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1.
一种能从观测到的斯托克斯轮廓中提取太阳表面矢量磁场信息的方法在本文中提出，它利用斯托克斯轮廓非线心的极值点处相应参量对波长的导数为零这一数学事实，假设表面附近磁场矢量及热力学参量的变化梯度足够小以致所考虑的极值点的波长位置不随深度改变或此变化呆忽则使得偏振辐射围方程组得到极大的简化；再应用数值方法从此简化方程组中解出辐射表面附近的磁场矢量参数。通过拟合理论轮廓表明该法确实可以得到表面近似的磁场矢量 相似文献
2.
The polarization-free (POF) approximation (Trujillo Bueno and Landi Degl'Innocenti, 1996) is capable of accounting for the approximate influence of the magnetic field on the statistical equilibrium, without actually solving the full Stokes vector radiative transfer equation. The method introduces the Zeeman splitting or broadening of the line absorption profile I in the scalar radiative transfer equation, but the coupling between Stokes I and the other Stokes parameters is neglected. The expected influence of the magnetic field is largest for strongly-split strong lines and the effect is greatly enhanced by gradients in the magnetic field strength. Formally the interaction with the other Stokes parameters may not be neglected for strongly-split strong lines, but it turns out that the error in Stokes I obtained through the POF approximation to a large extent cancels the neglect of interaction with the other Stokes parameters, so that the resulting line source functions and line opacities are more accurate than those obtained with the field-free approach. Although its merits have so far only been tested for a two-level atom, we apply the POF approximation to multi-level non-LTE radiative transfer problems on the premise that there is no essential difference between these two cases. Final verification of its validity in multi-level cases still awaits the completion of a non-LTE Stokes vector transfer code.For two realistic multi-level cases (CaII and MgI in the solar atmosphere) it is demonstrated that the POF method leads to small changes, with respect to the field-free method, in the line source functions and emergent Stokes vector profiles (much smaller than for a two-level atom). Real atoms are dominated by strong ultraviolet lines (only weakly split) and continua, and most lines with large magnetic splitting (in the red and the infrared) are at higher excitation energies, i.e. they are relatively weak and unable to produce significant changes in the statistical equilibrium. We find that it is generally unpredictable by how much the POF results will differ from the field-free results, so that it is nearly always necessary to confirm predictions by actual computations.The POF approximation provides more reliable results than the field-free approximation without significantly complicating the radiative transfer problem, i.e. without solving any extra equations and without excessive computational resource requirements, so that it is to be preferred over the field-free approximation. 相似文献
3.
A diagnostic method for the determination of the vector magnetic field through the interpretation of spectropolarimetric profiles observed in solar active regions is presented. An inversion routine, that is based on the analytical solution of the radiative transfer equation for polarized radiation given by Unno and Rachkowsky, is described; the routine performs a comparison among theoretical profiles depending on eight parameters and the observed profiles by means of a non linear least square fit. The routine has been applied to the interpretation of the spectropolarimetric profiles observed on 15 September, 1980 in a sunspot with the spectropolarimeter (Stokes II) of the High Altitude Observatory, National Center for Atmospheric Research*. One of the eight parameters (the line center) gives information on the plasma motions. The significance of these motions inside the sunspot is discussed.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
4.
Viik Tõnu 《Earth, Moon, and Planets》1989,46(3):261-284
The vector equation of radiative transfer is solved both for conservative and non-conservative planetary atmospheres using the method of discrete ordinates. The atmosphere, bounded by a Lambert bottom, is considered plane-parallel and homogeneous. The scattering in the atmosphere obeys the Rayleigh or Rayleigh-Cabannes law. The compiled package of FORTRAN codes allows us to find the Stokes parameters for such an atmosphere at arbitrary optical depth. 相似文献
5.
The transfer equations for the Stokes parameters, as derived under the assumption of LTE and in the general case of anomalous Zeeman multiplet, are solved by a perturbative method that reduces the system of four coupled linear differential equations to an iterative series of well known linear differential equations. The perturbation parameter turns out to be of the order of magnitude of the ratio of the Larmor frequency to the line Doppler half-width, so that the method appears to be particularly suitable for small magnetic fields.Some qualitative results on the importance of Faraday rotation and the orders of magnitude of the line profiles of the Stokes parameters are obtained. 相似文献
6.
A simple method is proposed to infer the vector magnetic field at the surface of the Sun from Stokes profiles. This is based on the assumption that the variations of thermodynamical and magnetic field parameters with depth near the surface are so small that the displacements of the wavelengths at which the Stokes profiles reach their extrema can be ignored. And hence the polarized radiative transfer equations are greatly reduced to a set of non-linear equations with vector magnetic field parameters (, , ) which can be solved by a numerical iteration method. By fitting the synthetic profiles, it is shown that this proposed method can produce information on the vector field at the surface. It is also used to revise the observed profiles and it is found that the observed sunspot has the magnetic field structure of the fan model with the lines of magnetic field twisted. 相似文献
7.
E. Landi Degl'innocenti 《Solar physics》1983,85(1):3-31
A unifying theoretical approach is presented to derive from the general principles of Quantum Electrodynamics both the radiative transfer equations for polarized radiation and the statistical equilibrium equations for an atomic system interacting with a polarized radiation field. The radiation field is described by means of Stokes parameters while the atomic system is described in terms of its density-matrix operator. The non-diagonal terms of the density matrix are fully accounted for so that this formalism can be suitably employed to describe a wide variety of physical phenomena like resonance scattering, the Hanle effect and the Zeeman effect, either in optically thin or optically thick atmospheres, together with all the possible intermediate situations.The general formulae derived in the first sections of the paper are subsequently particularized introducing the dipole approximation in the relevant matrix elements describing the interaction between the atomic system and the radiation field. The final equations assume a quite compact expression by the introduction of suitable spherical tensors connected with the components of the polarization unit vectors associated with each direction of the radiation field. The general expressions and the main properties of these tensors are discussed in the Appendix. 相似文献
8.
P. C. W. Fung 《Astrophysics and Space Science》1969,5(4):448-458
In this investigation, the polarization transfer equations in terms of the Stokes parameters are derived for electromagnetic waves propagating in an arbitrary direction in an inhomogeneous magnetized plasma. This system of transfer equations is then solved analytically in the case when the magnetized plasma is homogeneous. For simplicity in presentation, the source term in the equation of transfer has been omitted. Transitting to the special case of quasi-longitudinal propagation, the results obtained here are shown to be in agreement to that derived by Zheleznyakov earlier. 相似文献
9.
Michael J. Price 《Astrophysics and Space Science》1969,4(2):182-212
A general Monte Carlo relaxation method has been formulated for the computation of physically self-consistent model stellar atmospheres. The local physical state is obtained by solving simultaneously the equations of statistical equilibrium for the atomic and ionic level populations, the kinetic energy balance equation for the electron gas to obtain the electron temperature, and the equation of radiative transfer. Anisotropic Thomson scattering is included in the equation of transfer and radiation pressure effects are included in the hydrostatic equation. The constraints of hydrostatic and radiative equilibrium are enforced. Local thermodynamic equilibrium (L.T.E.) is assumed as a boundary condition deep in the atmosphere. Elsewhere in the atmosphere L.T.E. is not assumed.The statistical equilibrium equations are solved with no assumptions made concerning detailed balance for the bound-bound radiative processes. The source function is formulated in microscopic detail. All atomic processes contributing to the absorption and emission of radiation are included. The kinetic energy balance equation for the electron gas is formulated in detail. All atomic processes by which kinetic energy is gained and lost by the electron gas are included.The method has been applied to the computation of a model atmosphere for a pure hydrogen early-type star. An idealized model of the hydrogen atom with five bound levels and the continuum was adopted. The results of the trial calculation are discussed with reference to stability, accuracy, and convergence of the solution.Contribution No. 385 from the Kitt Peak National Observatory.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
10.
We present a cylindrically symmetric model for a sunspot atmosphere using the similarity principle of Schlüter and Temesvary for the magnetic field configuration. The equations of magnetostatic equilibrium are used, augmented by a radial Evershed flow. The LTE radiative transfer equations for the Stokes vector were solved under a variety of conditions for a ray emerging from a typical penumbral point. The contribution from isolated lines to the broadband circular polarization in sunspot penumbrae is evaluated using a more realistic model sunspot atmosphere than has hitherto been considered. Results indicate that the inclusion of a velocity field along B is unable to give a net circular polarization of sufficient magnitude, although the variation with the angle between the line-of-sight and B is in qualitative agreement with observations. The corresponding results for the net linear polarization are satisfactory. 相似文献
11.
We formulate rate equations for the reaction network coupling H, H–, H+, H2, and H2
+. We attempt to systematize the notation, and to write the equations in a form suitable for modern computational methods of handling the coupled rate equations and radiative transfer equations, for both dynamical and static atmospheres. We have accounted for more processes than are generally considered in most current work; some of these may have an impact on the equilibrium of H– (hence its opacity) and on charge conservation (hence the proton density) in the atmospheres of solar-type stars.Operated by the Association of Universities for Research in Astronomy, Inc. under Contract AST 78-17292 with the National Science Foundation.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
12.
A general formalism is presented to obtain an analytical solution of the radiative transfer equations for polarized radiation when the absorption Mueller matrix for the Stokes parameters is constant along the ray-path. The formalism is then applied to find an analytical approximation of the Stokes parameters profiles for a typical chromospheric line having an optical-depth dependence of the source function of the form S() = ( + )1/2(1 + )1/2. 相似文献
13.
The transfer equations for the Stokes parameters in the presence of magnetic field and under the hypothesis of LTE are derived in an original way by the use of density matrix techniques.The results are substantially the same as those previously obtained by other authors. We finally compare our results to the previous ones in order to clarify some discrepancies still present in the literature. 相似文献
14.
The comoving-frame equation of radiative transfer and moment equations are derived in orthogonal, curvilinear coordinates, inclusive of terms of orderv/c. The equation of radiative transfer, which contains the terms due to the effect of curvature of coordinate lines explicitly as well as those of Doppler shift and aberration, is the generalization of Castor's equation for spherical symmetry and of Buchler's equation for Cartesian coordinates. The moment equations agree with Buchler's. 相似文献
15.
The coupled set of equations of hydrodynamics and radiative transfer is derived for small disturbances in a plane, grey atmosphere. Only radiative transfer is taken into account in the energy equation; dynamical effects of radiation are ignored. A mean stationary radiative flux through the photosphere is taken into account. The radiative transfer equation is used by assuming the Eddington approximation, moreover, an exponential height profile of the temperature and an analytical opacity formula are supposed. For this model we obtained an asymptotic solution for plane nonadiabatic acoustic waves and radiation waves. The approach provides a detailed discussion of the interaction of nonadiabatic p‐modes and radiation waves in a realistic model of the photosphere of a solar‐like star. 相似文献
16.
The comoving-frame equations of radiative transfer and moment equations to accurate terms of all orders inv/c are derived in the modified Lagrangian form. The equations exactly describe the interaction of radiation with matter in a relativistically moving medium in flat or curved spacetime. Two specialized sets of equations are presented: (1) the equation of radiative transfer and moment equations accurate to terms of second order (v
2/c
2), and (2) the transfer equation and moment equations for a radial flow in curved spacetime with the Schwarzschild-type metric. 相似文献
17.
The application of Unno's (1956) solution of the transfer equation for polarized radiation to the determination of thevector magnetic field is investigated. An analysis procedure utilizing non-linear least squares techniques is developed that allows one to automate the reduction of measured spectral profiles of the Stokes parameters to determine the field angles, strength as well as other parameters. The method is applied to synthetic spectra generated using a model solar atmosphere and yields results of remarkably high accuracy. The influence of additional factors upon determination of the vector field are also considered. These factors include effects of asymmetric profiles, magneto-optical effects, magnetic field gradients, unresolved field elements, scattered light, and instrumental noise.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
18.
《Chinese Astronomy and Astrophysics》1982,6(1):13-19
In this paper the equations of transfer of Stokes parameters are solved under the hypothesis of the propogation of Alfven waves. The effects of Alfven waves on the magneto-sensitive line FeIλ6302. 499 in the spectra of sunspots are calculated. Besides, some methods have been proposed for the verification of theoretical computations with observational material and for estimating the energy flux of Alfven waves. 相似文献
19.
J. Heyvaerts 《Astrophysics and Space Science》1969,5(1):36-52
By a perturbation and diagram resummation method, a transport equation for the transverse field polarization matrix is established. This equation is then transformed into an equation for the Stokes parameters of the radiation. The equation takes the usual form of a transfer equation; the absorption and emission coefficients are matrix, the elements of which are given as a function of the dissipative part of the microcurrent correlation tensor and conductivity tensor. Finally this equation is expressed as a system for the intensities of the proper modes. The equations of the system are usually coupled. 相似文献
20.
Olav Kjeldseth Moe 《Solar physics》1968,4(3):267-285
The formation of spectral lines in a homogeneous magnetic field has been studied. A new method for solving the transfer equations for polarized light has been found. Using this method, the Stokes parameters may be derived without any special assumptions regarding the model atmosphere. With the line formed by pure absorption, the expressions for the Stokes parameters may easily be adapted to numerical calculations. In order to illustrate the method, the line profile for the Zeeman triplet 5250 has been calculated using a photospheric model atmosphere. 相似文献