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تسجيل مستخدم جديدA Deep Exposure in High Resolution X-Rays Reveals the Hottest Plasma in the $zeta,$Puppis Wind
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David P. Huenemoerder
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We have obtained a very deep exposure (813 ks) of $zeta,$Puppis (O4 supergiant) with the Chandra/HETG Spectrometer. Here we report on analysis of the 1-9 r{A} region, especially well suited for Chandra, which has a significant contribution from continuum emission between well separated emission lines from high-ionization species. These data allow us to study the hottest plasma present through the continuum shape and emission line strengths. Assuming a powerlaw emission measure distribution which has a high-temperature cut-off, we find that the emission is consistent with a thermal spectrum having a maximum temperature of 12 MK. This implies an effective wind shock velocity of $900,mathrm{km,s^{-1}}$, well below the wind terminal speed of $2250,mathrm{km,s^{-1}}$. For X-ray emission which forms close to the star, the speed and X-ray flux are larger than can be easily reconciled with strictly self-excited line-deshadowing-instability models, suggesting a need for a fraction of the wind to be accelerated extremely rapidly right from the base. This is not so much a dynamical instability as a nonlinear response to changing boundary conditions.
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Aims: zeta Puppis, one of the closest and brightest massive stars, was the first early-type object observed by the current generation of X-ray observatories. These data provided some surprising results, confirming partly the theoretical predictions w
hile simultaneously unveiling some problematic mismatches with expectations. In this series of papers, we perform a thorough study of zeta Puppis in X-rays, using a decade of XMM observations. Methods: zeta Puppis was observed 18 times by XMM, totaling 1Ms in exposure. This provides the highest-quality high-resolution X-ray spectrum of a massive star to date, as well as a perfect dataset for studying X-ray variability in an archetype object. Results: This first paper reports on the data reduction of this unique dataset and provides a few preliminary results. On the one hand, the analysis of EPIC low-resolution spectra shows the star to have a remarkably stable X-ray emission from one observation to the next. On the other hand, the fitting by a wind model of individual line profiles recorded by RGS confirms the wavelength dependence of the line morphology.
A subset (~ 10%) of massive stars present strong, globally ordered (mostly dipolar) magnetic fields. The trapping and channeling of their stellar winds in closed magnetic loops leads to magnetically confined wind shocks (MCWS), with pre-shock flow sp
eeds that are some fraction of the wind terminal speed. These shocks generate hot plasma, a source of X-rays. In the last decade, several developments took place, notably the determination of the hot plasma properties for a large sample of objects using XMM-Newton and Chandra, as well as fully self-consistent MHD modelling and the identification of shock retreat effects in weak winds. Despite a few exceptions, the combination of magnetic confinement, shock retreat and rotation effects seems to be able to account for X-ray emission in massive OB stars. Here we review these new observational and theoretical aspects of this X-ray emission and envisage some perspectives for the next generation of X-ray observatories.
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gnificance - of increased wind absorption signatures in its Doppler-broadened x-ray emission line profiles. We demonstrate this with non-parametric analysis of the profiles as well as Gaussian fitting and then use the line-profile model fitting to derive a mass-loss rate of $2.47 pm 0.09 times 10^{-6}$ Msun/yr, which is a 40 per cent increase over the value obtained from the cycle 1 data. The increase in the individual emission line fluxes is greater for short-wavelength lines than long-wavelength lines, as would be expected if a uniform increase in line emission is accompanied by an increase in the wavelength-dependent absorption by the cold wind in which the shock-heated plasma is embedded.
X-ray satellites since Einstein have empirically established that the X-ray luminosity from single O-stars scales linearly with bolometric luminosity, Lx ~ 10^{-7} Lbol. But straightforward forms of the most favored model, in which X-rays arise from
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