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1.
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
2.
The motion of spin particles in the Schwarzschild field is examined in this paper. It is shown that Mathisson-Papapetrou equations under additional conditions
, where
is the Lie derivative of the Killing vector
j
, permit only radial motion, motion in the equatorial plane and in the equilibrium points. All these types of motion are considered more in detail. 相似文献
3.
I. H. Urch 《Astrophysics and Space Science》1984,104(2):357-366
The diffusion of charged particles in a stochastic magnetic field (strengthB) which is superimposed on a uniform magnetic fieldB
0
k is studied. A slab model of the stochastic magnetic field is used. Many particles were released into different realizations of the magnetic field and their subsequent displacements z in the direction of the uniform magnetic field numerically computed. The particle trajectories were calculated over periods of many particle scattering times. The ensemble average
was then used to find the parallel diffusion coefficient
. The simulations were performed for several types of stochastic magnetic fields and for a wide range of particle gyro-radius and the parameterB/B
0. The calculations have shown that the theory of charged particle diffusion is a good approximation even when the stochastic magnetic field is of the same strength as the uniform magnetic field. 相似文献
4.
Werner Lohmann 《Astrophysics and Space Science》1979,66(1):103-111
The open star clusters M36, M38 and NGC 2477 were investigated by the strip method on charts of photographs taken with the Schmidt-Spiegel of the German Observatory Hoher List (M36/38) and the Curtis-Schmidt Telescope of the Cerro Tololo Interamerican Observatory (NGC 2477). The results are — Masses: 830, 2350, 4400
; radii: 6.4, 10.0, 10.0 pc; central densities: 9.9, 15.3, 32.5
pc–3; density laws: Gaussian (M36), generalized law of Schuster withn=3.00, 2.79; mean velocities of the stars 0.74, 1.01, 1.38 km s–1.
Mitteilungen Serie A. 相似文献
Mitteilungen Serie A. 相似文献
5.
We investigate static, spherical configurations of cold catalized matter in the Einstein-Cartan theory of gravitation. Assuming that density of spin is proportional to the number density of baryonsn and using an equation of state of a degenerate, relativistic Fermi gas, we numerically integrated the relativistic equation of equilibrium. We have also studied the stability of those configurations. Configurations with central number densityn
c
such that
where
is the effective pressure, are very similar to general relativistic configurations with the same central density. In the Einstein-Cartan theory there exists another disjoint family of equilibrium configurations for which
but
. Those configurations have very small masses 10–6 g and raddi 10–34 cm and are unstable.Supported in part by Research Grant MR-I-7. 相似文献
6.
James R. Ipser 《Astrophysics and Space Science》1970,7(3):361-373
This paper present two new theorems on the theory of the stability of highly relativistic stars. Thefirst theorem states that a highly relativistic, spherical star is stable if and only if its adiabatic index (assumed to be constant in the interior regions) is greater than a certain critical value,
crit which depends in a specified way on the high-density equation of state. This critical value is analogous to the Newtonian value
, but because of relativistic effects it is typically somewhat larger than
. Thesecond theorem shows that at high central densities, the curves of —(binding energy) vs. radius, —E
B
(R) for certain hot, isentropic sequences of stellar models must exhibit damped clockwise spirals. This spiraling reflects the onset of instability in one radial mode of pulsation after another as the central density increases along the sequence. 相似文献
7.
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
8.
The thermal equilibrium of a hydrogen plasma heated and ionized by an external radiation field, diluted by a factorW
* and defined by an effective temperatureT
*, is studied. In addition, the problem of propagation of acoustic and thermal waves in the above plasma model is also analysed. It is found that an external radiation field has stabilizing effects against wave amplification. From the dispersion relation obtained, the phase velocity
for sound and thermal waves and their respective scale-length of damping (or anti-damping)
is calculated as a function of the frequency
for representative values of the plasma temperature
and the external radiation fieldT
*. 相似文献
9.
B. -C. Kämper 《Astrophysics and Space Science》1986,120(2):167-189
A comprehensive period study of the times of minima observed from 1881 to 1985 has been performed. Previous interpretations of the O–C diagram based on light-time effect are confirmed. The light-time orbit of U Oph has been revised using a differential corrections procedure. We get an eccentric orbit withe=0.22±0.06,P=38.7±0.2 yr, and a mass function
. In addition, our analysis has revealed short-period apsidal motion (U/P=4515±75) in a slightly eccentric close orbit (e=0.0031±0.0003), allowing a reliable determination of the density concentration coefficient,k
2=0.0059±4. A comparison with stellar evolutionary models calculated by Jeffery (1984) yields the helium contentY=0.28±0.05 and an age of 3×107 yr for the components of U Oph. 相似文献
10.
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
11.
An exact analysis of Stokes' problem for an infinite vertical plate, whose temperature varies linearly with time, has been presented. It is observed that the velocity near the plate increases with the timet, and the Grashof numberGr. The skin-friction has been found to vary ast
7/2 and the Nusselt number varies as
or
whereP is the Prandtl number. 相似文献
12.
A procedure has been devised to construct a solution of the Clairaut equation in the form of an asymptotic expansion in terms of descending powers of
, wherej denotes the order of spherical-harmonic distortion. It has been shown that asj and, therefore increases, the foregoing series approaches asymptotically a solution of our equation. The procedure is similar to the WKB-method of theoretical physics. 相似文献
13.
A theoretical model for3He enrichments in solar energetic particles is developed. First, current-driven, electrostatic instabilities that have frequencies
(
is the cyclotron frequency of3He) are investigated for a plasma consisting of H,4He,3He, and electrons with the density of3He much lower than those of H and4He. It is found that in many cases the oblique ion-acoustic waves can have positive growth rates at frequencies
and, at the same time, negative growth rates at
and at H. This can occur near the marginal state of the instability. The wave damping at these frequencies is caused by the cyclotron resonances of4He and H. The cyclotron damping at
is negligible, however, because the abundance of3He is very small. The H cyclotron waves can be unstable at
for a wide region of plasma parameters; the electron-to-ion temperature ratio must beT
e
/T
H
1.5. To destabilize the4He cyclotron waves with
, high4He density and high electron temperature are both required. Then,3He enrichments are studied on the basis of the theory of nonlinear magnetosonic waves, which can promptly accelerate ions. The current-driven electrostatic waves with
can enhance fluctuation velocities of3He. Thus, in the presence of these waves, magnetosonic waves can selectively accelerate3He particles to high energies. Finally, cyclotron resonances of heavy ions with the waves
or
are briefly discussed. 相似文献
14.
The red shift and central intensity are given for eleven spectral lines having an observed reduced equivalent widthV ranging fromV=15 toV=200. The computations have been repeated for eight values of the scattering thickness of the chromosphere, from
to
. A theoretical interpretation of measurements in the Sun is also given. 相似文献
15.
This paper points out the errors in the solutions of a research work by N. Nanousis under the same title published in this journal, volume 199, 1993. The correct solutions of the problem for the velocity field and the drag on the plate, by the Laplace transform technique, are presented. The results are discussed for two cases of an arbitrary time-dependent forcing effect. It is shown that the viscoelastic parameterk > 0 influences the velocity and introduces reverse flow. For a suddenly accelerated plate,k > 0 increases the velocity forz <
and decreases it forz >
. In the case of the ramp-type boundary condition,k > 0 tends to decrease the velocity. 相似文献
16.
An estimate of the period of the rotation of the line of apsides of the double-star system Phe is obtained by representing the density function as a product of a normal Gaussian distribution and an associated Legendre polynomial
.The asymptotic behaviour of this function coincides with the results obtained by Zeldovichet al. (1981).The period of motion of the line of apsides of Phe (about 63 years) obtained in this way comes close to the period determined by an empirical formula for
of Batten (1973). 相似文献
17.
Vibrational transition probabilities-namely, Franck-Condon factors and
-centroids-have been evaluated using an approximate analytical method for theD-X system of SiS. Morse potential energy curves forD
1 andX
1+ states of SiS have been constructed using the latest spectroscopic data. The value of
-centroids for the band have been found to decrease linearly with the corresponding wavelength. 相似文献
18.
On the basis of a globular cluster study a crude estimate of the total mass of the galactic halo within 20 kpc from the centre is done. It gives a minimal halo mass of the order of
, yielding possibilities for a mass as large as
. The content of the interstellar matter in the halo is estimated too. It is found that the gas content is a few percents the minimal mass, the gas temperature is very high — about 1×106 K, the magnetic field weak — about 0.25 nT. A weak nonthermal radio emission might be expected from such a halo. 相似文献
19.
The integral balance method has been used to obtain an approximate analytical solution of a nonlinear boundary value problem which arises in the theory of diffusion with a concentration-dependent coefficient. It is the purpose of this paper to give an interpretation of the supposition of interface reactions which obey the law of kinetic mass action.Nomenclature
C(Z,t)
concentration
-
C
0
concentration at initial time
-
D
diffusivity
-
D
0
diffusivity at initial time
-
F(t)
a function of time
-
K
0
half-order reaction rate constant
-
k
1
first-order reaction rate constant
-
k
2
second-order reaction rate constante
-
L
characteristic length
-
n
parameter
-
t
time
-
Z
space variable
Dimensionless variables and similarity criteria
nondimensional half-order reaction rate constant
-
nondimensional first-order reaction rate constant
-
nondimensional second-order reaction rate constant
-
x=Z/L
dimensionless space variable
-
F
0=D
0
t/L
2
Fourier number
-
g(F
0)=[F(t)–C
0]/C
0
a function of generalized time
- (x, F
0)=[C(x,t)–C
0]/C
0
dimensionless concentration
- <(F
0)>
dimensionless average concentration 相似文献
20.
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