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1.
Svetozar A. Zhekov 《Monthly notices of the Royal Astronomical Society》2007,382(2):886-894
The effects of non-equilibrium ionization are explicitly taken into account in a numerical model which describes colliding stellar winds (CSW) in massive binary systems. This new model is used to analyse the most recent X-ray spectra of the WR+OB binary system WR 147. The basic result is that it can adequately reproduce the observed X-ray emission (spectral shape, observed flux) but some adjustment in the stellar wind parameters is required. Namely (i) the stellar wind velocities must be higher by a factor of 1.4–1.6 and (ii) the mass loss must be reduced by a factor of ∼2. The reduction factor for the mass loss is well within the uncertainties for this parameter in massive stars, but given the fact that the orbital parameters (e.g. inclination angle and eccentricity) are not well constrained for WR 147, even smaller corrections to the mass loss might be sufficient. Only CSW models with non-equilibrium ionization and equal (or nearly equal) electron and ion post-shock temperature are successful. Therefore, the analysis of the X-ray spectra of WR 147 provides evidence that the CSW shocks in this object must be collisionless . 相似文献
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A. V. Myasnikov S. A. Zhekov & N. A. Belov 《Monthly notices of the Royal Astronomical Society》1998,298(4):1021-1029
The properties of radiative steady-state colliding stellar winds in binary systems are studied. It is shown that the presence of a singularity at the stagnation point has a major influence on the structure of these flows. This problem is of great importance if their stability properties are considered. None of the existing models treats this mathematical problem properly, and special efforts must be undertaken in the future in order to come to a firm conclusion about the physical nature of possible instabilities. At the moment, neither numerical nor analytical models can be considered to be of acceptable accuracy in the case of highly radiative steady-state colliding stellar winds. 相似文献
4.
Svetozar A. Zhekov Francesco Palla 《Monthly notices of the Royal Astronomical Society》2007,382(3):1124-1132
Chandra grating spectra of a sample of 15 massive OB stars were analysed under the basic assumption that the X-ray emission is produced in an ensemble of shocks formed in the winds driven by these objects. Shocks develop either as a result of radiation-driven instabilities or due to confinement of the wind by a relatively strong magnetic field, and since they are radiative, a simple model of their X-ray emission was developed that allows a direct comparison with observations. According to our model, the shock structures (clumps, complete or fractional shells) eventually become 'cold' clouds in the X-ray sky of the star. As a result, it is expected that for large covering factors of the hot clumps, there is a high probability for X-ray absorption by the 'cold' clouds, resulting in blueshifted spectral lines. Our analysis has revealed that such a correlation indeed exists for the considered sample of OB stars. As to the temperature characteristics of the X-ray emission plasma, the studied OB stars fall in two groups: (i) one with plasma temperature limited to ∼0.1–0.4 keV and (ii) the other with X-rays produced in plasmas at considerably higher temperatures. We argue that the two groups correspond to different mechanisms for the origin of X-rays: in radiation-driven instability shocks and in magnetically confined wind shocks, respectively. 相似文献
5.
Two-dimensional calculations in the model of two colliding stellar winds are provided. The effects of energy losses on free-free emission and Comptonization are investigated. The expected X-ray emission of a typical WR+O binary system is calculated. 相似文献
6.
Krešimir Čolić Svetozar Petrović Hans Sünkel Miloslav Burda Miroslav Bielik Vincenc Vyskočil 《Studia Geophysica et Geodaetica》1994,38(2):131-139
Summary The Dinarides, the Eastern Alps and the Western Carpathians being situated at the borders of the Pannonian basin, are of very
similar origin. Therefore, the results obtained in the investigation of correlations between Earth gravity field parameters
(absolute geoid undulations, gravity anomalies), the surface topography and the shape of the Mohorovičić discontinuity, were
compared. It was found that these three regions have the same basic characteristics, but also their own specific features.
While the similarities follow clearly from these investigations, the found differences might partly be a consequence of non-uniformity
and unmatched quality of data sets used for the three regions.
A short version of this paper, entitled "Kindredness of three mountain belts at the border of the Pannonian basin — deduced
from the behavior of the Mohorovičić discontinuity" was presented at the 7th International Symposium "Geodesy and Physics
of the Earth", Potsdam, October 5–10, 1992 and published in the Proceedings.
Presently a visiting professor at the Graz University of Technology, Institute for Theoretical Geodesy, Department for Physical
Geodesy, Austria.
Presently at the Berlin University of Technology, Germany, as an Alexander von Humboldt Foundation Research Fellow. 相似文献
7.
A comparison between the stellar-wind interaction model with electron heat conduction and the ASCA X-ray observations of the (WR+O) binary system WR 140 has been made for the first time. This comparison shows that good agreement with observations can be achieved by varying the physical stellar-wind parameters within the ranges allowed by the accuracy of their determination. The self-consistent two-temperature model with heat conduction is an outgrowth of the model of interacting winds in such systems, which is required to properly interpret future detailed X-ray observations on the Chandra and Newton-XMM satellites. 相似文献
8.
Stephen Skinner Manuel Güdel Werner Schmutz Svetozar Zhekov 《Astrophysics and Space Science》2006,304(1-4):97-99
We present an overview of recent X-ray observations of Wolf-Rayet (WR) stars with XMM-Newton and Chandra. These observations are aimed at determining the differences in X-ray properties between massive WR + OB binary systems and putatively single WR stars. A new XMM spectrum of the nearby WN8 + OB binary WR 147 shows hard absorbed X-ray emission (including the Fe Kα line complex), characteristic of colliding wind shock sources. In contrast, sensitive observations of four of the closest known single WC (carbon-rich) WR stars have yielded only non-detections. These results tentatively suggest that single WC stars are X-ray quiet. The presence of a companion may thus be an essential factor in elevating the X-ray emission of WC + OB stars to detectable levels. 相似文献
9.
We review the recent hydrodynamic modelling of wind-blown bubbles (WBB) which are result of interaction of a stellar wind
with the circumstellar matter or the wind(s) emitted during the previous stages of the central star evolution. The much faster
computers becoming available in the last decade allow a more complete picture of the physics of these objects to be built.
Recent hydrodynamic models are capable of treating in detail different mechanisms as radiative plasma cooling, electron thermal
conduction and the effects of magnetic fields. We discuss the various mechanisms proposed for shaping these objects and we
emphasize on the problems related to the development of various instabilities and the X-ray emission from WBB.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
A. V. Myasnikov & S. A. Zhekov 《Monthly notices of the Royal Astronomical Society》1998,300(3):686-694
The influence of electron thermal conduction on the 2D gas dynamics of colliding stellar winds is investigated. It is shown that, as a result of the non-linear dependence of the electron thermal flux on the temperature, the pre-heating zones (in which the hot gas in the interaction region heats the cool winds in front of the shocks) have finite sizes. The dependence of the problem of the structure of the flow in the interaction region on the dimensionless parameters is studied, and a simple expression is derived for the size of the pre-heating zones at the axis of symmetry. It is shown that small values of the thermal conductivity do not suppress the Kelvin–Helmholtz instability if the adiabatic flow is subject to it. Further studies, both numerical and analytical, in this direction will be of great interest. The influence of thermal conduction on the X-ray emission from the interaction region is also estimated. 相似文献