KMS of Xinjiang Astronomical Observatory, CAS
| 低质量X射线双星的演化 | |
| Alternative Title | Evolution of Low Mass X-ray Binaries |
邓竺龄
| |
| Subtype | 硕士 |
| Thesis Advisor | 高志福 |
| 2021-06-01 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Name | 理学硕士 |
| Degree Discipline | 天体物理 |
| Keyword | 中子星 吸积 X射线双星 毫秒脉冲星 磁制动 |
| Abstract | 低质量X射线双星(LMXBs)由一颗普通小质量恒星和一颗致密天体（白矮星、中子星、黑洞）所组成。恒星充满其洛希瓣后，其表面物质在引力势的作用下被致密天体所吸积，吸积过程产生X射线辐射。本论文主要关注的为中子星LMXBs的演化。在此类致密天体的双星系统物质交流结束后，恒星的包层物质被剥离，剩下一颗简并的He或CO核，而中子星经历吸积过程自转周期加速至毫秒量级，最终形成毫秒脉冲星双星系统。第一章主要对研究背景作简单描述，然后介绍双星相互作用的基本物理过程，包括物质交流和轨道角动量损失。第二章主要讨论不同磁制动模型对低质量X射线双星演化的影响，包括对低质量X射线双星的吸积率、伴星质量和轨道周期的影响，以及形成的双星毫秒脉冲星的轨道周期的分布。传统的磁制动模型存在着以下几个问题：第一，理论上预言的LMXBs的物质传输率低于观测值；第二，极密近X射线双星(UCXB)很难在传统的磁制动模型下于哈勃时间内形成，数值模拟得到的UCXBs数量远小于观测的数量；第三，LMXBs的产物---双星毫秒脉冲星的轨道周期分布与观测上还存在较大的差异。因此，我们考虑另外的四种不同的磁制动模型，结合恒星演化模拟和星族合成程序，将这些不同模型应用在低质量X射线双星的演化上。最后，将得到的结果同观测相对比，结果表明$\tau-$boosted（Convection boosted）磁制动模型得到的演化结果最符合LMXBs的观测特性。该项研究为解决LMXBs演化理论与观测不相符的问题提供了新的思路，特别是吸积率问题和轨道分布问题，推动了对LMXBs演化的进一步的理解。第三章主要讨论了PSR J1640+2224的形成机制，此源为一颗自转周期为3.16毫秒的毫秒脉冲星，位于一个伴星为白矮星且轨道近圆的双星系统之中，其轨道周期为175天。根据理论计算，该白矮星伴星的质量应该在0.35-0.39倍太阳质量（Msun）之间。然而，观测和理论研究发现此白矮星伴星的质量大于0.4Msun。这意味着PSR J1640+2224既不属于低质量双星脉冲星，也不属于中等质量双星脉冲星系统，其形成过程成为X-射线双星演化领域的一个谜题。因此，我们使用恒星演化程序MESA，考虑不同的中子星初始质量和不同金属丰度，模拟LMXBs的演化。另外再结合中子星的自转演化，得出PSR J1640+2224系统很有可能起源于贫金属环境，其中子星在诞生之初质量大于2Msun。此外，我们还讨论了不同的对流超射参数对双星演化的影响。该项研究工作解释了特殊的双星毫秒脉冲星PSR J1640+2224的形成渠道，而且丰富了不同类别的毫秒脉冲星的形成。在第四章中，我们对已完成的工作进行总结，并对今后此领域的发展进行展望。随着计算机技术的发展和对X-射线双星探测设备不断地更新，我们的理论模型会在未来的观测中得到检验和发展。 |
| Other Abstract | Low-mass X-ray binaries (LMXBs) consist of a low-mass donor and an accretingcompact star(a white dwarf, a neutron star or a black hole). After the donor overflows itsRoche lobe, the compact star would accrete the donor’s surface materials, and producesX-ray emission. In this thesis, we focus on the evolution of LMXBs with a neutron star(NS). At the end of material exchange in the binary system of such compact objects, thematerial in the common envelope is stripped away, leaving a degenerate He or CO core,while the rotation period of the NS is often accelerated to the order of millisecond duringthe accretion process, and a millisecond pulsar binary will be formed eventually. Thefirst chapter gives a brief description of the research background, and then introducesthe basic physic process of binary interaction, including the mass transfer and amgularmomentum loss.In chapter 2, the effects of different magnetic braking (MB）prescriptions on theevolution of LMXBs are discussed, including the effects on the accretion rate, the massand orbital period of the companion stars, and the distribution of orbital periods of millisecondpulsar binaries. There are several conflicts between theories and observations.Firstly, the mass accretion rates inferred from observations are higher than those predictedtheoretically. Secondly, ultracompact X-ray binaries (UCXBs) can haldly formwithin Hubble time under the tranditional MB model, and then the number of UCXBsobtained from numerical simulations is lower than that from observations. Finally, thepredicted orbital period distribution of BMSPs descended from LMXBs, does not matchthe observations. Therefore, we consider four different MB models and apply themto the evolution of LMXBs in combination with stellar evolution simulations and starpopulation synthesis programs. Comparing the calculated results with observations, weconclude that the 𝜏−boosted MB law seems to best match the observational characteristics.This study provides a new way to solve the inconsistency between the theory andobservation of the evolution of LMXBs, especially the problems of accretion rate andorbital period distribution, and promotes the further understanding of the evolution ofLMXBs.The third chapter mainly discusses the formation mechanism of PSR J1640+2224.The source is a millisecond pulsar with a rotation period of 3.16 milliseconds, located ina binary star system with a white dwarf (WD) companion and a near-circle orbit with anorbital period of 175 days. Theoretically, there exist a relation between the orbital periodand the WD mass. However, according to the latest observation, the PSR J1640+2224system deviates this relation. According to theoretical calculations, the WD companionstar should have a mass between 0.35 and 0.39 solar masses. However, observationaland theoretical studies have found that the WD companion has a mass greater than 0.4solar masses. This means that PSR J1640+2224 is neither a low-mass binary pulsar(LMBP) nor a intermediate-mass binary pulsar (IMBP), and its formation process hasbecome a mystery in the field of X-ray binary research. Using stellar evolution codeand considering different initial masses and different metallicity of NSs, we explorethe influence of the mass of the NS and the chemical compositions of the companionstar on the formation of BMSPs. Combining the NS spin evolution, we conclude thatthe PSR J1640+2224 should form from Population II compositions, and the initial NSmass should no less than 2𝑀⊙. In addition, we discuss the influence of overshootingparameter for the evolution of LMXBs. This study not only explains the formationchannel of a particular BMXP, PSR J1640+2224, but also enriches the formation ofdifferent types of millisecond pulsars.The last chapter summarizes our works in the above chapters, and gives the prospectsfor our future work. With the development of computer technology and the continuousupdating of X-ray binary star detection, our theoretical model will be tested and developedin future observations. |
| Pages | 88 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/4730 |
| Collection | 研究生学位论文 |
| Affiliation | 中国科学院新疆天文台 |
| First Author Affilication | Xinjiang Astronomical Observatory, Chinese Academy of Sciences |
| Recommended Citation GB/T 7714 | 邓竺龄. 低质量X射线双星的演化[D]. 北京. 中国科学院大学,2021. |
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| 低质量X射线双星的演化_邓竺龄.pdf（2804KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
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