Irradiated atmospheres of accreting magnetic white dwarfs with an application to the polar AM Herculis

König, Michael; Beuermann, K.; Gänsicke, B. T.

doi:10.1051/0004-6361:20054336

Cited by 17 publications

(23 citation statements)

References 21 publications

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“…Strong evidence is found in most polars that the soft X-ray component arises in the WD photosphere primarly due to the heating by accretion of dense blobs (Kuijpers & Pringle 1982;Woelk & Beuermann 1996;Beuermann 1999Beuermann , 2004, with most of the reprocessed primary (hard X-rays and cyclotron) radiations mainly emitted in the far-UV (König et al 2006). As seen in Fig.…”

Section: Soft X-ray Ips: An Emerging New Class?mentioning

confidence: 92%

“…It has become evident that the soft and hard X-ray emissions in at least these systems are largely decoupled (see Beuermann 1999Beuermann , 2004, most of the Article published by EDP Sciences soft X-rays arising from accretion of dense blobs ("blobby accretion") which penetrate deep in the WD atmosphere. Irradiation of the WD atmospheric polar regions by hard X-rays and cyclotron radiation emitted in a stand-off shock has been recently discussed by König et al (2006), yelding to the conclusion that most of the reprocessed light appears in the far-UV rather than in the soft X-rays.…”

Section: Introductionmentioning

confidence: 99%

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Two new intermediate polars with a soft X-ray component

Anzolin

Martino

Bonnet‐Bidaud

et al. 2008

A&A

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Aims. We analyze the first X-ray observations with XMM-Newton of 1RXS J070407.9+262501 and 1RXS 180340.0+401214, in order to characterize their broad-band temporal and spectral properties, also in the UV/optical domain, and to confirm them as intermediate polars.Methods. For both objects, we performed a timing analysis of the X-ray and UV/optical light curves to detect the white dwarf spin pulsations and study their energy dependence. For 1RXS 180340.0+401214 we also analyzed optical spectroscopic data to determine the orbital period. X-ray spectra were analyzed in the 0.2-10.0 keV range to characterize the emission properties of both sources. Results. We find that the X-ray light curves of both systems are energy dependent and are dominated, below 3-5 keV, by strong pulsations at the white dwarf rotational periods (480 s for 1RXS J070407.9+262501 and 1520.5 s for 1RXS 180340.0+401214). In 1RXS 180340.0+401214 we also detect an X-ray beat variability at 1697 s which, together with our new optical spectroscopy, favours an orbital period of 4.4 h that is longer than previously estimated. Both systems show complex spectra with a hard (temperature up to 40 keV) optically thin and a soft (kT ∼ 85-100 eV) optically thick components heavily absorbed by material partially covering the X-ray sources. Conclusions. Our observations confirm the two systems as intermediate polars and also add them as new members of the growing group of "soft" systems which show the presence of a soft X-ray blackbody component. Differences in the temperatures of the blackbodies are qualitatively explained in terms of reprocessing over different sizes of the white dwarf spot. We suggest that systems showing cooler soft X-ray blackbody components also possess white dwarfs irradiated by cyclotron radiation.

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Section: Soft X-ray Ips: An Emerging New Class?mentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Two new intermediate polars with a soft X-ray component

Anzolin

Martino

Bonnet‐Bidaud

et al. 2008

A&A

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“…The theory of the heating and cooling processes in the individual subcolumns of the spot is not yet well developed (e.g. König et al 2006) and the present analysis may help to improve it.…”

Section: Modeling the Soft X-ray Component Of Am Hermentioning

confidence: 99%

“…Our model includes two dominant spectral components, thermal hard X-rays from the post-shock cooling flow (CF) and soft X-rays produced by various modes of reprocessing of the energy transported from the CF into the atmosphere of the white dwarf (Kuijpers & Pringle 1982;Frank et al 1988;Gänsicke et al 1995;König et al 2006). In addition, a small component of residual emission lines (RL) exists that is not explained by the CF model and may be due to photoionization (Mukai et al 2003;Girish et al 2007).…”

Section: Model Assumptionsmentioning

confidence: 99%

“…The fluxes F are converted to luminosities L = ηπd 2 F, assuming the geometry factors η given in the table and a distance d = 80 pc (Thorstensen 2003;Beuermann 2006). The ultraviolet flux from the heated polar cap of the white dwarf is not included, because it is created by the downward hard X-ray and cyclotron fluxes (Gänsicke et al 1995(Gänsicke et al , 1998König et al 2006) and is already accounted for by the choice of the geometry factors. The factor 3.3π for the hard X-rays accounts for the reflection albedo (van Teeseling et al 1996).…”

Section: Accretion Luminosity and Accretion Ratementioning

confidence: 99%

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A new soft X-ray spectral model for polars with an application to AM Herculis

Beuermann¹,

Burwitz

Reinsch³

2012

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We present a simple heuristic model for the time-averaged soft X-ray temperature distribution in the accretion spot on the white dwarf in polars. The model is based on the analysis of the Chandra LETG spectrum of the prototype polar AM Her and involves an exponential distribution of the emitting area vs. blackbody temperature a(T ) = a 0 exp(−T/T 0 ). With one free parameter besides the normalization, it is mathematically as simple as the single blackbody, but is physically more plausible and fits the soft X-ray and far-ultraviolet spectral fluxes much better. The model yields more reliable values of the wavelength-integrated flux of the soft X-ray component and the implied accretion rate than reported previously.

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Average‐atom model calculations of dense‐plasma opacities: Review and potential applications to white‐dwarf stars

Piron

Błeński

2017

Contrib. Plasma Phys

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Methods using average-atom models in order to calculate dense-plasma opacities and conductivities are reviewed. Dense plasmas at moderate temperatures, of interest in white-dwarf modelling, are considered. Due to their relative simplicity of implementation, compared to more detailed models (detailed-level accounting, detailed configuration accounting, etc.), average-atom models are a privileged framework for the application of the most involved dense-plasma statistical modelling. Moreover, the average-atom models are well suited to the calculation of some thermodynamic properties, such as the equation of state. They can also be used in order to estimate broadband radiative properties of dense plasmas. After an introduction to the opacity issue in the modelling of white dwarfs, we make a short review of average-atom models. We then address the methods of calculating the opacity starting from the average-atom model, see some of their limitations, and briefly discuss some problems that remain open, such as the modelling of fluctuations, or the accounting for channel mixing and collective phenomena in the photoabsorption. KEYWORDSaverage atom, conductivity, dense plasmas, photoabsorption, radiative properties, white dwarf INTRODUCTION: OPACITIES IN THE CONTEXT OF WHITE-DWARF MODELLINGOpacities play an essential role in the physics of white-dwarf (WD) stars. Knowledge of the opacity is, for example, required for the modelling of the WD cooling process [1] or of the accretion phenomena in cataclysmic variables.[2]Figure 1 presents the thermodynamic conditions in a 0.6 M ⊙ , DA-type WD going through its cooling process, according to Ref. 3. In this figure are also plotted the boundaries of the regions of electron degeneracy, ion and electron coupling, and partial ionization. The average-atom (AA) models we are dealing with, in this article, are mostly aimed at describing partially to fully ionized, moderately coupled plasmas, at any degeneracy. As shown in Figure 1, a large part of the WD-relevant plasmas falls into this category.However, in the core of WDs (see Figure 1a), the plasma is highly ionized and its electrons are highly degenerate. Thus, elementary models of plasma physics, such as the one-component classical plasma model (see, for instance, Ref. 4) for the nuclei, and the cold fermion gas model (see, for instance, Ref. 5) for the electrons should be valid. Within the core, due to the extreme electron degeneracy, the heat transfer is dominated by electron thermal conduction, which is very efficient in these conditions, and the temperature gradients are small.The whole cooling process of the WD may therefore be regulated by its outer, thin, isolating envelope, in which heat transfer occurs mostly by radiative transfer and convection, except for the coolest WDs (surface temperature ≲ 3000 K). The nucleosynthesis and stellar evolution result in stars entering the WD stage with a somewhat layered structure. Then, due to the strong gravity, the element-diffusion equilibrium of the WD results in an even-more strat...

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Irradiated atmospheres of accreting magnetic white dwarfs with an application to the polar AM Herculis

Cited by 17 publications

References 21 publications

Two new intermediate polars with a soft X-ray component

Two new intermediate polars with a soft X-ray component

A new soft X-ray spectral model for polars with an application to AM Herculis

Average‐atom model calculations of dense‐plasma opacities: Review and potential applications to white‐dwarf stars

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