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1.
A model of a first generation intermediate star of 5M
, with Z=0 has been considered. The model is at an advanced stage of its evolution and has a double shell burning. It burns helium in the inner shell, and hydrogen, via CNO cycle, in the outer shell.
=(log/log)
T
and
T
=(log/logT)
were computed allowing for the oscillations of the relative mass abundance of the reagents in nuclear reactions. Including
=(log/log)
T
and
=(log/logT)
of mean molecular weight and the effect of the oscillations of abundances due to nuclear reactions, stability was studied. Contrary to the results of the static calculations, we found that instability due to the excitation mechanism provided by the high temperature sensitivity of energy generation rate propagates up to the surface. Thus the model in question was found to be unstable against radial adiabatic pulsations, in its fundamental mode. 相似文献
2.
In a two-fluid component universe consisting of visible matter and neutrinos, the developed features of perturbations in the two components are quite different. If the densities 1 and 2, and the Jeans lengths 1J and 2J of the two components satisfy the relations 12, 1J2J, the developed inhomogeneities in the non-dominant component 1 are larger than those in the dominant component 2. Moreover, the increase of perturbations is in some situations not monotonous but oscillatory, and such oscillations in the two components are contrary. 相似文献
3.
We compare vector magnetograms of active region NOAA 5747 observed by two very different polarimetric instruments: the imaging vector magnetograph of Huairou Solar Observing Station (HSOS) and the Haleakala Stokes Polarimeter of Mees Solar Observatory (MSO). Unlike previous comparative studies, we concentrate our attention on differences in observations and data reduction techniques that can affect the helicity computation. Overall, we find a qualitative agreement between the HSOS and MSO vector magnetograms. The HSOS data show slightly higher field strength, but the distribution of inclination angles is similar in measurements from the two instruments. There is a systematic difference (up to 20°) in the azimuths of transverse fields, which is roughly proportional to the longitudinal field strength. We estimate that Faraday rotation in the HSOS magnetograms contributes 12° in the azimuth difference if possible sources of error are taken into account. Next, we apply two independent methods to both data sets to resolve 180° azimuth ambiguity and to compute two helicity measures – the force-free field parameter best and the current helicity fractional imbalance h. The methods agree reasonably well in sign and value of the helicity measures, but the HSOS magnetograms show systematically smaller values of h and best in agreement with an expected contribution of Faraday rotation. Finally, we discuss the role of Faraday rotation in computation of best and h and conclude that it does not affect the strength of the hemispheric helicity rule. The strength of the rule appears to be related to a helicity parameter: best shows weaker hemispheric asymmetry than h. 相似文献
4.
B. Vybíral 《Astrophysics and Space Science》1987,138(1):87-98
This article deals with the experimental verification of the generalized Newton's gravitational law, formulated by Z. Horák. According to this law, the gravitational force between two resting homogeneous bodies immersed in resting homogeneous fluids is dependent on the densities
1,
2 of both the bodies and densities1,2 of both the fluids: furthermore,F=(1–1/
1)(1–2/
2)F=h
1
h
2
F, whereF is the force between the bodies in a vacuum andh
1,h
2 are the density factors. The aim of the experimental verification of the law was to determine the density factors by exploring the phenomenon that is influenced by the gravitational interaction of the bodies immersed in different fluids.The dynamic torsion-balance method was applied, during which the period of swinging of the torsion pendulum in the gravitational field of two cast iron spheres in the water.The swings of the pendulum suspended on a torsion filament in a vacuum chamber were measured in three regimes: (1) without the spheres, (2) with the spheres in the air, (3) with the spheres in the water. The motion of the pendulum was scanned by a laser ray, the period of the swing was measured electronically. The density factor determined by the dynamic torsion-balance method was 0.8562±0.0035, whereas the same factor determined by direct calculation from the densities was 0.8542±0.0003. Thus, with the relative error of 0.4%, the validity of Horák's gravitational law was proved. 相似文献
5.
A three-component fluid model of the Universe during the recombination era is analysed for =
c
(
c
is the critical density). In addition to the well-known instability of the Jeans mode at 109
M
, we find two more unstable modes at 1012
M
. 相似文献
6.
The dynamical evolution of triple systems has been studied by computer simulations. A function (t) has been defined, where p is the maximum distance of the components from their centre of inertia, and t is the time. The value of is used to indicate the current size of the triple system. The minima of have been followed during the course of evolution of the triples. A distribution of f(min) has been obtained, which is described by the following statistical parameters: the mode is equal to 0.65d, the mean value min= 0.750d, r.m.s. is 0.477d, the asymmetry is 0.218, the excess is 2.04 where d is the mean harmonic distance between the bodies in the equilibrium state of the triple system. As a rule, escapes from triples occur only after close three-body approaches. 相似文献
7.
General theory of electrical conductivity of a multicomponent mixture of degenerate fermions in a magnetic fieldB, developed in the preceding article (this volume), is applied to a matter in neutron star interiors at densities 0, where 0 = 2.8×1014 g cm–3 is the standard nuclear matter density. A model of free-particle mixture ofn, p, e is used, with account for appearance of –-hyperons at >
c
, where
c
40. The electric resistivities along and acrossB, and , and the Hall resistivity
H
are calculated and fitted by simple analytical formulae at
c
and >
c
for the cases of normal or superfluid neutrons provided other particles are normal. Charge transport alongB is produced by electrons, due to their Coulombic collisions with other charged particles; is independent ofB and almost independent of the neutron superfluidity. Charge transport acrossB at largeB may be essentially determined by other charged particles. If
c
, one has = [1 + (B/B
0)2] for the normal neutrons, and for the superfluid neutrons, while
H
=
B/B
e
for both cases. HereB
e
109
T
8
2
G,B
01011
T
8
2
G, andT
8 is temperature in units of 108 K. Accordingly for the normal neutrons atBB
0, the transverse resistivity suffers an enhancement, 1/4 1. When 50 andB varies from 0 toBB
p
1013
T
8
2
G, increases by a factor of about 103–104 and
H
changes sign. WhenBB
p
, remains constant for the superfluid neutrons, and
H
B
2 for the normal neutrons, while
H
B for any neutron state. Strong dependence of resistivity onB, T, and may affect evolution of magnetic fields in neutron star cores. In particular, the enhancement of at highB may noticeably speed up the Ohmic decay of those electric currents which are perpendicular toB. 相似文献
8.
Carlo Denis 《Celestial Mechanics and Dynamical Astronomy》1983,31(1):81-94
For Jupiter, an overall density model of the form=
0(1–x
n
), withn1/3 and
, is consistent with information presently at hand; for Saturn, however, such a density law would lead to unacceptably high densities in the vicinity of the centre. The limiting cases of the previous law are shown to ben=+, corresponding to a homogeneous sphere, andn=–3, corresponding to a particular central particle model, investigated by a number of astronomers over the last hundred years. Forn0, the central density becomes +. Another possible representation, valid both for Jupiter and Saturn, is the density law=
0(1–x)
m
), with
in the case of Jupiter, and
in the case of Saturn. Graber's density law based on a maximum entropy principle leads to unacceptably high surface densities, both for Jupiter and Saturn. Finally, the paper investigates the problems involved in fitting two-layered parametrically simple density laws to theoretically derived much more elaborate models of the Jovian planets. 相似文献
9.
The 5-dimensional Jordan-Brans-Dicke cosmologies in vacuum are found for the Bianchi type I metric, their relation with general relativity cosmologies is studied. Two solutions are possible, both produce effective pressure and energy density in the 4-dimensional G.R.-universes. One is a power-law relation, with two cases, the first one is forp
eff=eff and the other forp
eff=eff(– 1 < < 1) has a behaviour as the open flat universe. The second solution is an exponential only valid forp
eff=–eff. In all cases the three-space expansion reaches infinity ast and the fifth dimension can be made to decrease approaching zero. The scalar field can increase or decrease with time. 相似文献
10.
The effect of overtaking disturbances upon the free propagation of strong cylindrical hydromagnetic shock through a self-gravitating gas has been studied by an approximating technique developed by Yadav. Assuming an initial density distribution law as 0=r–w, where is the density at the axis of symmetry and is a constant, the analytical relation for shock velocity and shock strength modified by overtaking waves has been obtained under two conditions: viz., (i) when the applied axial magnetic field is strong and (ii) when the field is weak. The results obtained here are compared with those for a freely propagating shock. The conclusions arrived at agreed with experimental results.It is shown that the applications of the CCW method and the neglect of overtaking disturbances are equivalent. 相似文献
11.
A. D. Sedrakian 《Astrophysics and Space Science》1996,236(2):267-276
The phonon excitation spectrum of Coulomb lattice in the neutron star crusts is studied by solving Dyson's equation for phonons. It is shown that a strong renormalization of the phonon spectrum occurs at densities
s
/4 for the crustal matter compositions with spherical nuclei, which imply relatively small nuclear mass numbers and charges. It is shown that, the lattice becomes unstable against density fluctuations above a critical density of the order of
s
/3, where
s
2.6x1014 g cm–3 is the nuclear saturation density. The neutron quasiparticle spectrum and the virtual mass of a nucleus are briefly discussed. 相似文献
12.
Strange quark stars with a crust and strange dwarfs consisting of a compact strange quark core and an extended crust are investigated in terms of a bag model. The crust, which consists of atomic nuclei and degenerate electrons, has a limiting density of cr=drip=4.3·1011 g/cm3. A series of configurations are calculated for two sets of bag model parameters and three different values of cr (109 g/cm3 cr drip) to find the dependence of a star's mass M and radius R on the central density. Sequences of stars ranging from compact strange stars to extended strange dwarfs are constructed out of strange quark matter with a crust. The effect of the bag model parameters and limiting crust density cr on the parameters of the strange stars and strange dwarfs is examined. The strange dwarfs are compared with ordinary white dwarfs and observational differences between the two are pointed out. 相似文献
13.
Low-mass strange stars with a crust are investigated within the framework of the bag model. The crust, which consists of degenerate electrons and atomic nuclei, has a limiting boundary density
cr
, which is determined by the mass of the crust, and it cannot exceed the value
drip
= 4.3·1011 g/cm3, corresponding to the density at which neutrons drip from nuclei. For different values of
cr
in the low-mass range (M 0.1 M) we calculate several series of configurations: we find the dependence of the stellar mass M on the central density
c
for
cr
= const, with 109 g/cm3
cr
drip
, and for each series we determine the parameters of the configuration for which the condition dM/d
c
> 0 is violated. When the boundary density of the crust decreases to 109 g/cm3, the minimum mass of a strange star decreases to M
min 10-3 M, while the radius reaches 600 km. 相似文献
14.
The process of re-escalation of the scalar field as R
3, the energy density as R
3, and the pressurep aspR
3P, lends itself to obtain a reduced equation that represents, for a wide variety of equations of state, the cosmological evolution of an homogeneous and isotropic, flat Universe. A particular solution to this equation is presented. 相似文献
15.
Using vector magnetograms of 40 active regions (ARs) of the maximum of solar cycle 22, we calculated the imbalance h (over the AR area) of the current helicity hc Bz ( × B)z in the photosphere. In 82.5% of the cases the predominant current helicity was negative (h < 0) in the northern hemisphere and positive (h > 0) in the southern hemisphere. Thus, the predominance of counter-clockwise (clockwise) vortices in the northern (southern) hemisphere seems to be valid not only for unipolar spots with obvious vortex structure (Hale, 1927; Richardson, 1941; McIntosh, 1979; Ding, Hong, and Wang, 1987) but also for ARs of different types. The forces of rotation of the Sun (Coriolis force and/or differential rotation) seem to take effect in the twisting of various magnetic structures. 相似文献
16.
The C.C.W. method has been used to investigate the propagation of converging and diverging cylindrical shock waves in a non-uniform medium under the influence of a magnetic field of constant strength. A comparison has also been made between the two types of cylindrical shock waves, simultaneously for both weak and strong cases of the magnetic field. Density distribution is assumed to be
o =
r
–, where
is the density at the axis of symmetry and a constant. The analytical expressions for shock velocity and shock strength as well as the pressure, the density, and the particle velocity just behind the shock front have been derived for both the cases. 相似文献
17.
M. A. Eritsian 《Astrophysics》2004,47(3):305-312
Of the 7500 stars cited in the Catalog of starlight polarization, those which satisfy the condition P
obs % and A
V 0m.5 are selected. It is presumed that the selected stars (n=216) have circularly polarized light. 相似文献
18.
We consider the possibility that gravitational energy may play a local as well as global role in the behavior of matter in strong gravitational fields. A particular idealized equation, suggested as representing uniform energy density in general relativity, is examined, and its stability with respect to oscillatory and convective perturbations shown to be consistent with general relativistic hydrodynamics, subject to a new physical effect predicted for the behavior of fluids moving in strong fields. We calculate from this idealized equation the mass of a non-rotating neutron star, obtaining a maximum surface redshift ofz=2.48 and a maximum core mass of 9.79
14
–1/2
M. This compares withz=2.00 and 11.4
14
–1/2
M for a Schwarzschild star (=const.) and 6.8
14
–1/2
M for a causal star (dP/d1). 相似文献
19.
Motion equations for the gravitationally coupled orbit-attitude motion of a spacecraft are presented. The gravitational force and torque are expanded in a Taylor series in the small ratio (spacecraft size/orbital radius). A recursive definition for higher moments of inertia is introduced which permits terms up tofourth order to be retained. The expressions are fully nonlinear in the attitude variables. A quasi-sunpointing (QSP) passive attitude-control mode is used to assess the effects of higher moments of inertia and gravitational coupling. The attitude motion is detectably coupled to the orbital motion. However, the higher moments of inertia influence only the attitude motion.Nomenclature
f
G
,g
G
,f
Gi
,g
Gi
total gravitational force and torque and their components of orderi in =/r
0
-
angular momentum of spacecraft about 0 and the spacecraft mass center
-
J
i
,I
i
general moment of inertia about 0 and the spacecraft mass center
-
second (dyadic), third (triadic), and fourth (tetradic) moment of inertia about 0 and the spacecraft mass center
-
A andB (and related components) of the second, third and fourth moments of inertia about 0, see Equation (9)
-
M, m
Earth's mass, spacecraft mass
-
Q
ba
rotation matrix taking a into b
-
position vector from attracting body's mass center to a general mass element, to 0 and to the spacecraft mass center
-
1,
2,
3
basis vectors of reference frame
- , ,
N
misalignment angle betweenb
3 and the (projected) true position of the Sun, its oscillatory component and nominal value
-
unit dyadic (-identity matrix)
-
ratio of characteristic spacecraft dimension to orbital radius
-
pitch angle (aboutb
2 axis)
-
Earth's gravitational parameter
-
,
position vector from 0 to a general mass element and the spacecraft mass center
- ,
the (projected) true longitude of the Sun and the true longitude of the spacecraft
-
/
angular velocity of reference frame with respect to
- (·), (*), (o)
d()/dt with respect to inertial space
I
, and orbiting frame O and a body-fixed spacecraft frame b
Presented at AAS/AIAA Astrodynamics Conference, Aug. 9–11, 1982. 相似文献
20.
Analytic structure of high-density steady isothermal spheres is discussed using the TOV equation of hydrostatic equilibrium which satisfies an equation of state of the kind:P = K
g
, =
g
c
2.Approximate analytical solutions to the Tolman-Oppenheimer-Volkoff (TOV) equations of hydrostatic equilibrium in (, ), (,U) and (u, v) phase planes in concise and simple form useful for short computer programmes or on small calculator, have been given. In Figures 1, 2, and 3, respectively, we display the qualitative behaviours of the ratio of gas density
g
to the central density
gc
,
g
/
gc
; pressureP to the
gc
,P/
gc
; and the metric componente
–, for three representative general relativistic (GR) isothermal configurations =0.1, 0.2, and 0.3. Figure 4 shows the solution curve (, ) for =0.1, 0.2, and 0.3 (=0 represents the classical (Newtonian) curve). Numerical values of physical quantitiesv (=4r
2
P
*(r)), in steps ofu (=M(r)/r)=0.03, and the mass functionU, in steps of =0.2 (dimensionless radial distance), are given, respectively, in Tables I and II. Other interesting features of the configurations, such as ratio of gravitational radius 2GM/c
2 to the coordinate radiusR, mass distributionM(r)/M, pressure (or density) distributionP/P
c
, binding energy (B.E.), etc., have also been incorporated in the text. It has further been shown that velocity of sound inside the configurations is always less than the velocity of light.Part of the work done at Azerbaijan State University, Baku, U.S.S.R., and Mosul University, Mosul, Iraq, 1985-1986 相似文献