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1.
Santosh Kumar 《Astrophysics and Space Science》1984,104(1):127-132
For spherical blast waves propagating through a self-gravitating gas with an energy inputE
=E
0
t
, whereE
is the energy released up to timet,E
0 is a functional constant, and is a constant, kinetic, internal heat, and gravitational potential energies have been computed. Taking the parameterA
2, which characterises the gravitational field, equal to 2, variations of the percentages of these energies for =0, 1/2, 4/3, and 3 with shock strength have been presented. For =3, the effect of cavitation on the percentages of kinetic energy and internal heat energies has been explored. 相似文献
2.
We develop an automatic, computer controlled procedure to select and to analyze the Network Bright Points (NBPs) on solar images. These have been obtained at the Sac Peak Vacuum Tower Telescope by means of the Universal Birefringent Filter and Zeiss H filters, tuned, respectively, along the profiles of the H, Mg-b1, Na-D2, and H lines.A structure is identified as an NBP if at the wavelength H- 1.5 A its maximum intensity is greater than I + 3 and its area is greater than 1.5 arc sec2 at I + 1.5, where I is the mean value and the standard deviation of the intensity distribution on the image. Each detected NBP is then searched and confirmed in all the remaining 31 images at different wavelengths.For each NBP several parameters are measured (position, area, mean and maximum contrast, Dopplergram velocity, compactness, and so on) and some identification constraints are applied.The statistical analysis of the various parameter distributions, for NBPs present within an active region and its surroundings, shows that two types of NBPs can be identified according to the value of their mean contrast C
min the H- 1.5 Å image (C
m 0.1 type I, C
m> 0.1 type II). The type I NBPs (all occurring on the boundaries of the supergranular network) appear to be much more frequent (180/26) than the type II ones.The size A of type I NBPs is less than 1.0 arc sec for H/H wings but of the order of 1.2 arc sec for Na-D2 and Mg-bl. The mean contrast C
m is around the value of 10% along the Na-D2 and Mg-bl profiles and of 20% along the H/H wings.The C
m - A scatter diagrams show, for the photospheric radiation (h < 100 km), a narrow range of variability for C
min correspondence with a wide range for A. For radiation orginated at higher levels (h > 200 km), the C
m- A scatter diagrams seem to indicate, even if with a large variance, that the highest C
m's tend to correspond to the highest A values.The mean Doppler shift is close to zero for Na-D2 and Mg-bl lines but negative (downward motion) for H and H lines.The type II NBPs tends to be preferentially located in the neighbourhood of small, compact sunspots and their detectability is almost constant through all the 4 studied line profiles. No conclusions can be derived on the mean size, contrast and Doppler shift values because their distributions are too dispersed. The only positive information is that its C
m- A scatter diagram, in H and H wings, indicates a wide range of variability for C
m in correspondence with very narrow range of variability for A. 相似文献
3.
General theory of electrical conductivity of a multicomponent mixture of degenerate fermions in a magnetic fieldB, developed in the preceding article (this volume), is applied to a matter in neutron star interiors at densities 0, where 0 = 2.8×1014 g cm–3 is the standard nuclear matter density. A model of free-particle mixture ofn, p, e is used, with account for appearance of –-hyperons at >
c
, where
c
40. The electric resistivities along and acrossB, and , and the Hall resistivity
H
are calculated and fitted by simple analytical formulae at
c
and >
c
for the cases of normal or superfluid neutrons provided other particles are normal. Charge transport alongB is produced by electrons, due to their Coulombic collisions with other charged particles; is independent ofB and almost independent of the neutron superfluidity. Charge transport acrossB at largeB may be essentially determined by other charged particles. If
c
, one has = [1 + (B/B
0)2] for the normal neutrons, and for the superfluid neutrons, while
H
=
B/B
e
for both cases. HereB
e
109
T
8
2
G,B
01011
T
8
2
G, andT
8 is temperature in units of 108 K. Accordingly for the normal neutrons atBB
0, the transverse resistivity suffers an enhancement, 1/4 1. When 50 andB varies from 0 toBB
p
1013
T
8
2
G, increases by a factor of about 103–104 and
H
changes sign. WhenBB
p
, remains constant for the superfluid neutrons, and
H
B
2 for the normal neutrons, while
H
B for any neutron state. Strong dependence of resistivity onB, T, and may affect evolution of magnetic fields in neutron star cores. In particular, the enhancement of at highB may noticeably speed up the Ohmic decay of those electric currents which are perpendicular toB. 相似文献
4.
Ernst A. Roth 《Celestial Mechanics and Dynamical Astronomy》1981,23(1):83-87
In this note a simple formula is given for the perturbation of the anomalistic period of a highly eccentric orbit due to the zonal harmonics. This perturbation depends essentially only on the semi-major axisa, the eccentricitye (or pericentre radius r =a(1-e)) and the latitude of the pericentre. 相似文献
5.
Magnetic dips are generally assumed to be basic equilibrium configurations in quiescent solar prominences. Here we discuss two types of the magnetic dips which were considered in the literature: (1) dips resulting from a force-free magnetic equilibrium in the corona, and (2) magnetic dips which are formed in situations where the Lorentz force balances the weight of the prominence plasma. An important parameter which decides between these two cases is the plasma . For 1, the effect of the prominence material on the equilibrium structure is quite negligible and the case (1) holds. If, however, is larger, say between 0.1 and 1 or even higher, magnetic dips of the second kind are formed and they can be characterized by the angle 1 between the vertical and the direction of the field lines at the surface of the prominence structure. A simple and illustratory formula is derived to relate this angle to the plasma at the prominence center, namely ccot21. c=1 thus corresponds to 1=45°. Finally, we discuss the range of values of both c and 1 as deduced from various observations and conclude that the dips of the second kind are important for the prominence equilibria. We also suggest a new method for determination of the field-line inclination. 相似文献
6.
M. V. Gyulzadyan J. A. Stepanian A. R. Petrosian D. Kunth B. McLean G. Comte 《Astrophysics》2003,46(2):131-143
The Second Byurakan Survey (SBS) is a well known combined survey, which uses the presence of UV-excess radiation in the continuum, or the presence of emission-lines in the spectra for the identification of active and star-forming galaxies. This paper reports on a comparative study of 77 galaxies identified with UV-excess, and 34 galaxies identified via emission-line techniques in the fields of the SBS. The spectroscopic parameters used for the comparison are the [OII]3727/H and [OIII]5007/H emission-lines ratios, the equivalent widths of [OII]3727, [OIII]5007 and H emission-lines, and the C
[OII]-C
H index. Spectroscopic parameters as well as new redshifts were determined from the spectra obtained with the 6m telescope of the Special Astrophysical Observatory (Russia). The main results are: 1) Galaxies discovered via UV-excess technique are preferably more active. 2) Galaxies discovered via emission-line technique are preferably high-excitation low-luminosity star-forming galaxies. 3) UV-excess galaxies with faintest UV-excess radiation are likely candidates to be LINER or Sy2 type objects. 相似文献
7.
A. A. Ubachukwu 《Astrophysics and Space Science》1995,232(1):23-25
The variation of radio luminosity with redshift and its effect on the analysis of the angular size-redshift ( –z) relation for a bright radio source sample (s
178 10Jy) has been investigated. By assuming a power law dependence of luminosity on redshift of the formP (1 +z), it was found that 4.4 (with correlation coefficientr 0.99) for at leastz 0.3. Correction for such a strongP – (1 +z) correlation when considering the –z data for the sample led to a steeper –z slope. This could be explained by assuming linear size evolution of the formD (1 +z)–n
withn = 2.8 – 3.3 consistent with both theoretical results and those obtained for more homogeneous source samples. 相似文献
8.
Teruaki Ohnishi 《Astrophysics and Space Science》1978,58(1):149-165
The effect of nuclear fissions occurring during ther-cooling stage is investigated. The initial conditions for ther-cooling process are derived from the final conditions of the dynamicalr-process. Neutron-excess nuclides in the region ofZ80 are all assumed to have finite probabilities for spontaneous fission, neutron-induced fission and -decay-induced fission. For the evaluation of the rates for delayed neutron emission, -decay-induced fission and -decay, three -decay theories—the Fermi theory, the Gross theory and the theory by Cameron, Delano and Truran—are used. It becomes clear that the -fissions and the symmetric spontaneous fissions duringr-cooling make a broad abundance peak of fission products, centring aroundA=128, whose effect is hidden by ther-abundance peak atA130. Asymmetric spontaneous fissions can form an apparent abundance peak atA105, with the position of this peak just corresponding to the position of the anomalous hump observed in ther-abundance curve. To explain the abundance of this observed hump by spontaneous fissions, ther-process must take place under conditions such that the number of free neutrons available for one seed nucleus is large enough to make the cyclicr-process, and that the final neutron-capture-path goes through the region of (neutron binding energy in the nuclei on the capture-path) 2 MeV. 相似文献
9.
A model of a first generation intermediate star of 5M
, with Z=0 has been considered. The model is at an advanced stage of its evolution and has a double shell burning. It burns helium in the inner shell, and hydrogen, via CNO cycle, in the outer shell.
=(log/log)
T
and
T
=(log/logT)
were computed allowing for the oscillations of the relative mass abundance of the reagents in nuclear reactions. Including
=(log/log)
T
and
=(log/logT)
of mean molecular weight and the effect of the oscillations of abundances due to nuclear reactions, stability was studied. Contrary to the results of the static calculations, we found that instability due to the excitation mechanism provided by the high temperature sensitivity of energy generation rate propagates up to the surface. Thus the model in question was found to be unstable against radial adiabatic pulsations, in its fundamental mode. 相似文献
10.
We compare microphotometer intensity traces perpendicular to dispersion in simultaneous spectrograms of good spatial resolution traced at various 's in each of the lines. Cross correlations between the different traces show the following: (a) For each
K there is a corresponding
b
1at which the coefficient of correlation, r, is a maximum, usually > 0.8. (b) No such high correlations are found between H and H. (c) Comparison of traces in the continuum and at all observed 's in K, H, b1, b2 show a range of 's in each line over which r is very significantly negative, while H shows no such peculiarity. 相似文献
11.
Conclusions In the Newtonian case we have obtained an isotropic self-consistent distribution of gravitationally interacting point masses which satisfies the transport equation without collisions, and the gravitational equation for an arbitrary powerfunction density distribution =r–s, s<3.For =r–2 the analogous self-consistent solution was obtained for the anisotropic distribution function both in Newtonian and GTR cases.The GTR solutions with =r–2 have central redshifts which increase without limit in accordance with the law 1+zr–1/ as we approach the center. In the isotropic case, they appear to be stable when the mean velocities are much less than the velocity of light u<0.2c, >21.The hydrodynamic GTR solution was found for a perfect gas at constant temperature (but variable T=T(g00)1/2) which also has z for r0.We should like to thank K. Thorne, L. Hazin, and M. Podurets for valuable discussions. K. Thorne was particularly helpful in supplying unpublished results on circular orbits obtained by American authors.Astrofizika, Vol. 5, No. 2, pp. 223–234, 1969 相似文献
12.
A study of pulsational properties with evolution has been done for a 15.6M
star withX
e
=0.90 andY
e
=0.08. Pulsational properties in the hydrogen-burning stages have been compared with those in helium-burning stages. A comparison with observed characteristics of Cepheids, classical Cepheids and supergiant variables has been made during the course of its evolution. In addition, models of 5,9 and 15M
withX
e
=0.708,Y
e
=0.272 have also been studied for pulsational properties during the helium burning stage. It is also seen that pulsational instability is sensitive to changes in initial chemical composition and opacity parameters,n ands. A low helium abundance could be a reason for the stability of the models, even when lying in the instability strip of the H-R diagram. 相似文献
13.
Horacio A. Dottori 《Astrophysics and Space Science》1981,80(2):267-280
The synthetic equivalent width (W
H) of the line H in emission is obtained for Hii regions opaque to the Lyman photon flux, with embedded OB associations with different initial chemical compositions and initial mass functions. The variation ofW
H as a function of the evolution of the ionizing stars is analysed. The observations ofW
H for M33, M101, and M51 by Searle (1971) are discussed. 相似文献
14.
A quantum mechanical treatment of an electron plasma in a constant and homogeneous magnetic field is considered, with the aim of (a) defining the range of validity of the magnetoionic theory (b) studying the deviations from this theory, in applications involving high densities, and intense magnetic field. While treating the magnetic field exactly, a perturbation approach in the photon field is used to derive general expressions for the dielectric tensor . The properties of are explored in the various limits. Numerical estimates on the range of applicability of the magnetoionic theory are given for the case of the one-dimensional electron gas, where only the lowest Landau level is occupied. 相似文献
15.
On the basis of the erenkov line emission theory in the optically thick case, a new interpretation of intensity ratios H/H and H/H in broad-line radio-galaxies (BLRGs) is reported. Calculation shows that if the theoretical ratio H/H is just taken to be the mean observed value 0.21, equivalently, the parameterX(H)=3.0, then the expected ratio H/H=6.70 is almost the same as the observations. By comparing these values with the previous investigations of QSOs (X(H)=20.9), we conclude that the number density of neutral hydrogen gas in BLRGs is almost one order-of-magnitude smaller than that in the QSOs.Preliminary verification of the erenkov line emission has been obtained by Xuet al. (1981) in the laboratory. 相似文献
16.
Two sets of accurate approximate expressions for the gyrosynchrotron radiation in the transverse propagation case are presented for the first time. They contain emissivity –/BNand absorptivity –
B/Nfor e-mode, effective temperature T
effand frequency of peak brightness p. The expressions are designed for the range 2 to 7 of electron energy spectral index and for the ranges from 2 to 10 and 10 to 100 of harmonic numbers s(=/B). Their statistical error is, respectively, ±18% and ±29% for –/BNand –
B/Nfor 10/B100, ±128% and and ±170% for 2/B10. 相似文献
17.
The stability of magnetic flux tubes embedded vertically in a convection zone is investigated. For thin tubes, the dominant instability is of the convective type, i.e. it is driven by buoyancy forces associated with displacements along the tube. The stability is determined by = 8P/B
2; if
c
the tube is convectively stable, otherwise it is unstable, where the critical value
c
depends on the stratification of the convection zone. For a solar convection zone model,
c
= 1.83, corresponding to a magnetic field strength of 1350 G at the surface of the Sun. It is concluded that the flux tubes making up the small scale field of the Sun are probably hydrodynamically stable.In tubes with >
c, the instability is expected to transform the tube either into a state of vanishing surface field strength (in the case of an upward flow), or one with a field strength higher than the original value (if the instability sets in as a downward flow). Following Parker, we suggest that this effect is related to the concentrated nature of the observed solar fields.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
18.
L. V. Mirzoyan L. G. Balazs A. Fronto A. T. Garibjanian V. V. Hambarian M. Kun J. Kelemen N. D. Melikian 《Astrophysics》1994,37(3):231-234
Spectral observations of 53 H-emission objects of the HII-region IC 1396 were carried out with moderate resolution using the 2.6m telescope of the Byurakan Astrophysical Observatory. Factor analysis of this observational material indicates that there are two dominant factors. Factor 1 (Fig. 1), which is the more significant factor, resembles the spectrum of a star of spectral type F5 with a strong H line in absorption. Factor 2 (Fig. 2), in contrast, appears as a later-type spectrum with H and H in emission. The result obtained can be explained by the transient nature of the H-emission.Translated fromAstrofizika, Vol. 37, No. 3, 1994. 相似文献
19.
P. C. Ram 《Astrophysics and Space Science》1991,176(2):263-270
An explicit finite-difference method is employed to study the MHD free convection heat generating fluid past an impulsively started vertical infinite plate when a strong magnetic field is applied perpendicular to the plate. The velocity and temperature profiles are shown on graphs and the results are discussed in terms of the non-dimensional parameters
e
(Hall parameter),
i
(ionslip parameter), (heat source parameter), and Gr (Grashof number). 相似文献
20.
In this paper, we present a model of the plasma beta above an active region and discuss its consequences in terms of coronal magnetic field modeling. The -plasma model is representative and derived from a collection of sources. The resulting variation with height in the solar atmosphere is used to emphasize that the assumption that the magnetic pressure dominates over the plasma pressure must be carefully employed when extrapolating the magnetic field. This paper points out (1) that the paradigm that the coronal magnetic field can be constructed from a force-free magnetic field must be used in the correct context, since the force-free region is sandwiched between two regions which have >1, (2) that the chromospheric Mgii–Civ magnetic measurements occur near the -minimum, and (3) that, moving from the photosphere upwards, can return to 1 at relatively low coronal heights, e.g., R1.2 R
s. 相似文献