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Stability and Structure of Spiral Galaxies with Finite Thickness

Chinese Physics Letters 2005年第3期22卷 776-779页

作者：林忆辉彭秋和邹志刚罗新炼 GraduateInstituteofAstronomy NationalCentralUniversityTaipei32054 DepartmentofAstronomy NanjingUniversityNanjing210093//BeijingAstrophysicalCentreChineseAcademyofSciencesPekingUniversityBeijing100871 DepartmentofPhysics ChineseCultureUniversityTaipei11192//NationalAstronomicalObservatoriesChineseAcademyofSciencesBeijing100012 DepartmentofAstronomy NanjingUniversityNanjing210093

We calculate the effect of finite disc thickness on the structure and stability of a differentially rotating three-dimensional spiral galaxy with stars and gases. The problem is solved exactly in terms of the rigorous mathematical method of Green function and Bessel--Fourier transform. By using the appropriate three dimensional self-gravitational potential due to the density perturbations of the spiral arms in the galactic disc, the dispersion relation for the quasi-stationary density waves are deduced for the composite disc model of stars and gases with finite thickness. The stability criterion depicted by the Toomre Q parameter for these spiral modes are investigated in detail. In contrast to the standard Q parameter for an infinitely thin two-dimensional disc, our generalized Toomre Q parameter depends explicitly on the disc thickness and the location. In the limit of an infinitely thin disc, our result naturally reduces to Toomre"s criterion for a stellar disc and to Kalnajs"s result for a gaseous disc. In addition, the significant role played by the finite thickness of the galactic disc on the spatial structure of the stellar arms and the gaseous arms in the galactic plane is also briefly discussed. Application of our theory to the disc models with two stellar arms and four gaseous arms, gas content 15% and the total surface density in the solar neighbourhood σ = 52M0pc-2 but with the thickness parameter α in the range of 3.0 < α < 4.0 (250pc < hz < 325pc) appropriate to our Galaxy yields good results in general agreement with recent observations.

关键词： Galaxies Spiral galaxies Stellar structure Stellar investigations Galactic models solar observations Wave dispersion solar models Dispersion of gases Dispersion models

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A Quasi—One—Dimensional Model for a solar Flux Tube

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Chinese Physics Letters 2002年第8期19卷 1217-1220页

作者：杨志良冯学尚等 solarPhysics BeijingAstronomicalObservatoryBeijing100012 SpaceWeatherLaboratory CenterforSpaceScienceandAppliedResearchChineseAcademyofSciencesBeijing100080

We develop the quasi-one-dimensional flux tube model with magnetohydrodynamical equations. In order to know whether themagnetic field can maintain their similar structure from photosphere to chromosphere, we suppose that the flux tube is thin inradius relative to the length, and that the quantities in the cross section are averaged. The radii of the flux tube and the magnetic field arenumerically simulated. One of the important results shows that the flux tube does not expand as quickly as the existing model when it is out ofthe photosphere with high velocity. This is consistent with observations of the magnetic field in the photosphere andchromosphere.

关键词： Magnetic fields Chromosphere solar models

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