YNAO OpenIR  > 双星与变星研究组
近相接型密近双星的观测与统计研究
Alternative TitlePhotometric and Statistical Study of Near Contact Binaries
朱俐颖
Subtype博士
Thesis Advisor钱声帮
2007-06-11
Degree Grantor中国科学院研究生院(云南天文台)
Place of Conferral北京
Degree Discipline天体物理
Keyword近相接双星 双星物质交流 角动量损失 双星结构和演化
Abstract近相接型密近双星是两子星均充满或接近充满洛希瓣的一类密近双星,与相接双星不同,其两子星没有形成公共包层,表面有效温度差别较大,展示出EB型的光变曲线。这种独特的几何结构使近相接双星成为人们关注的一类天体系统。这类星最主要的特征是其处于临近相接阶段,是联系相接双星与分离双星和半接双星的桥梁。本文主要对一批处于重要演化阶段上的近相接双星样本和个别W UMa型相接双星以及短周期Algol型双星系统进行了观测分析和研究。同时我们还收集了大量近相接双星样本,对这类系统光变曲线、轨道周期变化和一些物理量进行了统计分析研究,取得了如下的研究成果: 1、发现BL And 是一个主星充满洛希瓣的近相接型密近双星系统,其轨道周期长期减小(dp/dt =-2.36*10^-8 天/年),揭示了它是目前发现的少数几个处于从主星到次星物质交流演化进程中的双星样本之一。随着轨道周期的收缩,它将演化成一个相接的系统,同时BL And很可能是TRO理论所预言的相接破裂阶段的系统。 2、发现GW Tau、UU Lyn和AS Ser属于临近充满的近相接双星系统,它们几何上相接,有一定的相接度(GW Tau 是10.9%, UU Lyn 是2.3%, AS Ser是2.3%),但表面有效温度差别较大,分别为3000K(GW Tau)、1900K (UU Lyn)和2500K (AS Ser)。分析显示它们的轨道周期均有减小的趋势,揭示了它们是通过物质交流刚形成的几何相接双星。待公共包层形成以后,它们将有可能演化成为真正的热相接双星,同时它们也有可能是处于热驰豫震荡(TRO)理论预言的相接开始阶段的系统。研究这类系统对了解过相接双星对流公共包层的形成具有极为重要的意义。 3、发现RU UMi是一个次星充满洛希瓣的近相接双星。其轨道周期长期收缩(dp/dt = -1.72 * 10^-8 天/年)。次星充满的位型不足以解释轨道周期的减小,所以该系统除了有从次星到主星的物质交流外还应存在整个系统质量的损失。结合分光所得的质量函数,我们给出了RU UMi的绝对参量。同时分析得到了两颗短周期Algol型半接双星系统BF Vel和DF Pup的测光解,它们的次星均充满洛希瓣,主星的充满度分别是78% 和82%,因此它们也属于次星充满的近相接双星系统。由于次星充满的近相接双星和短周期的Algol型半接双星在赫罗图上的分布很接近,暗示着次星充满的近相接双星就是短周期的Algol型半接双星。 4、发现GSC 3658-0076和KM UMa均为临近分离的近相接双星系统,它们的次星临近充满洛希瓣,同时主星非常接近充满,充满度分别为97.4%和95.1%。GSC 3658-0076 的主星演化程度较次星高,而KM UMa的次星演化程度较主星高,它很可能是一个“Algol后”系统。这两个系统都是处于双星物质交换将要开始的系统,对研究双星的物质交换演化过程具有重要的作用。 5、发现主星充满的近相接双星系统VZ Psc和次星充满的近相接双星HL Aur的轨道周期都可能存在周期性的变化,且HL Aur的轨道周期还在长期的减小(dP/dt = -1.08*10^-7 天/年)。我们倾向于认为VZ Psc的周期性变化是由于次星的磁活动引起,且需要的引力四极矩的变化量应该是5.47 * 10^48gcm^2。而HL Aur的周期性变化更可能是由于第三天体的光时轨道效应所致,分析表明这个第三天体可能是在双星系统演化的某个阶段被俘获而来。 6、发现SS Com是一个质量比为0.29的A次型W UMa型过相接双星系统而PP Lac是一个质量比为2.3的W次型W UMa型过相接双星系统。SS Com的轨道周期长期增加(dP/dt = 6.59 * 10^-7 天/年),随着轨道周期的增加,质量比和相接度都将减小,它可能会演化成一个小质量比的A次型W UMa型过相接双星系统,然后进一步演化成一颗快速自转的单星。PP Lac的轨道周期没有长期变化,但有一个周期性的变化成分,这可能是由于第三天体的光时轨道效应引起的。PP Lac很可能就是处于热驰豫震荡主导和角动量损失主导阶段之间的系统。 7、对近相接双星光变曲线一些特征的统计显示,轨道倾角大于70度的近相接双才易被观测到,且近相接双星光变曲线中的O'Connell效应可能大部分是由于物质交流所致。 8、对近相接双星轨道周期变化的统计发现主星充满洛希瓣的近相接双星均表现出轨道周期的长期减小,减小率的量级在10^-7天/年到10^-8天/年之间,其它类型的近相接双星轨道周期有增有减。特别地,次星充满的近相接双星的轨道长期变化率和周期的关系非常符合轨道周期减小的Algol型半接双星的关系,以0.73(0.24)天为分界线,周期小于此值的这些系统的轨道演化以两子星间的物质交流主导,大于此值的可能以磁星风引起的角动量损失以及星周物质的影响为主导。另外第三天体很可能在近相接双星系统中普遍存在,轨道周期出现周期性变化的系统约占目前有周期分析的近相接双星的40%。 9、对近相接双星绝对参量的统计以及它们与W UMa型过相接双星和Algol型半接双星的对比研究发现:(1)大部分近相接双星两子星的平均密度相近,在赫罗图上的位置都接近零龄主序,它们可能是经由CaseA物质交换而来或者正在进行CaseA物质交换。(2)近相接双星有向着质量比减小的方向演化的趋势。(3)次星充满的近相接双星要损失比角动量才能演化成过相接双星,其它类型的近相接双星可以在守恒的情况下演化到过相接双星或Algol型半接双星。
Other AbstractNear Contact Binary(NCB) is a kind of close binary where both componentsfill or near fill their critical Roche Lobe. They are not in contact like W UMa systems, and show EB-type light variation. These special configurations make NCBs interesting. NCBs can be in the intermediate stage between detached or semi-detached state and contact state. They are the important observational targets which may be lying in key evolutionary states. In the present paper, a group of NCBs, a few W UMa and Algol systems were observed, analyzed and studied statistically. Meanwhile, we collected and studied available properties of light curves, orbital period variations and some absolute parameters of NCBs. Some results are obtained as follows: (1) We find that BL And is a semidetached system with the primary component filling its Roche lobe and the secondary one almost filling but still detached, and the orbital period of BL And is decreasing at the rate of dp/dt =-2.36 * 10^-8 d/yr. The derived configuration and secular period decrease for BL And combined with the asymmetry of the light curve indicate that this system may evolve from the present semidetached phase into a contact stage, with mass transfer from the primary component to the secondary one or that it might just undergo the broken stage predicted by the theory of thermal relaxation oscillations(TRO). (2) We find that GW Tau, UU Lyn and AS Ser are marginal-contact binary systems with a small degree of contact (f = 10.9%, 2.3%, 2.3%, respectively ) and a large temperature difference of about 3100 K, 1900 K, 2500 K, respectively.It is shown that the orbital periods of these three systems are decreasing. With the period decrease, GW Tau, UU Lyn and AS Ser will evolve into a contact binary systems with true thermal contact or may be at the beginning of the contact phase predicted by TRO. (3) RU UMi is found to be a semi-detached system with the secondary component filling its Roche lobe. While, the orbital period analysis shows thatthe orbital period of this system undergoes a continuous decrease at a rate of dp/dt =-1.72*10^-8 d/yr. Since the secondary component is filling the Roche lobe, the conservative mass transfer between the two components can not explain the present orbital period variation. The continuous period decrease may demonstrate that the system undergoes a secular mass and angular momentum loss, and it may evolve from the present short-period near-contact system into an A-type contact binary. Meanwhile, photometric solutions of two short-period Algol type binaries of BF Vel and DF Pup are derived. They are semi-detached systems with the secondary components filling their Roche lobe and primary components near filling with filling factors of 78% and 82% respectively. They may be the transitional systems between NCBs and Algols. (4) We find that GSC3658-0076 and KM UMa are marginal detached near contact binaries with the primary almost filling their Roche Lobe. Both of them may be at the beginning of the mass transfer phase and may evolve from the present detached systems into contact binaries. According to the mass-radius relation of unevolved (ZAMS) detached binaries, the primary component is more evolved for GSC3658-0076 and the secondary one is more evolved for KM UMa. (5) It is found that the periods of VZ Psc and HL Aur show small-amplitude cyclic oscillations, while the period of HL Aur undergoes a secular decrease at a rate of dp/dt = -1.08 * 10^-7 d/yr. The cyclic period oscillation can be interpreted either by the light-time effect of a third body or by magnetic activity cycles of the components. Since the third-body assumption is in agreement with the presence of a large amount of third light in the system discovered by Gray et al. (1997), we think that HL Aurigae may be a true triple system. And since both components of VZ Psc are strong chromospherically active, the period of this system may be more plausibly explained by cyclic magnetic activity. (6)We find that SS Com is an A-type W UMa contact binary with mass ratio of 0.29 and PP Lac is a W-type W UMa contact binary system with mass ratio of 2.3. Long-time period increases of SS Com is detached. With the period increase, SS Com will evolve toward extreme mass ratio and finally to coalesce to single rapidly rotating star. The period of PP Lac showed a small-amplitudecyclic oscillation with a period of 19.7 years and an amplitude of 0.0058 days, which can be explained as the light-time effect of an unseen third body. (7)It is discovered that NCBs with the orbital inclinations larger than 70 degree can be observed easily and most of the O'Connell effect existing in the light curves of NCBs are the result of the mass transfer between the components. (8) The orbital period variations of NCBs are investigated. It is shown that the period of all primary filling NCBs exhibit decreasing orbital periods with order of magnitude of 10^-7 to 10^-8 d/yr, and that of other type NCBs may be decreasing, increasing or exhibit more complex variations. Especially, the dP/dt - P relation of the secondary filling NCBs is agree well with that of Alogl systems with secular decreasing period. These systems are separated into two groups with period larger and smaller than 0.73 (0.24) days. The orbital evolution of systems with period larger than this value are dominated by the mass transfer between two components, while the evolution of the other group may be dominated by the mass and angular momentum loss from systems. Moreover, NCBs with periods showing cyclic oscillations occupy 40% of NCBs with available period investigations. This percentage may indicate that most NCBs may exist in multiple systems. (9)According to the statistical study of the absolute parameters of NCBs, we find that (i) Both components of most of NCBs have similar average densities and near the ZAMS in the HR diagram, which implies that NCBs may evolve from the Case A mass transfer or just undergoing Case A mass transfer. (ii) NCBs may evolve toward extreme mass ratio. (iii) The evolutionary direction of secondary filling NCBs to W UMa contact systems needs of angular momentum loss from the system. While, other types of NCBs can evolve to W UMa contact binaries or Algols under the mass and angular momentum conservation.
Subject Area天文学
Pages115
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/5972
Collection双星与变星研究组
Recommended Citation
GB/T 7714
朱俐颖. 近相接型密近双星的观测与统计研究[D]. 北京. 中国科学院研究生院(云南天文台),2007.
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