Iron Depletion in the Hot Bubbles in Planetary Nebulae

Георгиев, Л.; Richer, M. G.; Arrieta, A.; Zhekov, Svetozar A.

doi:10.1086/499218

Cited by 9 publications

(18 citation statements)

References 33 publications

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“…In our previous paper (Georgiev et al 2006b), we showed that the X-ray-emitting plasma in NGC 6543 is heavily depleted in iron. This chemical peculiarity allows one to determine the origin of this plasma by comparison with the iron abundances in the stellar wind and the nebular gas.…”

Section: Comparison Of the Abundances In The Stellar Wind And The X-rmentioning

confidence: 84%

“…They concluded that the iron forest in the UV is reproduced with an iron content equal to 1/4 of the solar value, but they cannot rule out the solar composition either. Previously, we have found the X-ray-emitting plasma to be depleted in iron by a factor of 8 (Georgiev et al 2006b). This result again implies that the hot gas arises from nebular material rather than from the stellar wind.…”

Section: Comparison Of the Abundances In The Stellar Wind And The X-rmentioning

confidence: 91%

“…A blue spectrum was obtained on 2004 May 26. The data and their reduction are described in Georgiev et al (2006b). This spectrum was obtained to maximize signal-to-noise ratio (S/N ).…”

Section: Observationsmentioning

confidence: 99%

“…In our previous paper (Georgiev et al 2006b), we tried to learn more about the X-ray emitting region using optical coronal lines of iron. Unfortunately, these lines were not detected, which set an upper limit on the iron composition of the X-ray emitting gas, a limit far below the solar metallicity.…”

Section: Introductionmentioning

confidence: 99%

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Non–Local Thermodynamic Equilibrium Model of NGC 6543’s Central Star and Its Relation to the Surrounding Planetary Nebula

Георгиев

Peimbert

Hillier

et al. 2008

ApJ

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We analyze the chemical composition of the central star of the planetary nebula NGC 6543 based on a detailed NLTE model of its stellar wind. The logarithmic abundances by number are H ¼ 12:00, He ¼ 11:00, C ¼ 9:03, N ¼ 8:36, O ¼ 9:02, Si ¼ 8:19, P ¼ 5:53, S ¼ 7:57, and Fe ¼ 7:24. Compared with the solar abundances, most of the elements have solar composition with respect to hydrogen, except C, which is overabundant by 0.28 dex, and Fe, which is depleted by $0.2 dex. Contrary to most previous work, we find that the star is not H-poor and has a normal He composition. These abundances are compared with those found in the diffuse X-ray plasma and the nebular gas. Compared to the plasma emitting in diffuse X-rays, the stellar wind is much less depleted in iron. Since the iron depletions in the nebular gas and X-ray plasma are similar, we conclude that the plasma emitting diffuse X-rays is derived from the nebular gas rather than the stellar wind. Excellent agreement is obtained between the abundances in the stellar wind and the nebular recombination line abundances for He, C, and O relative to H. On the other hand, the derived stellar N abundance is smaller than the nebular N abundance derived from recombination lines and agrees with the abundance found from collisionally excited lines. The mean temperature variation determined by five different methods indicates that the difference in the nebular abundances between the recombination lines and collisionally excited lines can be explained as due to the temperature variations in a chemically homogeneous medium. Subject headingg s: planetary nebulae: individual ( NGC 6543)

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Section: Comparison Of the Abundances In The Stellar Wind And The X-rmentioning

confidence: 84%

Section: Comparison Of the Abundances In The Stellar Wind And The X-rmentioning

confidence: 91%

“…A blue spectrum was obtained on 2004 May 26. The data and their reduction are described in Georgiev et al (2006b). This spectrum was obtained to maximize signal-to-noise ratio (S/N ).…”

Section: Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Non–Local Thermodynamic Equilibrium Model of NGC 6543’s Central Star and Its Relation to the Surrounding Planetary Nebula

Георгиев

Peimbert

Hillier

et al. 2008

ApJ

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“…For the time being, the existing observations do not seem to be consistent with such a limb brightening. Georgiev et al (2008) found recently that the wind of the central star of NGC 6543 is less depleted in iron compared to the plasma emitting the diffuse X-rays (Georgiev et al 2006). They concluded that the X-ray emitting plasma "is derived from nebular gas rather than the stellar wind".…”

Section: Discussionmentioning

confidence: 99%

The evolution of planetary nebulae

Steffen

Schönberner

Warmuth

2008

A&A

109

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Context. Observations with space-borne X-ray telescopes revealed the existence of soft, diffuse X-ray emission from the inner regions of planetary nebulae. Although the existing images support the idea that this emission arises from the hot shocked central-star wind which fills the inner cavity of a planetary nebula, existing models have difficulties to explain the observations consistently. Aims. We investigate how the inclusion of thermal conduction changes the physical parameters of the hot shocked wind gas and the amount of X-ray emission predicted by time-dependent hydrodynamical models of planetary nebulae with central stars of normal, hydrogen-rich surface composition. Methods. We upgraded our 1D hydrodynamics code NEBEL by to account for energy transfer due to heat conduction, which is of importance at the interface separating the hot shocked wind gas ("hot bubble") from the much cooler nebular material. With this new version of NEBEL we recomputed a selection of our already existing hydrodynamical sequences and obtained synthetic X-ray spectra for representative models along the evolutionary tracks by means of the freely available CHIANTI package. Results. Heat conduction leads to lower temperatures and higher densities within a bubble and brings the physical properties of the X-ray emitting domain into close agreement with the values derived from observations. The amount of X-rays emitted during the course of evolution depends on the energy dumped into the bubble by the fast stellar wind, on the efficiency of "evaporating" cool nebular gas via heat conduction, and on the bubble's expansion rate. We find from our models that the X-ray luminosity of a planetary nebula increases during its evolution across the HR diagram until stellar luminosity and wind power decline. Depending on the central-star mass and the evolutionary phase, our models predict X-ray [0.45−2.5 keV] luminosities between 10 −8 and 10of the stellar bolometric luminosities, in good agreement with the observations. Less than 1% of the wind power is radiated away in this X-ray band. Although temperature, density, and also the mass of the hot bubble is significantly altered by heat conduction, the dynamics of the whole system remains practically the same. Conclusions. Heat conduction allows the construction of nebular models which predict the correct amount of X-ray emission and at the same time are fully consistent with the observed mass-loss rate and wind speed. Thermal conduction must be considered as a viable physical process for explaining the diffuse X-ray emission from planetary nebulae with closed inner cavities. Magnetic fields must then be absent or extremely weak.

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High-resolution X-ray Spectroscopy of BD +30°3639

Kastner

Houck

et al. 2006

IAU

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We present preliminary results from the first X-ray gratings spectrometer observations of a planetary nebula (PN). We have used the Chandra X-ray Observatory Low Energy Transmission Gratings Spectrometer (LETGS) to observe the bright, diffuse X-ray source within the well-studied BD +30 • 3639. The LETGS spectrum of BD +30 • 3639 displays prominent and well-resolved emission lines of H-like C, O, and Ne and He-like O and Ne. Initial modeling indicates a plasma temperature TX ∼ 2.5 × 10 6 K and abundance ratios of C/O ∼ 20, N/O < ∼ 1, Ne/O ∼ 4, and Fe/O < ∼ 0.1. These results suggest that the X-ray-emitting plasma is dominated by the shocked fast wind from the emerging PN core, where this wind gas likely originated from the intershell region of the progenitor asymptotic giant branch star.

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Iron Depletion in the Hot Bubbles in Planetary Nebulae

Cited by 9 publications

References 33 publications

Non–Local Thermodynamic Equilibrium Model of NGC 6543’s Central Star and Its Relation to the Surrounding Planetary Nebula

Non–Local Thermodynamic Equilibrium Model of NGC 6543’s Central Star and Its Relation to the Surrounding Planetary Nebula

The evolution of planetary nebulae

High-resolution X-ray Spectroscopy of BD +30°3639

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