共查询到20条相似文献，搜索用时 15 毫秒
1.
R. Louise 《Astrophysics and Space Science》1982,86(2):505-508
The model is based on the assumption that logarithmic spiral arms of most spiral galaxies are due to the totating density wave
obeying the steady wave equation
. It is shown that this equation accounts also for the so-called Titius-Bode's law in the solar system. 相似文献
2.
S. A. Stephens 《Astrophysics and Space Science》1981,76(1):87-103
A reliable representation to the invariant cross-section for the production of antiprotons (
) in inclusive reactions has been obtained, which fits the data extremely well from threshold to ISR energies. Using this, the production spectrum of
by cosmic ray interaction with interstellar gas is calculated and is compared with other existing calculations. The equilibrium spectrum
in the Galaxy has been derived from about 100 MeV to a few hundred GeV in kinetic energy using Leaky Box Model for the propagation of cosmic rays, by taking into account all energy loss processes. It is found that
/P ratio calculated here is very much smaller than the observed ratio. In view of the fact that this excess of observed
/P ratio is much larger than the measured upper limits on the fraction of antimatter in the form of antinuclei, the excess
/P ratio has not been attributed to the existence of antimatter. Instead, it is shown that Closed Galaxy Model for the propagation of cosmic rays predicts more antiprotons than observed. Therefore, it is suggested that if cosmic rays contain about 50% new component of local origin, the resulting Closed Galaxy Model explains well the observations. The present calculations also predict too small a flux of
below a few hundred MeV to make this energy region ideally suited to look for antiprotons of primordial origin. 相似文献
3.
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
4.
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
5.
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
6.
The behaviour of the hardness ratio in low-mass X-ray binaries (LMXRB) indicates that at some value of mass accretion rate
, the X-ray intensity decreases with increasing
. It is suggested here that, at some
, wind from the accretion disk becomes appreciable and depletes the mass accretion on to the neutron star and thus reduces the X-ray intensity. This explains the behaviour of the hardness ratio in LMXRB. Possible implications of this on quasi-periodic oscillations are discussed. 相似文献
7.
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
8.
Modes of nonradial oscillations of six composite polytropic models have been investigated numerically to study the effect of central condensation parameter
being the density at the centre and
the mean density of a stellar model) on the modes of nonradial oscillations of stellar models. 相似文献
9.
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
10.
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
11.
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
12.
A linear excitation of electromagnetic modes at frequencies
, in a plasma through which two electron beams are contra-streaming along the magnetic field is investigated. This may be a source of the observed
emissions at auroral latitudes. 相似文献
13.
The paper is concerned with turbulent flow of incompressible, spatially homogeneous viscous fluid. A model for turbulence energy equation is obtained, ignoring the pressure redistribution term in dynamical equations for the Reynolds stresses. The mechanism of dissipation on turbulence production is discussed and shown that the turbulence kinetic energy decays upto a constant value as time becomes infinitely large, i.e., for isotropy, dissipation inhibits the production process and if
>
initially then dissipation causes reduction in anisotropy. 相似文献
14.
Using the leaky-box model the upper limit of the antiproton-proton flux ratio at the top of the atmosphere has been estimated from the latest primary nucleon spectrum and accelerator data on
inclusive reactions. The estimated value of
flux ratio comes out to be (3.6±0.3)×10–4 is in accord with the previous results but still far from the measurements. 相似文献
15.
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
16.
H. Rovithis-Livaniou 《Astrophysics and Space Science》1977,52(2):271-306
The aim of the present paper is to find the eclipse perturbations, in the frequency-domain, of close eclipsing systems exhibiting partial eclipses.After a brief introduction, in Section 2 we shall deal with the evaluation of thea
n
(l)
integrals for partial eclipses and give them in terms ofa
0
0
,a
0
0
(of the associated -functions) and
integrals; while Section 3 gives the eclipse perturbations
arising from the tidal and rotational distortion of the two components. The
are given for uniformly bright discs (h=1) as well as for linear and quadratic limb-darkening (h=2 and 3, respectively).Finally, Section 4 gives a brief discussion of the results and the way in which they can be applied to practical cases. 相似文献
17.
The light curved in the CM field 总被引：1，自引：0，他引：1
In this paper we introduce the CM field in Sections 2 and 3 based on the paper by Wang and Peng (1985), and calculate the light curved in the CM field in Section 4. The result shows thatP makes CM larger than C at
, and smaller at
. Under a special circumstance which source, CM lens, and observer are in the same line, if we get |
0=0
,
and |
=/2
, we can determine theP(M) andQ(M) of the CM lens,M is the mass of the CM lens. 相似文献
18.
The antiproton-proton flux ratio has been estimated from the closed galaxy model of Peters and Westergaard by using the latest primary nucleon spectrum and
inclusive reaction accelerator results. The derived
flux ratio is about three times higher than those expected from the leaky box model. The results have been compared with the previous estimates by different authors. 相似文献
19.
E. Evangelidis 《Astrophysics and Space Science》1977,46(2):309-319
The dispersion relation has been derived for density waves propagating at an arbitrary angle. The analysis has shown the existence of a resonance which for a two-arm galaxy can be stable, neutral or unstable as
}2$$
" align="middle" border="0">
, respectively. 相似文献
20.
The differential equations governing relativistic polytropic fluid spheres have been integrated numerically for polytropic indexn = 0.0 (0.1) 4.9 and relativity parameter = 0.0 (0.1) 0.9, and the resulting boundary conditions for
and other related quantities are presented in this paper. 相似文献