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1.
D. C. Schwank 《Astrophysics and Space Science》1976,43(2):459-468
Weight functions for the determination of the periods of linear adiabatic non-radial oscillations have been calculated in the same manner as Epstein's classic treatment of purely radial oscillations. Quadrupole (l=2) oscillations for thef and lower orderp andg-modes were considered. One group of static models were polytropes in the range 1.0n4.0 with
; thus included were configurations that were convectively stable, unstable and neutrally stable throughout. Another group consisted ofn=3.0 polytropes with convective shells or convective cores; 1 was set at different values in each region in order to produce stability (
) or instability (
). The weight function provides a pictorial means for assessing the relative importance of each region of a given static model with respect to generating a given non-radial mode. 相似文献
2.
If fluctuations in the density are neglected, the large-scale, axisymmetric azimuthal momentum equation for the solar convection zone (SCZ) contains only the velocity correlations
and
where u are the turbulent convective velocities and the brackets denote a large-scale average. The angular velocity, , and meridional motions are expanded in Legendre polynomials and in these expansions only the two leading terms are retained (for example,
where is the polar angle). Per hemisphere, the meridional circulation is, in consequence, the superposition of two flows, characterized by one, and two cells in latitude respectively. Two equations can be derived from the azimuthal momentum equation. The first one expresses the conservation of angular momentum and essentially determines the stream function of the one-cell flow in terms of
: the convective motions feed angular momentum to the inner regions of the SCZ and in the steady state a meridional flow must be present to remove this angular momentum. The second equation contains also the integral
indicative of a transport of angular momentum towards the equator.With the help of a formalism developed earlier we evaluate, for solid body rotation, the velocity correlations
and
for several values of an arbitrary parameter, D, left unspecified by the theory. The most striking result of these calculations is the increase of
with D. Next we calculate the turbulent viscosity coefficients defined by
whereC
ro
0
and C
o
0
are the velocity correlations for solid body rotation. In these calculations it was assumed that 2 was a linear function of r. The arbitrary parameter D was chosen so that the meridional flow vanishes at the surface for the rotation laws specified below. The coefficients v
ro
i
and v
0o
i
that allow for the calculation of C
ro
and C
0o
for any specified rotation law (with the proviso that 2 be linear) are the turbulent viscosity coefficients. These coefficients comply well with intuitive expectations: v
ro
1
and –v
0o
3
are the largest in each group, and v
0o
3
is negative.The equations for the meridional flow were first solved with
0 and
2 two linear functions of r (
0
1
= – 2 × 10 –12 cm –1) and (
2
1
= – 6 × 10 12 cm –1). The corresponding angular velocity increases slightly inwards at the poles and decreases at the equator in broad agreement with heliosismic observations. The computed meridional motions are far too large ( 150m s–1). Reasonable values for the meridional motions can only be obtained if
o (and in consequence ), increase sharply with depth below the surface. The calculated meridional motion at the surface consists of a weak equatorward flow for gq < 29° and of a stronger poleward flow for > 29°.In the Sun, the Taylor-Proudman balance (the Coriolis force is balanced by the pressure gradient), must be altered to include the buoyancy force. The consequences of this modification are far reaching: is not required, now, to be constant along cylinders. Instead, the latitudinal dependence of the superadiabatic gradient is determined by the rotation law. For the above rotation laws, the corresponding latitudinal variations of the convective flux are of the order of 7% in the lower SCZ. 相似文献
3.
For the theory described by the action
and taking the FRW flat space metric we find an exact non-singular de Sitter model universe exp(t
2), with
. It is also proved that the standard general relativity de Sitter cosmology
, >0 is also a model of this higher derivative theory of gravity. If the metric is conformally flatS could describe a consistent quantum theory and its classical solutions would correspond to cosmological models in this theory.This work was supported in part by CONACYT grand P228CCOX891723, and DGICSA SEP grant C90-03-0347. 相似文献
4.
J. A. Murdock 《Celestial Mechanics and Dynamical Astronomy》1978,18(3):237-253
A well-known simple model of spin/orbit coupling leads to the equation
periodic int and the angle . A mathematical study of this equation is carried out emphasizing the near-resonance behavior and the mechanism of resonance capture; the results are complementary to the author's previous global study showing how to locate the active responances. It is shown that the capture process is to a surprizing degree independent of the functional form off, making some of the detailed hypotheses of previous studies unnecessary. 相似文献
5.
I. H. Urch 《Astrophysics and Space Science》1977,49(2):443-472
The diffusion of charged particles through a weak stochastic electro-magnetic field which is superimposed on a constant background magnetic field
is considered. The stochastic electromagnetic fields are assumed to consist of unpolarized Alfvén waves propagating at arbitrary angles to the direction
. When the Alfvén waves are propagating in directions other than
and the particle gyro-radius,r
g, is sufficiently large (but may be smaller than the correlation length of the stochastic fields) it is shown that the particle flux perpendicular to the direction
is
, wherev is the particle speed andf the particle density. The expression forK
differs from those calculated by previous authors. For small particle gyro-radii the flux S has a different functional form and is identical to that found by Urch (1977) to describe particle diffusion when the Alfvén waves only propagate in the direction
. 相似文献
6.
The interaction between small-scale magnetic fields and horizontal photospheric flows has been studied from observations of high angular resolution
obtained with the Lockheed narrowband filter in the Swedish Vacuum Solar Telescope at La Palma. The measured magnetic flux density (B
) is in the range from a detection limit of 10 G to about 500 G, showing a good correspondence with the filigree. The magnetic flux elements take part in the local flows towards downdrafts at the supergranulation cell boundaries. The measured flux density, as well as the associated filigree intensity, decrease as the structures approach the downdrafts, presumably as a result of increased tilting and possibly submergence of flux into the downdrafts. 相似文献
7.
A physically based explanation is given for the distribution of flare energies N(E)E
– where 1.5. In contrast to previous approaches, the present treatment is based on a physical theory of the flare reconnection site. The central assumption is that topological flare energy, although released explosively, is slowly accumulated over several hundred Alfvén timescales. When coupled to the geometric properties of the reconnective flare source, this assumption is shown to lead naturally to a deduction of the flare energy distribution. Current sheet models yield the exponent
whereas more compact current structures imply steeper spectra
. 相似文献
8.
9.
K. A. Innanen 《Astrophysics and Space Science》1973,22(2):393-411
Three groups of galactic mass models, each consisting of nine inhomogeneous spheroids of two kinds are described, according to three adopted values of the total density near the Sun: 0.10, 0.15 and 0.20 M pc–3. Approximately 20% of the total mass of each model is in the halo, constructed to adequately fit recent RR Lyrae star observations. It is shown that the maxima found in the RR Lyrae star densities towards the galactic axis (Plaut, 1970) should not be interpreted as being associated with the galactic nucleus, but as the result of the greater decrease in density with increasingz over the increase in density as the galactic axis is approached. Even at the low galactic latitude of 5° (l=0°), this effect causes a 0.5 kpc correction to the distance to the galactic centre. A basic model for
kpc,
km s–1,
M
pc–3 is first constructed, mainly to satisfy structural conditions near the sun and in the halo. An attempt to optimize the basic model is made by scaling it so as to retain constant density and angular velocity near the sun, and to best fit kinematic data, including the recent re-examination of the 21-cm data of Simonson and Mader (1972). No unknown matter is required in the models, in accordance with the results of Weistrop (1972b), and, as pointed out earlier (Innanen, 1966b) the faintM-stars must be in a highly flattened spheroid. The optimizing indicates that an adequate fit to kinematics can be achieved for
km s–1. More detailed results are tabulated for a representative model for which
. Two new galactic density functions are discussed in the Appendix. 相似文献
10.
Toshiki Aikawa 《Astrophysics and Space Science》1985,110(1):125-131
The conclusions of the present paper broadly are: (a) The galactic concentration of doubles by comparing the distributions in galactic latitudes 0°<20° and >40° is nearly twice as large as the galactic concentration of stars in general. (b) The astrographic catalogues are not complete in the fainter magnitudes. (c) The large value of the ratioT:O
k (observed to optical number of pairs) from Kreiken's formula shows that almost all stars in the group 0<d5 and quite a few in the other two groups, viz., 5<d10 and 10<d15 might be shown true binaries. Consequently, Aitken's working definition of a true binary should be extended if it were to include all true binaries. (d) The doubles are probably stars of Population I. (e) The logarithm to the base 10 of the cumulative counts can be represented by an empirical relationA+B(m–1.5)+C(m–1.5)2.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846) 相似文献
11.
In this paper two sets of improved approximate expressions of emissivity
, absorptivity
, effective temperature Teff, and frequency of peak brightness _p of gyrosynchrotron radiation are presented respectively for the ranges from 5 to 10 and 10 to 100 of harmonic numbers s(= /_B). The expressions are designed for the range from 20° to 80° of viewing angle , and the range 2 to 7 of electron energy spectral index . They are expressed by a power-law function in which the indexes are fitted by polynomial expressions of . Their statistical errors are, respectively, 24% and 32% for
and
for
and 28% for
. Their accuracies are much better than those of linear fitting of the power-law index. 相似文献
12.
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
13.
The problem on linear waves in a radiating and scattering grey medium is studied using Whitham's method. Analysis of the basic equations distinguishes two limiting cases: the one is theequilibrium case in which the energy exchange between the gas and radiation plays an essential role, and the other is theScattering case in which the effect of energy exchange is negligible. A new type ofradiation acoustic wave with the speed
is found in the scattering case. The governing equations for linearized one-dimensional flow are reduced to one equation of radiative acoustics valid to order 1/c, and the criterion for the two limiting cases is derived from studying this equation. The harmonic solution is analytically studied to show that theeffective optical depth corresponding to the wavelength of perturbation gives the measure of the interaction between the gas and radiation. When eff1, the sound speeda
g
2
=P
g
/ and the propagating speed of radiative disturbancea
f
2
=fc
2 appear as the modified classical and radiation-induced modes respectively, wheref is the Eddington factor. When eff1, the isentropic sound speeda
s
2
=(P
g
+P
r
/ appears in the equilibrium case, and the radiation acoustic speeda
A
2
appears in the scattering case. The dispersion relation of the harmonic solution is numerically calculated. The result shows that the wave pattern depends critically on the ratio=P
g
/(P
g
+P
r
). When
, the speeda
S
anda
A
arise from the modified classical mode, and when
, they originate from the radiation-induced mode. 相似文献
14.
Werner Lohmann 《Astrophysics and Space Science》1977,51(1):173-176
The very young open star cluster NGC 2362 was investigated by the strip method on charts of two photographs taken with the 1-m Schmidt telescope of the European Southern Observatory. Up to the limiting magnitudeM
v
*
=5
.
m
8 the cluster contains 100 stars and can be described by the Gaussian density law (6). Further results are: Mass
= 246
, central mass density
0 = 43.1
= 246
pc-3 , radiusR2.6 pc, mean velocity of the stars
= 0.64 km s–1.
Mitteilungen Serie A. 相似文献
Mitteilungen Serie A. 相似文献
15.
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
16.
S. Kumar 《Astrophysics and Space Science》1984,106(1):53-59
The Chisnell-Chester-Whitham method has been used to investigate the propagation of diverging plane and cylindrical shock waves through an ideal gas in presence of a magnetic field having only constant axial
and variable azimuthal
components, simultaneously for both weak and strong cases. Assuming an initial density distribution 0=r
–w
, where is the density at the plane/axis of symmetry andw is a constant, the analytical expressions for shock velocity and shock strength have been obtained. The expressions for the pressure, the density, and the particle velocity immediately behind the shock have also been derived for both cases. 相似文献
17.
Jörn E. Kunstmann 《Earth, Moon, and Planets》1978,18(1):91-104
The frequency spectra of the interplanetary magnetic field fluctuations are the projection of their wavenumber spectra onto one dimension. Only the frequency spectra can be measured by spacecrafts. It is studied how their measured size depends on the direction of the mean fieldB
0, which structures the symmetry of the fluctuations relative to the solar wind system. It is specialized for the slab model, Alfvén waves, magneto-acoustic waves and the isotropic case. For the slab model the frequency spectra are proportional to
, whereq is the spectral index and the angle betweenB
0 and the radial direction. For the diffusion coefficientK
TT the relation
holds. 相似文献
18.
In this paper we discuss the particle flow or streaming and energy changes of cosmic rays in the interplanetary region via flow lines in momentum-position space. We consider the steady-state case where particles are released monoenergetically from the Sun or from infinity and study the cosmic-ray traffic pattern in momentum and position arising from monoenergetic sources. The analysis makes extensive use of the result
(wherep is the particle momentum,V the solar wind velocity andG the cosmic-ray density gradient) for the mean time rate of change of momentum of cosmic rays reckoned for a fixed volume in a reference frame fixed in the solar system, developed by us in several recent papers.Deceased. 相似文献
19.
Shuichi Tamazawa Kiyotaka Toyama Noboru Kaneko Yôrô Ôno 《Astrophysics and Space Science》1975,32(2):403-421
Spherically symmetric, steady-state, optically thick accretion onto a nonrotating black hole with the mass of
is studied. The gas accreting onto the black hole is assumed to be a fully ionized hydrogen plasma withn
0=108 cm–3 andT
0=104 K far from the black hole, and a new approximate expression for the Eddington factor is introduced. The luminosity is estimated to beL=1.875×1033 erg s–1, which primarily arises from the optical surface (1) ofT104 K. The accretion flow is characterized by 1 and (v/c)10. In the optically thin region, the flow remains isothermal, and the increase of temperature occurs at 1. The radiative equilibrium is strictly realized at (v/c)10. 相似文献
20.
Since there are reasons for expecting supersymmetry in an underlying quantum theory of gravity, one is led to study quantum and classical cosmology with supergravity. In particular, classical solutions corresponding to these models could also be used to generate the quantization of supersymmetric minisuperspaces. In generating these solutions, the solution to the Rarita-Schwinger field in the cosmological background is also obtained. In this paper the supercosmological equations of Einstein-Rarita-Schwinger are solved for the micro-superspace sector of the Taub model, under the assumption =11*22 and
. The solution for the parameters of the metric and are proportional to each other in each order, the zeroth-order and also the second-order terms. The zeroth-order terms correspond to the solution in general relativity and are logarithmic in time, the 12 terms have an hyperbolic time-dependence. The Rarita-Schwinger field has the form cos((2/D
3)ln |t–t
0|) and oscillates an infinite number of times astt
0. This oscillating behaviour of the solution for is not only present when spinor fields are treated in a curved background, but also some cosmological wave functions behave in this manner. This solution is at the same time the supercosmological solution for the microsuperspace sector of the Taub model and also the Rarita-Schwinger field in this background.This work was supported in part by CONACYT grant P228CCOX891723, and DGICSA SEP grant C90-03-0347. 相似文献