湍流压对中小质量恒星后期演化的影响（Ⅲ）红巨星和AGB星产生强？…

本提供了一个判别红巨星和ＡＧＢ星对流外壳中是否会产生动力学非稳定性的条件。根据这个条件和对２．８Ｍ⊙及７Ｍ⊙恒星从主序列到巨星阶段和ＡＧＢ阶段的演化计算,可以证明,湍流压效应是导致红居星和ＡＢＧ星靠近表达区域产生动力学非稳定性,从而造成质向外喷流的原因,并认为它就是造成红巨星和ＡＧＢ星表面温度很低（因而辐射压很低）从而产生强大星风物质损失的物理原因。     

湍流压对中小质量恒星后期演化的影响(I)湍流压、物态方程及热力学量的计算

本文以恒星结构演化理论中常用的混合程对流理论为基础，给出了湍流压以及考虑湍流压情况下恒星内部物态方程和各热力学量的表达式．在此基础上研究了质量为２．８Ｍ⊙和７Ｍ⊙的恒星由主序演化到红巨星和ＡＧＢ星阶段其湍流压的大小．结果证明，在红巨星和ＡＧＢ阶段，靠近恒星表面区域内湍流压可以达到总压强的３０％．     

湍流压对中小质量恒星后期演化的影响(I)湍流压对内部结构和演化的影响

本文研究了２８Ｍ⊙和７Ｍ⊙恒星由主序到红巨星和ＡＧＢ星阶段的演化．结果发现,湍流压的存在对质量较大的７Ｍ⊙恒星的内部结构有较大的影响,它将使氢燃烧壳层明显变厚并较早地消失;使恒星中心的温度降低;使ＨＲ图中的演化轨迹向温度降低和光度减小的方向变化;使氢壳层燃烧出现周期性脉动;氦壳层的热脉动周期变短等等．但是,对于质量较小的２８Ｍ⊙恒星,湍流压的效应很微小．     

湍流压对中小质量恒星后期演化的影响（II）湍流区对内部结构和演化…

本研究了２．８Ｍ⊙和７Ｍ⊙恒星由于主序到红巨星和ＡＧＢ星阶段的演化,结果发现,湍流压的存在质量较大的７Ｍ⊙恒星的内部结构有较大的影响,它将使氢燃烧壳屋明显变厚并较早地消失,使恒星中心的温度降低,使ＨＲ图中的演化轨迹向温度降低和光度减小的方向变化,使氢壳层燃烧出现周期性脉动,氦壳层的热脉动周期变短等等。但是,对于质量较小的２．８Ｍ⊙恒星,湍流压的效应很微小。     

湍流压对中小质量恒星后期演化的影响(Ⅲ)红巨星和AGB星产生强大星风物质损失的机理研究

本文提供了一个判别红巨星和ＡＧＢ星对流外壳中是否会产生动力学非稳定性的条件．根据这个条件和对２８Ｍ及７Ｍ恒星从主序到巨星阶段和ＡＧＢ阶段的演化计算,可以证明,湍流压效应是导致红巨星和ＡＧＢ星靠近表面区域产生动力学非稳定性,从而造成物质向外喷流的原因．并认为它就是造成红巨星和ＡＧＢ星表面温度很低（因而辐射压很低）从而产生强大星风物质损失的物理原因．     

湍流压对中小质量恒星后期演化的影响：（Ⅰ）湍流压,物态方程及热…

本以恒星结构演化理论中常用的混合程对流理论为基础，给出了湍流压以及考虑湍流压情况下恒星内部物态方程和各热力学量的表达式。在此基础上研究了质量为２．８Ｍ和７Ｍ的恒星由主序演化到红巨星和ＡＧＢ星阶段其湍流压的大小。结果证明，在红巨星和ＡＧＢ阶段，靠近恒星表面区域内湍流压可以达到总压强的３０％。     

AGB星的超星风与热脉动的研究

至今国际上对ＡＧＢ星的超星风、热脉动及振动的理论研究工作中都忽略了湍流压的存在，然而对于一个整个外壳都处于完全对流的ＡＧＢ星，湍流压是存在的，并且由于湍流压的存在将对气体压强、密度、温度以及各热力 学量产生影响，因而对ＡＧＢ星的超星风、热脉动脉振动产生影响。     

2.8M⊙碳AGB星的形成和演化

在混合程对流理论基础上建立了湍流压的恒星结构与演化理论,以及在对流外壳中出现动力学非稳定性的判据。在此基础上研究了初始质量为2.8M⊙的星族I恒星从主序星到碳AGB星的质量非守恒演化。结果表明,在RGB星和AGB星阶段,靠近恒星表面区域内湍流压可以达到总压强的30％。且湍流压效应可能是导致RGB星和AGB星靠近表面区域产生了动力学非稳定性,从而造成物质向外逃逸的原因,我们认为湍流压效应可能就是造成有效温度低因而辐射压也低的RGB星产生强星风,以及AGB星产生超星风的物理原因,还发现当氦燃烧层源厚度与层源质量的比值小于0.04R⊙／M⊙时,层源内会出现热核反应的非稳定现象,即出现热脉动,且2.8M⊙AGB星经过6次热脉动后,恒星表面的C／O超过1,恒星演化成碳AGB星。     

中等质量恒星在赫罗图中由E-AGB星进入TP-AGB星的分界点

通过对3～10 M_☉恒星在赫罗图上演化轨迹的研究,分析恒星内部氦壳层燃烧峰值处能量、密度、温度、氦壳层表面光度与恒星表面光度比及恒星半径的变化,给出了中等质量恒星由早期AGB星演化至热脉冲AGB星阶段在赫罗图上的分界点,与119颗碳星的观测结果吻合得相当好.同时提出:在恒星演化至该分界点之后,其星风物质损失公式可能需要引入一个与表面光度无关的量以主导超星风的形成.在此基础上,通过对考虑湍流压效应下5 M_☉恒星的结构和演化及星风物质损失率的分析,发现湍流压在热脉冲AGB星阶段对星风物质损失影响较大,从而使得热脉冲AGB星的湍流压不可忽略,进而提出了影响热脉冲AGB星星风物质损失的可能的物理因素.     

低质量AGB星重元素的核合成

本文以（１３）Ｃ（α，ｎ）（１６）Ｏ作为中子源，考虑到恒星核心质量随热脉冲数的变化及星风、超星风质量损失的影响，采用从（５６）Ｆｅ到（２１０）Ｂｉ的无分支ｓ过程反应通道，拟合了ＭＳ、Ｓ的重元素超丰．本文特别将恒星质量与ＡＧＢ内Ｓ过程核合成模型结合起来讨论．结果表明质量较大的恒星因对流较强而稀释因子较大，ＭＳ、Ｓ星在轻、重Ｓ元素丰度关系图中分别落入四个不同区域，由此可以粗略估计这些恒星的质量．２．５Ｍ　的ＡＧＢ星形成具有环状空腔的星体，最后演化成Ｔｃ—ｎｏ单星，可以解释双星系统伴星为主序星的ＡＧＢ星无Ｔｃ现象．     

High-dispersion Spectroscopic Observations of the T Tauri-type Stars with Weak Emission Lines

By using the 2.16 m telescope of Xinglong Observing Station of National Astronomical Observatories and its high-dispersion spectrograph, the high-dispersion spectroscopic observations of six T Tauri-type stars with weak emission lines (i.e., weak-line T Tauri-type stars, abbreviated as WTTS) were carried out. The lithium abundances of these weak-line T Tauri-type stars are calculated and the relationships of the lithium abundances with the rotation periods as well as the amplitudes of light variations of these stars are discussed. It is found by this study that the lithium abundance for the weak-line T Tauri-type stars with fast rotations tends to be less than that of those with slow rotations. However, for all these weak-line T Tauri-type stars, the lithium abundances have no conspicuous correlation with the amplitudes of light variations of these stars in the V waveband.     

The variation of the angle between the magnetic and rotation axes in a collapsing star

We derive the formula for the variation of the magnetic axis in a collapsing oblique rotator. Our results of calculation show that the case of the magnetic axis coincident with the rotation axis is unstable, and the angle between the two axes will grow on any small perturbation.     

The Effect of Method of Constructing the Mass Distribution on Single Stellar Populations

We use two methods of constructing the initial mass distribution, the traditional way and Monte Carlo simulation, to obtain integrated U - B, B - V, V-R and V-I colours and absorption-line indices denned by the Lick Observatory image dissector scanner (referred to as Lick/IDS), for instantaneous burst solarmetallicity single stellar populations with ages in the range 1-15 Gyr. We find that the evolutionary curves of all colours obtained by the traditional method are smoother than those by Monte Carlo simulation, that the U - B and B - V colours obtained by the two methods agree with one another, while the V - R and V - I colours by the traditional method are bluer than those by Monte Carlo simulation. A comparison of the Lick/IDS absorption-line indices shows that the variations in all the indices by the traditional method are smoother than that for the Monte Carlo simulation, and that all the indices except for TiO1 and TiO2 are consistent with those for the Monte Carlo simulation.     

Determination of the Proper Motions and Membership of the Globular Cluster M3 and of its Orbit in the Galaxy

We examine 14 plates of the globular cluster M3 (NGC 5272) taken with the 40 cm refractor at the Sheshan station of Shanghai Astronomical Observatory. The plates span over a period of about 77 years. The positions and absolute proper motions of eight stars in the Hipparcos Catalogue and of 49 stars in the Tycho-2 Catalogue are used as the reference frame. The astrometric reduction is made with the central overlapping principle. The absolute proper motions of 534 stars in a region of about 100' × 100' around the cluster are measured. With the new proper motion data the membership probabilities of the stars are determined. The average absolute proper motion obtained for the cluster is -0.06@0.30 mas yr-1 in R.A. and -2.6@0.30 mas yr-1 in Decl. By combining this result with the known distance and radial velocity of the cluster, we also obtained the Galactic orbit of M3 for a chosen three-component Galactic potential.     

裸奇异星研究进展

简要介绍了近几年来裸奇星研究的一些重要进展，包括裸奇异星表面的电学性质和辐射机制，夸克表面存在的一些可能天体物理后果（如射电脉冲星的漂移子脉冲现象和软γ射线重复源的超Eddington辐射现象）等。这些研究结果对从天文观测上区分中子星和奇异星、证认奇异星的存在具有重要意义。     

Research on Periodicity of Single Sector Variable Star of TESS Space Satellite

The short exposure and high precision photometry of TESS (Transiting Exoplanet Survey Satellite) space satellite provide good data for distinguishing variable stars and searching planets. In this paper, a series of methods, such as periodic spectrum and phase folding, are used to analyze 19995 target sources with high-quality variable data in TESS sector 21, and these sources are classified. A total of 4624 variable stars are obtained, including 322 binary stars, 470 pulsating variable stars, and 37 planetary transients. A total of 625 variable sources were cross matched with VSX (The International Variable Star Index). Among them, 131 were eclipsing binary systems and 31 were pulsating variables, whose periods are obtained by periodic spectrum. The other 59 variable stars have flare phenomena, and 8 stars have transiting planets, whose rotation periods are also obtained through the periodic spectrum. The feasibility of the analysis of variable stars by TESS space satellite data is verified. By comparing the period results obtained by TESS space satellite sector 21 with the variable star period provided by VSX variable star table, we found that the periods of most variable stars are consistent with those in this paper, and a few of them need to be corrected. Finally, the verified and corrected variable star tables are provided in this paper.     

Infrared observation and the energy distribution of silicate carbon stars

Near-infrared photometry of all 11 silicate carbon stars north of declination −10° is made. Combined with available data in the visible range and from IRAS, we discuss their distribution on the infrared two-color diagrams and their spectral distribution, and we compare with the results for normal carbons and so ascertain their evolutionary status.     

The pulsational stability of intermediate- and low-luminosity red giants in globular clusters

Some theoretical calculations of linear non-adiabatic pulsations of intermediate- and low- luminosity red giants in globular clusters have been carried out using a time-dependent theory of nonlocal stellar convection. As shown by the results, for all models with temperatures higher than 5400 K the modes up to the fourth overtone are pulsationally stable. With the increase of stellar luminosity, the low-order overtones also become pulsationally unstable. For red giants of intermediate and low luminosities, the pulsational stability is exceedingly low and is close to neutral stability. Therefore, they will be either non-variables or short-period variables (P < 2 days) with extremely small amplitudes.     

A High-accuracy, Small Field of View Star Guider with Application to SNAP

To accomplish its mission, the spaceborne observatory SNAP (SuperNova Acceleration Probe) requires a pointing stability of <0.03 arcseconds during exposures lasting up to 500 sec. A Monte Carlo simulation of the photoelectron statistics from the guiding star investigates geometrical (such as the pixel size of the detector or the plate scale) and physical parameters (such as the magnitude of the star). It is shown that simple centroiding calculations can lead to the desired accuracy with guide stars as faint as magnitude 16. Availability of these stars is verified thanks to the HST Guide Star Catalog complemented with a statistical model of the distribution of stars. Thus a through-the-lens sensor that uses stars as faint as magnitude 16 to provide the necessary guiding signals is feasible. This revised version was published online in July 2006 with corrections to the Cover Date.     

Star Formation in Violent and Normal Evolutionary Phases

Mergers of massive gas-rich galaxies trigger violent starbursts that - over timescales of > 100 Myr and regions > 10 kpc - form massive and compact star clusters comparable in mass and radii to Galactic globular clusters. The star formation efficiency is higher by 1–2 orders of magnitude in these bursts than in undisturbed spirals, irregulars or even BCDs. We ask the question if star formation in these extreme regimes is just a scaled-up version of the normal star formation mode of if the formation of globular clusters reveals fundamentally different conditions. This revised version was published online in September 2006 with corrections to the Cover Date.