共查询到20条相似文献，搜索用时 15 毫秒
1.
T. Aikawa 《Astrophysics and Space Science》1993,210(1-2):269-280
Phenomena of bifurcation in hydrodynamic stellar models of radial pulsation are reviewed. By changing control parameters of models, we can see qualitatively different pulsation behaviors in hydrodynamic models with transitions due to various types of bifurcation.In weakly dissipative models (classical Cepheids), the bifurcation is induced by modal resonances. Two types of the modal resonances found in models are discussed: The higherharmonic resonances of the second overtone mode in the fundamental mode pulsator and of the fourth overtone mode in the first overtone pulsator are relevant to observations. The subharmonic resonance between the fundamental and first overtone modes is confirmed in classical Cepheid models.In strongly dissipative models (less-massive supergiant stars), the bifurcation of nonlinear pulsation is induced by the hydrodynamics of ionization zones as well as modal resonances. The sequence of the bifurcation sometimes leads to chaotic behaviors in nonlinear pulsation. The transition routes from regular to the chaotic pulsations found in models are discussed with respect to the theory of chaos in simple dynamical systems: The cascade of period-doubling bifurcation is confirmed to cause chaotic pulsation in W Virginis models. For models of higher luminosity, the tangent bifurcation is found to lead intermittent chaos.Finally, hydrodynamic models for chaotic pulsation with small amplitudes observed in the post-AGB stars are briefly discussed. 相似文献
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Several models are available to describe precession instability of SS433: 6- and 7-parameter models, sinusoidal and damped sinusoidal models etc. From the available observation data, it appears that 6- and 7-parameter models are most likely to be incorrect. We have analyzed and compared the sinusoidal and damped sinusoidal models in terms of figures of phase residual, and then proposed and improved a damped sinusoidal model. The data from the three models (sinusoidal, damped sinusoidal, and improved damped sinusoidal model) have been subjected to regression analysis for the purpose of determining the differences among the models. 相似文献
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N. N. Klimenko 《Solar System Research》2016,50(7):523-532
Analytical models of weight and energy balances, aerodynamic models, and solar irradiance models to perform pseudo-satellite preliminary design are presented. Feasibility criteria are determined in accordance with the aim of preliminary design dependent on mission scenario and type of payload. 相似文献
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In this paper we have studied the anisotropic and homogeneous Bianchi type-I universe filled with interacting Dark matter and Holographic dark energy. Here we discussed two models, in first model the solutions of the field equations are obtained for constant value of deceleration parameter where as in the second model the solutions of the field equations are obtained for special form of deceleration parameter. It is shown that for suitable choice of interaction between dark matter and holographic dark energy there is no coincidence problem (unlike ΛCDM). Also, in all the resulting models the anisotropy of expansion dies out very quickly and attains isotropy after some finite time. The Statefinder diagnostic is applied to both the models in order to distinguish between our dark energy models with other existing dark energy models. The physical and geometrical aspects of the models are also discussed. 相似文献
7.
The study of the solar corona has been strewn with great discoveries, surprises and controversies. The major steps since van
de Hulst's (1953)and Chapman's (1957) early hydrostatic models of the extended corona, until the most recent generations of
kinetic models of the coronal expansion and of the supersonic solar wind flows, are presented. These models are compared to
in-situ observations. Progress in polar wind models went through a somewhat similar evolution that is outlined also. The advantages
and limitations of the successive brands of solar wind and polar wind models are considered.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Axially symmetric string cosmological models are obtained in a scalar- tensor theory of gravitation proposed by Brans and
Dicke (Phys. Rev. 124:925, 1961). Some physical and geometrical properties of the models are also discussed. The models are anisotropic and free from singularities. 相似文献
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We present hydrogen emission-line profile models of magnetospheric accretion on to classical T Tauri stars. The models are computed under the Sobolev approximation using the three-dimensional Monte Carlo radiative-transfer code torus . We have calculated four illustrative models in which the accretion flows are confined to azimuthal curtains – a geometry predicted by magnetohydrodynamic simulations. Properties of the line profile variability of our models are discussed, with reference to dynamic spectra and cross-correlation images. We find that some gross characteristics of the observed line profile variability are reproduced by our models, although in general the level of variability predicted is larger than that observed. We conclude that this excessive variability probably excludes dynamical simulations that predict accretion flows with low degrees of axisymmetry. 相似文献
11.
Prolate Jaffe models for galaxies 总被引：1，自引：0，他引：1
We introduce a class of prolate Jaffe models for elliptical galaxies, which are a further extension of Jaffe's spherical models of axisymmetric elliptical systems, and study the properties of their densities, circular velocities, velocity dispersions and two-integral even distribution functions. The form of the potential allows the density to be expressed simply as a function of the potential and radial coordinate R . The models have finite total mass and their densities at large distances decay radially as r −4 , except on the major axis, where the densities decay as r −3 . It is known from Hunter's formulae that the velocity dispersions for prolate models can be expressed in terms of elementary functions of R and z , unlike those for the oblate Jaffe models recently given by Jiang, and that the prolate models have anisotropic velocity distributions. Thus the prolate models are easier to study than the oblate models. It is also found that the two-integral even distribution functions on the physical boundary of the galaxies increase monotonically with the relative energy, for the prolate models. Furthermore, numerical calculation shows that the two-integral even distribution functions generated from their densities are non-negative, even for very 'squeezed' prolate Jaffe models. However, the edge-on projected surface densities for these prolate models cannot be expressed as simply as for the oblate models. 相似文献
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I review the processes that shape the evolution of protoplanetary discs around young, solar-mass stars. I first discuss observations of protoplanetary discs, and note in particular the constraints these observations place on models of disc evolution. The processes that affect the evolution of gas discs are then discussed, with the focus in particular on viscous accretion and photoevaporation, and recent models which combine the two. I then discuss the dynamics and growth of dust grains in discs, considering models of grain growth, the gas–grain interaction and planetesimal formation, and review recent research in this area. Lastly, I consider the so-called “transitional” discs, which are thought to be observed during disc dispersal. Recent observations and models of these systems are reviewed, and prospects for using statistical surveys to distinguish between the various proposed models are discussed. 相似文献
13.
Plane Symmetric string cosmological models are presented in Barber’s second self creation theory of gravitation and obtained
Einstein’s plane symmetric string cosmological models as a special case. Some physical and geometrical properties of the models
are also discussed. 相似文献
14.
Shwetabh Singh 《Journal of Astrophysics and Astronomy》1999,20(1-2):67-77
Cosmological models involving shear and rotation are considered, first in the general relativistic and then in the Newtonian
framework with the aim of investigating singularities in them by using numerical and analytical techniques. The dynamics of
these rotating models are studied. It is shown that singularities are unavoidable in such models and that the centrifugal
force arising due to rotation can never overcome the gravitational and shearing force over a length of time. 相似文献
15.
《Astroparticle Physics》2006,24(6):467-483
Lateral distributions for electrons and muons in extensive air showers measured with the array of the KASCADE experiment are compared to results of simulations based on the high-energy hadronic interaction models QGSJet and SIBYLL. It is shown, that the muon distributions are well described by both models. Deviations are found for the electromagnetic component, where both models predict a steeper lateral shape than observed in the data. For both models the observed lateral shapes of the electron component indicate a transition from a light to a more heavy composition of the cosmic ray spectrum above the knee. 相似文献
16.
Koijam Manihar Singh 《Astrophysics and Space Science》2010,325(2):293-302
Investigations are made on slowly rotating radiating Universes coupled with a scalar field in the spherically symmetric Einstein
formalism, and some new interesting solutions are obtained. Their physical and geometrical properties are studied from various
angles. The rotational perturbations of such models are examined in order to substantiate the possibility that the universe
is endowed with some rotation. The nature and role of the metric rotation as well as that of the rotation of matter are studied,
and the effects of radiation and scalar fields on them are discussed. The models here turn out to be rotating as well as expanding
ones, which may be taken as good examples of real astrophysical objects in this universe. The periods of the physical validity
and the restrictions on the radii of the models for real astrophysical situations are obtained and discussed. The models obtained
here are theoretically satisfactory and therefore there is a possibility that there may be less known objects in this universe
which may be represented by our model Universes obtained here and many unknown properties of this universe may be explored
and unfolded in the study of these models. 相似文献
17.
A.R. Bell 《Astrophysics and Space Science》1997,256(1-2):13-35
This paper reviews the use of computational simulation in plasma physics. It describes a range of numerical models varying from particle models of low density collisionless plasmas to fluid models of high density collision-dominated plasmas. Some applications of these models, particularly to laser-produced and astrophysical plasmas, are described. 相似文献
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M. Mollá M. L. García-Vargas A. Bressan 《Monthly notices of the Royal Astronomical Society》2009,398(1):451-470
We present new evolutionary synthesis models for simple stellar populations for a wide range of ages and metallicities. The models are based on the Padova isochrones. The core of the spectral library is provided by the medium resolution Lejeune et al. atmosphere models. These spectra are complemented by Non Local Thermodynamic Equilibrium (NLTE) atmosphere models for hot stars that have an important impact on the stellar cluster's ionizing spectra: O, B and WR stellar spectra at the early ages, and spectra of post asymptotic giant branch stars and planetary nebulae, at intermediate and old ages. At young ages, our models compare well with other existing models, but we find that the inclusion of the nebular continuum, not considered in several other models, significantly reddens the integrated colours of very young stellar populations. This is consistent with the results of spectral synthesis codes particularly devised for the study of starburst galaxies. At intermediate and old ages, the agreement with the literature model is good and, in particular, we reproduce the observed colours of star clusters in Large Magellanic Cloud well. Given the ability to produce good integrated spectra from the far-ultraviolet to the infrared at any age, we consider that our models are particularly suited for the study of high-redshift galaxies. These models are available on the web site http://www.fractal-es.com/SEDmod.htm and also through the Virtual Observatory Tools on the PopStar server. 相似文献
20.
Shashi M. Kanbur Chow-Choong Ngeow 《Monthly notices of the Royal Astronomical Society》2006,369(2):705-722
Period–colour (PC) and amplitude–colour (AC) relations are studied for the Large Magellanic Cloud (LMC) Cepheids under the theoretical framework of the hydrogen ionization front (HIF)–photosphere interaction. LMC models are constructed with pulsation codes that include turbulent convection, and the properties of these models are studied at maximum, mean and minimum light. As with Galactic models, at maximum light the photosphere is located next to the HIF for the LMC models. However, very different behaviour is found at minimum light. The long-period ( P > 10 d) LMC models imply that the photosphere is disengaged from the HIF at minimum light, similar to the Galactic models, but there are some indications that the photosphere is located near the HIF for the short-period ( P < 10 d) LMC models. We also use the updated LMC data to derive empirical PC and AC relations at these phases. Our numerical models are broadly consistent with our theory and the observed data, though we discuss some caveats in the paper. We apply the idea of the HIF–photosphere interaction to explain recent suggestions that the LMC period–luminosity (PL) and PC relations are non-linear with a break at a period close to 10 d. Our empirical LMC PC and PL relations are also found to be non-linear with the F -test. Our explanation relies on the properties of the Saha ionization equation, the HIF–photosphere interaction and the way this interaction changes with the phase of pulsation and metallicity to produce the observed changes in the LMC PC and PL relations. 相似文献