共查询到20条相似文献，搜索用时 15 毫秒
1.
K. E. Papadakis 《Astrophysics and Space Science》1995,232(2):337-354
The aim of the paper is to study the geometry of the Roche curvilinear coordinates (, , ) in the photogravitational circular restricted three-body problem, with varying radiation pressure, and special attention is given to the geometry of zero-velocity curves specified by the coordinate. The radiation pressure exerted by the primary bodies on the infinitesimal third body is considered the same (q
1 =q
2), and the primaries are taken to have equal masses (m
1 =m
2). The full range of values of the common radiation factor is explored, from the valueq
1 =q
2 = 1 (the gravitational three-body problem) down toq
1 =q
2 0. It is found that radiation has a strong influence on the geometry of the Roche coordinates and the zero-velocity curves. 相似文献
2.
Peter Rovithis 《Astrophysics and Space Science》1982,88(1):5-13
The sidereal daily rotation of the Sun, (), depends on the data used. From an appropriate selection of the data — sunspots with regular motion — it is found that ()=14.31–2.70 sin2 , where denotes the heliographic latitude. Moreover, it seems that there is a variation, of the order of 3%, with the solar activity. 相似文献
3.
S. P. Tarafdar 《Astrophysics and Space Science》1976,39(2):419-427
A perusal of the observed column densities of different ions towards two stars, 2 Vel and Pup, has indicated the presence of an ionization mechanism, the rate of which depends exponentially on the ionization potential. An examination of two such mechanisms, collisional ionization and ionization by UV-photon with flux depending exponentially on frequency has shown that the collisional ionization is possibly the dominant one in the intercloud medium towards 2 Vel and Pup. 相似文献
4.
The recent discovery of localised intense magnetic fields in the solar photosphere is one of the major surprises of the past few years. Here we consider the theoretical nature of small amplitude motions in such an intense magnetic flux tube, within which the field strength may reach 2 kG. We give a systematic derivation of the governing expansion equations for a vertical, slender tube, taking into account the dependence upon height of the buoyancy, compressibility and magnetic forces. Several special cases (e.g., the isothermal atmosphere) are considered as well as a more realistic, non-isothermal, solar atmosphere. The expansion procedure is shown to give good results in the special case of a uniform basic-state (in which gravity is negligible) and for which a more exact treatment is possible.The form of both pressure and velocity perturbations within the tube is discussed. The nature of pressure perturbations depends upon a critical transition frequency,
p
, which in turn is dependent upon depth, field strength, pressure and density in the basic (unperturbed) state of the tube. At a given depth in the tube pressure oscillations are possible only for frequencies greater than
p
for frequencies below
p
exponentially decaying (evanescent) pressure modes occur. In a similar fashion the nature of motions within the flux tube depends upon a transition frequency,
v
. At a given depth within the tube vertically propagating waves are possible only for frequencies greater than
v
; for frequencies below
v
exponentially decaying (evanscent) motions occur.The dependence of both
v
and
p
on depth is determined for each of the special cases, and for a realistic solar atmosphere. It is found that the use of an isothermal atmosphere, instead of a more realistic temperature profile, may well give misleading results.For the solar atmosphere it is found that
v
is zero at about 12 km above optical depth 5000= 1, thereafter rising to a maximum of 0.04 s–1 at some 600 km above 5000 = 1. Below 5000 = 1, in the convection zone,
v
has a maximum of 0.013 s–1. The transition frequency,
p
, for the pressure perturbations, is peaked at 0.1 s–1 just below 5000 = 1, falling to a minimum of 0.02 s–1 at about one scale-height deeper in the tube 相似文献
5.
Qiuhe Peng 《Astrophysics and Space Science》1989,154(2):271-279
Both the critical content
c
( N
m
/N
B
, whereN
m
,N
B
are the total numbers of monopoles and nucleons, respectively, contained in the object), and the saturation content
s
of monopoles in a rotating relativistic object are found in this paper. The results are:
|
相似文献
6.
R. Caimmi 《Astrophysics and Space Science》1993,209(1):1-17
The present attempt aims to predict the dependence of the spin parameter, , the angular momentum,J, and the typical radius,a
vir, on the mass,M, which have been found inN-body simulations of expanding density perturbations in hierarchical clustering, when virialization is attained. We show that M
0 for systems with same adimensional density distribution and velocity distribution, and in particular for scale-free density perturbations in hierarchical clustering. In the special case of ellipsoidal perturbations, it is also found:J M
7/4,a
vir M
1/2. All these results turn out to be in close agreement withN-body simulations, despite the simple model adopted. Expanding and virialized perturbations are modelled, respectively, by homogeneous and heterogeneous, similar ellipsoids which allow flat rotation curves far from the centre. Both energy and angular momentum maintain from a given time on, lying between the beginning of strong decoupling from the Hubble flow and the occurrence of maximum volume. Then the whole set of virialized ellipsoidal configurations with same energy and angular momentum are derived, and the dependence of the spin parameter on the anisotropy parameter, pec is investigated. Turning our attention to the formation of galaxies, we derive the total mass as a function of the collapse factor, using the empirical anticorrelation between dark to visible mass ratio within the optical radius of disk galaxies and their luminous masses. Observational data related to a sample of elliptical galaxies provide evidence that the contraction in these bodies occurred in proportion to the square root of the ratio of total to luminous mass. On the contrary, it is deduced that dissipation of angular momentum in elliptical galaxies occurred more or less at the same rate. If both shape and anisotropy parameter are preserved during the collapse, typical axis rations 21 = 0.98, 31 = 0.69, are found to correspond to a moderate anisotropy, pec 0.27, with a small dependence on the spin parameter in the range allowed. 相似文献
7.
A theory with variable gravitational constant, based on the bimetric formulation of general relativity, is suggested. It is in agreement with the Newtonian and post-Newtonian approximations of the theory of gravitation when the theory parameter ||4×10–6. The statical spherical-symmetric distribution of gravitating masses is investigated. It is shown that the total action (including the own gravitational field of the system)S=–M, where is the time in the remote system of reference, relative to which the celestial body is in rest. In the Brans-Dicke theory ||1 andS–M. The Tolman formula for the massM in the Einstein theory is also valid in the suggestedGeneralized Bimetric Theory of Gravitation. External analytical and internal numerical solutions of the field equations are found for the case of incompressible matter. It is shown that static and supermassive configurations may exist if –0.13<0. 相似文献
8.
Emission gradient curves for extreme ultraviolet (EUV) resonance lines of O vi and Mg x have been constructed from spectroheliograms of quiet limb regions observed with the Harvard experiment on Skylab. An analysis of these data suggests that the coronal temperature rises throughout the height range 1.03R
r1.3R
. This result implies that in quiet regions there is significant coronal heating beyond r = 1.3R
.Now at E.O. Hulburt Center for Space Research, Naval Research Laboratory, Washington, D.C., U.S.A. 相似文献
9.
Shiv S. Kumar 《Astrophysics and Space Science》1972,17(1):219-222
It is suggested that the minimum mass of a star at the time of its formation is approximately 0.01M
. Making use of this fact and the stellar mass functionF(M) M
–, it is found that the hidden mass (or the missing mass) in the solar neighborhood may be explained by the presence of a large number of invisible stars of very low mass (0.01M
M<0.07M
). 相似文献
10.
The binding energy and stability of supermassive stars (SMS's) is examined in the framework of the Parametrized Post-Newtonian (PPN) formalism of Will and Nordvedt. The PPN formalism encompasses the post-Newtonian limit of virtually every theory of gravity, differentiating between theories by means of nine PPN parameters. A general expression is derived for the energy integral in the PPN framework, and it is found that only in those theories in which the parameters 1=2=3=4=3=0 will the energy be conserved. In all such theories, a SMS of radius less than a critical radius will be unstable against adiabatic radial perturbations. Present experimental limits on the PPN parameters and do not exclude the possibility of the existence of stable, non-rotating, hydrogen-burning SMS's of masses an order of magnitude larger than the upper limit for the mass of such stars predicted in general relativity. 相似文献
11.
Jiann-Tsorng Horng 《Astrophysics and Space Science》1975,34(2):L1-L5
Cyclotron waves in the solar wind near 1 AU with frequencies well below the electron cyclotron frequency and wavelengths much larger than the electron cyclotron radius but less than the proton cyclotron radius are considered. The cyclotron radii are defined from parallel thermal velocity of electron component and proton component with respect to the interplanetary magnetic field. No LH cyclotron waves are found to propagate for
p
< 0, where
p
1 –T
p/T
p is the temperature anisotropy of the proton component with respect to the interplanetary magnetic field. The damping or growth of RH cyclotron waves is found to depend on the frequency range and the temperature anisotropy of the proton component. The RH cyclotron waves are damped in the frequency range
r
|
p
|
p
for
p
< 0, where
p
is the proton cyclotron frequency. RH cyclotron instabilities occur in the frequency range |
p
|
p
>
r
> |
p
|
p
/(1–
r
) for
p
< 0. The marginal state is at
r
=|
p
|
p
.Abstract presented at theInternational Symposium on Solar-Terrestrial, São Paulo, Brazil, 17–22 June, 1974 相似文献
12.
The orbital perturbations induced by the librational motion and flexural oscillations are studied for satellites having large flexible appendages. Using a Lagrangian procedure, the equations for coupled motion are derived for a satellite having an arbitrary number of appendages in the nominal orbital plane and two flexible members normal to it. The formulation enables one to study the influence of flexibility on both the orbital and attitude motions. The orbital coordinates are expanded as perturbation series in =(l/a
0)2,l anda
0 being a characteristic length of the satellite and unperturbed semi-major axis of the orbit, respectively. The first order perturbation equations are solved in terms of elastic deformations and librational angles using the WKBJ method in conjunction with the variation of parameter technique. Existence of secular perturbations is noted for certain librational flexural motions. Three specific examples, Alouette II, Radio Astronomy Explorer and Tethered Orbiting Interferometer, are considered subsequently and their possible secular drifts estimated.List of Symbols
A
ij, Bij
coefficients in the eigenfunction expansion ofv
i andw
i respectively, Equation (10)
-
C
k, Dk
constants, Equation (21)
-
EI
i
flexural rigidity of theith appendage
-
E(u0)
2(1+e
0 cosu
0)2
h
0
3
-
F(u0)
perturbation function, Equation (17b)
-
F
,F
,F
functions of librational angles and flexural displacements, Equation (11i)
-
F
,F
,F
F
,F
,F
with change of independent variable fromt tou
0
-
I
xx, Iyy, Izz
principal moments of inertia of the undeformed satellite
- [J
i]
inertia dyadic of the deformedith appendage
- [J
d]
inertia dyadic of the deformed satellite
-
M
mass of the satellite
-
P
R, Pu
functions of librational angles and flexural displacements, Equation (15d) and (15e), respectively
-
R
c
magnitude ofR
c
-
R
c0, R1
unperturbed value and first order perturbation ofR
c, respectively
-
R
c
,R
0
position vectors of the c.m. of the deformed and undeformed satellite, respectively
-
T
kinetic energy of the satellite
-
U
potential energy of the satellite
-
U
e, Ug
elastic and gravitational potential energy, respectively
-
X, Y, Z
orbital co-ordinate axes, located at the c.m. of the deformed satellite
-
Y
1(u0), Y2(u0)
functions ofu
0, Equation (18b) and (18c), respectively
-
a
semi-major axis
-
a
0
unperturbed value ofa
-
e
eccentricity
-
e
0
unperturbed value ofe
-
h
0
unperturbed angular momentum per unit mass of the satellite
-
i
inclination of the orbital plane to the ecliptic
-
i, j, k
unit vectors alongx (or ),y (or ) andz (or ) axes, respectively
-
l
characteristic length of the satellite
-
l
i
length of theith appendage
- [l
i]
matrix of direction cosines ofx
i, vi andw
i
-
l
,l
,l
direction cosines ofR
c
-
m
0, mi
mass of the main body andith appendage, respectively
-
p
i
2
-
q
m, Qm
generalized co-ordinate and force, respectively
-
r
1
R
1/Rc0
-
r
position vector of an element of the body referred toxyz axes
-
r
u
position vector of an element after deformation, referred to axes
-
r
c
x
c
i+y
c
j+z
c
k, position vector of the c.m. of the deformed body referred toxyz axes
-
s
x
i/li
-
t
time
-
u
true anomaly
-
u
0, u1
unperturbed value and the first order perturbation ofu, respectively
-
u
elastic displacement vector
-
u
c
u–r
c
-
velocity of an element relative to axes
-
v
i, wi
flexural deformations
-
x, y, z
body co-ordinate axes with origin at the c.m. of the undeformed satellite
-
x
i
distance of an element of theith appendage from the root
-
j
jth eigenfunction (normalized) of a cantilever
-
angle between the line of nodes and vernal equinox
-
,
,
components of nondimensionalized angular velocity of the satellite
- , ,
pitch (spin), yaw and roll, respectively
- i
nominal inclination of theith appendage in the orbital plane
-
-
small parameter, (l/a
0)2
- j
jth eigenvalue of a cantilever
-
gravitational constant
-
jk
constant, Equation (11j)
- , ,
body co-ordinate axes with origin at the c.m. of the deformed satellite
-
(
i +
j +
k), angular velocity of the satellite 相似文献
13.
D. L. Lambert 《Solar physics》1968,3(1):118-124
A simplified representation of the temperature distribution in the solar photosphere is proposed: (
0) =
0 -
1 log
0. An expression is derived for the emergent continuous spectrum from the simple model. The limitations and applications of the simple model are discussed. 相似文献
14.
A model of the galactic centre with magnetic monopole has been presented here. The positron can be produced continuously through magnetic monopoles to induce baryon decay (Rubakov catalytic reaction) and a lot of energy can be released as well. The calculation results show that even if the galactic center contains only a few magnetic monopoles (=N
M/NB10–24), this massive object can not collapse into a black hole. This model can explain the observed intensities of the annihilation line and higher energy photons ofE
>511 keV from the galactic centre.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
15.
G. Dautcourt 《Astrophysics and Space Science》1976,43(2):L1-L2
Low-frequency gravitational radiation, with wavelengths reaching or exceeding interplanetary distances, and with a mean energy density of the order of the critical cosmological density
c
, generates a frequency-shift of order/10–15
h
0(1/108km)(/
c
)1/2 in electromagnetic signals transponded by interplanetary spacecraft at a distancel from the Earth. 相似文献
16.
A surprisingly good correlation has been found for SPA measured at VLF propagation () and 7 GHz solar microwave burst energies (E
). The data are correlated in the form = a log E
+ b and include all kind of solar events, irrespectively from type, complexity or duration. Soft X-ray peak fluxes (I
x) have a known similar correlation to SPA, and a functional relationship of the form 479-01 can be established. As one practical application, the energies from solar events can be reasonably well inferred from SPA data, which are quite reliable and easily obtainable. 相似文献
17.
R. V. Isakov A. A. Ruzmaikin D. D. Sokoloff M. V. Faminskaya 《Astrophysics and Space Science》1981,80(1):145-155
The asymptotic properties of a turbulent disk dynamo at large dimensionless numbersR
andR
characterizing the helicity and the differential rotation are analysed. Three types of generations in the dependence of the relations betweenR
andR
are found: 2-dynamo and two types of -dynamo. For each of these types the rates of growth are obtained and the forms of solution are pointed out. Boundaries of the disk dynamo approximation are given. 相似文献
18.
Peter Musen 《Celestial Mechanics and Dynamical Astronomy》1971,3(3):289-311
This work contains a transformation of Hill-Brown differential equations for the coordinates of the satellite to a type which can be integrated in a literal form using an analytical programming language. The differential equation for the parallax of the satellite is also established. Its use facilitates the computation of Hill's periodic intermediary orbit of the satellite and provides a good check for the expansion of the coordinates and frequencies. The knowledge of the expansion of the parallax facilitates the formation of differential equations for terms with a given characteristic. These differential equations are put into a form which favors the solution by means of iteration on the computer. As in the classical theory we obtain the expansions of the coordinates and of the parallax in the form of trigonometric series in four arguments and in powers of the constants of integration. We expand the differential operators into series in squares of the constants of integration. Only the terms of order zero in these expansions are employed in the integration of the differential equations. The remaining terms are responsible for producing the cross-effects between the perturbations of different order. By applying the averaging operator to the right sides of the differential equations we deduce the expansion of the frequencies in powers of squares of the constants of integration.Basic Notations
f
the gravitational constant
-
E
the mass of the planet
-
M
the mass of the satellite
-
t
dynamical time
-
x, y, z
planetocentric coordinates of the satellite
-
u
x+y–1
-
s
x–y–1
-
the planetocentric distance of the satellite
-
w
1/
- 0
the variational part of
-
w
0
the variational part ofw,
-
n
the mean daily sidereal motion of the satellite
-
a
the mean semi-major axis of the satellite defined by means of the Kepler relation:a
3
n
2=f(E+M)
-
a
the mean semi-major axis defined as the constant factor attached to the variational solution
-
e
the constant of the eccentricity of the satellite
-
the sine of one half the orbital inclination of the satellite relative to the orbit of the sun
-
c(n–n)
the anomalistic frequency of the satellite
-
c
0
the part ofc independent frome,e, and
-
g(n–n)
the draconitic frequency of the satellite,
-
g
0
the part ofg independent frome,e, and
-
exp (n–n)t–1
-
D
d/d
-
e
the eccentricity of the solar planetocentric orbit
-
a
the semi-major axis of the solar orbit
-
n
the mean daily motion of the sun in its orbit around the planet
-
m
n/(n–n)
-
a/a-the parallactic factor
-
the disturbing function 相似文献
19.
Hubble Space Telescope observations by Savage, Cardelli and Sofia (1992) and Cardelliet al. (1993) have led to improved gas phase abundances for many elements in the diffuse cloud towards the star Oph. Most remarkably, it was found that oxygen is much more strongly depleted than previousCopernicus observations indicated. As a consequence, chemical models of the Oph cloud are severely affected by the drop in the observed oxygen abundance by almost a factor of two; some previous model calculations for the Oph cloud failed to reproduce-even approximately-the observed high CO column density. The model calculations for the Oph cloud developed by Wagenblast (1992) in which the abundance of all observed neutral molecules could be reproduced have been revised and it is found that oxygen and nitrogen hydrides are required to be formed efficiently on the surface of grains; further, there are indications for a high cosmic ray ionization rate of the order 10–16 s–1. 相似文献
20.
Four spectrograms of the cepheid Geminorum at different phases have been analysed for the determination of the abundances of various elements. The analysis shows that the atmosphere of Gem has an essentially solar composition. 相似文献
|