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1.
A model equation of state that describes the phase transition to quark matter is proposed. This equation of state is used to construct hydrostatically equilibrium stellar models for various values of the entropy and the negative bag constant B added to the pressure of quarkmatter. Parameters of the calculated models and conditions for their stability are discussed. 相似文献
2.
Gravitational instabilities with respect to warp modes of vertical oscillations are examined for nonlinearly nonequilibrium
disk models with isotropic and anisotropic velocity diagrams. Nonstationary analogs of the dispersion relations for vertical
oscillations in these models are derived in a general form. A detailed study is made of the major large scale oscillatory
modes, which correspond primarily to the most common type of warp in the form of an integral sign, as well as to dome-shaped,
U-shaped, and precessional warps. Critical diagrams showing the initial virial relation as a function of the rotation parameter
for the nonstationary model are constructed for each of these vertical oscillation modes. A comparative analysis is made of
the growth rates of the instabilities for these modes in order to determine the dependence of the characteristic times for
their appearance on the basic physical parameters of the two models. 相似文献
3.
K. V. Manukovskii 《Astronomy Letters》2010,36(3):191-203
A series of numerical models has been constructed for the three-dimensional explosion dynamics of a low-mass neutron star
in a binary system that results from the collapse of the rotating iron core of a massive supernova. The numerical solution
has been obtained by the particle method with an adaptive time step that allows the computational accuracy to be controlled
automatically. The constructed numerical models include the proper motion of the massive component in the binary system of
neutron stars, their finite sizes, the graduality of energy release during the explosive disruption of a critical-mass neutron
star, and the nonuniform expansion velocity distribution of iron ejecta. The extent to which each of the listed parameters
affects the explosion characteristics has been determined. The total explosion energy and the pulsar escape velocity have
been estimated. A sizable fraction of the material of the exploded neutron star has been found to remain gravitationally bound
to the massive component of the binary system. A further study of its dynamics is of interest in its own right, because the
captured material can be considered as an additional source of muon neutrinos. 相似文献
4.
M. A. Falkenberg R. Kotulla U. Fritze 《Monthly notices of the Royal Astronomical Society》2009,397(4):1954-1965
In a previous paper, we have shown that the classical definition of E+A galaxies excludes a significant number of post-starburst galaxies. We suggested that analysing broad-band spectral energy distributions (SEDs) is a more comprehensive method to select and distinguish post-starburst galaxies than the classical definition of measuring equivalent widths of (Hδ) and [O ii ] lines.
In this paper, we will carefully investigate this new method and evaluate it by comparing our model grid of post-starburst galaxies to observed E+A galaxies from the MORPHS catalogue.
In the first part, we investigate the UV-optical-NIR (near-infrared) SEDs of a large variety in terms of progenitor galaxies, burst strengths and time-scales of post-starburst models and compare them to undisturbed spiral, S0 and E galaxies as well as to galaxies in their starburst phase. In the second part, we compare our post-starburst models with the observed E+A galaxies in terms of Lick indices, luminosities and colours. We then use the new method of comparing the model SEDs with SEDs of the observed E+A galaxies.
We find that the post-starburst models can be distinguished from undisturbed spiral, S0 and E galaxies and galaxies in their starburst phase on the basis of their SEDs. It is even possible to distinguish most of the different post-starbursts by their SEDs. From the comparison with observations, we find that all observed E+A galaxies from the MORPHS catalogue can be matched by our models. However, only models with short decline time-scales for the star formation rate are possible scenarios for the observed E+A galaxies in agreement with our results from the first paper. 相似文献
In this paper, we will carefully investigate this new method and evaluate it by comparing our model grid of post-starburst galaxies to observed E+A galaxies from the MORPHS catalogue.
In the first part, we investigate the UV-optical-NIR (near-infrared) SEDs of a large variety in terms of progenitor galaxies, burst strengths and time-scales of post-starburst models and compare them to undisturbed spiral, S0 and E galaxies as well as to galaxies in their starburst phase. In the second part, we compare our post-starburst models with the observed E+A galaxies in terms of Lick indices, luminosities and colours. We then use the new method of comparing the model SEDs with SEDs of the observed E+A galaxies.
We find that the post-starburst models can be distinguished from undisturbed spiral, S0 and E galaxies and galaxies in their starburst phase on the basis of their SEDs. It is even possible to distinguish most of the different post-starbursts by their SEDs. From the comparison with observations, we find that all observed E+A galaxies from the MORPHS catalogue can be matched by our models. However, only models with short decline time-scales for the star formation rate are possible scenarios for the observed E+A galaxies in agreement with our results from the first paper. 相似文献
5.
A. A. Saharian 《Astrophysics》1997,40(2):154-166
The problems of flat directions and supersymmetry breaking are fundamental problems that are still unsolved in the comparison
of string theory with low-energy physics. A possible nonperturbative dilaton potential may play an important role in their
solution. In the present paper we consider D-dimensional, low-energy, string cosmological models with a di/aton potential.
Exact solutions are written for several simple potentials. The picture of cosmological evolution of a gravi-dilaton model
is investigated by methods of the qualitative theory of dynamical systems for different cases of the behavior of the potential
in the domain of strong coupling. Features of models having potentials that take negative values in certain ranges of values
of the dilaton field are discussed. A specific mechanism of generation of a nonperturbative potential, based on gaugino condensation
in the hidden sector of the gauge group, is considered.
Translated from Astrofizika, Vol. 40, No. 2, pp. 233–251, April–June, 1997. 相似文献
6.
Yu. A. Rylov 《Astrophysics and Space Science》1984,107(2):381-401
A self-consistent pulsar magnetospheric model with electron-positron pair production is considered. Unlike conventional models, the primary particles (electrons) are accelerated towards the neutron star and their curvature radiation towards a star generates electron-positron plasma near the neutron star. Inside an outflow channel, the generated plasma flows away from the pulsar magnetosphere. A part of the plasma electrons returns and, being accelerated towards the star, regenerate the plasma by their curvature radiation. It is shown that plasma production near the star causes an appearance of positron and electron equatorial belts. The plasma concentration and the flux of the returning electrons are estimated. The portion of the energy entering into the pulsar magnetosphere and its dependence on pulsar parameters are estimated. 相似文献
7.
8.
Rosa M. González Delgado 《Astrophysics and Space Science》2009,324(2-4):231-239
Stellar population models are a very useful tool to derive the stellar cluster age and luminosity mass from its integrated light. Evolutionary synthesis models depend on the stellar evolutionary tracks and the stellar libraries used to predict the spectral energy distribution of the stellar populations. In this review, I briefly comment on the new models that have incorporated the new evolutionary tracks with rotation and new computations for the evolutionary tracks of the TP-AGB. A more extended summary is also given of the current status of the most recent high-resolution stellar libraries at optical wavelengths and their implementation in evolutionary synthesis models. A comparison of the results obtained fitting the optical spectra of LMC and SMC stellar clusters with different high spectral resolution evolutionary synthesis models is also presented. 相似文献
9.
Shyamal K. Banerjee Jayant V. Narlikar 《Monthly notices of the Royal Astronomical Society》1999,307(1):73-78
The data on angular sizes and redshifts of ultracompact radio sources used by Jackson & Dodgson in a recent paper have been applied to the various theoretical models in the framework of the quasi-steady-state cosmology proposed by Hoyle, Burbidge & Narlikar. It is found that although acceptable fits to the data are available for the flat models, those with a negative curvature of spatial sections provide a better fit. These latter models require low densities of matter and as such do not demand too high a proportion of dark matter. A comparison is made with the work of Jackson & Dodgson and theoretical implications of the test are discussed. 相似文献
10.
N. N. Kondrashova 《Kinematics and Physics of Celestial Bodies》2011,27(2):86-91
This paper investigates the physical state of the photosphere in the main phase of the two-ribbon solar flare on June 3, 1979.
The derived models show that the photosphere was in a disturbed state for a long time during the main phase of the flare.
In the models, the temperature in the upper photospheric layers is higher and that in the lower layers is lower than in the
quiet-sun model atmosphere. During the flare, the heating extends to the lower photospheric layers, and the upper layers cool
down. A comparison of the obtained models to those for the two-ribbon solar flare on October 7, 1979, shows that the height
distributions of the temperature in the main phase of the flares are strongly different. 相似文献
11.
D. Lorenz-Petzold 《Journal of Astrophysics and Astronomy》1986,7(3):155-170
We present a detailed study of the inhomogeneous Stephani-Krasinski solution with time-dependent curvature index. In general,
the cosmological behaviour of the models depends on six arbitrary functions of time. Such models are termed ‘private universes’
and cannot be in accord with observation in the most general case. Two simple models with changing topology are considered
as illustrating examples. In one of these models the pressure turns out to be negative and hence a violation of the weak energy
condition in the singularity theorems is possible. A brief review of other inhomogeneous cosmologies is included for the sake
of clarity. It is shown that the geodesic equation can be reduced to a complicated differential equation, which depends on
the three arbitrary functions involved. Therefore, it is difficult to obtain explicit formulas for the various observational
relations. 相似文献
12.
A model of rapidly rotating globular clusters is constructed assuming uniform angular velocity and a truncated Maxwellian distribution in the stellar velocities. Since the first-order theory developed by Woolley and Dickens becomes inaccurate for rapid rotation, a small-mass envelope is fitted to their models by the method of Monaghan and Roxburgh. A comparison is made of the critical values derived by the two methods. 相似文献
13.
Osman Demircan 《Astrophysics and Space Science》1983,91(2):407-416
All methods existing today for computation of the elements of eclipsing binaries require photometric observations to cover the complete revolution of binaries, outside as well as within the eclipses. The maximum light and the depth of the eclipses are to be determined prior to any analysis, and the light curves are to be expressed in terms of the total light at quadratures. A method has been introduced in the present paper to enable us to obtain the elements of eclipsing binaries by an analysis of, not the whole, but a part of their eclipse light curves. In the new method no empirical knowledge of the maximum light or depth of eclipes is needed, and no normalization is necessary. The method can be used in any models (ellipsoidal, Roche, etc.). However, the larger the phase coverage of the light changes considered for the computation of the elements, the better the determinacy (or smaller the errors) is obtained. 相似文献
14.
KJ. Maniharsingh 《Astrophysics and Space Science》1993,202(2):247-257
In the course of obtaining three collapsing models of the charged viscous-fluid distribution, the dynamics of gravitational collapse are investigated with respect to them, and their physical and geometrical properties are studied critically, In all the cases, with a proper choice of the mass, the interior solution can be matched to the exterior Schwarzschild vacuum solution, thereby the solution being continuous at the boundary of the star. In all these models the matter inside is found to be radiating thus giving us the opportunity of identifying the gravitational collapse of a realistic astrophysical object. At the boundary of these model stars the matter distribution comes out to be that of dust and thereby comoving with respect to the coordinate system used. All the models are seen to be physically acceptable; they come out to be realistic models of collapsing astrophysical objects which will be of much interest in studying the phenomenon of black holes in this Universe. 相似文献
15.
Friedmann Robertson Walker cosmological models with bulk viscosity are constructed in the scale covariant theory of gravitation.
A new class of solutions for the field equations of the model is found by applying variable deceleration parameter. Some physical
models of these solutions are briefly discussed in this paper. 相似文献
16.
Alfonso Aragón-Salamanca Carlton M. Baugh & Guinevere Kauffmann 《Monthly notices of the Royal Astronomical Society》1998,297(2):427-434
We analyse the K -band Hubble diagram for a sample of brightest cluster galaxies (BCGs) in the redshift range 0< z <1. In good agreement with earlier studies, we confirm that the scatter in the absolute magnitudes of the galaxies is small (0.3 mag). The BCGs exhibit very little luminosity evolution in this redshift range: if q 0 =0.0, we detect no luminosity evolution; for q 0 =0.5, we measure a small negative evolution (i.e., BCGs were about 0.5 mag fainter at z =1 than today). If the mass in stars of these galaxies had remained constant over this period of time, substantial positive luminosity evolution would be expected: BCGs should have been brighter in the past, since their stars were younger. A likely explanation for the observed zero or negative evolution is that the stellar mass of the BCGs has been assembled over time through merging and accretion, as expected in hierarchical models of galaxy formation. The colour evolution of the BCGs is consistent with that of an old stellar population ( z for >2) that is evolving passively. We can thus use evolutionary population synthesis models to estimate the rate of growth in stellar mass for these systems. We find that the stellar mass in a typical BCG has grown by a factor ≃2 since z ≃1 if q 0 =0.0, or by factor ≃4 if q 0 =0.5. These results are in good agreement with the predictions of semi-analytic models of galaxy formation and evolution set in the context of a hierarchical scenario for structure formation. The models predict a scatter in the luminosities of the BCGs that is somewhat larger than the observed one, but that depends on the criterion used to select the model clusters. 相似文献
17.
The stability of the solutions of the mean-field theories of turbulent media is questioned. It is done here for the model equations for the solar convection zone which have been used, in particular, to explain the differential rotation. We present an approximation valid for axisymmetric, short-wave disturbances. A critical local Rayleigh number can be defined - involving eddy diffusivities - above which the stratification becomes unstable. For mixing-length models of the solar convection zone we always find sub-critical Rayleigh numbers. One must be careful, however, with other theoretical models. Those we have considered do not reach sufficiently high surface pressure values so that there the associated Rayleigh numbers exceed their critical limits. In the outermost layers in such models, therefore, the solutions could really be unstable. 相似文献
18.
E. A. Baranovskii N. N. Kondrashova M. N. Pasechnik V. P. Tarashchuk 《Bulletin of the Crimean Astrophysical Observatory》2014,110(1):101-104
Chromosphere layers of solar flares were investigated according to the observed profiles of the Hα line. A two-strand flare was observed on September 4, 1990. Spectra were obtained with the ATsU-26 solar horizontal telescope at Terskol Peak Observatory (3100 m). Spectra photometry is performed for two bright nodes of one strand of the flare. Some profiles are superposed to the ejection. The observed profiles are characterized by high emissions in the wings of the Hα line (up to 10–12 Å) under relatively low intensity in the center of Hα (r = 0.35–0.6). To explain such profile behavior we calculated flare models with two or three components. Separate components of the model correspond to unresolved details in the flare area and therefore the averaged profile is calculated. Emission in the far wings is explained by model components with deep heating of chromosphere layers. These occupy 5–12% of the total area. Noticeable emission asymmetry is explained by ray velocities of up to 70 km/s and more. The models are determined by agreement of the observed and calculated profiles. We processed several photometric profiles for seven observations. The temperature in the models with deep heating in the lower cromosphere is increased by 1000–2500 K with respect to the model with an undisturbed chromosphere VAL-C. The second feature of the observed profiles is their high asymmetry and shift with respect to the undisturbed profiles. This can be explained by the opposite motion of the material. We revealed that for the most of the profiles the line-of-sight velocities were directed to the observer in the upper chromosphere (10–100 km/s) and from the observer in the lower chromosphere (5–20 km/s). 相似文献
19.
《New Astronomy》2016
In this paper, the average energy variation with respect to the density of a system of nucleons is theoretically studied. A new formula is proposed for the nuclear equation of state. This formula is related to an infinite system of protons and neutrons with relatively small thermal excitation. It is shown that the presented formulation for the nuclear equation of state reproduces the results obtained in the Skyrme–Hartree–Fock (SHF) and Relativistic Mean-Field (RMF) models of nuclear matter. It should be realized that the consistency of the obtained results for nuclear matter with the predictions of the well-known SHF and RMF models for symmetric and asymmetric system of nucleons indicates the reliability of this formulation for various types of nuclear matter in large scales such as neutron stars. 相似文献
20.
Hideyuki Saio C. Simon Jeffery 《Monthly notices of the Royal Astronomical Society》2000,313(4):671-677
We have examined the evolution of merged low-mass double white dwarfs which become low-luminosity (or high-gravity) extreme helium stars. We have approximated the merging process by the rapid accretion of matter, consisting mostly of helium, on to a helium white dwarf. After a certain mass is accumulated, a helium shell flash occurs, the radius and luminosity increase and the star becomes a yellow giant. Mass accretion is stopped artificially when the total mass reaches a pre-determined value. As the helium-burning shell moves inwards with repeating shell flashes, the effective temperature gradually increases as the star evolves towards the helium main sequence. When the mass interior to the helium‐burning shell is approximately 0.25 M⊙ , the star enters a regime where it is pulsationally unstable. We have obtained radial pulsation periods for these models.
These models have properties very similar to those of the pulsating helium star V652 Her. We have compared the rate of period change of the theoretical models with that observed in V652 Her, as well as with its position on the Hertzsprung–Russell diagram. We conclude that the merger between two helium white dwarfs can produce a star with properties remarkably similar to those observed in at least one extreme helium star, and is a viable model for their evolutionary origin. Such helium stars will evolve to become hot subdwarfs close to the helium main sequence. We also discuss the number of low-luminosity helium stars in the Galaxy expected for our evolution scenario. 相似文献
These models have properties very similar to those of the pulsating helium star V652 Her. We have compared the rate of period change of the theoretical models with that observed in V652 Her, as well as with its position on the Hertzsprung–Russell diagram. We conclude that the merger between two helium white dwarfs can produce a star with properties remarkably similar to those observed in at least one extreme helium star, and is a viable model for their evolutionary origin. Such helium stars will evolve to become hot subdwarfs close to the helium main sequence. We also discuss the number of low-luminosity helium stars in the Galaxy expected for our evolution scenario. 相似文献