Planetary Nebulae and Their Central Stars in the X-ray and EUV Regions

Guerrero, M. A.

doi:10.1017/s1743921306002900

Cited by 4 publications

(1 citation statement)

References 24 publications

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“…Since the surface brightness in X-rays is expected to be quite small (see Volk & Kwok 1985), only very few positive detections have been reported to date. Summaries of X-ray observations of PNe conducted to date with the different satellites are presented in Chu et al (2003), Guerrero (2006), and Kastner (2007).…”

Section: Introductionmentioning

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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Section: Introductionmentioning

confidence: 99%

The evolution of planetary nebulae

Steffen

Schönberner

Warmuth

2008

A&A

109

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Radiation-driven winds of hot luminous stars

Hoffmann

Pauldrach

Kaschinski

2016

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Stellar wind models of central stars of planetary nebulae

Krtička

Kubát

Krtičková

2020

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1 Ústav teoretické fyziky a astrofyziky, Masarykova univerzita, Kotlářská 2, CZ-611 37 Brno, Czech Republic 2 Astronomický ústav, Akademie vědČeské republiky, Fričova 298, CZ-251 65 Ondřejov, Czech Republic Received ABSTRACTContext. Fast line-driven stellar winds play an important role in the evolution of planetary nebulae, even though they are relatively weak. Aims. We provide global (unified) hot star wind models of central stars of planetary nebulae. The models predict wind structure including the mass-loss rates, terminal velocities, and emergent fluxes from basic stellar parameters. Methods. We applied our wind code for parameters corresponding to evolutionary stages between the asymptotic giant branch and white dwarf phases for a star with a final mass of 0.569 M ⊙ . We study the influence of metallicity and wind inhomogeneities (clumping) on the wind properties. Results. Line-driven winds appear very early after the star leaves the asymptotic giant branch (at the latest for T eff ≈ 10 kK) and fade away at the white dwarf cooling track (below T eff = 105 kK). Their mass-loss rate mostly scales with the stellar luminosity and, consequently, the mass-loss rate only varies slightly during the transition from the red to the blue part of the Hertzsprung-Russell diagram. There are the following two exceptions to the monotonic behavior: a bistability jump at around 20 kK, where the massloss rate decreases by a factor of a few (during evolution) due to a change in iron ionization, and an additional maximum at about T eff = 40 − 50 kK. On the other hand, the terminal velocity increases from about a few hundreds of km s −1 to a few thousands of km s −1 during the transition as a result of stellar radius decrease. The wind terminal velocity also significantly increases at the bistability jump. Derived wind parameters reasonably agree with observations. The effect of clumping is stronger at the hot side of the bistability jump than at the cool side. Conclusions. Derived fits to wind parameters can be used in evolutionary models and in studies of planetary nebula formation. A predicted bistability jump in mass-loss rates can cause the appearance of an additional shell of planetary nebula.

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Planetary Nebulae and Their Central Stars in the X-ray and EUV Regions

Cited by 4 publications

References 24 publications

The evolution of planetary nebulae

The evolution of planetary nebulae

Radiation-driven winds of hot luminous stars

Stellar wind models of central stars of planetary nebulae

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