X-ray emission lines from inhomogeneous stellar winds

Oskinova, L. M.; Feldmeier, Achim; Hamann, Wolf-Rainer

doi:10.1051/0004-6361:20047187

Cited by 69 publications

(136 citation statements)

References 28 publications

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“…Accounting for macroclumping reduces the wavelength dependence of opacity. In its limit (when clumps are fully opaque), the opacity becomes grey (Oskinova et al 2004).…”

Section: Discussionmentioning

confidence: 99%

X-ray emission from hydrodynamical simulations in non-LTE wind models

Krtička

Feldmeier

Oskinova

et al. 2009

A&A

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Hot stars are sources of X-ray emission originating in their winds. Although hydrodynamical simulations that are able to predict this X-ray emission are available, the inclusion of X-rays in stationary wind models is usually based on simplifying approximations. To improve this, we use results from time-dependent hydrodynamical simulations of the line-driven wind instability (seeded by the base perturbation) to derive the analytical approximation of X-ray emission in the stellar wind. We use this approximation in our non-LTE wind models and find that an improved inclusion of X-rays leads to a better agreement between model ionization fractions and those derived from observations. Furthermore, the slope of the L X − L relation is in better agreement with observations, however the X-ray luminosity is underestimated by a factor of three. We propose a possible solution for this discrepancy.

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“…Accounting for macroclumping reduces the wavelength dependence of opacity. In its limit (when clumps are fully opaque), the opacity becomes grey (Oskinova et al 2004).…”

Section: Discussionmentioning

confidence: 99%

X-ray emission from hydrodynamical simulations in non-LTE wind models

Krtička

Feldmeier

Oskinova

et al. 2009

A&A

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“…To this end, we use a numerical code to simulate the column density between the observer and a point-like X-ray source, as the source orbits around a companion whose wind is composed of discrete clumps. For simplicity, the code does not account for the focussed wind properties of the system; moreover, the clumps are assumed to be spherical, rather than the pancake morphologies considered by other authors (e.g., Feldmeier et al 2003;Oskinova et al 2004). At a given orbital phase, the column-density evaluation is performed by casting a ray from the source to the observer, determining which ray segments lie inside clumps, and summing up the contributions from these segments (as the product of the segment length and the clump density).…”

Section: Clumpy Wind Model For the Hard Statementioning

confidence: 99%

Long term variability of Cygnus X-1

Grinberg

Leutenegger

Hell

et al. 2015

A&A

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Binary systems with an accreting compact object offer a unique opportunity to investigate the strong, clumpy, line-driven winds of early-type supergiants by using the compact object's X-rays to probe the wind structure. We analyze the two-component wind of HDE 226868, the O9.7Iab giant companion of the black hole Cyg X-1, using 4.77 Ms Rossi X-ray Timing Explorer (RXTE) observations of the system taken over the course of 16 years. Absorption changes strongly over the 5.6 d binary orbit, but also shows a large scatter at a given orbital phase, especially at superior conjunction. The orbital variability is most prominent when the black hole is in the hard X-ray state. Our data are poorer for the intermediate and soft state, but show signs for orbital variability of the absorption column in the intermediate state. We quantitatively compare the data in the hard state to a toy model of a focussed Castor-AbbottKlein wind: as it does not incorporate clumping, the model does not describe the observations well. A qualitative comparison to a simplified simulation of clumpy winds with spherical clumps shows good agreement in the distribution of the equivalent hydrogen column density for models with a porosity length on the order of the stellar radius at inferior conjunction; we conjecture that the deviations between data and model at superior conjunction could either be due to lack of a focussed wind component in the model or to a more complicated clump structure.

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“…Stellar rotation (e.g., Puls et al 1999 and references therein), and the intrinsic instability of the line-driving mechanism (see below), produce nonspherical and inhomogeneous structure, observationally evident from, e.g., X-ray emission and line-profile variability (for summaries, see Oskinova et al 2004 regarding the present status of X-ray line emission). As long as the time-dependent structuring of stellar winds is not well understood, we cannot be sure about even their "average" properties, such as mass-loss rates and emergent ionizing fluxes.…”

Section: Introductionmentioning

confidence: 99%

Bright OB stars in the Galaxy

Puls¹,

Маркова²,

Scuderi³

et al. 2006

A&A

291

391

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Context. Recent results strongly challenge the canonical picture of massive star winds: various evidence indicates that currently accepted mass-loss rates,Ṁ, may need to be revised downwards, by factors extending to one magnitude or even more. This is because the most commonly used mass-loss diagnostics are affected by "clumping" (small-scale density inhomogeneities), influencing our interpretation of observed spectra and fluxes. Aims. Such downward revisions would have dramatic consequences for the evolution of, and feedback from, massive stars, and thus robust determinations of the clumping properties and mass-loss rates are urgently needed. We present a first attempt concerning this objective, by means of constraining the radial stratification of the so-called clumping factor. Methods. To this end, we have analyzed a sample of 19 Galactic O-type supergiants/giants, by combining our own and archival data for H α , IR, mm and radio fluxes, and using approximate methods, calibrated to more sophisticated models. Clumping has been included into our analysis in the "conventional" way, by assuming the inter-clump matter to be void. Because (almost) all our diagnostics depends on the square of density, we cannot derive absolute clumping factors, but only factors normalized to a certain minimum. Results. This minimum was usually found to be located in the outermost, radio-emitting region, i.e., the radio mass-loss rates are the lowest ones, compared toṀ derived from H α and the IR. The radio rates agree well with those predicted by theory, but are only upper limits, due to unknown clumping in the outer wind. H α turned out to be a useful tool to derive the clumping properties inside r < 3. . .5 R . Our most important result concerns a (physical) difference between denser and thinner winds: for denser winds, the innermost region is more strongly clumped than the outermost one (with a normalized clumping factor of 4.1 ± 1.4), whereas thinner winds have similar clumping properties in the inner and outer regions. Conclusions. Our findings are compared with theoretical predictions, and the implications are discussed in detail, by assuming different scenarios regarding the still unknown clumping properties of the outer wind.

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X-ray emission lines from inhomogeneous stellar winds

Cited by 69 publications

References 28 publications

X-ray emission from hydrodynamical simulations in non-LTE wind models

X-ray emission from hydrodynamical simulations in non-LTE wind models

Long term variability of Cygnus X-1

Bright OB stars in the Galaxy

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