食双星V375 Cas的光电测光研究

本文给出了首次食双星V375 Cas的BV两色光电测光资料和新的历元,并用Wilson-Devinney综合光变曲线方法取得测光解。结果表明:V375 Cas是一个类似RZ Dra的早型半相接双星系统,小质量子星充满了临界等位面,而大质量子星几乎充满了临界等位面,此星对于了解早型密近双星的演化是很有意义的。     

密近双星自转的测量和研究(Ⅲ)──同步性的统计性质

我们对前文（Ⅰ）和（Ⅱ）的实测和计算结果进行了统计分析，讨论了自转同步与相对半径、轨道周期间的关系．结果表明：几乎所有r＞0．18的不相接双星系统子星都是同步的，而r＜0．10的子星均处于非同步自转．在相接、半相接双星系统中，同步性与相对半径r也有很好的相关性，但由于子星间物质交流的影响，它们的同步性临界相对半径为0．21，大于不相接双星系统的0.18．     

密近双星自转的测量和研究（III）同步性的统计性质

我们对前（Ｉ）和（Ⅱ）的实测和计算结果进行了统计分析，讨论了自转同步与相对半径，轨道周期间的关系，结果表明，几乎所有ｒ〉０．１８的不相接双星系统子星都是同步的，而ｒ〈０．１０的子星均处于非同步自转，在相接，半相接双星系统中，同步性与相对半径ｒ也有很好的相关性，但由于子星间物质交流的影响，它们的同步性临界相对半径的０．２１，大于不相接双星系统的０．１８。     

早型半接食双星猎户座UW的光电测光研究

本文给出UW Ori的首次光电测光结果及新的历元公式。应用Wilson-Devinney综合光变曲线方法得到了初步测光解，结果表明此星是一早型几乎相接的大质量半接双星，质比m2/m1＝0．513,小质量子星临界等位面。由结果的分析指出如大质量子星为零龄主序星，则小质量子星已离开零龄主序。由极小时刻的O－C分析表明周期可能有增长趋势。     

食双星RT Per光变和视向速度曲线统一解

本文基于可靠分光质比q=0.2824的条件下，用Wilson-Devinney方法重新求解RT Per统一的光变和视向工线的Roche模型解，以及它统一的几何尺度和物理参量几乎没有什么差别。进一步确认它是半相接食双星，伴子星是一颗K4V主序星而不是早先确定的G5V星，距离估算为140pc，主、伴子星均有主序演化效应。     

存在非同步转动的双星演化模型

通过计算双星演化中的角动量转移,研究了潮汐作用下双星系统自转与公转周期的变化以及潮汐作用对双星演化的影响.结果表明,密近双星系统在主序演化时,潮汐摩擦会在较短的时间内使自转与公转达到比较接近的状态,此后经过一个较长时间的调整才能使自转与公转达到同步转动.物质交换阶段开始后,半相接双星系统更容易出现非同步转动,而相接双星系统物质交换很难破坏系统的同步状态.同时比较了非同步双星模型与同步双星模型演化曲线在赫罗图上的不同,结果表明非同步模型在物质交换阶段主星演化曲线向赫罗图光度和有效温度高的方向移动.最后通过对统计的观测数据进行分析后发现,采用该模型可以解释观测上双星超过潮汐锁定时标后仍然存在非同步转动的现象.     

不相接双星的相互照射吸收和子星表面温度的变化

本文对不相接双星系统的子星间相互照射吸收进行了计算,从理论上得到子星的表面温度分布情况．对已知基本参数的３３个晚型双星系统中的反映子星等温面和等势面偏离程度的量进行了统计．结果表明,冷子星上等温面和等势面的偏离程度普遍较热子星的要大,该结果支持了Ｚｈｏｕ和Ｌｅｕｎｇ所提出的用气旋和反气旋来解释恒星黑子和太阳黑子巨大差别的可能性．本文还考虑了临边昏暗效应在晚型双星系统中对子星之间相互照射吸收的影响,这种影响达１８％以上．临边昏暗效应对热子星的影响普遍比冷子星要大．     

不相接双星的相互照射吸收和子星表面温度的变化

本对不相接双星系统的子星间相互照射吸收进行了计算,从理论上得到子星的表面温度分布情况,对已知基本参数的３３个晚型双星系统中的反映了星等温面和等势面偏离程度的量进行了统计,结果表明,冷子星上等温面向和等热面的偏离程度普遍较热子星的要大。该结果支持了ＺｈｏｕＬｅｕｎｇ所提出了用气旋和反气旋来解释恒星黑子和太阳黑子巨大差别的可能性,本还考虑了临边昏暗效应在晚型双星系统中对子星之间相互照射吸收的影响。     

相接双星大熊座AW的基本参量

根据作者提出的确定食双星基本参量的一个新方法,由光变极小时刻求出了相接双星大熊座AW的基本参量。证实了Rensing等人为了矫正相接双星邻近效应引起的谱线轮廓畸变所提出的模型对该双星的适用性;同时也证实了Mochnaski提出的计算相接双星质量的理论模型对该双星的适用性。另外还确认了大熊座AW是一个已演化的零龄相接双星。     

聚星和星团中相接双星的观测与研究

大熊W型相接双星是两颗子星均充满并溢出各自洛希瓣、具有对流公共包层的双星系统.相接双星中存在各种各样的相互作用,给理论模型带来许多可变参量,对理论研究提出了挑战.上世纪六七十年代,经过激烈的争论,相接双星的对流公共包层模型得到公认,相接双星的热弛豫震荡模型、相接不连续模型及角动量损失理论相继被提出.然而,在过去的近40 yr中,理论研究似乎遇到了瓶颈.大量未知参量的共存,使相接双星的理论研究难以进一步开展.研究相接双星的聚星、星团环境,能为相接双星的形成和演化提供丰富的信息,因而是探索相接双星演化问题潜在的生长点.越来越多的观测证据表明,大量相接双星存在于聚星系统或者星团当中.作为母系统的聚星、星团为研究其中的相接双星提供了丰富的演化信息.本文针对这些重要天体系统中的相接双星进行了成员认证、测光观测、周期分析和基本物理参量求解等多项研究,同时对相接双星研究的现状做了简要概述.主要成果如下:     

Evolution of close binaries and origin of Algol-type systems

The evolution of close binary systems was followed for ten systems with the initial mass of the primary in the range 1–4M and with different initial mass ratios and initial separations. A brief discussion of the evolution of the contact component is presented for two separate cases: when the primary reaches its Roche lobe during central hydrogen burning (case A) and after the exhaustion of hydrogen in the center (case B).The models obtained are compared with observed semi-detached systems separately for massive (with total mass greater than 5M ) and low mass (with total mass below 4M ) binaries. It is shown that the contact components of the observed massive binaries are probably burning hydrogen in the core. On the contrary, the majority of contact components of the observed low-mass binaries are burning hydrogen in the shell. The observed distribution of such binaries as a function of different luminosity excesses of contact components seems to indicate that their origin is connected with case A rather than with case B.     

Structure and evolution of low-mass W Ursae Majoris type systems – III. The effects of the spins of the stars

In a previous paper, using Eggleton's stellar evolution code, we have discussed the structure and evolution of low-mass W Ursae Majoris (W UMa) type contact binaries with angular momentum loss owing to gravitational radiation or magnetic braking. We find that gravitational radiation is almost insignificant for cyclic evolution of low-mass W UMa type systems, and it is possible for angular momentum to be lost from W UMa systems in a magnetic stellar wind. The weaker magnetic activity shown by observations in W UMa systems is likely caused by the lower mass of the convective envelopes in these systems than in similar but non-contact binaries. The spin angular momentum cannot be neglected at any time for W UMa type systems, especially for those with extreme mass ratios. The spin angular momenta of both components are included in this paper and they are found to have a significant influence on the cyclic evolution of W UMa systems. We investigate the influence of the energy transfer on the common convective envelopes of both components in detail. We find that the mass of the convective envelope of the primary in contact evolution is slightly more than that in poor thermal contact evolution, and that the mass of the convective envelope of the secondary in contact evolution is much less than that in poor thermal contact evolution. Meanwhile, the rate of angular momentum loss of W UMa type systems is much lower than that of poor thermal contact systems. This is indeed caused by the lower masses of the convective envelopes of the components in W UMa type systems. Although the models with angular momentum loss for W UMa systems exhibit cyclic evolution, they seem to show that a W UMa system cannot continue this type of cyclic evolution indefinitely, and it might coalesce into a fast-rotating star after about 1200 cycles of evolution (about  7.0 × 10⁹ yr  ).     

Monte Carlo simulations of star clusters – III. A million-body star cluster

A revision of Stodółkiewicz's Monte Carlo code is used to simulate the evolution of million-body star clusters. The new method treats each superstar as a single star and follows the evolution and motion of all individual stellar objects. The evolution of N -body systems influenced by the tidal field of a parent galaxy and by stellar evolution is presented. All models consist of 1 000 000 stars. The process of energy generation is realized by means of appropriately modified versions of Spitzer's and Mikkola's formulae for the interaction cross-section between binaries and field stars and binaries themselves. The results presented are in good agreement with theoretical expectations and the results of other methods. During the evolution, the initial mass function (IMF) changes significantly. The local mass function around the half-mass radius closely resembles the actual global mass function. At the late stages of evolution, the mass of the evolved stars inside the core can be as high as 97 per cent of the total mass in this region. For the whole system, the evolved stars can compose up to 75 per cent of the total mass. The evolution of cluster anisotropy strongly depends on initial cluster concentration, IMF and the strength of the tidal field. The results presented are the first step in the direction of simulating the evolution of real globular clusters by means of the Monte Carlo method.     

A Model for Contact Binary Systems

A model for contact binary systems is presented, which incorporates the following special features: a) The energy exchange between the components is based on the understand-ing that the energy exchange is due to the release of potential, kinetic and thermal energies of the exchanged mass. b) A special form of mass and angular momentum loss occurring in contact binaries is losses via the outer Lagrangian point. c) The effects of spin, orbital rota-tion and tidal action on the stellar structure as well as the effect of meridian circulation on the mixing of the chemical elements are considered. d) The model is valid not only for low-mass contact binaries but also for high-mass contact binaries. For illustration, we used the model to trace the evolution of a massive binary system consisting of one 12M and one 5M star. The result shows that the start and end of the contact stage fall within the semi-detached phase during which the primary continually transfers mass to the secondary. The time span of the contact stage is short and the mass transfer rate is very large. Therefore, the contact stage can be regarded as a special part of the semi-detached phase with a large mass transfer rate. Both mass loss through the outer Lagrangian point and oscillation between contact and semi-contact states can occur during the contact phase, and the effective temperatures of the primary and the secondary are almost equal.     

A Binary Evolution Model with Non-synchronous Rotations

By calculating the angular momentum transport during the evolution of a binary system, the variations of the rotational and revolution periods of the binary system under the tidal action, as well as the tidal effect on the evolution of the system are investigated. The calculated results indicate that when a close binary system evolves in the main sequence, the tidal friction will make the rotation and revolution approach to a closed state in a short time, but it takes a long time to attain a complete synchronization. After mass exchange started, the synchronous rotation can be changed more easily into the non-synchronous rotation for the semi-detached binaries. But for the contact binaries, the mass exchange is not strong enough to break the synchronization. The evolutionary tracks of the synchronization and non-synchronization models in the HR diagram are also compared with each other, and the result shows that for the non-synchronization model, the evolutionary curve of the primary star moves toward the direction of high luminosity and high effective temperature on the HR diagram at the mass exchange stage. Finally, by analyzing the statistical data of observations, it is found that the observed fact that the non-synchronous rotation exists in a period even longer than the tide-locking timescale can be explained by this model.     

On rejuvenation in massive binary systems

We introduce a set of stellar models for massive stars whose evolution has been affected by mass transfer in a binary system, at a range of metallicities. As noted by other authors, the effect of such mass transfer is frequently more than just rejuvenation. We find that, whilst stars with convective cores which have accreted only H-rich matter rejuvenate as expected, those stars which have accreted He-rich matter (e.g. at the end stages of conservative mass transfer) evolve in a way that is qualitatively similar to rejuvenated stars of much higher metallicity. Thus, the effects of non-conservative evolution depend strongly on whether He-rich matter is amongst the portion accreted or ejected. This may lead to a significant divergence in binary evolution paths with only a small difference in initial assumptions. We compare our models to observed systems and find approximate formulae for the effect of mass accretion on the effective age and metallicity of the resulting star.     

Evolution of close binaries of shorter period and moderate mass

Evolution of close binaries is investigated in which the more massive component has a mass of 5m and reaches the Roche limit when hydrogen is burning in its convective core. It is shown that a large-scale mass transfer occurs, during which the initial primary develops into a contact subgiant or giant, and the mass ratio is reversed or more than reversed.Although the process and its outcome depend on the initial conditions, in particular on the degree of chemical inhomogeneity in the interior of the primary component, the picture of evolution is essentially the same. We can distinguish and describe quantitatively the following phases: (1) Premain-sequence contraction, when the less massive component is an undersize subgiant. (2) Both components are on the main sequence. (3) Rapid mass exchange, when the roles of the components are interchanged. (4) Slow mass transfer, when the system is semi-detached; this phase is typical for the Algol-like binaries. Further evolution depends on the rate of evolution of the components: either we get another phase with an undersize subgiant, or a complicated system in which both stars lose mass. Probabilities of discovery are calculated for the various phases of evolution.The paper is based on the calculations of stellar models with decreasing mass by means of Henyey's method.     

Violent relaxation and mixing in non-uniform one-dimensional gravitational systems

A series of numerical experiments on non-uniform one-dimensional gravitational systems have been performed with the aim of testing the conflicting models of violent relaxation, developed by Lynden-Bell and by Shu. It is shown that the phase fluid model of Lynden-Bell ceases to apply to the particle systems investigated already at the end of the virialisation phase. From then on the particle nature of the system dominates its evolution: a very efficient mixing process, driven by the mean field fluctuations, washes out all memory of the initial phase densities. During this collisionless mixing process and in the absence of formation of structure, the system evolves towards a configuration characterized by a single temperature per unit mass in accordance with the Shu model of violent relaxation.     

A review of early-type close binary systems

This is a review of close binary systems with very early spectral types (B, O, Of, and WR stars). We limit our selection to systems with Roche model photometric solution only. There are 10 contact systems known at present. Three of them (V701 Sco, BH Cen, and RZ Pyx) are located in the vicinity of the zero-age contact (ZC) according to a Spectral Type — Period diagram. Only the first two systems have absolute dimensions available. Both of these fall into the ZC zone in the logP-logm diagram and the logm-logR diagram. The system TU Mus was thought to be a ZC system is located in the evolved contact zone (EC) in the above diagrams. Both V701 Sco and BH Cen were thought to be having mass ratios about unity. With the much improved light curves of BH Cen and new analysis the mass ratio has been revised to 0.84! This result may favor Shu's model for early-type zero-age contact systems. The evolved systems might be undergone Case A mass exchange except for two systems (V729 Cyg and RY Sct) which might be from Case B. The systems V367 Cyg was classified by Plavec as a W Ser system may be a evolved contact system.It is interesting to note that V729 Cyg (O7f+OfIa), UW CMa(O7f+O) and CQ Cep(WN7+O) are all highly evolved contact systems. The Max II of UW CMa and CQ Cep are displaced to 0.78 and 0.80 phase, respectively. The displacement for V729 Cyg is not known due to poor coverage at this phase. The most distinct feature going from Of to Wolf-Rayet stars is the increasing domination of emission lines. It is suspected that this phaseshifts reflect the increasing activity of mass-flow in the common envelope.There are 8 semidetached systems with reliable absolute dimensions. It is believed that 6 of them are derived from Case A while the remaining 2 are from Case B mass exchange.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80, on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.