共查询到20条相似文献，搜索用时 15 毫秒
1.
N. R. Ikhsanov 《Astrophysics》2005,48(3):400-410
In the evolutionary tracks of magnetized compact stars the subsonic propeller state is intermediate between the supersonic propeller and accretor states. The rotation rate of a star in this stage decreases because of the interaction of its magnetosphere with the surrounding hot quasistatic shell. The radius of the magnetosphere is less than the corotation radius, and the boundary of the magnetosphere is stable with respect to inter-change instabilities. The mass flow rate from the inner radius of the shell to the surface of the compact object is limited by the rate at which plasma diffuses into the magnetic field of the star. Because of this, a subsonic propeller will show up as a low (or moderate) luminosity accretion pulsar with a soft x-ray spectrum.__________Translated from Astrofizika, Vol. 48, No. 3, pp. 477–490 (August 2005). 相似文献
2.
We analyze the statistical distribution of neutron stars at the stage of a supersonic propeller. An important point of our analysis is allowance for the evolution of the angle of inclination of the magnetic axis to the spin axis of the neutron star for the boundary of the transition to the supersonic propeller stage. We have determined the spin period distributions of pulsars at the propeller stage for two models: the model with hindered particle escape from the stellar surface and the model with free particle escape. As a result, we have shown that consistent allowance for the evolution of the inclination angle in the region of extinct radio pulsars for the two models leads to an increase in the total number of neutron stars at the supersonic propeller stage. This increase stems from the fact that when allowing for the evolution of the inclination angle χ for neutron stars in the region of extinct radio pulsars and, hence, for the boundary of the transition to the propeller stage, this transition is possible at shorter spin periods (P ～ 5–10 s) than assumed in the standard model. 相似文献
3.
Zi-Bo Jiang Xiang-Dong Li Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2005,5(5):487-494
Disks originating from supernova fallback have been suggested to surround young neutron stars. Interaction between the disk and the magnetic field of the neutron star may considerably influence the evolution of the star through the so called propeller effect. There are many controversies about the efficiency of the propeller mechanism proposed in the literature. We investigate the fallback disk-involved spin-down of young pulsars. By comparing the simulated and measured results of pulsar evolution, we present some possible constraints on the propeller torques exerted by the disks on neutron stars. 相似文献
4.
Steven W. Stahler Jeffrey J. Yen 《Monthly notices of the Royal Astronomical Society》2009,396(1):579-588
The dense molecular cloud cores that form stars, like other self-gravitating objects, undergo bulk oscillations. Just at the point of gravitational instability, their fundamental oscillation mode has zero frequency. We study, using perturbation theory, the evolution of a spherical cloud that possesses such a frozen mode. We find that the cloud undergoes a prolonged epoch of subsonic, accelerating contraction. This slow contraction occurs whether the cloud is initially inflated or compressed by the oscillation. The subsonic motion described here could underlie the spectral infall signature observed in many starless dense cores. 相似文献
5.
By using a non-local convection theory, both the local and nonlocal convective envelope models of evolutionary series of stars with masses from 1 to 30 solar masses are calculated. The problem of supersonic convection is reviewed. The results show that the convective velocities in the stellar atmosphere are seriously overestimated by the local mixing-length theory. Convection is strongly supersonic in the atmospheres of yellow giant and super-giants, while the local mixing-length theory is used. However, it becomes subsonic for most stars when convection returns to the normal nonlocal treatment. Convection velocities increase with increase of luminosities of stars. There is still weak supersonic convection in few red and yellow giant and super-giants. It is suspected whether this supersonic convection in stellar atmospheres is true. 相似文献
6.
By performing Monte-Carlo calculations of the spin-down of young pulsars surrounded by a supernova fallback disk, we present
possible constraints on the propeller torques exerted by the disks on neutron stars.
This work was supported by the National Natural Science Foundation of China. 相似文献
7.
1引言尽管有诸多的不满之处,由于其物理上的直观性和应用上的简单性,至今混合长理论仍几乎是唯一一个广泛用于恒星结构、演化和脉动计算的恒星对流理论.混合长理论预言,在红、黄巨星和超巨星大气中,对流是超声速的.我们曾指出,混合长理论隐含了一个假定,对流是亚声速的.对于超声速对流,无论从物理的真实性,还是从混合长公式的数学表述来看,混合长理论都是不正确的.因此超声对流的真实性是存在问题 相似文献
8.
V. Urpin D. Konenkov & U. Geppert 《Monthly notices of the Royal Astronomical Society》1998,299(1):73-77
We consider the evolution of neutron stars during the X-ray phase of high-mass binaries. Calculations are performed assuming a crustal origin of the magnetic field. A strong wind from the companion can significantly influence the magnetic and spin behaviour of a neutron star even during the main-sequence life of the companion. In the course of evolution, the neutron star passes through four evolutionary phases ('isolated pulsar', propeller, wind accretion, and Roche lobe overflow). The model considered can naturally account for the observed magnetic fields and spin periods of neutron stars, as well as the existence of pulsating and non-pulsating X-ray sources in high-mass binaries. Calculations also predict the existence of a particular sort of high-mass binary with a secondary that fills its Roche lobe and a neutron star that does not accrete the overflowing matter because of fast spin. 相似文献
9.
A. Rodríguez-González J. Cantó A. Esquivel A. C. Raga P. F. Velázquez 《Monthly notices of the Royal Astronomical Society》2007,380(3):1198-1206
We present the analytic and numerical models of the 'cluster wind' resulting from the multiple interactions of the winds ejected by the stars of a dense cluster of massive stars. We consider the case in which the distribution of stars (i.e. the number of stars per unit volume) within the cluster is spherically symmetric, has a power-law radial dependence, and drops discontinuously to zero at the outer radius of the cluster. We carry out comparisons between an analytic model (in which the stars are considered in terms of a spatially continuous injection of mass and energy) and 3D gasdynamic simulations (in which we include 100 stars with identical winds, located in 3D space by statistically sampling the stellar distribution function). From the analytic model, we find that for stellar distributions with steep enough radial dependencies, the cluster wind flow develops a very high central density and a non-zero central velocity, and for steeper dependencies, it becomes fully supersonic throughout the volume of the cluster (these properties are partially reproduced by the 3D numerical simulations). Therefore, the wind solutions obtained for stratified clusters can differ dramatically from the case of a homogeneous stellar distribution (which produces a cluster wind with zero central velocity, and a fully subsonic flow within the cluster radius). Finally, from our numerical simulations, we compute predictions of X-ray emission maps and luminosities, which can be directly compared with observations of cluster wind flows. 相似文献
10.
We discuss dust formation in steady state dust driven winds around oxygen-rich AGB stars, including not only homogeneous Al2O3 and silicate grains but also heterogeneous grains consisting of an Al2O3 core and a silicate mantle. In the inner subsonic region, Al2O3 grains with radii of ∼ 0.15 μm condense first, then condensation of silicate on Al2O3 starts slightly inside the sonic point, which accelerates the gas flow into the supersonic region. Also small silicate grains,
whose radii are a few tens of ?ngstroms form beyond the sonic point. The carrier of 13 μm feature observed towards oxygen-rich
AGB stars is considered to be the core-mantle grains consisting of an α-Al2O3 core and a silicate mantle from the radiation transfer calculations based on the results of dust formation calculations.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
11.
12.
Anticipating forthcoming Chandra X-ray observations, we describe the continuation of interstellar cooling flows deep into the cores of elliptical galaxies. Interstellar gas heated to T>1 keV in the potential of massive black holes (r less, similar50 pc) should be visible unless thermal heating is diluted by nonthermal pressure. Since our flows are subsonic near the massive black holes, distributed cooling continues within approximately 300 pc. Dark, low-mass stars formed in this region may be responsible for some of the mass attributed to central black holes. 相似文献
13.
The state of supranuclear matter in compact stars remains puzzling, and it is argued that pulsars could be strangeon stars. What would happen if binary strangeon stars merge? This kind of merger could result in the formation of a hyper-massive strangeon star, accompanied by bursts of gravitational waves and electromagnetic radiation(and even a strangeon kilonova explained in the paper). The tidal polarizability of binary strangeon stars is different from that of binary neutron stars, because a strangeon star is self-bound on the surface by the fundamental strong force while a neutron star by the gravity, and their equations of state are different. Our calculation shows that the tidal polarizability of merging binary strangeon stars is favored by GW170817. Three kinds of kilonovae(i.e., of neutron, quark and strangeon) are discussed, and the light curve of the kilonova AT 2017 gfo following GW170817 could be explained by considering the decaying strangeon nuggets and remnant star spin-down. Additionally,the energy ejected to the fireball around the nascent remnant strangeon star, being manifested as a gamma-ray burst, is calculated. It is found that, after a prompt burst, an X-ray plateau could follow in a timescale of 10~2-10~3 s. Certainly, the results could be tested also by further observational synergies between gravitational wave detectors(e.g., Advanced LIGO) and X-ray telescopes(e.g., the Chinese HXMT satellite and e XTP mission), and especially if the detected gravitational wave form is checked by peculiar equations of state provided by the numerical relativistical simulation. 相似文献
14.
A. R. Harutyunyan 《Astrophysics》2002,45(2):248-251
Models of neutron stars with a quark core are calculated on the basis of an extensive set of equations of state for superdense matter. The possible existence of a new branch of stable layered neutron stars is revealed for some realistic equations of state of neutron matter. 相似文献
15.
Trapezium type multiple stars are centers of star formation in stellar associations. Theoretical and observational studies
show that they are dynamically instable. Due to the special space configurations of the components, Trapezium type multiple
stars disintegrate completely or partly after several rotations around their centers. These stars have a main role in the
origin and evolution of stars on OB- and T-associations. According to observations of 15 Trapezium type multiple stars having
the brightest star of OB-class 14 are in expansion. The age of the Trapezium type multiple stars is of the order of 21(P years.
There are weighty arguments to assume that the majority of them are in a state of expansion with positive total energy.
Translated from Abastumani Astrophysical Observatory, Academy of Sciences, Georgia. Published in Astrofizika, Vol. 41, No.
1, pp. 91–100, January-March, 1998. 相似文献
16.
We analyze the most powerful X-ray outbursts from neutron stars in eleven Magellanic high-mass X-ray binaries and three pulsating ultraluminous X-ray sources. Most of the outbursts rise to L_(max) which is about the level of the Eddington luminosity, while the remaining more powerful outbursts also appear to recognize that limit when their emissions are assumed to be anisotropic and beamed toward our direction. We use the measurements of pulsar spin periods P_S and their derivatives P_S to calculate the X-ray luminosities L_p in their faintest accreting("propeller-line") states. In five cases with unknown P_S, we use the lowest observed X-ray luminosities, which only adds to the heterogeneity of the sample. Then we calculate the ratios L_p/L_(max) and we obtain an outstanding confluence of theory and observations from which we conclude that work done on both fronts is accurate and the results are trustworthy: sources known to reside on the lowest Magellanic propeller line are all located on/near that line, whereas other sources jump higher and reach higher-lying propeller lines. These jumps can be interpreted in only one way, higher-lying pulsars have stronger surface magnetic fields in agreement with previous empirical results in whichP_S and L_p values were not used. 相似文献
17.
S. Chandrasekhar 《Journal of Astrophysics and Astronomy》1994,15(2):119-125
It is shown that forall stars for which the radiation-pressure is greater than a tenth of the total pressure, an appeal to theFebmi-Dirac statistics to avoid the central singularity which arises in the discussions of the centrally condensed and the collapsed stars cannot be made. The bearing of this result on the possible state of matter in the interior of stars is indicated. 相似文献
18.
Javier Ballesteros-Paredes 《Astrophysics and Space Science》2004,292(1-4):193-205
We review the main results from recent numerical simulations of turbulent fragmentation and star formation. Specifically, we discuss the observed scaling relationships, the “quiescent” (subsonic) nature of many star-forming cores, their energy balance, their synthesized polarized dust emission, the ages of stars associated with the molecular gas from which they have formed, the mass spectra of clumps, and the density and column density probability distribution function of the gas. We then give a critical discussion on recent attempts to explain and/or predict the star formation efficiency and the stellar initial mass function from the statistical nature of turbulent fields. Finally, it appears that turbulent fragmentation alone cannot account for the final stages of fragmentation: although the turbulent velocity field is able to produce filaments, the spatial distribution of cores in such filaments is better explained in terms of gravitational fragmentation. 相似文献
19.
Cornelis de Jager 《Astronomy and Astrophysics Review》1998,8(3):145-180
We list the main stellar data of known hypergiants and similarly luminous stars, and then concentrate on a review of the
yellow hypergiants. These stars are post-red supergiants evolving along blueward loops in the Hertzsprung-Russell diagram.
Their properties, their location in the Hertzsprung-Russell diagram and their occasional mass ejections are related to a region
of atmospheric instability in the H-R diagram, the Yellow Void. The ‘bouncing against the border of the Void’ of three objects:
Cas, HR8752 and IRC+10420, is described. The apparent atmospheric instability of yellow hypergiants is related to the atmospheric
pulsations. There are indications that the approach to the Void is associated with an increased amplitude of the pulsation
and with enhanced mass loss. The observed small-scale motion field is only apparently strongly supersonic; the observed large
stochastic velocities are the quasi-stochastically varying thermal motions in the many hot sheets that occur in the wakes
of many small shocks, while the real hydrodynamic velocity component is small and subsonic. This shock-wave field is also
responsible for the observed rate of mass loss and for emission in the wings of H. Most yellow hypergiants have envelopes containing gas and dust, but a thick extended envelope, presumably dissipating and
showing bipolar outflow, is only known around IRC+10420. At the interface of the bipolar wind and the interstellar medium
one or more stationary shocks may develop as is observed in the case of IRC+10420 and suspected with Cas.
Received 1 July 1997 相似文献