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1.
大质量双星系统的非守恒演化   总被引：1，自引：0，他引：1  
由于大质量双星系统有强大的星风物质损失,因而在研究其结构和演化时必须考虑星风物质损失,动量损失,物质交换以及由以上原因引起的轨道参量的变化,此外,天文观测又证实,一些大质量双星系统中存在星风冲击波,有Ｘ射线辐射以及有致密天体（白矮星,中子星）的存在,因此在研究大质量双星的演化时,又会遇到在星风冲击波理论及其对演化的影响,双星系统何时会演化成为公共外壳的系统,以及双星系统中如果发生超新星爆发,是否会  相似文献   

2.
In this paper, we compute theoretically the flux density and the spectral index of the free–free radiation at radio wavelengths produced by shocks in the inner bipolar emission nebula called the little Homunculus around the star η Carinae. The little Homunculus is believed to have formed as a result of the minor eruption suffered by the star in the 1890s. In our model, we consider a simplified interacting stellar wind scenario where the post-outburst η Carinae wind collides with the eruptive outflow (both assumed to be bipolar with conical symmetry). As a result of the interaction, shock-wave structures are formed and generate the development of two polar caps moving in opposite directions. After ∼100 yr (i.e. at present times), the polar caps are located ±2.3 arcsec on each side of the star, and remain embedded within the larger bipolar Homunculus that extends from −8 to +8 arcsec along its major axis. Using observational estimates of the characteristics of the eruptive event of the 1890s, and of the ambient wind powered by η Carinae in the decades after the eruption ended, we study the evolution of the polar caps formed as a result of a sudden increase in the wind velocity and an instantaneous drop in the mass-loss rate (just after the eruption) at the injection radius. We found that the little Homunculus emits continuum radiation that can be detected at radio frequencies and that indeed represents an important contribution to the total free–free emission detected from the η Carinae nebula.  相似文献   

3.
We use ideal axisymmetric relativistic magnetohydrodynamic simulations to calculate the spin-down of a newly formed millisecond,   B ∼ 1015 G  , magnetar and its interaction with the surrounding stellar envelope during a core-collapse supernova (SN) explosion. The mass, angular momentum and rotational energy lost by the neutron star are determined self-consistently given the thermal properties of the cooling neutron star's atmosphere and the wind's interaction with the surrounding star. The magnetar drives a relativistic magnetized wind into a cavity created by the outgoing SN shock. For high spin-down powers  (∼1051–1052 erg s−1)  , the magnetar wind is superfast at almost all latitudes, while for lower spin-down powers  (∼1050 erg s−1)  , the wind is subfast but still super-Alfvénic. In all cases, the rates at which the neutron star loses mass, angular momentum and energy are very similar to the corresponding free wind values (≲30 per cent differences), in spite of the causal contact between the neutron star and the stellar envelope. In addition, in all cases that we consider, the magnetar drives a collimated  (∼5–10°)  relativistic jet out along the rotation axis of the star. Nearly all of the spin-down power of the neutron star escapes via this polar jet, rather than being transferred to the more spherical SN explosion. The properties of this relativistic jet and its expected late-time evolution in the magnetar model are broadly consistent with observations of long duration gamma-ray bursts (GRBs) and their associated broad-lined Type Ic SN.  相似文献   

4.
We present results of the 2D simulations of magnetorotational mechanism for the rotating magnetized cloud. It was found that amplification of the toroidal magnetic field leads to the transformation of the part of the rotational energy of the cloud to the kinetic energy of radial motion. A compression wave appearing in the transition region between the core of the cloud and the envelope transforms soon to the MHD shock wave and pushes away part of the envelope of the cloud. Time evolution of the thrown away mass and energy are given. Simulations have been made on the base of the conservative implicit Lagrangian scheme on triangular grid with grid reconstruction. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

5.
We present hydrodynamical simulations illustrating the instability of stellar wind bowshocks in the limit of an isothermal equation of state. In this limit, the bowshock is characterized by a thin dense shell bounded on both sides by shocks. In a time-averaged sense the shape of this bowshock shell roughly matches the steady state solution of Wilkin (1996)[ApJ, 459, L31], although the apex of the bowshock can deviate in or out by a factor of two or more. The shape of the bowshock is distorted by large amplitude kinks with a characteristic wavelength of order the standoff distance from the star. The instability is driven by a strong shear flow within the shock-bounded shell, suggesting an origin related to the nonlinear thin-shell instability. This instability occurs when both the forward bowshock and the reverse wind shock are effectively isothermal and the star is moving through the interstellar medium with a Mach number greater than a few. This work therefore suggests that ragged, clumpy bowshocks should be expected to surround stars with a slow, dense wind (which leads to rapid cooling behind the reverse wind shock), whose velocity with respect to the surrounding interstellar medium is of order 60 km s−1 (leading both to rapid cooling behind the forward bowshock and sufficiently high Mach numbers to drive the instability).  相似文献   

6.
The optical light of the symbiotic binary BF Cyg during its last eruption after 2006 shows orbital variations because of an eclipse of the outbursting compact object. The first orbital minimum is deeper than the following ones. Moreover, the Balmer profiles of this system acquired additional satellite components indicating a bipolar collimated outflow at one time between the first and second orbital minima. This behaviour is interpreted in the framework of the model of a collimated stellar wind from the outbursting object. It is supposed that one extended disc‐like envelope covering the accretion disc of the compact object and collimating its stellar wind forms in the period between the first and second minima. The uneclipsed part of this envelope is responsible for the decrease of the depth of the orbital minimum. The calculated UBVRCIC fluxes of this uneclipsed part are in agreement with the observed residual of the depths of the first and second orbital minima. The parameters of the envelope require that it is the main emitting region of the line Hα but the Hα profile is less determined from its rotation and mostly from other mechanisms. It is concluded that the envelope is a transient nebular region and its destruction determines the increase of the depth of the orbital minimum with fading of the optical light. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
New high-resolution spectroscopic and medium-resolution spectropolarimetric data of the B[e] star HD 87643 are presented, complemented with optical broad- and narrow-band imaging. The spectrum of HD 87643 exhibits the hybrid characteristics well known to be representative of the group of B[e] stars; a fast wind with an expansion velocity in excess of 1000 km s−1 is measured in the hydrogen and helium lines, while a slower component is traced by lower excitation lines and forbidden lines. Clues to the geometry of the rapidly expanding circumstellar shell are provided by the startling polarization changes across Hα. Comparison with published schematic calculations indicates that the polarizing material is located in a slowly rotating, expanding disc structure. A hydrodynamical model is then presented, the results of which are consistent with the original two-wind concept for B[e] stars, and which exhibits kinematic properties that may well explain the observed spectral features in HD 87643. The model calculations use as input a B star undergoing mass loss, surrounded by an optically thick disc. The resulting configuration consists of a fast polar wind from the star and a slowly expanding disc wind. The model also predicts that the stellar wind at intermediate latitudes is slower and denser than in the polar region.  相似文献   

8.
The time dependent one dimensional hydrodynamic equations describe the evolution of the thermal plasma flow along closed magnetic field lines outside of the plasmasphere. The convection of the supersonic polar wind onto a closed field line results in the assumed formation of collisionless plasma shocks. These shocks move earthward as the field line with its ‘frozen-in’ plasma remains fixed or contracts with time to smaller L coordinates. The high equatorial plasma temperature (of the order of electron volts) produced by the shock process decreases with time if the flow is isothermal but it will increase if the contraction is under adiabatic conditions. Assuming adiabaticity a peak in the temperature forms at the equator in conjunction with a depression in the ion density. After an initial contraction, if the flux tube drifts to higher L coordinates the direction of the shock motion can be reversed so that the supersonic region will expand along the field line towards the state characterizing the supersonic polar wind. A rapid expansion will lower the equatorial density while the temperature decreases with time under adiabatic but not isothermal conditions.  相似文献   

9.
We conclude that the magnetospheric structure around an aligned rotating magnetized neutron star, in the case of a completely charge-separated plasma, consists of a dome of charge about the polar caps and an equatorial disk of opposite charge which, together, entirely envelope the surface but do not fill the magnetosphere. Although the aligned rotator is a standard model for analyzing pulsar emission, the magnetosphere we obtain need not emit particles and need not generate a stellar wind, contrary to previous expectations. Pair production only seems to modify the detailed shape of the dome and disk, such modification serving to shut off further pair production. Such a magnetohydrodynamically inactive object may have difficulty simulating pulsar emission.Research support in part by the National Science Foundation under grant AST 77-22675.  相似文献   

10.
《New Astronomy Reviews》1999,43(1):31-65
Hypersonic bipolar outflows are a ubiquitous phenomena associated with both young and highly evolved stars. Observations of Planetary Nebulae, the nebulae surrounding Luminous Blue Variables such as η Carinae, Wolf Rayet bubbles, the circumstellar environment of SN 1987A and Young Stellar Objects all reveal high velocity outflows with a wide range of shapes. In this paper the current state of our theoretical understanding of these outflows is reviewed. Beginning with Planetary Nebulae considerable progress has been made in understanding bipolar outflows as the result of stellar winds interacting with the circumstellar environment. In what has been called the “Generalized Wind Blown Bubble” (GWBB) scenario, a fast tenuous wind from the central star expands into a ambient medium with an aspherical (toroidal) density distribution. Inertial gradients due to the gaseous torus quickly lead to an expanding prolate or bipolar shell of swept-up gas bounded by strong shock waves. Numerical simulations of the GWBB scenario show a surprisingly rich variety of gasdynamical behavior, allowing models to recover many of the observed properties of stellar bipolar outflows including the development of collimated supersonic jets. In this paper the physics behind the GWBB scenario is reviewed in detail and its strengths and weakness are considered. Alternative models involving MHD processes are also examined. Applications of these models to each of the principle classes of stellar bipolar outflow (YSO, PNe, LBV, SN87A) are then reviewed. Outstanding issues in the study of bipolar outflows are considered as are those questions which arise when the outflows are viewed as a single class of phenomena occurring across the HR diagram.  相似文献   

11.
We present results of 2-D hydrodynamical simulations of a radiatively driven stellar wind from a rapidly rotating Be-star. These generally confirm predictions of the semi-analytic Wind-Compressed-Disk model recently proposed by Bjorkman and Cassinelli to explain the circumstellar disks inferred observationally to exist around such rapidly rotating stars. However, our numerical simulations are able to incorporate several important effects not accounted for in the simple model, including a dynamical treatment of the outward radiative driving and gas pressure, as well as a rotationally distorted, oblate stellar surface. This enables us to model quantitatively the compressed wind and shock that forms the equatorial disk. The simulation results thus do differ in several important details from the simple model, showing, for example, an inner diskinflow not possible in the heuristic approach of assuming a fixed outward velocity law. There is also no evidence for the predicted detachment of the disk that arises in the fixed outflow picture. The peak equatorward velocity in the dynamical models is furthermore about a factor of two smaller than the analytically predicted value of 50% the stellar equatorial rotation speed. As a result, the dynamical disks are somewhat weaker than predicted, with a wider opening angle, lower disk/pole density ratio, and smaller shock velocity jump (each by roughly the same factor of two).  相似文献   

12.
Based on the model of interaction between spherically symmetric expanding matter and the external medium, we have estimated the parameters of the matter heated by the shock that was produced in the envelope ejected by the explosion of a classical nova during its interaction with the stellar wind from the optical companion. Using this model, we have shown that the matter ejected during the outburst in the system CI Camelopardalis had no steep velocity gradients and that the reverse shock could heat the ejected matter only to a temperature of ∼0.1 keV. Therefore, this matter did not contribute to the mean temperature and luminosity of the system observed in the energy range 3–20 keV.  相似文献   

13.
《New Astronomy Reviews》1999,43(1):67-77
There is a growing number of observational indicators for the presence of bipolar outflows in massive, young stellar objects that are still accreting mass as part of their formation process. In particular, there is evidence that the outflows from these objects can attain higher velocities and kinetic luminosities than their lower-mass counterparts. Furthermore, the higher-mass objects appear to smoothly continue the correlation found in T Tauri stars between outflow and accretion signatures, and in several cases there are direct clues to the existence of a circumstellar disk from optical and infrared imaging and spectroscopy as well as from millimeter-wavelength interferometry. These results suggest that the disk-outflow connection found in low-mass pre-main-sequence stars extends to more massive objects, and that a similar physical mechanism may drive the outflows in both cases. We examine the observational basis for this hypothesis and consider how the commonly invoked centrifugally driven wind models of bipolar outflows in low-mass stars would be affected by the various physical processes (such as photoionization, photoevaporation, radiation pressure, and stellar wind ram pressure) that operate in higher-mass stars. We then list some of the interesting questions that one could hope to address as this young field of research continues to develop.  相似文献   

14.
The propagation of a magnetogasdynamic shock wave originating in a stellar interior, is ocnsidered when it approaches the surfaces of the star. The flow behind the shock wave is assumed isothermal rather than adiabatic to stimulate the conditions of large radiative transfer near the stellar surface. The product solution of McVittie has been used to obtain exact solution of the problem. It has been obtained that velocity, density, pressure and magnetic field increases as we move from shock surface towards the nucleus of the star.  相似文献   

15.
During the previous years spacecraft observations of so-called Energetic Neutral Atoms (ENAs) have become an important remote-sensing technique in planetary science for analyzing the solar wind plasma flow around the upper atmospheric environments of Solar System bodies. ENAs are produced whenever solar- or stellar wind protons interact via charge exchange with a neutral particle from a planetary atmosphere so that their signals constrain both, ion distributions and neutral gas densities. The observation of ENAs which have been generated due to charge exchange with stellar wind plasma have been used for the indirect mass loss and stellar wind property estimation of Sun-like stars by observing the interaction regions carved out by the collisions between stellar winds and the interstellar medium. In this work we review ENA-observations and data interpretations at Solar System planets and recent hydrogen-cloud observations in UV Lyman-α absorption around hydrogen-rich extra-solar gas giants. We discuss the production of stellar wind related hydrogen ENA-clouds around close-in exoplanets and show how a detailed analysis of attenuation spectra obtained for transiting hydrogen-rich close-in gas giants can be used for the study of the upper atmosphere structure, the planet’s magnetosphere and to obtain information on stellar wind properties. Finally, we discuss how future hydrogen cloud observations around exoplanets by space observatories like the Russia-led World Space Observatory-UV (WSO-UV) together with ESAs planned PLATO mission can be used for the reconstruction of the solar wind history or the test of magnetosphere evolution hypotheses.  相似文献   

16.
Very Large Array surface brightness and spectral index maps of the evolving extended emission of the triple symbiotic star CH Cygni are presented. These are derived from observations at 4.8, 8.4 and 14 GHz between 1985 and 1999. The maps are dominated by thermal emission around the central bright peak of the nebula, but we also find unambiguous non-thermal emission associated with the extended regions. Our observations confirm that this is a jet. The central region has been associated with the stellar components through Hubble Space Telescope imaging. If the jets are the result of ejection events at outburst, expansion velocities are consistent with those from other measurement methods. We propose that the non-thermal emission is caused by material ejected in the bipolar jets interacting with the circumstellar wind envelope. The resulting shocks lead to local enhancements in the magnetic field from the compact component of the order of 3 mG.  相似文献   

17.
The pumping of 22.2-GHz H2O masers in the circumstellar envelopes of asymptotic giant branch stars has been simulated numerically. The physical parameters adopted in the calculations correspond to those of the circumstellar envelope around IK Tau. The one-dimensional plane-parallel structure of the gas-dust cloud is considered. The statistical equilibrium equations for the H2O level populations and the thermal balance equations for the gas-dust cloud are solved self-consistently. The calculations take into account 410 rotational levels belonging to the five lowest vibrational levels of H2O. The stellar radiation field is shown to play an important role in the thermal balance of the gas-dust cloud due to the absorption of emission in rotational-vibrational H2O lines. The dependence of the gain in the 22.2-GHz maser line on the gas density and H2O number density in the gas-dust cloud is investigated. Gas densities close to the mean density of the stellar wind, 107?108 cm?3, and a high relative H2O abundance, more than 10?4, have been found to be the most likely physical conditions in maser sources.  相似文献   

18.
We present the results of our numerical simulations of the cyclic brightness modulation in young binary systems with eccentric orbits and low-mass secondary components. We suggest that the binary components accrete matter from the remnants of the protostellar cloud, with the main accretor (according to current models) being the low-mass component. The brightness variations of the primary are attributable to the periodic extinction variations on the line of sight caused by the disk wind from the secondary and by the common envelope produced by this wind. The distribution of matter in the envelope was calculated in the ballistic approximation. When calculating the optical effects produced by the dust component of the disk wind, we adopted the dust-to-gas mass ratio of 1:100 characteristic of the interstellar medium and the optical parameters of the circumstellar dust typical of young stars. Our calculations show that the theoretical light curves for binaries with elliptical orbits exhibit a wider variety of shapes than those for binaries with circular orbits. In this case, the parameters of the photometric minima (their depth, duration, and shape of the light curve) depend not only on the disk-wind parameters and the orbital inclination of the binary to the line of sight, but also on the longitude of the periastron. We investigate the modulation of the scattered radiation from the common envelope with orbital phase in the single-scattering approximation. The modulation amplitude is shown to be at a maximum when the system is seen edge-on and to be also nonzero in binaries seen pole-on. We discuss possible applications of the theory to young stellar objects. In particular, several model light curves have been found to be similar to those of candidate FU Orionis stars (FUORs).  相似文献   

19.
The initial stages of deceleration in the circumstellar medium of a stellar envelope, thrown off by a shock wave, are investigated. The equations of spherical-symmetric adiabatic hydrodynamics are shown to have a similarity solution in the case of the density of the expanding envelope being approximated by a reasonable power law. The overall flow pattern has such a form that the stellar material is decelerated in the internal shock wave while another shock propagates through the circumstellar matter. Between the shocks there is a contact discontinuity separating the circumstellar and stellar matter. The characteristics of the similarity solution are calculated for various exponents in the density laws of an expanding envelope and circumstellar matter and for two values of the adiabatic index (=5/3, 4/3). Some parts of the flow exhibit Rayleigh-Taylor instability.Special attention is paid to the validity of the hydrodynamics. In full agreement with D'yachenkoet al. (1969), we conclude that the kinetic and collisionless processes are of great importance if the initial stages of stellar envelope deceleration are to be properly monitored.The results obtained can also be employed to describe the interaction between the exploding core of a red giant star and its rarefied envelope. This is of interest for explosive nucleosynthesis.The similarity solution is applied to the envelopes expelled both by type-II supernovae and by rapid novae. In particular, the thermalization time-scale of circumstellar plasma is estimated. For SNii this time-scale proves to be of the order of 60 yr. This confirms with the observational data on the moment of the maximum radio-emission of young SNRs. In the case of rapid novae, this time is less by a factor of 10. Therefore, the peak radio and X-ray (2 keV) lumnosity may occur several years after the rapid nova outburst. The explosion of a degenerate carbon core is found to result in the heating of the hydrogen-helium envelope of a red giant star up to 3×106 K.  相似文献   

20.
I examine the question of purely accreting protostars, and set limits to the breakout time of a protostellar wind within the accretion flow forming the new star. Hypothesizing a wind launched from the protostellar surface, three temporal phases are derived: a crushed wind, a trapped wind, and an escaping wind. In the current model, evolution from one phase to the next is a consequence of the growing anisotropy of the infalling flow, a natural outcome of the collapse of a rotating cloud core. During the crushed wind phase, infall overcomes the wind at all solid angles, and the accretion directly strikes the protostellar surface. The trapped phase consists of a wind sufficiently strong to push material back from the stellar surface, but too weak to carry the heavy, shocked and swept-up infall out of the star's gravitational potential. Unless the wind turns on impulsively, a significant fraction of the pre-breakout life of the protostar may be spent in this trapped wind phase in which gas is launched from the protostar but is pulled back, crashing onto the protostellar and disk surfaces. It may be that some `starless cores' contain as-yet undetected, very young accreting protostars, and that episodic luminosity fluctuations associated with this trapped wind could be observed.  相似文献   

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