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1.
The tidal force effects of a spherical galaxy passing head-on through a disk galaxy have been studied for various orientations of the disk galaxy with respect to the direction of relative motion of the two galaxies. The density distribution of the spherical galaxy is taken to be that of a polytrope of indexn=4 and that of the disk galaxy is taken to be, (r)=ce–4r/R, where c is the central density andR the radius of the disk. It is found that the disruptive effects due to the tidal force are minimum when the plane of the disk lies along the direction of relative motion, but are maximum when the plane of the disk is slightly inclined to this direction (about 15°). The tidal force effects at the median radius have also been computed. The tadal force effects are much higher in the interior region of the disk. 相似文献
2.
The study of uniformly polytropes with axial symmetry is extended to include all rotational terms of order 4, where is the angular velocity, consistently within the first post-Newtonian approximation to general relativity. The equilibrium structure is determined by treating the effects of rotation and post-Newtonian gravitation as independent perturbations on the classical polytropic structure. The perturbation effects are characterized by a rotation parameter = 2/2G
c
and a relativity parameter, =p
c
/
c
C
2
, wherep
c
and c are the central pressure and density respectively. The solution to the structural problem is obtained by following Chandrasekhar's series expansion technique and is complete to the post-Newtonian rotation terms of order
2. The critical rotation parameterv
c
, which characterizes the configuration with maximum uniform rotation, is accurately evaluated as a function of . Numerical values for all the structural parameters needed to determine the equilibrium configurations are presented for polytropes with indicesn=1, 1.5, 2, 2 5, 3, and 3.5. 相似文献
3.
Tapan K. Chatterjee 《Astrophysics and Space Science》1981,76(2):491-502
The tidal force effects of a spherical galaxy passing head-on through a disk galaxy have been studied at various regions of the disk galaxy and for various orientations of the disk galaxy with respect to the direction of relative motion of the two galaxies. The density distribution of the disk galaxy is taken to be, (r)=ce–4r/R
, where c is the central density andR is the radius of the disk. The density distribution of the spherical galaxy is taken to be that of a oolytrope of indexn=4. It is found that as a result of the collision, through the central parts and the outer parts of the disk galaxy remain intact, the region in between these two regions disrupts. Thus a ring galaxy with a nucleus embedded in the ring-i.e., a ring galaxy of the RN-type, is formed. 相似文献
4.
A critical analysis of the methods and results of estimating the optical thickness of the dust component in the Martian atmosphere 0, the particle size r
0, and the imaginary part of the refractive index n
ihas shown the following. (1) Observational data on the brightness distribution over the Martian disk as well as the phase dependences of diffusely reflected light and the azimuthal dependences of diffusely transmitted light are most appropriate to use only for verifying the reliability of the aerosol parameters determined by other methods. (2) If the morning and evening fogs in the atmosphere are disregarded, the Bouguer–Lambert–Beer method used to analyze the solar-brightness attenuation measured on the planetary surface yields overestimated extraatmospheric solar intensity I
0and atmospheric optical depth 0. At the Viking 1landing site, I
0and 0could be overestimated by a factor of 1.7 and by 0.35, respectively. (3) The aerosol size determined by analyzing measurements of the azimuthal dependences for the Martian sky brightness at low elevations of the Sun most likely corresponds to the fog particles. (4) If overestimated values of I
0were used to standardize the observations of the solar radiation transmitted by the Martian atmosphere, then n
iwere also overestimated; using overestimated 0also affected the reliability of the latter. (5) The problem of reliability of the available 0and r
0estimates for periods of high atmospheric transparency is yet to be solved. For the highest activity of the dust storm in 1971, it was found that 4.5 r
0 7.5 m for the lognormal particle size distribution with 2= 0.2 and the optical thickness of a dust cloud 0 15. (6) The spectral values of the apparent albedo of Mars measured in October 1971 at a phase angle of 42° in the spectral range 0.250 0.717 allowed the imaginary part of the refractive index to be estimated in terms of a model of a dust cloud composed of spherical particles with the lognormal size distribution with r
0= 4.5 m and 2= 0.2. 相似文献
5.
Mitchell F. Struble 《Astrophysics and Space Science》1979,64(2):319-337
The time evolution of the velocity dispersion as a function of radius, called v-profiles, of threeN-body simulations of Wielen are presented in units ofr/R
G (whereR
G is the gravitational or virial radius) and discussed as a function of mass sample. The evolution of the radial and tangential components of the velocity dispersion is discussed, and each v-profile is fitted to a simple power law in the halo (0.15r/R
G2.0). Several structural features appear at late time intervals: (a) an upturn in the radial component of v which occurs in a decreasing shell (closer to the core) in time, (b) the v-profile of the massive particles mimics that of the total sample, since equipartition of kinetic energy does not obtain, and (c) a local minimum atr0.3–0.5R
G appears in one model which coincides with the local minimum in the number density profiles and possibly with feature (a).The line-of-sight v-profile, called LS-profile, of each model as a function of time and mass sample are also presented and discussed. They contain the same structural features as the v-profiles. Projection factors at small radii are also discussed. The LS-profiles of the models can be compared with the observed velocity dispersion profiles of clusters of galaxies in Struble (1979a). 相似文献
6.
Masaya Saitou 《Astrophysics and Space Science》1989,162(1):47-56
Some peculiarities in the behaviour of a model self-gravitating system described by hydrodynamical equations and isothermal equation of state connected with the presence of thermodynamical fluctuations in real systems were investigated in numerical experiment. The values of density and velocity , , respectively, were computed by numerical code perturbed on each time-step and in each computational cell by random values , for modeling such fluctuations. Perturbed values
i
=
i
+
i
,v
i
=
i
+ v
i
were used to initiate the next step of computations. This procedure is equivalent to an introduction into original hydrodynamical equations of Langevin sources which are random functions. It is shown that these small fluctuations (= v =0,2 =v
2 = 10–8) grow many times in marginally-stable state. 相似文献
7.
Raj Bali 《Astrophysics and Space Science》1985,116(1):81-88
The object of this paper is to investigate the behavior of a magnetic field in a viscous fluid cosmological model. It has been assumed that the expansion () is proportional to the eigenvalue
1
of the shear tensor
i
j
and the coefficient of shearing viscosity is proportional to the scalar of expansion. The paper also discusses the behavior of the model when the magnetic field tends to zero and comments on some other physical properties. 相似文献
8.
The results of the experimental study of the interaction of polyethylene impactors with a massive flat organic-glass target are presented. The impactor speed ranged from 3.2 to 5.84 km/s. A statistical analysis of the mass and size distributions of fragments of the impact and chop craters of the target is done. As a result, some scaling relations are established for the geometric size of the craters, the cumulative ejected mass, the mass of the largest fragment ejected from the impact crater, and for the dust mass. The mass distribution of the impact-crater fragments is shown to obey a power law and agrees well with other authors" data for some materials. The critical impact energy
k
, resulting in the catastrophic disruption of the target into individual fragments, is estimated. For organic glass, the value of
k
is found to be 4 × 104J/kg. The mass of the largest (central) fragment accounts for 27 to 33% of the overall mass ejected from the impact crater. The use of the parameter 3=
p
/
p
v
2
0gives the best fit to the observational data for the masses released from the impact and chop craters. 相似文献
9.
V. N. Fedorenko 《Astrophysics and Space Science》1990,163(2):187-200
I give an interpretation of a result of Simpsonet al. (1988) on the variation with kinetic energyT
i
of the mean pathlengthX
m
(T
i
) of the galactic cosmic rays (CGRs) in the range 0.1T
i
10.0 GeV nucl–1. I argue that the data onX
m
(T
i
) may be interpreted in terms of a model of GCR diffusion on the one-dimensional Alfvén-wave turbulence, having a cutoff in the spectrum at frequencies
h
, where
h
is the proton gyrofrequency. The cutoff results in changing of the character of variation of the GCR diffusion coefficientD(T
i
)T
a
in the rangeT
i
1 GeV nucl–1 towards some more complicated variation at 0.1T
i
1.0 GeV nucl–1 due to the peculiarities of the pitch-angle scattering at 900. 相似文献
10.
Basil Zafiropoulos 《Astrophysics and Space Science》1987,139(1):111-128
The equations for the variation of the osculating elements of a satellite moving in an axi-symmetric gravitational field are integrated to yield the complete first-order perturbations for the elements of the orbit. The expressions obtained include the effects produced by the second to eighth spherical harmonics. The orbital elements are presented in the most general form of summations by means of Hansen coefficients. Due to their general forms it is a simple matter to estimate the perturbations of any higher harmonic by simply increasing the index of summation. Finally, this paper gives the respective general expressions for the secular perturbations of the orbital elements. The formulae presented should be useful for the reductions of Earth-satellite observations and geopotential studies based on them.List of Symbols
semi-major axis
- C
jk
n
(, )
cosine functions of and
-
e
eccentricity of the orbit
-
f
acceleration vector of perturbing force
-
f
sin2t
- i
inclination of the orbit
-
J
n
coefficients in the potential expansion
-
M
mean anomaly
-
n
mean motion
-
p
semi-latus rectum of the orbit
-
R, S, andW
components of the perturbing acceleration
-
r
radius-vector of satellite
-
r
magnitude ofr
-
S
jk
n
(, )
sine functions of and
-
T
time of perigee passage
-
u
argument of latitude
-
U
gravitational potential
-
true anomaly
-
V
perturbing potential
-
G(M++m) (gravitational constant times the sum of the masses of Earth and satellite)
- n,k
coefficients ofR component of disturbing acceleration (funtions off)
- n,k
coefficients ofS andW components of disturbing acceleration (functions off)
-
mean anomaly at timet=0
-
X
0
n,m
zero-order Hansen coefficients
-
argument of perigee
-
right ascension of the ascending node 相似文献
11.
A detailed study of classical polytropes in general relativity has been presented for O ((dP/dE)O) 1.0 and O((P/E
O)O. The behaviour of various structural parameters with O/O, O and O are the values ofP/E and dP/dE at the centre) has been studied. The most important result of this study is the fact the qualitative behaviour of all the structural parameters depends only on the value of µO for the various assigned O values. The maximum value of surface red shift occurs when µO=0.6 and for O=1.0 it equals 0.618. These structures are gravitationally bound for µO0.8 and most so for µO=0.4. The maximum value of binding coefficient comes out to be 0.181 when O=1.0. These structures have been used to model neutron stars. The maximum mass of neutron star based upon such a model comes out to be 2.55M
(for µO=0.4 and O=1.0) and maximum size comes out to be 15.0 km (for µO=0.2 and O=1.0). It is also seen that the structures are pulsationally stable for µ0.6. 相似文献
12.
S. Yabushita 《Celestial Mechanics and Dynamical Astronomy》1992,54(1-3):161-178
Claim for periodicity in the crater formation rate is reinvestigated using a criterion proposed by Broadbent, and data sets of Rampino and Stothers and of Grieve are shown to satisfy the periodicity criterion (P 30 Myr).On the other hand, currently observed impactors are mainly asteroids, while long and short periodic comets whose fluxes may vary by external disturbances occupy only a small fraction. Using a Monte Carlo simulation, constraints are obtained for the dispersion Q(Myr) from an exact periodicity and for the periodic components (F
tp) in the signals for their periodicity to be detected. It is found that for = 5, 6 and 7 Myr, F
tp, would have to be 40% or greater, 60% or greater and 80% or greater, respectively. These constraints are used to discuss whether the giant molecular cloud perturbations can give rise to the periodicity in the impact events. The amplitude of the solar Z-motion need to be some 100pc for = 6 Myr, which requires the periodic component (SP and LP comets, if the former originate from the latter) to be 60%, while for = 7 Myr, the periodic component need to be 80%. The GMC perturbation model consistent with the periodicity appears to be the one where the amplitude is 100pc and the periodic component - 60% of the impactors. If SP comets mainly originate from a source such as the hypothetical Kuiper belt, the GMC perturbation would not be consistent with the periodicity. 相似文献
13.
We have attempted to extend existing lists of log(gf) values for singly-ionized elements of the iron group introducing systematic corrections to Warner's determinations (Warner, 1967). The suggested corrections shift Warner's-log(gf) system into Kurucz-Peytremann's system. We compare Warner's corrected log(gf) with other modern values; results are quite satisfactory for iron although not as good for titanium, which still shows residuals correlating with the strength of the line. Abundances consistent with those currently accepted are obtained for the iron group in the solar photosphere if our proposed corrected log(gf) values are used.Once systematic corrections to Warner's original values are applied, and after eliminating some individual log(gf) which are probably wrong, the internal consistency of Warner's corrected log(gf) is found to be 0.20 dex (=standard deviation of a single log(gf)).Research supported in part by the SECYT. 相似文献
14.
L. O. Hanlon K. Bennett T. Galama T. A. Th. Spoelstra 《Astrophysics and Space Science》1995,231(1-2):307-310
The COMPTEL instrument onboard theCompton Gamma-Ray Observatory imaged the bright gamma-ray burst GRB 940301 within 1.6 hours of the event, with a mean 1 error radius of 1.5°. The error region was subsequently refined by combining the COMPTEL location with the arc derived from differences in the event arrival time at the Ulysses and BATSE detectors. Westerbork observations of the COMPTEL error region began on March 4 1994 at 21 cm, however coverage of the refined position was not obtained until 32 days after the GRB occurrence, by which time the operating wavelength had changed to 92 cm. We have constrained the level of variability of sources within the triangulation arc-COMPTEL 2 error box region to be less than 40 mJy (5 upper limit) at 92 cm 41 days after the burst. 相似文献
15.
The stability of the origin of an autonomous Hamiltonian system is investigated when the system possesses a third or fourth-order resonance.H
2, the quadratic part ofH isH
2=n
i=1
i
J
i
and the resonance condition is n
i=1
k
i
i
where thek 0,i = 1, 2, ...,n are the natural or fundamental frequencies. It is shown that the only case in which the origin can be unstable is ifk
i0,i=1,2,...,n. The condition for instability is then given in terms of the coefficients of the higher order terms in the Hamiltonian. The transfer of energy between modes is also investigated when a near-resonant condition exists. 相似文献
16.
R. Grant Athay 《Solar physics》1988,116(2):223-237
An attempt is made in this paper to determine the coefficient a in a power-law relationship of the form V
~T
between the r.m.s. velocity fluctuation, V
for raster images with 3 resolution and the temperature, T of line formation using SMM solar data. For T between 8000 and 105 K, the data suggest a best fit with 3/4 < 1. It is argued, however, that unresolved fine structure tends to reduce the observed value of V
and that higher resolution data may yield different values for . Skylab data have shown that the non-thermal line broadening velocity, , is proportional to T
1/2. Also, for all temperatures less than 105 K, V
. This latter result, however, is again dependent on spatial resolution and may not be true in observations made with sufficient spatial resolution. The magnitudes of both V
and indicate that bulk motions play important roles in the structure of the solar atmosphere as well as in its energy and momentum balance. It is important, therefore, to identify the true nature of such motions with better accuracy than is possible with currently available data.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
17.
Fluctuations in the angle-of-arrival of a luminous wavefront are investigated by placing a narrow slit over the image of the solar limb, and observing the entrance pupil through this diaphragm. Measurement of the standard deviation
AA
of these fluctuations, in a direction perpendicular to the solar limb, provides sufficient information to estimate an absolute parameter characterizing the seeing, i.e. Fried's parameter r
0 or the equivalent parameter
L
C
N
2(h) dh which gives the integral, over an atmosphere thickness L which depends on the spatial and angular filterings performed by the slit, of the structure constant C
N
2
characterizing fluctuations in the air's refractive index. Simultaneous estimations of
AA
2
and
L
C
N
2
(h) dh permit a linear relationship to be established between these two quantities. The result is interpreted theoretically by integration of the two-dimensional power spectrum for the angle-of-arrival fluctuations. The influence of filtering effects is discussed.Such a calibration can be performed for a given telescope and slit, enabling the system to be used as a seeing monitor. 相似文献
18.
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
19.
M. Hack 《Astrophysics and Space Science》1969,5(4):403-419
The spectrum of the peculiar Bp star HD 36916 has been studied on plates with dispersion 9.7 A/mm and compared with those of Aur, B3V andi And, B8V. A comparison of the observed contours of H, H and of the Balmer discontinuity D with those computed by Mihalas gives the following results: HD 36916: e=0.347, logg=3.8;i And: e=0.383, logg=3.2; Aur: e=0.302, logg=3.6. HD 36916 presents the characteristics of the Si-4200 stars: strong deficiency in helium and probably also in oxygen and nitrogen, strong excess of silicon and strontium; 3984 Hgii is present. Moreover this star also has characteristics which are not common to Si-4200 stars but rather to Mn stars: excess by a factor of ten of the elements of the iron group and an excess larger, probably of the order of 100, for manganese. The star is a member of the Sword subgroup of the Orion association. 相似文献
20.
Radial velocity observations of V 1010 Oph obtained at Asiago from 23 spectra combined with those published by Guinan and Koch (1977) reveal a significant eccentricity (e0.20±0.03) with a periastron angle close to 90° at 1 level. This underlines the need for a new analysis of the light curve for photometric elements.On leave from Konkoly Observatory, Budapest, Hungary 相似文献