中等质量恒星星风物质损失的机制

在考虑引力对星风物质损失的制约效果及辐射压与湍流压对其扰动效果的同时,通过引入可压缩流机制,考虑了恒星外壳对流区对星风物质损失的促进作用,从而建立了新的星风物质损失公式.之后,通过对3～5 M_⊙恒星理论模型的星风物质损失率计算,发现:从主序直至中心氦核燃烧结束阶段,新的星风物质损失公式计算所得星风物质损失率与经典星风物质损失公式计算结果几乎一致;而在TP-AGB阶段,应用新的星风物质损失公式计算的恒星模型则不受光度影响产生了持续的较大的星风物质损失,比较符合实际观测结果.     

恒星物质的不透明度

简介介绍了恒星物质的透明性质在恒星结构、演化、振动等许多恒星物理基本问题研究中的重要性和决定恒星物质不透明度的物理过程,回顾了第一代不透明度数据ＬＡＯＬ的发展历程与存在的问题,介绍了新一代不透明度数据ＯＰＡＬ的发展和目前观测与理论之间依然不一致的地方。     

潮汐效应,系统自转效应对双星物质交换过程的影响

现今双星演化理论中,以子星的半么等于临界洛希瓣半径,作为双星中发生物质交换过程的判据,仅仅是一个为了将三维计算简化为一维计算而引入的近似判据,它在理论上不严格的。本给出了一个理论严格而又有一维计算的判据,并用新的判据和用子星半径等于临界洛希瓣半径的判据,对一个由９Ｍ⊙和６Ｍ⊙恒星组成的双星系统,进行了情况Ａ的演化计算。结果证明,用新的判据时,双星中发生物质交换过程的起始时间提前,快速物质交换过程     

恒星演化晚期核素K壳层连续态电子俘获过程中微子能量损失

基于Weinberg-Salam理论,考虑Coulomb效应对连续态电子气体的影响,对恒星演化晚期核素12C、16O、20Ne、24Mg、28Si和56Fe在完全电离环境下的K壳层连续态自由电子俘获过程的中微子能量损失进行了讨论.根据Beaudet、Petrosian和Salpeter (BPS)的方法所得结果与我们的结果进行了比较.结果表明:相对较高温度环境(如T9=0.1和T9=1.T9是以109 K为单位的温度),两种结果符合很好;而低温环境(如T9=0.01和T9=0.001)核素16O、20Ne、24Mg和28Si的中微子能量损失,BPS的结果比我们的结果高10～70倍,对核素12C甚至高出2个数量级.我们的研究可能对恒星演化晚期尤其是白矮星核坍塌到相对低温和中等密度阶段冷却机制的研究具有重要意义.     

OPAL不透明度对恒星结构和演化模型的影响

本利用国际上最新公司的ＯＰＡＬ不透明度表及相应的化学丰度，计算了三颗不同初始质量的星族Ｉ恒星的非守恒演化模型，并和过去长期采用的ＬＡＯＬ不透明度的结果进行详细比较，得出以下主要结论：（１）恒星ＨＲ图中的演化轨迹光度降低，主序位置明显向红方向移动；（２）恒星中心Ｈ，Ｈｅ燃烧寿命大大延长了；（３）小质量星氢燃烧核和对流核都变小，大、中质量星的中心对流核和燃烧核都有所增大；（４）恒星中心温度－密度关系     

潮汐效应、系统自转效应对双星物质交换过程的影响

现今双星演化理论中,以子星的半径等于临界洛希瓣半径,作为双星中发生物质交换过程的判据,仅仅是一个为了将三维计算简化为一维计算而引入的近似判据．它在理论上是不严格的．本文给出了一个理论严格而又能一维计算的判据．并用新的判据和用子星半径等于临界洛希瓣半径的判据,对一个由９Ｍ和６Ｍ恒星组成的双星系统,进行了情况Ａ的演化计算（即物质交换过程发生在主星中心氢燃烧阶段）．结果证明,用新的判据时,双星中发生物质交换过程的起始时间提前,快速物质交换过程变短,平均物质交换率增大,但慢速物质交换过程变长．在物质交换过程结束时,主星和次星的质量、双星系统的轨道周期以及主星在赫罗图中的位置,都与采用子星半径等于相应洛希瓣半径作为判据的计算结果明显不同．这说明,发生物质交换过程的判据是否严格,对于双星演化的影响是不可忽略的．     

大质量双星非守恒演化

主要讨论建立大质量双星非守恒演化理论中的一些重要问题。     

稳定物质转移通道形成双黑洞

由于缺乏足够的观测数据,大质量恒星的研究进展缓慢,到目前为止大质量恒星演化和黑洞详细的形成过程还存在较大争议。LIGO首次探测到恒星级双黑洞并合产生的引力波信号,这不但验证了爱因斯坦20世纪的预言,而且还证实了大质量双黑洞的存在。研究工作采用恒星演化程序MESA (Modules for Experiments in Stellar Astrophysics)计算孤立双星的演化,主星初始质量为20 M⊙～80 M⊙,金属丰度为0.000 1～0.002,初始双星质量比为0.7～0.9。双星系统通过稳定物质转移通道,形成总质量(15～110) M⊙范围内的双黑洞。形成双黑洞的并合时标强烈依赖于初始轨道周期,只有初始轨道周期不大于5 d的双星系统演化形成的双黑洞,通过引力波辐射损失角动量,最终可能在哈勃时标内并合。研究工作得到的结果可以解释部分现阶段已经探测到的引力波事件。     

钡星的形成机制(I)完备模型

本文系统地研究了钡星的形成,提出了钡星形成的四种机制：星风吸积、星风暴露、稳定的洛希瓣物质交流和公共包层的抛射,从而建立了钡星形成的完备模型     

探索恒星的物质、能源与演化

人们所见天空中的星星几乎全部是恒星,而且许多是与太阳类似的恒星,它们的核心正熊熊燃烧着氢。通过多种天文观测手段（例如光谱学）,人们可得到恒星的大气成分、光度、表面温度、质量、半径、磁场强度、自转情况等资料,然后运用物理规律和数学方法可以推算出恒星内部各种物理参量的分布情况。     

Photometric Mass Ratios of Eclipsing Binary Stars

Following a brief history of measurement of eclipsing binary mass ratios from light curves, we show that photometric mass ratios for overcontact and semi-detached binaries are reliable because the relative stellar radii, R/a, are accurately measured and not, as commonly claimed, because of information in the light variation outside eclipse. We explore the accuracy of photometric mass ratios by solving synthetic data of typical precisions for a semi-detached and an overcontact binary for orbital inclinations from 89^∘ down into the partial eclipse range.     

Dust Formation and Mass Loss in Evolved Stars

The problem of dust formation in the circumstellar envelopes of Asymptotic Giant Branch stars is addressed. We summarize the basic thermodynamic prerequisites necessary to enable the formation and growth of solid particles from the gas phase and draw some conclusions on the evolution of the emergent dust component. In a circumstellar environment the dust grains interact with the stellar radiation field, which leads to a strong coupling among the local thermodynamic conditions and the dust formation process itself. By a consistent treatment of the physics describing the dust forming circumstellar shells of evolved stars we demonstrate, that the non-linear interaction among the dust formation process and the hydrodynamic and thermodynamic conditions of the dust forming system leads to a complex dynamical structure of these shells. Some observable consequences resulting from corresponding model calculations are given. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mass Loss and Circumstellar Dust Shells at T Tauri Stars

The mass loss of T Tauri stars leads to the production of dust in circumstellar space. The total amount of lost mass (and therefore of produced dust) is observed to be positiv correlated with the intensity of the H and Call emission lines of the objects. This fact is used in the present paper to explain quantitatively another correlation, namely the observation, that the interstellar extinction which is found by star counts in the wider surroundings of a T Tauri star is roughly proportional to the intensity of its Hα emission. By this, the outflow of circumstellar matter into the interstellar space seems to be observable directly.     

Mechanism of Mass Loss of Stellar Wind for Medium-mass Stars

Along with the considerations of the effect of constraint of gravitation on the matter loss of stellar wind and the disturbances of the radiation pressure and turbulent pressure on it, by introducing the mechanism of compressible flow, the effect of promotion of the convective region in stellar outer shell on the matter loss of stellar wind is investigated. Hence a new formula of matter loss of stellar wind is established. After this and via the computation of the rate of mass loss of stellar wind in the theoretical model of 3∼5M? stars, the following is revealed. From the main sequence up to the stage of termination of central helium-core burning, the rate of mass loss of stellar wind calculated with the new formula agrees almost completely with that given by the classical formula. But in the TP-AGB stage the stellar model calculated with the new formula of mass loss of stellar wind is not affected by luminosity and gives rise to the persistent and large matter loss of stellar wind. This rather well agrees with the results of actual observations.     

Gasdynamics of Detached Shells Around Carbon Stars With Variable Mass Loss

Gasdynamic features of detached shells around carbon stars with variable mass loss rate are investigated in detail numerically. It is shown that a shell is unstable and also, 2D perturbations are less developed that 3D ones. The structure of perturbed flows corresponding to different evolution scenarios is compared. The results obtained seem to be promising for interpretation of observations, in particular, the recently obtained detailed data of TT Cyg. This revised version was published online in July 2006 with corrections to the Cover Date.     

Eclipsing Binary Stars in Nearby Galaxies

We briefly discuss the survey programme we are conducting to detect eclipsing binaries in local group galaxies. Some lightcurves from studies of M31, IC 1613 and NGC 6822 are presented along with details of future work.     

On the Relations between Infrared Colors and Mass Loss Rates for S Stars

A relation between the infrared color K-[12] and the mass loss rate, dM/dt,is found for the intrinsic S stars. This relation is qualitatively similarto the ones for carbon stars and oxygen-rich Mira stars, but quantitativelydifferent. It could be useful in the context of the near infrared surveys,DENIS and 2MASS, which are in progress. Correlations between J-K and[12]–[25] indices and dM/dt are found to be loose for S stars.     

Orbits of Ten Visual Binary Stars

We present the orbits of ten visual binary stars: WDS 01015 6922, WDS 01424– 0645, WDS 01461 6349, WDS 04374–0951, WDS 04478 5318, WDS 05255–0033, WDS 05491 6248, WDS 06404 4058, WDS 07479–1212, and WDS 18384 0850. We have also determined their masses, dynamical parallaxes and ephemerides.