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

Георгиев, Л.; Peimbert, M.; Hillier, D. J.; Richer, M. G.; Arrieta, A.; Peimbert, Antonio

doi:10.1086/587864

Cited by 23 publications

(22 citation statements)

References 52 publications

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“…Although we assume in our models a single set of abundances for both the nebular and CSPN fast wind material, in reality these could be different, with the CSPN abundances being metal-enriched due to the expulsion of the hydrogenrich envelope (Georgiev et al 2008;Morisset & Georgiev 2009). Thus, the change in the relative importance of the hot, shocked stellar wind gas and the heated nebular material seen in Figure 15 should also manifest itself as an evolution of the abundances responsible for the X-ray spectra of these objects.…”

Section: Discussionmentioning

confidence: 99%

Formation and X-ray emission from hot bubbles in planetary nebulae – II. Hot bubble X-ray emission

Toalá¹,

Arthur²

2016

Mon. Not. R. Astron. Soc.

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We present a study of the X-ray emission from numerical simulations of hot bubbles in planetary nebulae (PNe). High-resolution, two-dimensional, radiation-hydrodynamical simulations of the formation and evolution of hot bubbles in PNe, with and without thermal conduction, are used to calculate the X-ray emission and study its timedependence and relationship to the changing stellar parameters. Instabilities in the wind-wind interaction zone produce clumps and filaments in the swept-up shell of nebular material. Turbulent mixing and thermal conduction at the corrugated interface can produce quantities of intermediate temperature and density gas between the hot, shocked wind bubble and the swept-up photoionized nebular material, which can emit in soft, diffuse X-rays. We use the chianti software to compute synthetic spectra for the models and calculate their luminosities. We find that models both with conduction and those without can produce the X-ray temperatures and luminosities that are in the ranges reported in observations, although the models including thermal conduction are an order of magnitude more luminous than those without. Our results show that at early times the diffuse X-ray emission should be dominated by the contribution from the hot, shocked stellar wind, whereas at later times the nebular gas will dominate the spectrum. We analyse the effect of sampling on the resultant spectra and conclude that a minimum of 200 counts is required to reliably reproduce the spectral shape. Likewise, heavily smoothed surface-brightness profiles obtained from low-count detections of PNe do not provide a reliable description of the spatial distribution of the X-ray emitting gas.

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Section: Discussionmentioning

confidence: 99%

Formation and X-ray emission from hot bubbles in planetary nebulae – II. Hot bubble X-ray emission

Toalá¹,

Arthur²

2016

Mon. Not. R. Astron. Soc.

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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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“…The spectrum is similar to that of NGC 6572. Georgiev et al (2008) analyzed a high quality spectrum of this star. Although they did not propose any spectral classification, they confirmed that the star is not H poor.…”

Section: Stellar Descriptions and Classifications: Notes On Individuamentioning

confidence: 99%

Improved spectral descriptions of planetary nebulae central stars

Weidmann

Méndez

Gamen

2015

A&A

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Context. At least 492 central stars of Galactic planetary nebulae (CSPNs) have been assigned spectral types. Since many CSPNs are faint, these classification efforts are frequently made at low spectral resolution. However, the stellar Balmer absorption lines are contaminated with nebular emission; therefore in many cases a low-resolution spectrum does not enable the determination of the H abundance in the CSPN photosphere. Whether or not the photosphere is H deficient is arguably the most important fact we should expect to extract from the CSPN spectrum, and should be the basis for an adequate spectral classification system. Aims. Our purpose is to provide accurate spectral classifications and contribute to the knowledge of central stars of planetary nebulae and stellar evolution. Methods. We have obtained and studied higher quality spectra of CSPNs described in the literature as weak emission-line star (WELS). We provide descriptions of 19 CSPN spectra. These stars had been previously classified at low spectral resolution. We used medium-resolution spectra taken with the Gemini Multi-Object Spectrograph (GMOS). We provide spectral types in the Morgan-Keenan (MK) system whenever possible. Results. Twelve stars in our sample appear to have normal H rich photospheric abundances, and five stars remain unclassified. The rest (two) are most probably H deficient. Of all central stars described by other authors as WELS, we find that at least 26% of them are, in fact, H rich O stars, and at least 3% are H deficient. This supports the suggestion that the denomination WELS should not be taken as a spectral type, because, as a WELS is based on low-resolution spectra, it cannot provide enough information about the photospheric H abundance.

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

Cited by 23 publications

References 52 publications

Formation and X-ray emission from hot bubbles in planetary nebulae – II. Hot bubble X-ray emission

Formation and X-ray emission from hot bubbles in planetary nebulae – II. Hot bubble X-ray emission

The evolution of planetary nebulae

Improved spectral descriptions of planetary nebulae central stars

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