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1.
含粘滞的弱磁化吸积盘的非轴对称脉动不稳定性 总被引：1，自引：0，他引：1
本文讨论了一种含扩散型粘滞的弱磁化等温吸积盘模型．在作者原有工作的基础上研究了吸积盘对非轴对称扰动（含径向、环向和垂向三个方向的扰动）所表现的脉动不稳定性．结果表明，径向扰动是最重要、最根本的扰动：在无径向扰动时，吸积盘中不存在环向扰动与垂向扰动所产生的脉动不稳定性．在径向扰动存在时，吸积盘除了可能存在纯径向脉动不稳定性外，还可能存在由于径向扰动与垂向扰动的耦合所引起的轴对称脉动不稳定性，以及由于径向扰动与环向扰动的耦合所引起的非轴对称脉动不稳定性．当上述三个方向的扰动并存时，对应的非轴对称脉动不稳定性也可能存在． 相似文献
2.
Some aspects for efficient computation of the tidal perturbation due to the ellipticity effects of the Earth, the luni-solar potential on an Earth-orbiting satellite and the perturbations of the satellite's radial, transverse and normal position components due to the effects of the Earth's gravitational and ocean tide fields are presented. A straightforward method for computing the spectrum of the geopotential and the tidal-induced perturbations of the orbit elements and the radial, transverse and normal components is described. 相似文献
3.
The effect of a weak magnetic field on the adiabatic radial and non-radial oscillations of a stellar configuration is studied by means of a perturbation method. Special attention is devoted to the perturbation of the oscillation frequencies resulting from the change of the boundary conditions caused by the magnetic field. This change is related to the fact that the introduction of a magnetic field removes the singularity at the surface of the equilibrium configuration. The perturbation method is applied to Ferraro's model and the influence of a magnetic field on the frequencies of the different types of oscillation modes is discussed. 相似文献
4.
A perturbation method is derived forr-modes in a slowly and uniformly rotating star. In contrast to previous studies, the perturbation of the gravitational potential is included in the perturbation method.On the assumption that the effects of the centrifugal force are taken into account in the equilibrium model up to the second order in the angular velocity, an eigenvalue problem of sixth-order in the radial coordinate is derived that allows one to determine the zeroth-order toroidal displacement field and the third-order term in the expansion of the eigenfrequency. Furthermore, another eigenvalue problem is derived that governs the first-order toroidal displacement field and the fourth-order term in the expansion of the eigenfrequency. This second eigenvalue problem is also of the sixth-order in the radial coordinate.It is shown that the third-order term in the expansion of the eigenfrequency is real, and that the fourth-order term is zero. 相似文献
5.
In this study V2109 Cyg (a pulsating δ Scuti star) has been modelled. In treating the oscillation equations perturbation in gravitational potential energy has been taken into account. Both radial and nonradial oscillations are treated with adiabatic approximation. The so called radial fundamental frequency (5.3745 c/d) and the nonradial frequency (5.8332 c/d) were obtained within a satisfactory precision. It was found that the Cowling approximation introduced more error as one went from low overtones to high overtones in radial oscillations. A similar trend was observed in nonradial case with low values of l. By keeping the effective temperatures almost the same as with V2109 Cyg two more models with different masses have also been calculated to see the effect of inclusion of perturbation in gravitational potential energy on oscillation frequencies in different masses. Conclusion arrived is that one must be careful to employ the Cowling approximation especially for high nonradial oscillation frequencies. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
Linear analysis shows that radial oscillations in accretion disks around compact object are overstable to axisymmetric perturbation under a variety of conditions. Furthermore, numerical simulations confirm that the radial oscillations induce quasi-periodic modulations of the disk luminosity. The disk oscillation model may be responsible for quasi-periodic oscillations (QPOs) observed in low mass X-ray binaries (LMXBs), cataclysmic variables (CVs), and other compact objects. 相似文献
7.
Stefano Casotto 《Celestial Mechanics and Dynamical Astronomy》1993,55(3):223-241
Kaula's celebrated solution to the problem of satellite motion in the gravitational field of a rigid body is transformed to give the perturbation spectra in both position and velocity in the radial, transverse and normal directions of the orbital reference frame. This work is an extension and a refinement of the theory of orbital perturbations due to the geopotential previously published by Rosborough and Tapley (1987). 相似文献
8.
Stefano Casotto 《Celestial Mechanics and Dynamical Astronomy》1995,62(1):1-22
A new method for calculating the perturbation spectrum in the framework of Kaula's linear satellite theory (LST) is introduced. The novelty of this approach consists in using recent results on the spectral decomposition of the perturbation frequencies in LST to provide a closed formulation for the amplitude and the phase of each line in the perturbation spectrum. The theory presented here can be applied to perturbations in the elements or in the radial and transverse directions due to the geopotential or to the tides. Separate algorithms are developed for application to orbits with circulating or frozen perigee. 相似文献
9.
S. C. Tripathy C. B. Dwivedi A. C. Das A. R. Prasanna 《Journal of Astrophysics and Astronomy》1993,14(2):103-114
In this paper, the analytical and numerical results of the stability analysis of the accretion disk at the inner boundary
is presented. Including the effect of finite conductivity in the disk dynamics, a simple calculation considering only the
radial perturbation has been carried out. Within local approximation, it is concluded that the disk is stable to Kelvin-Helmholtz
and resistive electromagnetic modes whereas the magnetosonic mode can destabilise the disk structure. 相似文献
10.
André Deprit 《Celestial Mechanics and Dynamical Astronomy》1981,24(2):111-153
When the perturbation affecting a Keplerian motion is proportional tor
–n
(n3), a canonical transformation of Lie type will convert the system into one in which the perturbation is proportional tor
–2. Because it removes parallactic factors, the transformation is called the elimination of the parallax.In the main problem for the theory of artificial satellites, the elimination of the parallax has been conducted by computer to order 4. The first order in the reduced system may now be integrated in closed form, thereby revealing the fundamental property of the first-order intermediary orbits in line with Newton's Propositio XLIV.Extension beyond order 1 leads to identify a new class of intermediaries for the main problem in nodal coordinates, namely the radial intermediaries.The technique of smoothing a perturbation prior to normalizing the perturbed Keplerian system, of which the elimination of the parallax is an instance, is applied to derive the intermediaries in nodal coordinates proposed by Sterne, Garfinkel, Cid-Palacios and Aksnes, and to find the canonical diffeomorphisms which relate them to one another and to the radial intermediaries. 相似文献
11.
The influence of latitudinally dependent boundary conditions on the large radius values of meridional flow in the distant solar wind is examined through a double perturbation expansion of the magnetohydrodynamic equations. A general result is derived for the meridional velocity which allows arbitrary specification of radial velocity, radial magnetic field, and mass flux, as a function of colatitude at some coronal reference surface. Three specific examples are treated, including the model of Pneuman and Kopp (1971). The latter example indicates that there may be flow toward the equator at large radii, as opposed to the pure equatorial divergence of internally generated motion due to a flow which is latitudinally uniform at the reference radius. A solar cycle effect most probably averages the boundary conditions so that only the equatorial divergence from an average spherically symmetric corona is seen in comet-tail observations. This may also explain the off-and-on-again nature of the meridional gradient in the radial velocity of the solar wind as seen in radio scintillation observations. 相似文献
12.
Yu -Qing Lou 《Astrophysics and Space Science》1994,219(2):211-220
A perturbation formulation is presented for steady three-dimensional compressible structures embedded in a background relativistic magnetohydrodynamic (RMHD) radial outflow with spherical symmetry. The property of the two concurred RMHD fast and slow critical points is examined. Explicit perturbation solutions at large radii are derived analytically in a polytropic background wind. This perturbation approach for compressible structures together with our recent analyses on propagation of Alfvénic perturbations in a RMHD wind forms a useful starting basis for modeling a broad class of complex structures in magnetized relativistic astrophysical outflows. 相似文献
13.
This study deals with the singular character of the perturbation introduced into the eigenvalue problem of the linear and adiabatic oscillations of a gaseous configuration by a magnetic field that is non-zero on the boundary surface of the configuration. This singular character implies that a regular perturbation scheme cannot yield uniformly valid expansion for the eigenfunctions.This investigation considers the application of the Method of Matched Asymptotic Expansions (M.M.A.E.) to the latter singular perturbation problem in order to obtain uniformly valid expansions for the eigenfunctions and first-order expressions for the eigenfrequencies. As an illustrative example, the M.M.A.E. is applied to the eigenvalue problem of the linear, radial, and adiabatic oscillations of a homogeneous cylindrical plasma with a constant longitudinal magnetic field. 相似文献
14.
《New Astronomy》2014
We propose a mechanism to produce fluctuations in the viscosity parameter (α) in differentially rotating discs. We carried out a nonlinear analysis of a general accretion flow, where any perturbation on the background α was treated as a passive/slave variable in the sense of dynamical system theory. We demonstrate a complete physical picture of growth, saturation and final degradation of the perturbation as a result of the nonlinear nature of coupled system of equations. The strong dependence of this fluctuation on the radial location in the accretion disc and the base angular momentum distribution is demonstrated. The growth of fluctuations is shown to have a time scale comparable to the radial drift time and hence the physical significance is discussed. The fluctuation is found to be a power law in time in the growing phase and we briefly discuss its statistical significance. 相似文献
15.
《New Astronomy》2017
We investigate the stability of stationary integral solutions of an ideal irrotational fluid in a general static and spherically symmetric background, by studying the profile of the perturbation of the mass accretion rate. We consider low angular momentum axisymmetric accretion flows for three different accretion disk models and consider time dependent and radial linear perturbation of the mass accretion rate. First we show that the propagation of such perturbation can be determined by an effective 2 × 2 matrix, which has qualitatively similar acoustic causal properties as one obtains via the perturbation of the velocity potential. Next, using this matrix we analytically address the stability issues, for both standing and travelling wave configurations generated by the perturbation. Finally, based on this general formalism we briefly discuss the explicit example of the Schwarzschild spacetime and compare our results of stability with the existing literature, which instead address this problem via the perturbation of the velocity potential. 相似文献
16.
M. Goossens 《Astrophysics and Space Science》1972,16(3):386-404
A generalization of the perturbation method is applied to the problem of the radial and the non-radial oscillations of a gaseous star which is distorted by a magnetic field. An expression is derived for the perturbation of the oscillation frequencies due to the presence of a weak magnetic field when the equilibrium configuration is a spheroid. The particular application to the homogeneous model with a purely poloidal field inside, due to a current distribution proportional to the distance from the axis of symmetry, and a dipole type field outside is considered in detail. The main result is that the magnetic field has a large and almost stabilizing effect on unstableg-modes, particularly on higher order modes. With the considered magnetic field the surface layers appear to have a large weight. 相似文献
17.
Carl A. Rouse 《Solar physics》1986,106(2):205-216
The high-Z core (HZC) model of the Sun, supported in Rouse (1985) by superior agreements of nonradial g-mode periods of oscillation with long period observations, is used to calculate frequencies of oscillation in the five-minute band (5MB). Allowing for the fact that the present HZC model profile does not include an upper photosphere and self-consistent chromosphere, the HZC model of the Sun is also supported by the very good agreements of the 5MB nonradial frequencies of oscillation with observations for HZC l degrees 0 to 19 and orders n 20, and the good agreement of the HZC purely radial frequencies of oscillation with about the same n-orders with observations previously identified as l = 0 oscillations. Two important aspects of these agreements are (1) the nonradial frequencies were calculated with the equations that neglect the gravitational perturbation (the Cowling approximation), and (2) the radial frequencies were calculated with the equation that includes the gravitational perturbation. The present agreements suggest that for solar-type stars, the gravitational perturbation may not affect the nonradial p-modes of oscillation as much as it affects the radial modes and the nonradial g-modes. More research will be performed. 相似文献
18.
David Moss 《Astrophysics and Space Science》1978,56(2):473-478
First-order perturbation theory results for the changes in pulsation frequencies of a Cowling model star containing a magnetic field with both poloidal and toroidal components are presented. A toroidal field large enough to stabilize the poloidal field may reverse the sign of the frequency change caused by a purely poloidal field for some modes, including the fundamental radial mode. 相似文献
19.
J. Daszy&#;ska-Daszkiewicz P. Walczak 《Monthly notices of the Royal Astronomical Society》2009,398(4):1961-1969
We present results of a comprehensive asteroseismic modelling of the β Cephei variable θ Ophiuchi. We call these studies complex asteroseismology because our goal is to reproduce both pulsational frequencies and corresponding values of a complex, non-adiabatic parameter, f , defined by the radiative flux perturbation. To this end, we apply the method of simultaneous determination of the spherical harmonic degree, ℓ, of excited pulsational mode and the corresponding non-adiabatic f parameter from combined multicolour photometry and radial velocity data. Using both the OP and OPAL opacity data, we find a family of seismic models which reproduce the radial and dipole centroid mode frequencies, as well as the f parameter associated with the radial mode. Adding the non-adiabatic parameter to seismic modelling of the B-type main-sequence pulsators yields very strong constraints on stellar opacities. In particular, only with one source of opacities it is possible to agree the empirical values of f with their theoretical counterparts. Our results for θ Oph point substantially to preference for the OPAL data. 相似文献