共查询到20条相似文献，搜索用时 25 毫秒
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Fast rotation of compact stars (at sub-millisecond period) and, in particular, their stability, are sensitive to the equation of state (EOS) of dense matter. Recent observations of XTE J1739-285 suggest that it contains a neutron star rotating at 1122 Hz. At such rotational frequency the effects of rotation on star’s structure are significant. We study the interplay of fast rotation, EOS, and gravitational mass of a sub-millisecond pulsar. We discuss the EOS dependence of spin-up to a sub-millisecond period, via mass accretion from a disk in a low-mass X-ray binary. 相似文献
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J. C. Sherman 《Astrophysics and Space Science》1973,24(2):459-485
A review is given of the experimental investigations concerning the critical velocity of the interaction between a neutral
gas and a plasma in relative motion. In most of the experiments this critical velocity is equivalent to a voltage limitation
of a discharge through a partially ionized magnetized plasma. The critical velocity phenomenon can have been of importance
in a large number of experiments but it has been observed in rather few cases and studied in detail in less than half a dozen
plasma machines. The major investigations were made in rotating plasma devices like the Homopolar, plasma guns and a plasma-neutral
gas impact experiment. The emphasis of this paper is concentrated, though not limited, to collision-free plasmas. Thus the
(MPD-)arc experiments are not extensively treated. It is concluded that the existence, under certain conditions, of a critical
velocity, critical voltage or criticalE/B (depending on the particular observation) is proved by sufficient experimental evidence.
In a following article in this issue by J. Sherman the theoretical work in the same field is discussed. 相似文献
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The stability of a rotating gas-dust gravitating disk in the zone of a possible inflection in the angular velocity is examined
theoretically. The stability limits are found for a rather wide range of curves in a special model of a dusty, pressure-free
medium with the general gravitational field of the galaxy taken into account. Applications to real galaxies are discussed.
Translated from Astrofizika, Vol. 51, No. 4, pp. 523–533 (November 2008). 相似文献
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The behaviour of a subsystem of a many-body problem may be studied using the hierarchical relative coordinates defined by Nugeyre and Bouvier (1981), The present article employs a notation allowing the position vectors of the particles to be expressed explicity as functions of the hierarchical relative coordinates, This machinery is used to generalize a result of Patnaik's (1975) concerning escape from a many-body system. 相似文献
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L. V. Kozak R. I. Kostyk O. K. Cheremnykh 《Kinematics and Physics of Celestial Bodies》2013,29(2):66-70
Observations obtained at the 70-cm vacuum tower telescope (VTT) at Izaña (Tenerife, Spain) are analyzed to show that turbulent processes in the solar photosphere have two distinct spectra of turbulence. The first is the well-known Kolmogorov spectrum, which describes plasmas with a zero mean magnetic field, and the second is the Kraichnan spectrum with a nonzero mean magnetic field. The transition from one spectrum type to another is found to occur at a scale of 3 Mm. This scale is consistent with the typical size of mesogranular structures, which indicates a transition to large-scale self-organizing magnetic structures. 相似文献
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The atmospheric circulation of Titan is investigated with a general circulation model. The representation of the large-scale dynamics is based on a grid point model developed and used at Laboratoire de Météorologie Dynamique for climate studies. The code also includes an accurate representation of radiative heating and cooling by molecular gases and haze as well as a parametrization of the vertical turbulent mixing of momentum and potential temperature. Long-term simulations of the atmospheric circulation are presented. Starting from a state of rest, the model spontaneously produces a strong superrotation with prograde equatorial winds (i.e., in the same sense as the assumed rotation of the solid body) increasing from the surface to reach 100 m sec-1 near the 1-mbar pressure level. Those equatorial winds are in very good agreement with some indirect observations, especially those of the 1989 occultation of Star 28-Sgr by Titan. On the other hand, the model simulates latitudinal temperature contrasts in the stratosphere that are significantly weaker than those observed by Voyager 1 which, we suggest, may be partly due to the nonrepresentation of the spatial and temporal variations of the abundances of molecular species and haze. We present diagnostics of the simulated atmospheric circulation underlying the importance of the seasonal cycle and a tentative explanation for the creation and maintenance of the atmospheric superrotation based on a careful angular momentum budget. 相似文献
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D. M. Sedrakian 《Astrophysics》2000,43(3):275-281
The influence of the effect of entrainment of superconducting protons by superfluid neutrons on the distribution of neutron
vortices in a rotating neutron star is investigated. It is shown that the proton vortex clusters generated by entrainment
currents create the magnetic structure of a neutron vortex. The average magnetic field induction in a neutron vortex is calculated.
The presence of the magnetic field of a neutron vortex considerably alters the radius of the vortex zone. The width of the
vortex-free zone at the surface of the neutron star’s core increases, reaching macroscopic values on the order of several
meters. This result considerably changes earlier concepts of the distribution of neutron vortices in a neutron star.
Translated from Astrofizika, Vol. 43, No. 3, pp. 377-386, July–September, 2000. 相似文献
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William B. Heard 《Astrophysics and Space Science》1976,43(1):63-82
The dynamics of an ensemble of particles emanating from a common point with a distribution of velocities is modeled as a continuum of particles described by a phase space distribution function. A general solution for the distribution function and the associated spatial density function is obtained for a general dynamical system. The special cases of linear dynamical systems and slow dispersion from a circular orbit are treated in detail. A transcendental equation is derived, the roots of which determine the time since initial dispersion from knowledge of the spatial density function at later times. 相似文献
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A. P. Markeev 《Astronomy Letters》2005,31(9):627-633
We investigate the stability of the periodic motion of a satellite, a rigid body, relative to the center of mass in a central Newtonian gravitational field in an elliptical orbit. The orbital eccentricity is assumed to be low. In a circular orbit, this periodic motion transforms into the well-known motion called hyperboloidal precession (the symmetry axis of the satellite occupies a fixed position in the plane perpendicular to the radius vector of the center of mass relative to the attractive center and describes a hyperboloidal surface in absolute space, with the satellite rotating around the symmetry axis at a constant angular velocity). We consider the case where the parameters of the problem are close to their values at which a multiple parametric resonance takes place (the frequencies of the small oscillations of the satellite’s symmetry axis are related by several second-order resonance relations). We have found the instability and stability regions in the first (linear) approximation at low eccentricities. 相似文献
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Peter Bodenheimer 《Icarus》1977,31(3):356-368
The planet Jupiter is assumed to have formed as a subcondensation in the solar nebula. The initial phase of its evolution is one of hydrostatic contraction with radiative energy transport. Calculations of evolutionary sequences through this phase are presented, including the effects of angular momentum. The calculations are carried out in two space dimensions under the assumptions of axial symmetry, constancy of angular velocity on cylindrical surfaces about the rotation axis, a pressure-density relation given by the polytrope of index 3, conservation of angular momentum, and a homogeneous composition. The results show that under certain physically reasonable initial distributions of density and angular momentum the formation of a central planet and a rotating circumplanetary envelope is possible, while under assumptions a point of instability is reached that probably results in the breakup of the condensation by fission into two or more parts. The models are discussed with reference to the present angular momenta of Jupiter and its regular satellites. 相似文献
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Bibhas R. De 《Solar physics》1973,31(2):437-447
A mechanism is suggested for the formation of loop-type prominences in solar-active regions following flare events. The mechanism is based on the already existing idea of compression of a coronal plasma element resulting in enhanced radiation and consequent cooling of the element. A model is suggested for such a compression based on the concept of a contracting, force-free filamentary structure. If the current in a filament increases with time, then there is a radial contraction of the filament. Since the coronal plasma is frozen into the magnetic field lines of the filament, a contraction of the filament causes a compression of the filamentary plasma. This model of compression is shown to be in approximate qualitative and quantitative agreement with observations. 相似文献
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V. Belokurov M. G. Walker N. W. Evans G. Gilmore M. J. Irwin M. Mateo L. Mayer E. Olszewski J. Bechtold T. Pickering 《Monthly notices of the Royal Astronomical Society》2009,397(4):1748-1755
We announce the discovery of a new Milky Way satellite Segue 2 found in the data of the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We followed this up with deeper imaging and spectroscopy on the Multiple Mirror Telescope (MMT). From this, we derive a luminosity of M v =−2.5 , a half-light radius of 34 pc and a systemic velocity of ∼−40 km s−1 . Our data also provide evidence for a stream around Segue 2 at a similar heliocentric velocity, and the SEGUE data show that it is also present in neighbouring fields. We resolve the velocity dispersion of Segue 2 as 3.4 km s−1 and the possible stream as ∼7 km s−1 . This object shows points of comparison with other recent discoveries, Segue 1, Boo II and Coma. We speculate that all four objects may be representatives of a population of satellites of satellites – survivors of accretion events that destroyed their larger but less dense parents. They are likely to have formed at redshifts z > 10 and are good candidates for fossils of the reionization epoch. 相似文献
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S. I. Syrovatski 《Astrophysics and Space Science》1969,4(2):246-251
The motion of a plasma in a time-dependent dipole magnetic field is considered. It is shown that the increase of the magnetic moment of the dipole (for example, as the result of the explosion of a magnetic star) leads to a concentration of a plasma in the polar regions. Likewise, a decrease of the magnetic moment (contraction of a star) would lead to the concentration of surrounding plasma in the equatorial plane. This process may be of importance in astrophysics and, particularly, in the dynamics of nebulae and non-stationary star envelopes.Translated from the Russian by P. Foukal and D. F. Smith. 相似文献
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Time scales of the transition from contact binary systems of the W UMa type to single stars of the blue straggler type are estimated. A model of one-way mass transfer from the primary component to the companion inside a common envelope (Eggen et al.) and a model of a contact binary lying on the zero-age main sequence with a companion that is losing mass (F. van't Veer) are used to calculate these scales. The merging times of components were calculated for 304 contact systems of the W UMa type from the Catalog of Approximate Photometric and Absolute Elements of Eclipsing Variable Stars on a scale of loss of mass and orbital angular momentum due to magnetic braking, under the assumption of synchronization of the axial rotation and orbital revolution. On the basis of the resulting statistics, the characteristic merging scales are 0.4-0.6 and 0.5-0.7 Gyr, respectively, for the above two models. The results of a comparison with the work of other authors are discussed. 相似文献