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1.
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2.
We discuss in this contribution constraints on the origin of mass-loss from young stars brought by recent observations at high angular resolution (0.1″ = 14 AU) of the inner regions of winds from T Tauri stars. Jet widths and collimation scales, the large extent of the velocity profile as well as the detection of rotation signatures agree with predictions from magneto-centrifugal disk wind ejection models. However dynamically cold disk wind solutions predict too large terminal velocities and too low jet densities and ionisation fractions, suggesting that thermal gradients (originating in an accretion heated disk corona for example) may play an important role in accelerating the flow.  相似文献   

3.
We study the effects of outflow/wind on the gravitational stability of accretion discs around supermassive black holes using a set of analytical steady-state solutions. Mass-loss rate by the outflow from the disc is assumed to be a power-law of the radial distance and the amount of the energy and the angular momentum which are carried away by the wind are parameterized phenomenologically. We show that the mass of the first clumps at the self-gravitating radius linearly decreases with the total mass-loss rate of the outflow. Except for the case of small viscosity and high accretion rate, generally, the self-gravitating radius increases as the amount of mass-loss by the outflow increases. Our solutions show that as more angular momentum is lost by the outflow, then reduction to the mass of the first clumps is more significant.  相似文献   

4.
We study the effects of winds on the time evolution of isothermal, self-gravitating accretion discs by adopting a radius-dependent mass-loss rate because of the existence of the wind. Our similarity and semi-analytical solution describes time evolution of the system in the slow accretion limit. The disc structure is distinct in the inner and outer parts, irrespective of the existence of the wind. We show that the existence of wind will lead to a reduction of the surface density in the inner and outer parts of the disc in comparison to a no-wind solution. Also, the radial velocity significantly increases in the outer part of the disc, however, the accretion rate decreases due to the reduced surface density in comparison to the no-wind solution. In the inner part of the disc, mass loss due to the wind is negligible according to our solution. But the radial size of this no-wind inner region becomes smaller for stronger winds.  相似文献   

5.
The problem of magnetic field generation and advection in accretion discs is considered, in the context of wind launching and angular momentum extraction. A dipole-symmetry solution of the dynamo equations is found, with force-free boundary conditions appropriate for matching to a wind solution. Consideration of the curved field geometry and diffusive nature of the disc enables the position of the sonic point to be calculated and related to the field inclination at the disc surface. A critical inclination of 20° to the horizontal results, for which the sonic point lies in the disc surface and there is no potential barrier to wind launching. Hence the wind mass-loss rate will only become excessive, leading to disc disruption, for large field bending. The compressional effect of the horizontal magnetic field enhances the wind mass flux.  相似文献   

6.
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7.
We have obtained complete phase coverage of the WC7+O binaries WR 42 = HD 97152 and WR 79 = HD 152270 with high signal-to-noise ratio (S/N), moderate-resolution spectra. Remarkable orbital phase-locked profile variations of the C  iii λ 5696 line are observed and interpreted as arising from colliding wind effects. Within this scenario, we have modelled the spectra using a purely geometrical model that assumes a cone-shaped wind–wind interaction region which partially wraps around the O star. Such modelling holds the exciting promise of revealing a number of interesting parameters for WR+O binaries, such as the orbital inclination, the streaming velocity of material in the interaction region and the ratio of wind momentum flux. Knowledge of these parameters in turn leads to the possibility of a better understanding of WR star masses, mass-loss rates and wind region characteristics.  相似文献   

8.
We consider the existence of a neutron star magnetic field by the detected cyclotron lines. We collected data on nine sources of high-mass X-ray binaries with supergiant companions as a test case for our model, to demonstrate their distribution and evolution. The wind velocity, spin period and magnetic field strength are studied under different mass loss rates. In our model, correlations between mass-loss rate and wind velocity are found and can be tested in further observations. We examine the parameter space where wind accretion is allowed, avoiding the barrier of rotating magnetic fields, with robust data on the magnetic field of neutron stars. Our model shows that most sources(six of nine systems) can be fed by the wind with relatively slow velocity, and this result is consistent with previous predictions. In a few sources,our model cannot fit the standard wind accretion scenario. In these peculiar cases, other scenarios(disk formation, partial Roche lobe overflow) should be considered. This would provide information about the evolutionary tracks of various types of binaries, and thus exhibit a clear dichotomy behavior in wind-fed X-ray binary systems.  相似文献   

9.
洪雅芳  蒋苏云 《天文学报》2011,52(5):365-376
在考虑引力对星风物质损失的制约效果及辐射压与湍流压对其扰动效果的同时,通过引入可压缩流机制,考虑了恒星外壳对流区对星风物质损失的促进作用,从而建立了新的星风物质损失公式.之后,通过对3～5 M_⊙恒星理论模型的星风物质损失率计算,发现:从主序直至中心氦核燃烧结束阶段,新的星风物质损失公式计算所得星风物质损失率与经典星风物质损失公式计算结果几乎一致;而在TP-AGB阶段,应用新的星风物质损失公式计算的恒星模型则不受光度影响产生了持续的较大的星风物质损失,比较符合实际观测结果.  相似文献   

10.
将作者在变质量天体力学所得理论结果应用于太阳质量损失对流星群轨道根数变化的长期效应上。太阳质量损失包括光子辐射和太阳风造成的质量损失。利用G—M型变质量天体轨道根数变化方程的一阶和二阶解对15个流星群轨道半长轴、近日点距离、轨道周期和近日点经度因太阳质量损失造成的每世纪的长期改变效应做了数值计算,并得出计算结果。其计算结果表明,太阳质量损失使流星群轨道半长轴每世纪的改变效应较明显,它们同太阳距离的扩大影响值得关注,但对轨道周期的拉长每世纪的影响甚小,对近日点经度只有量级变化小到可以略而不计。  相似文献   

11.
The stability of the solar wind is studied in the case of spherical symmetry and constant temperature. It is shown that the stability problem must be formulated as a mixed initial and boundary-value problem in which are prescribed the perturbation values of velocity and density at an initial time and additionally the velocity perturbation at the base of the corona for all times. The solution is constructed by linear superposition of normal solutions, which contain the time only in an exponential factor. The stability problem becomes a singular eigenvalue problem for the amplitudes of the velocity and pressure perturbations, since additionally to the boundary condition at the base of the corona one must add the condition that the amplitudes behave regularly at the critical point. It is proved that only stable eigenvalues exist.  相似文献   

12.
We present new radio and optical observations of the colliding-wind system WR 146 aimed at understanding the nature of the companion to the Wolf–Rayet (WR) star and the collision of their winds. The radio observations reveal emission from three components: the WR stellar wind, the non-thermal wind–wind interaction region and, for the first time, the stellar wind of the OB companion. This provides the unique possibility of determining the mass-loss rate and terminal wind velocity ratios of the two winds, independent of distance. Respectively, these ratios are 0.20±0.06 and 0.56±0.17 for the OB-companion star relative to the WR star. A new optical spectrum indicates that the system is more luminous than had been believed previously. We deduce that the 'companion' cannot be a single, low-luminosity O8 star as suggested previously, but is either a high-luminosity O8 star, or possibly an O8+WC binary system.  相似文献   

13.
Noam Soker   《New Astronomy》2008,13(7):491-497
I suggest the existence of an extended zone above the surface of asymptotic giant branch (AGB), as well as similar stars experiencing high mass-loss rates. In addition to the escaping wind, in this zone there are parcels of gas that do not reach the escape velocity. These parcels of dense gas rise slowly and then fall back. The wind and bound gas exist simultaneously to distances of 100AU. I term this region the effervescent zone. In this phenomenological study I find that the density of the bound material in the effervescent zone falls as r−5/2, not much faster than the wind density. The main motivation to propose the effervescent model is to allow wide binary companions to influence the morphology of the descendant planetary nebulae (PN) by accreting mass from the effervescent zone. Accretion from the effervescent zone is more efficient than accretion from the wind in forming an accretion disk around the companion. The companion might then blow two jets that will shape the descendant PN.  相似文献   

14.
We calculate the X-ray emission from both constant and time-evolving shocked fast winds blown by the central stars of planetary nebulae (PNe) and compare our calculations with observations. Using spherically symmetric numerical simulations with radiative cooling, we calculate the flow structure and the X-ray temperature and luminosity of the hot bubble formed by the shocked fast wind. We find that a constant fast wind gives results that are very close to those obtained from the self-similar solution. We show that in order for a fast shocked wind to explain the observed X-ray properties of PNe, rapid evolution of the wind is essential. More specifically, the mass-loss rate of the fast wind should be high early on when the speed is  ∼300–700 km s−1  , and then it needs to drop drastically by the time the PN age reaches ∼1000 yr. This implies that the central star has a very short pre-PN (post-asymptotic giant branch) phase.  相似文献   

15.
We analyze the wind generated by the great 20 yr-long super-Eddington outburst of eta Carinae. We show that by using the classical stellar atmosphere and wind theory, it is impossible to construct a consistent wind model in which a sufficiently small amount of mass, like the one observed, is shed. One expects the super-Eddington luminosity to drive a thick wind with a mass-loss rate substantially higher than the observed one. The easiest way to resolve the inconsistency is if we alleviate the implicit notion that atmospheres are homogeneous. An inhomogeneous, or "porous," atmosphere allows more radiation to escape while exerting a smaller average force. Consequently, such an atmosphere yields a considerably lower mass-loss rate for the same total luminosity. Moreover, all the applications of the Eddington luminosity as a strict luminosity limit should be revised or at least reanalyzed carefully.  相似文献   

16.
Mass-loaded models can explain how a cometary morphology, ultracompact H II region can arise around a stationary star. The star is located in a density gradient in the mass-loading sources. Continuous mass-loss from the clumps embedded in the ionized gas allows the region to remain compact. The wind and radiation field from the central star set up a fully supersonic flow that is bounded by a recombination front. We develop the models further by calculating the velocity and density structure in detail for a variety of viewing angles, mass-loading laws and density scaleheights. The results are compared with observational work, and the agreements and differences are highlighted.
We extend this model to show how a massive star located in a dense molecular ridge can give rise to a bipolar or ring morphology, depending on the viewing angle.  相似文献   

17.
The Weber-Davis model of the solar wind is generalized to include the effects of latitude. The principal assumptions of perfect electrical conductivity, rotational symmetry, a polytropic relation between pressure and density, and a flow aligned magnetic field in a system rotating with the Sun, are retained. A flow aligned magnetic field in the rotating system may be expressed in terms of the flow velocity and density. Rotational symmetry fixes the longitudinal flow velocity Vφ in terms of the flow in the r?θ plane. Thus, the original three dimensional magnetohydrodynamic flow problem is reduced to a two dimensional hydrodynamic flow problem in the r?θ plane.There are three critical surfaces associated with the equations which supply conditions to determine three of six required boundary conditions. The specified boundary conditions at the base of the corona are the temperature, density, and magnitude of the magnetic field. The equations are then expanded about the radial, nonrotating Parker solution and an analytic solution is obtained for the resulting first order equations. The results show that for constant coronal boundary conditions there is a latitudinal flow toward the solar poles, as a result of magnetic stresses, which persists out to large distances for the Sun. Associated with this flow is a latitudinal component of the magnetic field. The radial flow parameters are, to within small first order differences, in agreement with those of the Parker and the Weber-Davis models of the solar wind.The equations are further generalized to permit first order latitudinal variations in the specified coronal boundary conditions. Results at 1 a.u. are presented for 5 per cent latitudinal differences between the equatorial and polar values. These results show that the solution at 1 a.u. is most sensitive to a latitudinal dependence in the boundary temperature and least sensitive to a latitudinal dependence in the magnetic field magnitude.A solution is then obtained for an approximate dipolar variation in the coronal magnetic field magnitude. This solution predicts that the latitudinal flow is initially toward the Equator due to magnetic channeling; however, this effect is rapidly overcome and the latitudinal flow at 1 a.u. is toward the pole and not significantly different from the solution for constant boundary conditions.  相似文献   

18.
We investigate the dynamical response, in terms of disc size and rotation velocity, to mass loss by supernovae in the evolution of spiral galaxies. A thin baryonic disc having the Kuzmin density profile embedded in a spherical dark matter halo having a density profile proposed by Navarro, Frenk & White is considered. For the purpose of comparison, we also consider the homogeneous and   r −1  profiles for dark matter in a truncated spherical halo. Assuming for simplicity that the dark matter distribution is not affected by mass-loss from discs and the change of baryonic disc matter distribution is homologous, we evaluate the effects of dynamical response in the resulting discs. We found that the dynamical response only for an adiabatic approximation of mass-loss can simultaneously account for the rotation velocity and disc size as observed particularly in dwarf spiral galaxies, thus reproducing the Tully–Fisher relation and the size versus magnitude relation over the full range of magnitude. Furthermore, we found that the mean specific angular momentum in discs after the mass-loss becomes larger than that before the mass-loss, suggesting that the mass-loss would most likely occur from the central disc region where the specific angular momentum is low.  相似文献   

19.
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20.
Data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses and synoptic maps from Kitt Peak are used to analyze the polar coronal holes of solar activity cycles 22 and 23 (from 1990 to end of 2003). In the beginning of the declining phase of solar cycles 22 and 23, the north polar coronal holes (PCHs) appear about one year earlier than the ones in the south polar region. The solar wind velocity and the solar wind ionic charge composition exhibit a characteristic dependence on the solar wind source position within a PCH. From the center toward the boundary of a young PCH, the solar wind velocity decreases, coinciding with a shift of the ionic charge composition toward higher charge states. However, for an old PCH, the ionic charge composition does not show any obvious change, although the latitude evolution of the velocity is similar to that of a young PCH.  相似文献   

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