Turbulent mixing in wind-blown HII regions     

D. Breitschwerdt  F. D. Kahn 《Astrophysics and Space Science》1994,216(1-2):297-301

We describe the process of turbulent mixing, occuring at the interface between the stellar wind bubble and the overlying, compressed HII layer. It is shown that hot electrons from the bubble can penetrate into the mixing region, where they deposit some fraction of their thermal energy. This first leads to an expansion of the gas at constant pressure, which soon becomes too inefficient to carry away the additional energy. Therefore pressure can build up in the mixing layer, forcing the gas to expand into the bubble. We also discuss the effect of the over-pressure on the HII shell and find that it is possible to punch a hole at the polar caps, where mixing is most efficient. This may lead to the formation of bipolar outflows. We apply our model to the wind-blown HII region NGC 6334(A), and show that it can explain the observed distortion of the bubble and the bipolar ionization cones.  相似文献   

Spectropolarimetric modelling of hot star wind structure     

John C Brown 《Astrophysics and Space Science》1994,221(1-2):357-364

A short overview is given of some recent progress in the theory of spectropolarimetry as a diagnostic of axisymmetric hot star wind density and velocity structure, covering the inferences possible from broad band polarimetry, from polarimetric light curves and simultaneous absorption line data, and from spectropolarimetric line profiles. Recent work on joint spectro-, photo-, and polari-metric study of the properties of wind inhomogeneities is also summarised. One of the most important conclusions is that the blobs necessary in WR winds to produce narrow emission line features cannot also produce polarimetric light curve features unless they originate in enhanced mass loss sources at the stellar surface rather than solely in density redistribution processes, such as turbulence, in the wind itself.  相似文献   

Modelling the continuous radio outbursts in AE Aquarii     

P. J. Meintjes  L. A. Venter 《Monthly notices of the Royal Astronomical Society》2003,341(3):891-900

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Interaction of accretion shocks with winds     

Kinsuk Acharya  Sandip K. Chakrabarti  D. Molteni 《Journal of Astrophysics and Astronomy》2002,23(1-2):155-164

Accretion shocks are known to oscillate in presence of cooling processes in the disk. This oscillation may also cause quasi-periodic oscillations of black holes. In the presence of strong winds, these shocks have oscillations in vertical direction as well. We show examples of shock oscillations under the influence of both the effects. When the shocks are absent and the flow is cooler, the wind becomes weaker and the vertical oscillation becomes negligible.  相似文献   

Wind signatures in the X-ray emission-line profiles of the late-O supergiant ζ Orionis     

David H. Cohen  Maurice A. Leutenegger  Kevin T. Grizzard  Catherine L. Reed  Roban H. Kramer  Stanley P. Owocki 《Monthly notices of the Royal Astronomical Society》2006,368(4):1905-1916

X-ray line-profile analysis has proved to be the most direct diagnostic of the kinematics and spatial distribution of the very hot plasma around O stars. The Doppler-broadened line profiles provide information about the velocity distribution of the hot plasma, while the wavelength-dependent attenuation across a line profile provides information about the absorption to the hot plasma, thus providing a strong constraint on its physical location. In this paper, we apply several analysis techniques to the emission lines in the Chandra High Energy Transmission Grating Spectrometer (HETGS) spectrum of the late-O supergiant ζ Ori (O9.7 Ib), including the fitting of a simple line-profile model. We show that there is distinct evidence for blueshifts and profile asymmetry, as well as broadening in the X-ray emission lines of ζ Ori. These are the observational hallmarks of a wind-shock X-ray source, and the results for ζ Ori are very similar to those for the earlier O star, ζ Pup, which we have previously shown to be well fit by the same wind-shock line-profile model. The more subtle effects on the line-profile morphologies in ζ Ori, as compared to ζ Pup, are consistent with the somewhat lower density wind in this later O supergiant. In both stars, the wind optical depths required to explain the mildly asymmetric X-ray line profiles imply reductions in the effective opacity of nearly an order of magnitude, which may be explained by some combination of mass-loss rate reduction and large-scale clumping, with its associated porosity-based effects on radiation transfer. In the context of the recent reanalysis of the helium-like line intensity ratios in both ζ Ori and ζ Pup, and also in light of recent work questioning the published mass-loss rates in OB stars, these new results indicate that the X-ray emission from ζ Ori can be understood within the framework of the standard wind-shock scenario for hot stars.  相似文献   

Assimilation of GMS-5 satellite winds using nudging method with MM5   总被引：2，自引：0，他引：2  

高山红  吴增茂杨波 《中国海洋湖沼学报》2006,24(3):215-224

With the aid of Meteorological Information Composite and Processing System （MICAPS）, satellite wind vectors derived from the Geostationary Meteorological Statellite-5 （GMS-5） and retrieved by National Satellite Meteorology Center of China （NSMC） can be obtained. Based on the nudging method built in the fifth-generation Mesoscale Model （MM5） of Pennsylvania State University and National Center for Atmospheric Research, a data preprocessor is developed to convert these satellite wind vectors to those with specified format required in MM5. To examine the data preprocessor and evaluate the impact of satellite winds from GMS-5 on MM5 simulations, a series of numerical experimental forecasts consisting of four typhoon cases in 2002 are designed and implemented. The results show that the preprocessor can process satellite winds smoothly and MM5 model runs successfully with a little extra computational load during ingesting these winds, and that assimilation of satellite winds by MM5 nudging method can obviously improve typhoon track forecast but contributes a little to typhoon intensity forecast. The impact of the satellite winds depends heavily upon whether the typhoon bogussing scheme in MM5 was turned on or not. The data preprocessor developed in this paper not only can treat GMS-5 satellite winds but also has capability with little modification to process derived winds from other geostationary satellites.  相似文献   

Instabilities in two-fluid magnetized media with inter-component drift     

P. V. Tytarenko  R. J. R. Williams  S. A. E. G. Falle 《Monthly notices of the Royal Astronomical Society》2002,337(1):117-132

We analyse the stability of a magnetized medium consisting of a neutral fluid and a fluid of charged particles, coupled to each other through a drag force and exposed to differential body forces (for example, as the result of radiation forces on one phase). We consider a uniform equilibrium and simple model input physics, but do not arbitrarily restrict the relative orientations of the magnetic field, slip velocity and wavevector of the disturbance. We find several instabilities and classify these in terms of wave resonances. We briefly apply our results to the structure of SiO maser regions appearing in the winds from late-type stars.  相似文献   

Active galactic nuclei jet mass loading and truncation by stellar winds     

A. Hubbard  E. G. Blackman 《Monthly notices of the Royal Astronomical Society》2006,371(4):1717-1721

Active galactic nuclei can produce extremely powerful jets. While tightly collimated, the scale of these jets and the stellar density at galactic centres implies that there will be many jet/star interactions, which can mass load the jet through stellar winds. Previous work employed modest wind mass outflow rates, but this does not apply when mass loading is provided by a small number of high mass-loss stars. We construct a framework for jet mass loading by stellar winds for a broader spectrum of wind mass-loss rates than has previously been considered. Given the observed stellar mass distributions in galactic centres, we find that even highly efficient (0.1 Eddington luminosity) jets from supermassive black holes of masses M _BH≲ 10⁴ M_⊙ are rapidly mass loaded and quenched by stellar winds. For  10⁴ M_⊙ < M _BH < 10⁸ M_⊙  , the quenching length of highly efficient jets is independent of the jet's mechanical luminosity. Stellar wind mass loading is unable to quench efficient jets from more massive engines, but can account for the observed truncation of the inefficient M87 jet, and implies a baryon-dominated composition on scales ≳2 kpc therein even if the jet is initially pair plasma dominated.  相似文献   

Dissecting the Homunculus nebula around Eta Carinae with spatially resolved near-infrared spectroscopy     

Nathan Smith †‡ 《Monthly notices of the Royal Astronomical Society》2002,337(4):1252-1268

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Chemical abundances and winds of massive stars in M31: a B-type supergiant and a WC star in OB 10     

S.J. Smartt  P.A. Crowther  P.L. Dufton †  D.J. Lennon  R.P. Kudritzki  A. Herrero  J.K. McCarthy  F. Bresolin 《Monthly notices of the Royal Astronomical Society》2001,325(1):257-272

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