼1.2 R*), as has been found when modelling the winds of (massive) O stars. The inclusion of X‐ray fluxes, presumably from shocks, in the model atmosphere calculations is found to improve the fit of the O viλλ1032, 38 line (and other features) for stars with 55 ≤ Teff≤ 80 kK, and to be absolutely necessary to match this feature for the coolest stars in our sample (Teff≲ 45 kK). These findings suggest that shocks originating from line‐driven wind instabilities leading to the formation of clumped winds and X‐rays may be a common characteristic of CSPN, as has been found for the winds of massive O‐type stars. We also find interesting results for some individual stars. NGC 1360 (Teff≃ 105 kK) displays the signature of a (previously undetected) weak stellar wind in its O vi 1032, 38 profile, and probably has the lowest mass‐loss rate ( M⊙ yr−1) of any known CSPN. In contrast, we find the wind terminal velocity of NGC 2392 ( Teff≃ 45 kK) to be v∞≃ 300 km s−1, one of the slowest CSPN wind known, probably related to its subsolar metallicity. We have included in the model calculations many elements and high‐ionization species previously neglected in analyses of this type, providing additional wind diagnostics such as Ne viiλ973 and Ar viiλ1064. The effects of including these as well as other line‐blanketing elements are discussed.

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Section: Modelingsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

The winds of hydrogen-rich central stars of planetary nebulae

Herald¹,

Bianchi²

2011

Monthly Notices of the Royal Astronomical Society

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“…The rates of formation and destruction of H 2 for Model B06 are shown in Figure 3, where it can be seen that the destruction rate (bottom panel) has a narrow peak at the leading edge of Zone IIa, due to collisional processes with protons and electrons, together with a broader peak covering Zones IIa and IIb, due to photoionization by hard EUV photons. The principal reaction channel for the H 2 + ions formed by these processes is dissociative recombination with free electrons (e.g., McCandliss et al 2007), with only ∼ 10% reacting with H 0 to re-form H 2 . Other H 2 formation mechanisms have even smaller rates (top panel), with the result that, once they have been destroyed, most H 2 molecules never re-form during the 300 yr that they remain in the DF.…”

Section: Predicted Model Structurementioning

confidence: 99%

Merged Ionization/Dissociation Fronts in Planetary Nebulae

Henney

Williams

Ferland

et al. 2007

ApJ

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The hydrogen ionization and dissociation front around an ultraviolet radiation source should merge when the ratio of ionizing photon flux to gas density is sufficiently low and the spectrum is sufficiently hard. This regime is particularly relevant to the molecular knots that are commonly found in evolved planetary nebulae, such as the Helix Nebula, where traditional models of photodissociation regions have proved unable to explain the high observed luminosity in H 2 lines. In this paper we present results for the structure and steady-state dynamics of such advection-dominated merged fronts, calculated using the Cloudy plasma/molecular physics code. We find that the principal destruction processes for H 2 are photoionization by extreme ultraviolet radiation and charge exchange reactions with protons, both of which form H 2 + , which rapidly combines with free electrons to undergo dissociative recombination. Advection moves the dissociation front to lower column densities than in the static case, which vastly increases the heating in the partially molecular gas due to photoionization of He 0 , H 2 , and H 0 . This causes a significant fraction of the incident bolometric flux to be re-radiated as thermally excited infrared H 2 lines, with the lower excitation pure rotational lines arising in 1000 K gas and higher excitation H 2 lines arising in 2000 K gas, as is required to explain the H 2 spectrum of the Helix cometary knots.

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“…Beckwith et al 1978;Zuckerman & Gatley 1988;Aspin et al 1993;Kastner et al 1996;Hora et al 1999;McCandliss et al 2007;Sterling et al 2005;Herald & Bianchi 2004). The H 2 molecules can be excited by UV photons, collisions with the gas, or by formation on excited levels.…”

Section: Introductionmentioning

confidence: 99%

H₂infrared line emission from the ionized region of planetary nebulae

Aleman

Gruenwald

2011

A&A

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Context. The analysis and interpretation of the H 2 line emission from planetary nebulae have been done in the literature by assuming that the molecule survives only in regions where the hydrogen is neutral, as in photodissociation, neutral clumps, or shocked regions. However, there is strong observational and theoretical evidence that at least part of the H 2 emission is produced inside the ionized region of these objects. Aims. The aim of the present work is to calculate and analyze the infrared line emission of H 2 produced inside the ionized region of planetary nebulae using a one-dimensional photoionization code. Methods. The photoionization code Aangaba was improved in order to calculate the statistical population of the H 2 energy levels, as well as the intensity of the H 2 infrared emission lines in the physical conditions typical of planetary nebulae. A grid of models was obtained and the results then analyzed and compared with the observational data. Results. We show that the contribution of the ionized region to the H 2 line emission can be important, particularly in the case of nebulae with high-temperature central stars. This result explains why H 2 emission is more frequently observed in bipolar planetary nebulae (Gatley's rule), since this kind of object typically has hotter stars. Collisional excitation plays an important role in populating the rovibrational levels of the electronic ground state of H 2 molecules. Radiative mechanisms are also important, particularly for the upper vibrational levels. Formation pumping can have minor effects on the line intensities produced by de-excitation from very high rotational levels, especially in dense and dusty environments. We included the effect of the H 2 molecule on the thermal equilibrium of the gas, concluding that, in the ionized region, H 2 only contributes to the thermal equilibrium in the case of a very high temperature of the central star or a high dust-to-gas ratio, mainly through collisional de-excitation.

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

Cited by 15 publications

References 87 publications

The winds of hydrogen-rich central stars of planetary nebulae

The winds of hydrogen-rich central stars of planetary nebulae

Merged Ionization/Dissociation Fronts in Planetary Nebulae

H₂infrared line emission from the ionized region of planetary nebulae

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

Cited by 15 publications

References 87 publications

The winds of hydrogen-rich central stars of planetary nebulae

The winds of hydrogen-rich central stars of planetary nebulae

Merged Ionization/Dissociation Fronts in Planetary Nebulae

H2infrared line emission from the ionized region of planetary nebulae

Contact Info

Product

Resources

About

H₂infrared line emission from the ionized region of planetary nebulae