有限厚度旋涡星系密度螺旋形扰动的Poisson方程渐近解

本文是在一个特殊模式下,对于有限厚度旋涡星系物质密度螺旋形扰动的三维引力势Poisson方程,用速变相法求出了一级渐近解。 为了解释旋涡星系的螺旋结构,林家翘等[1][2]曾求出引力势Poisson方程的渐近解。这一渐近解对于应用密度波的概念去解释旋涡形式星系的理论起着重要的作用。但是,这一渐近解是把星系中的物质近似地看成集中于星盘平面上,求解二维Poisson方程得到的。所以,不能用它讨论物质的垂直分布与垂直运动对螺旋结构的影响。后来,徐遐生[3]研究了星系盘有限厚度效应,但是他没有解出引力势的三维Poisson方程。我们根据旋涡星系中物质分布的实际情况,求出了三维Poisson方程在一个特殊模式下的解。     

星系盘厚度效应的研究

在三维引力Poisson方程严格解基础上，探讨了有限厚星系盘基盘的动力学性质，并进一步讨论了盘的厚度效应对银河系所需晕质量的影响。研究了扰动盘的动力学性质，通过将扰动引力势Poisson方程的严格解与林家翘、徐遐生提出的自维持密度波理论相结合，建立了三维旋涡星系有限厚盘上密度波的色散关系。在此色散关系的基础上讨论了盘的局域稳定性，研究了旋涡星系旋臂的形态、三维盘状星系密度波的群速度。研究表明厚度是星系盘研究中不容忽略的重要参量。另外在有限厚盘星系密度波色散关系的基础上还探讨了一种确定星系厚度的新方法。     

面向类旋涡星系盘有效厚度的获取及图像处理方法

面向类(face-on)旋涡星系盘的有效厚度或标高不能通过表面亮度测光的方式测量.为了获得面向类旋涡星系盘的厚度参数,将基于三维星系盘引力势Poisson方程在等角对数螺旋型物质密度扰动情形下的解,运用一种解析法对面向类旋涡星系盘的标高进行测算.为了去除星系核球的光污染而获得旋臂最内点位置(r0)的重要参数,使用了在星系观测图像中扣除双成份(盘+核球)测光模型的图像处理方法.通过对旋涡星系相关结构参数的拟合测量,各得到了一个普通旋涡星系(S)与棒旋星系(SB)的有效厚度与相关参数,并给出了它们的球盘比(rb/rd)和星系盘的标长与厚度之比(rd/H).采用这种在观测图像中扣除双成份测光模型的方法,将更容易看清旋臂结构的最内端,因而这里获得的禁区半径r0的数值往往比从原星系图像上直接测量的数值要小,获得的星系盘有效厚度将更薄.     

三维旋涡星系的动力学研究

在三维对数螺线型密度扰动的引力Poisson方程严格解基础上,导出了对称平面(z=0)上三维混合盘密度波的色散关系,并以此讨论了对于不同类型扰动盘的局域稳定性,同时还计算了盘面上密度波的群速度．数值计算表明对数螺线型密度扰动,能比较好地满足扰动密度与扰动势反相位的关系;厚度和旋臂数目的增加有利于盘的稳定,而气体成分将导致盘不稳定;考虑厚度效应,银河系密度波传播的动力学时标与Toomre估计的数值相比将大大延长,至少需要4．17×109年,约占宇宙年龄的三分之一,从而可使以往密度波理论中得出的群速度太大的问题得到缓解．     

旋涡星系中对任意旋臂倾角一致有效的密度-引力势渐近关系

本文给出对于臂数m≥2的旋涡星系(正常旋涡星系或棒旋星系),对任意旋臂倾角(0≤|β|≤π/2)一致有效的扰动密度-扰动引力势渐近关系。在|β|≤1的特殊情形,它回到紧卷波的各种已知渐近关系;在|β|不小的情形,这一新结果适用于讨论构成棒旋星系的“开展模式”(open mode)。     

倾斜冷暗物质谱与宇宙中可观测结构

为了缓解标准冷暗物质模型在解释一些观测现象时所遇到的困难，本文考察了倾斜冷暗物质谱模型。在ＢＢＫＳ原初扰动场统计理论的基础上，本文根据天体质量函数的计算公式和背景－天体相互作用的估计方法，计算了星系群和星系团的质量函数，并与最新观测质量函数作了对比，又分析和计算了在各种空洞尺度上天体密度的变化。计算结果表明，倾斜冷暗物质谱模型在与ＣＯＢＥ卫星观测结果相容的前提下，能在上述两个方面缓解标准冷暗物质模型所遇到的困难。     

星系的转动与黑洞形成的判据

本文通过数值计算解出稳态星系模型，并与椭圆星系及旋涡星系核球的自转和弥散速度曲线相比较。由星系运动曲线传合出的星系半径与从光度曲线拟合出的潮汐半径不一致，后者总是前者的３倍左右，这是由于分布函数的截断方式不妥造成的。我们的结论是：该模型虽不能正确描述整个星系，但却能正确描述星系的较内部区域。我们分析了三个速度曲线资料的星系黑洞候选者：Ｍ１０４、Ｍ３１和银河系，发现它们由于有太快的自转，都不可能在达     

星系盘中的磁重平衡:星系贮留原初磁场的观测证据

邻近旋涡星系中观测到的磁场被理论学家解释为发电机作用的结果.而我们发现,在邻近的星系中,磁场的强度与中性氢的柱密度紧密相关.星系盘中的磁场处于磁重平衡状态.这一结果与发电机放大机制相悖,从而支持星系磁场是原初起源的假说.     

河外IRAS暗源大尺度分布的二维分析

本文对ＩＲＡＳ暗源表中４个选区的ＩＲＡＳ星系的两点角相关函数，关联分维进行了计算，结果表明，所有选区内的星系呈现小角尺度上的成团，在较大角尺度上，分布可以用多级分形很好地表示，在更大角尺度上，用非归一星系对计数可以探测到密度分布中可能存在的典型惊讶，当取４个选区的平均值作为ＩＲＡＳ星系在宙宇中分布情况的代表时，所得结果与用全于ＩＲＡＳ点源表和其他巡天资料得到的结果一致。     

径移主导吸积盘的含时数值模拟

黑洞吸积被认为是活动星系核的能量来源,而研究黑洞吸积最主要的难题是要解释吸积气体的角动量是如何转移出去的.黑洞吸积盘理论提出通过粘滞力矩转移角动量.径移主导吸积盘模型(advection-dominated accretion flow,简称ADAF)是几何厚、光学薄的低吸积率吸积盘模型,它在解释低光度活动星系核的一些观测现象时获得了很大的成功.近年来,随着计算机技术的迅猛发展,数值模拟在天体物理研究中获得了广泛的应用,也取得了突破性的进展.主要工作是用数值模拟方法研究ADAF整体解作为初始条件模拟黑洞的吸积过程.     

Acceleration of Numerical Integration of the Equations of Motion of Asteroids

Solar System Research - Finding and studying possible collisions of asteroids approaching the Earth requires a significant amount of computation. This paper describes the R0 program created to...     

Graphical representation of periodic motion of the line of nodes of the Moon

In the text-books of astronomy, sections generally related to the Moon deal with the orbital elements of the Earth-Moon system such asa, e, i, , and the time of perigee passage. While the MEAN of the first of the three elements do not vary, mean longitude of the ascending node-mean longitude of the lunar perigee and the time of perigee passage undergoes secular as well as periodic changes due predominantly to the action of the Sun's gravitational attraction. While to a certain degree, explanations related to the calculation of the lunar orbit parameters are given, not a single graphical representation of these short- or long-periodic changes are presented. We allow the number of data related to these periodic changes must cover a large span of time; and if regression of the line of nodes or advances of the line of apses are to be graphically seen, data covering 18.61 and 8.85 yr, respectively, are needed. In this work we particularly aim at the graphical representation of the periodic changes of the line of nodes.     

A survey of orbits of co-orbitals of Mars

Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF₃₁, were discovered, librating about the L₅ Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ₇, to be a Trojan, associated with the L₄ Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND₄₃) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW₁₅ and 2000 TG₂, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion.     

Observations of the intensity of the penumbra of sunspots

Observations of the penumbral intensity of sunspots in 13 wavelength regions are presented. In 4 wavelength regions 54 sunspots are measured. In the other wavelength regions the number of sunspots considered ranges from 3–19.The penumbral intensity alters with position within the spot. This intensity variation is found to be comparable with the change in intensity from one spot to another. The penumbral intensity is found to be independent of spot size in the sample considered.The penumbra model of Kjeldseth Moe and Maltby (1969) with = 0.055 is supported by the measurements.     

Equation of state and anisotropy of pressure of magnetars

Magnetars are the neutron stars with the highest magnetic fields up to 10¹⁵–10¹⁶ G. It has been proposed that they are also responsible for a variety of extra-galactic phenomena, ranging from giant flares in nearby galaxies to fast radio bursts. Utilizing a relativistic mean field model and a variable magnetic field configuration, we investigate the effects of strong magnetic fields on the equation of state and anisotropy of pressure of magnetars. It is found that the mass and radius of low-mass magnetars are weakly enhanced under the action of the strong magnetic field, and the anisotropy of pressure can be ignored. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars.