共查询到20条相似文献，搜索用时 406 毫秒
1.
Delaney Farrell Fridolin Weber Jia Jie Li Armen Sedrakian 《Astronomische Nachrichten》2024,345(2-3):e230160
Neutron stars may experience differential rotation on short, dynamical timescales following extreme astrophysical events like binary neutron star mergers. In this work, the masses and radii of differentially rotating neutron star models are computed. We employ a set of equations of states for dense hypernuclear and -admixed-hypernuclear matter obtained within the framework of CDF theory in the relativistic Hartree-Fock (RHF) approximation. Results are shown for varying meson- couplings, or equivalently the -potential in nuclear matter. A comparison of our results with those obtained for nonrotating stars shows that the maximum mass difference between differentially rotating and static stars is independent of the underlying particle composition of the star. We further find that the decrease in the radii and increase in the maximum masses of stellar models when -isobars are added to hyperonuclear matter (as initially observed for static and uniformly rotating stars) persist also in the case of differentially rotating neutron stars. 相似文献
2.
A. Allen 《Astrophysics and Space Science》2004,292(1-4):361-364
Theoretical models of star formation from the collapse of molecular cloud cores have been evolving in complexity for many years. This work describes the evolution of models from the nonrotating, nonmagnetized singular isothermal sphere to rotating, magnetized singular isothermal toroids. Four members of the same family are studied–the four combinations of nonrotation/rotation and nonmagnetization/magnetization. It is found that although rotation alone can hinder collapse to a pointmass, addition of braking from a magnetic field can transport away much of the angular momentum upward in a low-velocity outflow during the collapse phase. For all magnetized cases, accretion proceeds at a constant rate similar to that of the isothermal sphere. 相似文献
3.
Arun V. Thampan & Bhaskar Datta 《Monthly notices of the Royal Astronomical Society》1998,297(2):570-578
We calculate the disc and boundary layer luminosities for accreting rapidly rotating neutron stars with low magnetic fields in a fully general relativistic manner. Rotation increases the disc luminosity and decreases the boundary layer luminosity. A rapid rotation of the neutron star substantially modifies these quantities as compared with the static limit. For a neutron star rotating close to the centrifugal mass shed limit, the total luminosity has contribution only from the extended disc. For such maximal rotation rates, we find that well before the maximum stable gravitational mass configuration is reached, there exists a limiting central density, for which particles in the innermost stable orbit will be more tightly bound than those at the surface of the neutron star. We also calculate the angular velocity profiles of particles in Keplerian orbits around the rapidly rotating neutron star. The results are illustrated for a representative set of equation of state models of neutron star matter. 相似文献
4.
S. S. Gershtein 《Astronomy Letters》2000,26(11):730-735
It is hypothesized that thermonuclear burning of the matter from the envelope of a massive compact star accreting onto a hot neutron star produced by spherically symmetric collapse of a stellar iron core can proceed in oscillation mode (much as is the case during thermal explosions of carbon-oxygen cores in lower mass stars). Local density oscillations near the neutron-star surface can generate shock waves; in these shocks, the electron-positron plasma is stratified from the remaining matter, and shells of an expanding relativistic fireball with an oscillation time scale in cosmological gamma-ray bursts (GRBs) of ～10?2 s are formed. It is pointed out that the GRB progenitors can be nonrotating massive Wolf-Rayet (WR) stars whose collapse, according to observational data, can proceed without any substantial envelope ejection. 相似文献
5.
Sunetra Giridhar N. Kameswara Rao David L. Lambert 《Journal of Astrophysics and Astronomy》1992,13(4):307-318
A detailed spectroscopic investigation of LR Sco which was earlier misclassified as R CrB star is made. Atmospheric parameters
and elemental abundances are determined using detailed depth-dependent model atmospheres and line synthesis technique. Most
of the elements show near solar abundances.
The strength of circumstellar components seen in Na D lines are used to derive the mass loss rate. Another independent estimate
of mass loss rate is made using the observed infrared flux from 1–100Μm. These two approaches lead to nearly the same value
of mass loss rate whenM
vis assumed to be – 4.5 for this star. 相似文献
6.
We have investigated the interacting winds model (IWM) in which the shapes of elliptical Planetary Nebulae (PNe) can be explained
by the asymmetric mass loss produced by a rotating AGB star. The mass loss mechanism is based on a dust driven wind calculated
for stationary situations. Already for small rotation rates of the AGB star we get a significantly angle-dependent mass loss
which is concentrated towards the equatorial plane. This pole to equator density variation in the space surrounding the star
influences the shape of the later developed PN. We compare these theoretical shapes with observed PNe and for some objects
with well known quantities our model can fit the observations quite well.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
We consider and numerically solve the problem of the relativistic gravitational collapse of a spherically symmetric cool nonrotating white dwarf with allowance for the neutronization kinetics. We propose a model equation of state and analyze the neutronization kinetics under simplifying assumptions. A comprehensive mathematical model is constructed for the phenomenon. The system of equations is integrated numerically. The gravitational collapse of a white dwarf that lost its stability is shown to lead to the envelope ejection and to the final state of a hot static neutron star. For comparison, we solve the problem with an equilibrium equation of state. We show that in this case, the entire mass ultimately goes under the gravitational radius to form a black hole. 相似文献
8.
《天文和天体物理学研究(英文版)》2017,(7)
We present a new tool for color-magnitude diagram(CMD) studies, Powerful CMD. This tool is built based on the advanced stellar population synthesis(ASPS) model, in which single stars, binary stars, rotating stars and star formation history have been taken into account. Via Powerful CMD, the distance modulus, color excess, metallicity, age, binary fraction, rotating star fraction and star formation history of star clusters can be determined simultaneously from observed CMDs. The new tool is tested via both simulated and real star clusters. Five parameters of clusters NGC 6362, NGC 6652, NGC 6838 and M67 are determined and compared to other works. It is shown that this tool is useful for CMD studies, in particular for those utilizing data from the Hubble Space Telescope(HST). Moreover, we find that inclusion of binaries in theoretical stellar population models may lead to smaller color excess compared to the case of single-star population models. 相似文献
9.
《New Astronomy》2013
We investigate the effect of mass on the radiation of a relativistically rotating neutron star. The method of Haxton and Ruffini is used to find the radiation flux from a relativistically rotating neutron star. By extending the idea of a point charge orbiting a black hole, a pulsar is modeled by simulating a relativistically rotating magnetic dipole embedded within a neutron star. The resulting equations retain the mass of the neutron star, thereby introducing effects of general relativity on the radiation from the dipole. We present exact solutions to the modeling equation as well as plots of energy spectra at different rotational velocities and inclination angles. We also present plots of total energy versus mass and two tables containing a comparison of energy ratios. These demonstrate that, for realistic neutron star masses, the high speed enhancement of the radiation is always more than compensated by the frame dragging effect, leading to a net reduction of radiation from the star. It is found that the inclusion of mass not only reduced the special relativistic enhancement, but negates it entirely as the mass of the neutron star approaches the mass limit. 相似文献
10.
F. C. Fekel M. H. Wiliamson M. Weber K. G. Strassmeier D. Pourbaix 《Astronomische Nachrichten》2013,334(3):223-231
We have determined an improved orbit for the bright, evolved, double lined binary γ Canis Minoris. The system has an orbital period of 389.31 days and an eccentricity of 0.2586. We have revised the secondary to primary mass ratio to 0.987. The spectral types of the primary and secondary are K4 III and K1: III, respectively, and the components have a V magnitude difference of 2.2. Orbital fits to the Hipparcos astrometry are not definitive, but they suggest an orbital inclination of ∼ 66°, which produces masses of 1.88 and 1.85 M⊙ for the components. A comparison with evolutionary tracks results in an age of 1.3 Gyr. STELLA very low amplitude radial velocity residuals of the secondary indicate a period of 278 days. We interpret this as the rotation period of the secondary, detectable because of star spots rotating in and out of view. This period is nearly identical to the pseudosynchronous rotation period of the star. The primary is rotating more slowly than its pseudosynchronous rate. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
11.
Christoph Schaab Manfred K. Weigel 《Monthly notices of the Royal Astronomical Society》1999,308(3):718-730
Recently discovered quasi-periodic oscillations in the X-ray brightness of low-mass X-ray binaries are used to derive constraints on the mass of the neutron star component and the equation of state of neutron star matter. The observations are compared with models of rapidly rotating neutron stars which are calculated by means of an exact numerical method in full relativity. For the equations of state we select a broad collection of models representing different assumptions about the many-body structure and the complexity of the composition of superdense matter. The mass constraints differ from their values in the approximate treatment by ∼10 per cent. Under the assumption that the maximum frequency of the quasi-periodic oscillations originates from the innermost stable orbit, the mass of the neutron star is in the range M ∼1.92–2.25 M⊙ . The quasi-periodic oscillation in the Atoll-source 4U 1820−30 in particular is only consistent with equations of state that are rather stiff at high densities, which is explainable, so far, only with pure nucleonic/leptonic composition. This interpretation contradicts the hypothesis that the protoneutron star formed in SN 1987A collapsed to a black hole, since this would demand a maximum neutron star mass below 1.6 M⊙ . The recently suggested identification of quasi-periodic oscillations with frequencies of about 10 Hz with the Lense–Thirring precession of the accretion disc is found to be inconsistent with the models studied in this work, unless it is assumed that the first overtone of the precession is observed. 相似文献
12.
We investigate the general relativistic magnetohydronadynamic (GRMHD) equations for hot plasmas in a Veselago medium around the Reissner-Nordström (RN) black hole. Using the 3+1 formalisms of spacetime, we write the GRMHD equations and perturb them linearly. These are then Fourier analyzed for the magnetized and nonmagnetized plasmas in rotating and nonrotating backgrounds. We derive dispersion relations and analyze the wave properties by the graphs of wave vector, refractive index and change in refractive. The results confirm the presence of Veselago medium for rotating magnetized/nonmagnetized and nonrotating nonmagnetized plasmas. 相似文献
13.
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
14.
Noam Soker 《Monthly notices of the Royal Astronomical Society》1998,299(4):1242-1248
I propose a mechanism for axisymmetrical mass loss on the asymptotic giant branch (AGB) that may account for the axially symmetric structure of elliptical planetary nebulae. The proposed model operates for slowly rotating AGB stars, having angular velocities in the range of 10−4 ω Kep ω 10−2 ωKep , where ωKep is the equatorial Keplerian angular velocity. Such angular velocities could be gained from a planet companion of mass 0.1 M Jupiter , which deposits its orbital angular momentum to the envelope at late stages, or even from single stars that are fast rotators on the main sequence. The model assumes that dynamo magnetic activity results in the formation of cool spots, above which dust forms much more easily. The enhanced magnetic activity towards the equator results in a higher dust formation rate there, and hence higher mass-loss rate. As the star ascends the AGB, both the mass-loss rate and magnetic activity increase rapidly, and hence the mass loss becomes more asymmetrical, with higher mass-loss rate closer to the equatorial plane. 相似文献
15.
In this paper, the equilibrium configurations of rapid rotating compact stars and some gravitational effects are studied within the general relativity by use of the Harrison-Wheeler equation of state and by the self-consistent field method. Numerical calculations show that the equilibrium configuration of a rotating star is a spheroid. For large spin velocities, say, ω > 3.0 × 102 sec−1 the eccentricity and mass increase very rapidly as the angular velocity increases, for the critical angular velocity of the rotating star, the eccentricity is about 0.7, the increase in mass is about 10–35%. The difference of the gravitational redshifts at the surface of the star caused by rotation, and the difference of the light bending when the beam moves in the direction of rotation or in the opposite direction are obvious. 相似文献
16.
Bruce G. Elmegreen 《Astrophysics and Space Science》2003,284(2):819-832
Gas processes affecting star formation are reviewed with an emphasis on gravitational and magnetic instabilities as a source
of turbulence. Gravitational instabilities are pervasive in a multi-phase medium, even for sub-threshold column densities,
suggesting that only an ISM with a pure-warm phase can stop star formation. The instabilities generate turbulence, and this
turbulence influences the structure and timing of star formation through its effect on the gas distribution and density. The
final trigger for star formation is usually direct compression by another star or cluster. The star formation rate is apparently
independent of the detailed mechanisms for star formation, and determined primarily by the total mass of gas in a dense form.
If the density distribution function is a log-normal, as suggested by turbulence simulations, then this dense gas mass can
be calculated and the star formation rate determined from first principles. The results suggest that only 10-4 of the ISM mass actively participates in the star formation process and that this fraction does so because its density is
larger than 105 cm-3, at which point several key processes affecting dynamical equilibrium begin to break down.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
We have investigated magnetostatic equilibria for coronal loops embedded in a potential magnetic field on a rotating star. We find that for any given star, there is a maximum value of the plasma pressure inside a single loop, above which no equilibrium exists. This maximum internal pressure depends on the ratio of the temperatures inside and outside the loop, and on the ratio of the plasma pressure to the magnetic pressure at the base of the external field. Thus, any loop of a large-scale field which is heated or cooled to a different temperature from its immediate surroundings, or which experiences a change in its internal pressure may eventually lose equilbrium. For some values of the base pressure and temperature ratio the relation between summit height and footpoint separation is double-valued. As the summit height of a loop is increased, its footpoint separation increases to a critical value, then decreases to zero at the maximum possible summit height. At the critical footpoint separation the slope of the loop height-footpoint separation relation becomes infinite, and no equilibrium solution exists for greater footpoint separations.We find also that the strength and scale of the field external to the flux tube is the most important factor in determining its maximum height. The effects of varying the stellar rotation rate - and, hence, the variation in pressure with height - are comparatively unimportant, even for very high rotation rates at which the point of balance between gravitational and centrifugal forces lies close to the stellar surface. In this case it is possible to find equilibrium loop solutions whose summits lie outside the centrifugal balance point.We have also investigated the effects of varying the stellar surface gravity. For stellar of fixed mass and rotation rate, the loop dimensions scale approximately linearly with the stellar radius. 相似文献
18.
Natural, low-frequency, hydromagnetic oscillations of an isolated, nonrotating neutron star, which are localized in the peripheral
crust, the structure of which is determined by the electron-nuclear plasma (the Ae phase), are studied. The plasma medium
of the outer crust is treated as a homogeneous, infinitely conducting, incompressible continuum, the motions of which are
determined by the equations of magnetohydrodynamics. In the approximation of a constant magnetic field inside the crust (the
magnetic field outside the star is assumed to have a dipole structure), the spectrum of normal poloidal and toroidal hydromagnetic
oscillations, due to presumed residual fluctuations of flow and their associated fluctuations in magnetic field strength,
is calculated. Numerical estimates given for the periods of MHD oscillations fall in the range of periods of radio pulsar
emission, indicating a close connection between the residual hydromagnetic oscillations and the electromagnetic activity of
neutron stars.
Translated from Astrofizika, Vol. 40, No. 1, pp. 77–86, January–March, 1997. 相似文献
19.
S. A. Gasanov 《Astronomy Letters》2007,33(12):827-843
The problem of the motion of a star inside a layered inhomogeneous rotating elliptical galaxy with a variable mass is considered. We have found an analogue of the Jacobi integral and determined the possible regions of motion. A solution to the equations of perturbed motion has been obtained. 相似文献
20.
PSR B1259-63 is the only known binary system with a radio pulsar from which the non-pulsed radio and X-ray emission was detected.
The companion star in this system is a Be star SS 2883. A rapidly rotating radio pulsar is expected to produce a wind of relativistic
particles. Be stars are known to produce highly asymmetric mass loss. Due to the interaction of the pulsar wind and the Be
star wind the system of two shocks between the pulsar and the Be star forms. In this paper we show that the observed non-pulsed
radio emission from the system is a result of the synchrotron emission of the relativistic particles in the outflow beyond
the shock wave and that the non-pulsed X-ray emission is due to the inverse Compton scattering of the Be star photons on this
particles.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献