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1.
E. I. Staritsin 《Astronomy Letters》2009,35(6):413-423
We consider the evolution of a rotating star with a mass of 16M ⊙ and an angular momentum of 3.25 × 1052 g cm2 s?1, along with the hydrodynamic transport of angular momentum and chemical elements in its interiors. When the partial mixing of matter of the turbulent radiative envelope and the convective core is taken into account, the efficiency of the angular momentum transport by meridional circulation in the stellar interiors and the duration of the hydrogen burning phase increase. Depending on the Schmidt number in the turbulent radiative stellar envelope, the ratio of the equatorial rotational velocity to the circular one increases with time in the process of stellar evolution and can become typical of early-type Be stars during an additional evolution time of the star on the main sequence. Partial mixing of matter is a necessary condition under which the hydrodynamic transport processes can increase the angular momentum of the outer stellar layer to an extent that the equatorial rotational velocity begins to increase during the second half of the evolutionary phase of the star on the main sequence, as shown by observations of the brightest stars in open star clusters with ages of 10–25 Myr. When the turbulent Schmidt number is 0.4, the equatorial rotational velocity of the star increases during the second half of the hydrogen burning phase in the convective core from 330 to 450 km s?1. 相似文献
2.
3.
4.
E. I. Staritsin 《Astronomy Letters》2007,33(2):93-102
The evolution of a rotating star with a mass of 16M ⊙ at the hydrogen burning phase is considered together with the hydrodynamic processes of angular momentum transport in its interior. Shear turbulence is shown to limit the amplitude of the latitudinal variations in mean molecular weight on a surface of constant pressure in a layer with variable chemical composition. The resulting nonuniformity in the mean molecular weight distribution and the turbulent energy transport along the surface of constant pressure reduce the absolute value of the meridional circulation velocity. Nevertheless, meridional circulation remains the main mechanism of angular momentum transport in the radial direction in a layer with variable chemical composition. The intensity of the processes of angular momentum transport by meridional circulation and shear turbulence is determined by the angular momentum of the star. At a fairly high angular momentum, more specifically, at J = 3.69 × 1052 g cm2 s?1, the star during the second half of the hydrogen-burning phase in its convective core has characteristics typical of classical early Be stars. 相似文献
5.
Mohammad Hassan Murad 《Astrophysics and Space Science》2013,343(1):187-194
The paper presents a new class of parametric interior solutions of Einstein–Maxwell field equations in general relativity for a static spherically symmetric distribution of a charged perfect fluid with a particular form of electric field intensity. This solution gives us wide range of parameter, K (0.69≤K≤7.1), for which the solution is well behaved hence, suitable for modeling of superdense star. For this solution the gravitational mass of a superdense object is maximized with all degree of suitability by assuming the surface density of the star equal to the normal nuclear density ρ nm=2.5×1017kg?m?3. By this model we obtain the mass of the Crab pulsar M Crab=1.401M ⊙ and the radius, R Crab=12.98 km constraining the moment of inertia I NS,38>1.61 for the conservative estimate of Crab nebula mass 2M ⊙ and M Crab=2.0156M ⊙ with radius, R Crab=14.07 km constraining the moment of inertia I NS,38>3.04 for the newest estimate of Crab nebula mass 4.6M ⊙ which are quite well in agreement with the possible values of mass and radius of Crab pulsar. Besides this, our model yields the moments of inertia for PSR J0737-3039A and PSR J0737-3039B are I A,38=1.4624 and I B,38=1.2689 respectively. It has been observed that under well behaved conditions this class of parametric solution gives us the maximum gravitational mass of causal superdense object 2.8020M ⊙ with radius 14.49 km, surface redshift z R =0.4319, charge Q=4.67×1020 C, and central density ρ c =2.68ρ nm. 相似文献
6.
This paper presents a new family of interior solutions of Einstein–Maxwell field equations in general relativity for a static spherically symmetric distribution of a charged perfect fluid with a particular form of charge distribution. This solution gives us wide range of parameter, K, for which the solution is well behaved hence, suitable for modeling of superdense star. For this solution the gravitational mass of a star is maximized with all degree of suitability by assuming the surface density equal to normal nuclear density, ρ nm=2.5×1017 kg?m?3. By this model we obtain the mass of the Crab pulsar, M Crab, 1.36M ⊙ and radius 13.21 km, constraining the moment of inertia >?1.61×1038 kg?m2 for the conservative estimate of Crab nebula mass 2M ⊙. And M Crab=1.96M ⊙ with radius R Crab=14.38 km constraining the moment of inertia >?3.04×1038 kg?m2 for the newest estimate of Crab nebula mass, 4.6M ⊙. These results are quite well in agreement with the possible values of mass and radius of Crab pulsar. Besides this, our model yields moments of inertia for PSR J0737-3039A and PSR J0737-3039B, I A =1.4285×1038 kg?m2 and I B =1.3647×1038 kg?m2 respectively. It has been observed that under well behaved conditions this class of solutions gives us the overall maximum gravitational mass of super dense object, M G(max)=4.7487M ⊙ with radius $R_{M_{\max}}=15.24~\mathrm{km}$ , surface redshift 0.9878, charge 7.47×1020 C, and central density 4.31ρ nm. 相似文献
7.
A numerical method presented by Imshennik et al. (2002) is used to solve the two-dimensional axisymmetric hydrodynamic problem on the formation of a toroidal atmosphere during the collapse of an iron stellar core and outer stellar layers. An evolutionary model from Boyes et al. (1999) with a total mass of 25M⊙ is used as the initial data for the distribution of thermodynamic quantities in the outer shells of a high-mass star. Our computational region includes the outer part of the iron core (without its central part with a mass of 1M⊙ that forms the embryo of a protoneutron star at the preceding stage of the collapse) and the silicon and carbon-oxygen shells with a total mass of (1.8–2.5)M⊙. We analyze in detail the results of three calculations in which the difference mesh and the location of the inner boundary of the computational region are varied. In the initial data, we roughly specify an angular velocity distribution that is actually justified by the final result—the formation of a hydrostatic equilibrium toroidal atmosphere with reasonable total mass, Mtot=(0.117–0.122)M⊙, and total angular momentum, Jtot=(0.445–0.472)×1050 erg s, for the two main calculations. We compare the numerical solution with our previous analytical solution in the form of toroidal atmospheres (Imshennik and Manukovskii 2000). This comparison indicates that they are identical if we take into account the more general and complex equation of state with a nonzero temperature and self-gravitation effects in the atmosphere. Our numerical calculations, first, prove the stability of toroidal atmospheres on characteristic hydrodynamic time scales and, second, show the possibility of sporadic fragmentation of these atmospheres even after a hydrodynamic equilibrium is established. The calculations were carried out under the assumption of equatorial symmetry of the problem and up to relatively long time scales (～10 s). 相似文献
8.
We consider an equation of state that leads to a first-order phase transition from the nucleon state to the quark state with a transition parameter λ>3/2 (λ=ρQ/(ρN+P0/c2)) in superdense nuclear matter. Our calculations of integrated parameters for superdense stars using this equation of state show that on the stable branch of the dependence of stellar mass on central pressure dM/dPc>0) in the range of low masses, a new local maximum with Mmax=0.082⊙ and R=1251 km appears after the formation of a toothlike kink (M=0.08M⊙, R=205 km) attributable to quark production. For such a star, the mass and radius of the quark core are Mcore=0.005M⊙ and Rcore=1.73 km, respectively. In the model under consideration, mass accretion can result in two successive transitions to a quark-core neutron star with energy release similar to a supernova explosion: initially, a low-mass star with a quark core is formed; the subsequent accretion leads to configurations with a radius of ～1000 km; and, finally, the second catastrophic restructuring gives rise to a star with a radius of ～100 km. 相似文献
9.
This paper aims to investigate what kind of density perturbations did lead to elliptical galaxies and what kind to spiral galaxies, in the context of a CDM scenario. Previous work by HP (Heavens and Peacock, 1988) is reviewed and extended; more particularly: (i) a theoreticalJM
relation is derived for virialized configurations, with a slope increasing with the mass, in the range 5/3<<2, and compared with its counterpart deduced by HP for expanding configurations; (ii) an non-dimensional angular momentum =J/(G
2
M
5
t
ff
)1/3; witht
ff
free-fall time at turnaround, is calculated explicitly and compared with the usual spin parameter =J(–E)
1/2/(GM
5/2), in the special case of polytropic spheres and for different peak heights; (iii) a model is built up where the ellipsoidal density perturbations described by HP are approximated as spherical density perturbations with the same mass and the same rate of acquisition of angular momentum, and the contribution of the latter to the expansion is also taken into account. The calculations are limited to the special case of Einstein-de Sitter universes (of dust only), in the whole range of HP distributions of angular momenta. If a massM=1012
m
is typical for galaxies, the results are consistent with both an inferred difference roughly in a factor of six times between angular momenta of ellipticals and spirals, and a continuous transition from the former to the latter, for each peak height. It is argued that star formation together with angular momentum, instead of peak height alone, makes the fate of a given proto-object; more specifically, if star formation is high enough and/or angular momentum is low enough, the system will be frozen as an elliptical galaxy; if, on the other hand, the rate of star formation is low enough, and/or angular momentum is high enough, the system will be frozen as a spiral galaxy. In addition, the results lead to an obvious trend: more ellipticals are associated with higher peak heights and more spirals with lower peak heights. 相似文献
10.
An analytic solution has been found in the Roche approximation for the axially symmetric structure of a hydrostatically equilibrium atmosphere of a neutron star produced by collapse. A hydrodynamic (quasione-dimensional) model for the collapse of a rotating iron core in a massive star gives rise to a heterogeneous rotating protoneutron star with an extended atmosphere composed of matter from the outer part of the iron core with differential rotation (Imshennik and Nadyozhin, 1992). The equation of state of a completely degenerate iron gas with an arbitrary degree of relativity is taken for the atmospheric matter. We construct a family of toroidal model atmospheres with total masses M≈ 0.1?2M ⊙ and total angular momenta J≈(1?5.5)×49 erg s, which are acceptable for the outer part of the collapsed iron core, in accordance with the hydrodynamic model, as a function of constant parameters ω0 and r 0 of the specified differential rotation law Ω=ω0exp[?(rsinθ)2/r 0 2 ] in spherical coordinates. The assumed rotation law is also qualitatively consistent with the hydrodynamic model for the collapse of an iron core. 相似文献
11.
A quantitative re-formulation of Hoyle's theory on the formation of the solar system is attempted, according to a three-dimensional scheme based on the assumption that the original magnetic field of the star is a dipole field. This allows us to obtain analytic expressions for the main paraeters describing the different phases of the process. The protostar is assumed to evolve in gravitational contraction along the Hayashi track, along which, for a given value of the radiusR 0 depending on the total angular momentum, matter begins to be shed at the equator as a consequence of centrifugal instability. However, owing to the geometry of the dipole field and to Hoyle's assumption that, for a star with a convective envelope, the sign of the inward magnetic pressure determines whether the magnetic lines do wind up or not, it turns out that the magnetic coupling between the star and the disk formed at the equator starts only when the radius of the contracting star has reached the value ofR s=4/5R 0; and that the shedding of matter stops for a radius valueR d, depending on the strength of the magnetic field. One is thus able to calculate the total quantity of matter emitted at the solar equator and the distance reached by the rings thus formed as functions of the radius of the star, of the initial values of the magnetic field, of the total angular momentum and of the structural factors of the star. The quantitative results are discussed in order to see whether it is possible to deduce the main characteristics of the disk, from which the solar system should have originated, for reasonable values of these main parameters. 相似文献
12.
In wind-fed X-ray binaries the accreting matter is Compton-cooled and falls freely on to the compact object. The matter has a modest angular momentum l and accretion is quasi-spherical at large distances from the compact object. Initially small non-radial velocities grow in the converging supersonic flow and become substantial in the vicinity of the accretor. The streamlines with l >( GMR ∗)1/2 (where M and R ∗ are the mass and radius of the compact object) intersect outside R ∗ and form a two-dimensional caustic which emits X-rays. The streamlines with low angular momentum, l <( GMR ∗)1/2 , run into the accretor. If the accretor is a neutron star, a large X-ray luminosity results. We show that the distribution of accretion rate/luminosity over the star surface is sensitive to the angular momentum distribution of the accreting matter. The apparent luminosity depends on the side from which the star is observed and can change periodically with the orbital phase of the binary. The accretor then appears as a 'Moon-like' X-ray source. 相似文献
13.
The models of non-rotating and rotating 2.31M
\ stars of Population I composition have been calculated, starting at the threshold of stability. A 2.31M
\ star was chosen to compare the results with the observational parameters of the primary component of the well-known detached binary YZ Cassiopeiae. The effects of rotation on the internal structure during the evolution of the star were studied by constructing sequences of axisymmetric rotating models under the assumption that angular momentum was conserved according to a predetermined angular velocity distribution depending on the structure of the star.The first section of this paper deals with effects of rotation on the evolutionary behaviours of the 2.31M
\ star through the pre-Main-Sequence evolution as well as the zero-age Main Sequence.In the second section of this paper, the evolutionary studies have been extended up to near-hydrogen exhaustion phase in order to obtain a theoretical model corresponding to the given mass and radius of the primary component of YZ Cassiopeiae. The theoretical models were found to be in a good agreement with observational parameters. The computed rotating models of the primary of YZ Cassiopeiae indicates that its evolutionary age is 6.01×108 years; and the central hydrogen content 0.183 — which means that about 75% of its original value was depleted. 相似文献
14.
We suggest that the mass of four compact stars SAX J1808.4-3658, KS 1731-260, SAX J1750.8-2900 and IGR J17191-2821 can be determined from the difference in the observed kiloHertz quasi periodic oscillations (kHz QPO-s) of these stars. The stellar radius is very close to the marginally stable orbit Rms as predicted by Einstein’s general relativity. It may be noted that the first of these stars was suggested to be a strange star more than a decade back by Li et al. (1999a) from the unique millisecond X-ray pulsations with an accurate determination of its rotation period. It showed kHz QPO-s eight years back and so far it is the only set that has been observed. This is the first time we give an estimate of the mass of the star and of three other compact stars in low-mass X-ray binaries using their observed kHz QPO-s. 相似文献
15.
S. Yabushita 《Astrophysics and Space Science》1992,193(2):173-183
As shown by Chiéze, polytropic gas spheres imbedded in an ambient medium with a given pressure exhibit a relation between the mass and radius similar to isothermal gas spheres, providedn(polytropic index)>3 or <–1. Here, further investigation is made of the polytropic spheres. Not only the relation between radius and external pressure, but the relation between the central density (
c
) and the mass (M) is similar to isothermal spheres and neutron star models. Dynamical calculation shows that the stability of polytropic spheres is lost at the configuration which corresponds to the first peak in the
c
—M relation, as is the case for neutron star models in general relativity. 相似文献
16.
We can define some adiabatic exponents for neutron star cores. The equality of and 3 leads to an equation of stateE=P ln(K/P) orP=K exp(–E/P). This equation has been solved alongwith equations for hydrostatic equilibrium for different physical conditions at the centre. The parameters of isothermal neutron star cores have been computed by taking surface densityE
a=2×1014 g cm–3. ForP
0=E
0 the maximum mass and radius of neutron star core are 3.25M
and 17.14 km, respectively. 相似文献
17.
18.
In this paper, using 2MASS photometry, we study the structural and dynamical properties of four young star clusters viz. King 16, NGC 1931, NGC 637 and NGC 189. For the clusters King 16, NGC 1931, NGC 637 and NGC 189, we obtain the limiting radii of 7′, 12′, 6′ and 5′ which correspond to linear radii of 3.6 pc, 8.85 pc, 3.96 pc and 2.8 pc respectively. The reddening values E(B?V) obtained for the clusters are 0.85, 0.65–0.85, 0.6 and 0.53 and their true distances are 1786 pc, 3062 pc, 2270 pc and 912 pc respectively. Ages of the clusters are 6 Myr, 4 Myr, 4 Myr and 10 Myr respectively. We compare their structures, luminosity functions and mass functions (φ(M)=dN/dM ∝ M ?(1+χ)) to the parameter τ=t age /t relax to study the star formation process and the dynamical evolution of these clusters. We find that, for our sample, mass seggregation is observed in clusters or their cores only when the ages of the clusters are comparable to their relaxation times (τ≥1). These results suggest mass seggregation due to dynamical effects. The values of χ, which characterize the overall mass functions for the clusters are 0.96±0.11, 1.16±0.18, 0.55±0.14 and 0.66±0.31 respectively. The change in χ as a function of radius is a good indicator of the dynamical state of clusters. 相似文献
19.
The investigation of the angular momentum vs mass relation for binary stars is completed with a study of the 847 systems contained in theFourth Catalog of Orbits of Visual Binary Stars. Because bothJ andM of a visual binary depend steeply on the distance to the system (5th and 3rd powers, respectively), and many of the distances are not well known, the study makes use of an auxiliary parameterR which is independent of distance and proportional toJM
–5/3.R appears to be uncorrelated withM for the 789 systems for which both can be determined. The non-correlation implies thatJ M
5/3, expected from Kepler's third law, provides a better fit to the visual binaries than doesJ M
2, predicted by some more complex considerations.The distribution functionf(q=M
2/M1) of mass ratios for the visual binaries results as a byproduct of the investigation. It peaks extremely sharply towardq=1.0 (much more so than for spectroscopic binaries). Because most visual binaries are wide enough to consist of stars that condensed independently (and so that can be thought of as chosen at random from an initial mass function), one expects the realf(q) to rise toward low ratios. Observational selection against the discovery and study of systems with large magnitude differences between the components must be very large indeed to account for the discrepancy between expectation and observation. The alternative is a mechanism for formation of wide binaries that favours equal components. The distribution of mass ratios for eclipsing binaries is given in an appendix. It peaks strongly atq=0.6–0.75 and largely reflects processes of angular momentum, mass, and energy exchange between the stars in contact systems. 相似文献
20.
It is proposed that a new mechanism—angular momentum drain—helps account for the relatively slow rotation rates of intermediate-sized asteroids. Impact ejecta on a spinning body preferentially escape in the direction of rotation. This material systematically drains away spin angular momentum, leading to the counterintuitive result that collisions can reduce the spin of midsized objects. For an asteroid of mass M spinning at frequency ω, a mass loss δM correspond to an average decrease in rotation rate . A. W. Harris' (1979), Icarus40, 145–153) theory for the collisional evolution of asteroidal spins is significantly altered by inlusion of this effect. While the modified theory is still somewhat artificial, comparison of its predictions with the data of S. F. Dermott, A. W. Harris, and C. D. Murray (1984, Icarus57, 14–34) suggests that angular momentum drain is essential for understanding the statistics of asteroidal rotations. 相似文献