太阳P模振动理论的研究

日震学是太阳物理的一个前沿分支学科,是根据太阳振动的观测来研究太阳的内部结构与运动的一种方法学。太阳５ｍｉｎ振动频率的理论计算和实测之间存在显著偏差和振动模的激发问题一直是困扰日震学的两大难题。经过多年的研究仍然没有解决。然而太阳表面层内绝热假设条件与真实情况有很大的偏差,我们认为绝大多数标准太阳模型的Ｐ模频率计算忽略了非绝热效应对频率的影响,忽略了振动的激发和衰减机制以及缺乏振动与对流湍流相互作     

非绝热过程对太阳p模振动的影响

本文讨论了与非绝热性有关的辐射损失和对流转移对太阳ｐ模振动的影响．在非绝热情况下，ｐ模的本征频率增加了虚部σ（１）ｉ和σ（２）ｉ．本文试图探讨一种渐进方法研究非绝热效应对太阳ｐ模振动的影响．在渐进近似失效的太阳外大气层，利用表面相移的相关关系给出了非绝热振动方程的严格解．对低、中间频率的振动模，通过渐进解和表面解在外大气层的拟合，得到表面相移只是频率的函数．与绝热振动相比，考虑非绝热效应有可能改善太阳５分钟振动的理论频率和观测频率之间存在的偏差．     

90年代太阳模型和太阳震荡研究进展(II):太阳振荡研究进展(英)

太阳振荡研究现已成为研究太阳内部性质的新手段,也成为检验太阳模型构造时输入物理参量的最重要工具。90年代以来理论与观测日震频率的差别已随输入物理参量及太阳振荡理论的改进而大为减小,可是现有的差别仍远大于观测误差。由日震反演可对太阳内部对流区、表面氦丰度及自转随纬度和径向的分布都有更多了解。太阳振荡的湍动随机激发及激发源的位置都已得到研究,不过现在问题还未完全解决。今后一方面要探测更多的振动方式,另一方面也需要解决不同观测者得到的结果存在系统差的问题,而最外层的非绝热现象及理论与观测存在差别仍是最关键的难题。     

太阳p模振动的激发机制

本估计了激发单个太阳ｐ模振动需要的能量输入率Ｅ≡ＥＴ,其中谱线宽度Г假设是振动模能量衰减率的观测值,在改进后的对流湍流三维时空分离描述的基础上,利用太阳对流区的混合长流模型计算了振动模的激发率,认为太阳Ｐ模振动主要是由雷诺应力扰动激发的,即Ｐ模激发对应着地流湍流运动引起声波发射,对于频率ｖ〈３ｍＨｚ,振动模的激发率为Ｅ∝ｖ＾７频率ｖ〉３ｍＨｚ,振动模的激发率为Ｅ∝ｖ＾－５,理论计算的振动能谱与观     

太阳p模振动的激发机制

本文估计了激发单个太阳ｐ模振动需要的能量输入率Ｅ≡ＥΓ,其中谱线宽度Γ假设是振动模能量衰减率的观测值．在改进后的对流湍流三维时空分离描述的基础上,利用太阳对流区的混合长模型计算了振动模的激发率．认为太阳ｐ模振动主要是由雷诺应力扰动激发的,即ｐ模激发对应着对流湍流运动引起的声波发射．对于频率ν＜３ｍＨｚ,振动模的激发率为Ｅ∝ν７;频率ν＞３ｍＨｚ,振动模的激发率为Ｅ∝ν－５．理论计算的振动能谱与观测结果基本符合．     

磁对流湍流对太阳P模振动的影响(英文)

为了进一步探索太阳对流区的物理性质 ,我们利用高精度N的日震观测数据来研究太阳内部扰动磁场对低阶太阳P模振动的影响。对于一个时间相关的MHD湍流源 ,我们给出了导致频率变化的各种可能性。如果只考虑磁扰动的贡献 ,不同值的振动模的频率变化仅只是涨落磁场能谱的函数。我们发现频率的变化随着太阳内部磁场强度增加而变大 ,并且和太阳活动周期密切相关。我们的计算表明太阳磁活动导致的频率变化可达 0 .3μΗz。     

表面边界位置对太阳ρ模本征振荡频率的影响

本文研究了表面边界位置对太阳ρ模绝热本征振荡频率的影响。数值计算结果表明，对于ｖ４０００μＨｚ的中低阶ｐ模，表面边界置于温度极小点所引起的本征振荡频率的计算误差随着ｖ和ｌ的增大，表面边界点位置对太阳理论振荡频率的影响增大，色球结构对太阳ｐ模振荡频率的影响已变得不可忽略。     

非绝热过程对太阳P模振动的影响

本讨论了与非绝热性有关的辐射损失和对流转移对太阳ｐ模振动的影响。在非绝热情况下，Ｐ模的本征频率增加虚σｉ和σ＾２（）ｉ。本试图探讨一种渐进方法研究非绝热产应对太阳Ｐ模振动的影响。在渐近近拟效的太阳外大气层，利用表面相移的相关关系给出了非绝热振动方程的严格解。     

太阳存在脉动不稳定的低球谐阶p1模吗?

利用一种非局部和非定常的恒星对流理论,计算了太阳中低球谐阶(l＜25)模的非绝热脉动.结果表明,低阶(0＜l＜6)非径向p1模是脉动不稳定的,而与之相邻的g模、f模和p2-p5模都是脉动稳定的.根据累积功图的分析,发现振荡的激发来自对流区底部区域.太阳是否存在不稳定的低球谐阶p1模对判断太阳5 min振荡的激发机制有重要意义.     

太阳5分钟振荡的激发机制

1 引言 太阳5分钟振荡是上世纪1个重要的发现[1],它使得人们可以通过观测太阳表面的振动来探测其内部的结构,日震学已取得了巨大的进展,然而我们至今仍不了解其脉动的激发机制,它依然是1个存在争议的问题.太阳位于造父变星脉动不稳定区之外,所以大多数人都相信,由于对流的阻尼,太阳是脉动稳定的,太阳和太阳型恒星的振荡都是由所谓的湍流随机激发机制所激发[2-8].     

Seismic view of the solar interior

The interior of the Sun is not directly observable to us. Nevertheless, it is possible to infer the physical conditions prevailing in the solar interior with the help of theoretical models coupled with observational input provided by measured frequencies of solar oscillations. The frequencies of these solar oscillations depend on the internal structure and dynamics of the Sun and from the knowledge of these frequencies it is possible to infer the internal structure as well as the large scale flows inside the Sun, in the same way as the observations of seismic waves on the surface of Earth help us in the study of its interior. With the accumulation of seismic data over the last six years it has also become possible to study temporal variations in the solar interior. Some of these seismic inferences would be described.     

Solar oscillations and the equation of state

Summary Accurate measurements of observed frequencies of solar oscillations are providing a wealth of data on the properties of the solar interior. The frequencies depend on solar structure, and on the properties of the plasma in the Sun. Here we consider in particular the dependence on the thermodynamic state. From an analysis of the equations of stellar structure, and the relevant aspects of the properties of the oscillations, we argue that in the convection zone one can isolate information about the equation of state which is relatively unaffected by other uncertainties in the physics of the solar interior. We review the different treatments that have been used to describe the thermodynamics of stellar plasmas. Through application of several of these to the computation of models of the solar envelope we demonstrate that the sensitivity of the observed frequencies is in fact sufficient to distinguish even quite subtle features of the physics of solar matter. This opens up the possibility of using the Sun as a laboratory for statistical mechanics, under conditions that are out of reach in a terrestrial laboratory.     

Inverting helioseismic data

Methods by which the observed frequencies of solar oscillations can be, and in some cases have been used to infer the internal structure of the Sun are discussed. Attention is confined to so-called inverse methods that identify and extract the information that is actually contained in the data. Because only a finite quantity of data can ever be acquired, the functions describing the interior stratification of the Sun can never be established completely without the acceptance of certain assumptions. Nevertheless, the assumptions that are required are simple to understand, and the results do not depend on the complicated and uncertain theory of stellar evolution which has traditionally been used to construct solar models. First results of the inversions have given us an estimate of the sound speed and the angular velocity throughout much of the solar interior. These estimates have already stimulated speculation which hopefully will encourage further theoretical and observational research that will improve our understanding of the Sun.     

Solar interior structure and luminosity variations

The assumptions of standard solar evolution theory are mentioned briefly, and the principle conclusions drawn from them are described. The result is a rationalization of the present luminosity and radius of the Sun. Because there is some uncertainty about the interior composition of the Sun, a range of models is apparently acceptable.To decide which model is the most accurate, other more sensitive comparisons with observations must be made. Recent measurements of frequencies of dynamical oscillations are particularly valuable in this respect. The most accurate observations are of the five-minute oscillations, which suggest that the solar composition is not atypical of other stars of the same age as the Sun.The theory predicts that the solar luminosity has risen steadily from about 70% of its current value during the last 4.7 x 10⁹yr. Superposed on this there might have been variations on shorter timescales. Variations lasting about 10⁷yr and occurring at intervals of 10⁸yr have been suggested as being the cause of terrestrial ice ages. Moreover, there may be other variations, associated with instabilities arising from the coupling between the convection zone and the radiative interior, that occur on a timescale of 10⁵yr and which also have climatic consequences. These issues are quite uncertain.We do know that the Sun varies magnetically with a period of about 22 yr, and that this oscillation is modulated irregularly on a timescale of centuries. This appears to be a phenomenon associated with the convection zone and its immediate neighbourhood, though control from a more deeply-seated mechanism is not out of the question. There is a small luminosity variation associated with this cycle, and the way by which this might come about is discussed in terms of certain theories of the solar dynamo.Finally, there must be small surface flux variations associated with the dynamical oscillations mentioned above. Though the total luminosity variations are extremely small, the flux in any specific direction, and in particular that of the earth, may be measurable.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Solar p and g modes in a model with a convection layer above a sub-adiabatic interior

We study high-order acoustic modes which reside in the outer layers of the solar interior. Magnetic field effects are not taken into account in this paper as we wish first to filter out how the modal frequencies depend on physical characteristics of a particular model structure of the Sun. In particular, we are interested in how the modal frequencies of solar global oscillations depend on the thickness of the convection layer and on the temperature gradient of the solar interior below. The model we use consists of three planar layers: an isothermal atmosphere, while the convection layer and the interior have temperature gradients that are adiabatic and sub-adiabatic, respectively. The presence of a convection layer with a finite thickness brings in additional modes while the variations in temperature gradient of the interior cause shifts in eigenfrequencies that are more pronounced for the p modes than for the g modes. These shifts can easily be of the order of several hundreds of Hz, which is much larger than the observational accuracy.     

Helioseismology

The sun being the nearest star, seismic observations with high spatial resolution are possible, thus providing accurate measurement of frequencies of about half million modes of solar oscillations covering a wide range of degree. With these data helioseismology has enabled us to study the solar interior in sufficient detail to infer the large-scale structure and rotation of the solar interior. With the availability of high quality helioseismic data over a good fraction of a solar cycle it is also possible to study temporal variations in solar structure and dynamics. Some of these problems and recent results will be discussed.     

Solar oscillations: Past,present, and future

Observation of global oscillations of the Sun constitutes a primitive seismology of the solar interior. The frequencies, if correctly identified with definite normal modes of vibration, provide a measure of the average velocity of sound in the interior and thereby of its composition and temperature. Fine structure in the frequencies of nonradial modes may provide information on their character (multiplicity) and on the rotation of the solar interior. Study of the amplitudes and phase fluctuations of the vibrations may clarify the excitation and damping of the vibrations.After a brief historical review emphasizing global velocity spectroscopy an account is given of the present status of the observations of global oscillations in the range of periods of 3 to 160 min.Finally the future capabilities of the observational techniques and their resultant potential is discussed.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Analytical signal as a tool for studying solar p-modes

A technique for analyzing periodic processes based on the introduction of an analytical signal is described. This technique allows the instantaneous frequency, amplitude, and phase of oscillations to be obtained. The data on solar brightness fluctuations collected with the DIFOS multichannel photometer onboard the CORONAS-F satellite are processed. The p-mode spectral lines are broadened mainly by amplitude fluctuations, while the frequency stability appears to be high (～10^?4). A method for separating signals with close frequencies is developed. The p-mode with l = 0 and n = 21 is used as an example to show that the separation of signals with close frequencies is possible when the conventional spectral methods are inefficient. Analysis of the phase shifts between the oscillations observed in various optical channels of the DIFOS photometer has revealed that the five-minute oscillations travel from the upper and deep photospheric layers toward the middle photospheric layers. This effect directly proves that the evanescent p-modes in the photosphere are nonadiabatic.     

Accurate Intensity – Velocity Phase Difference in the Potassium Resonance Line Obtained with VAMOS

We present new results about the phase difference between the intensity and velocity fluctuations of the solar photosphere obtained with the Velocity And Magnetic Observations of the Sun (VAMOS) instrument, which uses the magneto-optical filter (MOF) technique. Before this observing run, we applied the calibration method described in Magrì, Oliviero, and Severino (Solar Phys. 232, 159, 2005) to reduce the instrumental cross-talk which was present in previous VAMOS data. The quality of this calibration, which can be easily applied to any MOF-based instrument, has been confirmed by comparing with the MOF transmission-profile measurements obtained with a diode laser system. Finally, we discuss the new VAMOS phase-difference value in relation to data obtained by other authors in the same potassium spectral line and in other lines that can be used to study nonadiabatic effects of solar global oscillations.