【作者】 刘伟；

【导师】 刘庆忠；

【作者基本信息】 中国科学技术大学 ， 天体物理， 2022， 博士

【摘要】 Be/X射线双星是一类大质量X射线双星,其光学伴星是一颗Be星。Be星是光度型在Ⅲ-Ⅴ、具有或曾经具有发射线的B型星。Be星的赤道平面上有一个星周盘,当致密星过近星点时能从星周盘上吸积物质,物质落入致密星的引力阱中,其引力势能最终转化为X射线辐射出来。Be星在光学和红外波段有两个重要的观测特征,分别是发射线和红外超。发射线和红外超都源于Be星的星周盘。Be/X射线双星在光学波段的辐射变化由Be星的星周盘主导。我们的目标是研究巨型X射线爆发前后Swift J0243.6+6124、1A 0535+262,和KS 1947+300的多波段长期变化。在巨型爆发发生的前与后,我们通过观测来获得目标源的光谱和测光数据。目标源的长期光变曲线以及Hα和He I λ6678线的等值宽度被我们用来监测Be星星周盘的状态。Hα线谱线轮廓定性地显示了 V/R变化的证据,而V/R是通过用两个高斯函数拟合Hα线谱线轮廓来获得的。另外,我们会根据X射线、光学,和红外辐射的强度将数据划分为不同的阶段以更明确地研究目标源的变化。在第一章中,我们简介了 X射线双星的分类、Be/X射线双星暂现源的两种爆发活动,以及Be星与Be/X射线双星的光学和红外特性。第二章介绍了我们所用的望远镜、利用的数据库,以及观测策略和数据处理。在第三章中,根据Swift J0243.6+6124观测参数的变化,以MJD 58180和MJD 58530为界,我们将我们的观测分成了三个阶段。Swift J0243.6+6124的第一阶段覆盖了 2017年10月到1 1月发生的巨型X射线爆发的上升期和衰减期。我们认为第二阶段是Be星星周盘的消散期,而第三阶段是它的恢复期。星周盘一个完整的形成和消散过程的时标约为1250天。消散过程停止和恢复期开始的时刻估计在MJD 58530左右。我们发现X射线爆发后光学或红外强度的最小值与Hα线的强度的最小值之间存在～100-200天的延迟,这可能表明星周盘的消散是从内区开始的。星周盘内密度扰动的进动方向是顺行的,V/R变化的准周期约为4年。Swift J0243.6+6124的(B-V)色指数与V波段星等图中呈现正相关关系,这意味着系统倾角小或中等。第四章描述了我们从2010年到2021年对Be/X射线双星1A 0535+262进行的长期的光谱和测光观测。我们的观测覆盖了 2020年的巨型X射线爆发以及之前一个月和一年的时间段。我们发现V波段的亮度、IR波段的亮度,和Hα谱线的强度是依次发生变化的,这可能是Be星星周盘上物质粘滞扩散的结果。星周盘内密度扰动的进动方向是逆行的,且星周盘的内区和外区的密度扰动在2021年是不一致的。另外,时期Ⅰ→Ⅱ→Ⅲ→Ⅳ在(B-V)色指数与V波段星等图中构成了一个环。第五章描述了 2013年至2021年间,我们用中色散光谱仪对KS 1947+300进行的八年的监测,揭示了 Be星星周盘的自身演化及其与目标源多波段活动的关系。从2000年到2021年,目标源的长期变化趋势可以分为两个阶段,这两个阶段以2013年10月为界。KS 1947+300的两组Ⅰ型爆发总体上没有偏好的轨道相位,但临近的爆发经常发生在相近的相位。根据目标源临近的Ⅰ型爆发的时间间隔可以得出Pburst<N×Porb,从而我们可以推断出其星周盘的进动方向与中子星公转的方向相反。我们在ZTF-g和r波段的光变中发现了的周期性的信号,测量值分别为198天和193天,此周期信号可能起源于Be星的星周盘或环双星系统物质团块的轨道运动。(B-V)色指数与V波段星等之间的关系显示KS 1947+300的倾角是小角度或中等角度;而且2013-2021年的星周盘的结构与1990-1991年的不同。第六章对整篇论文做出了总结并对未来的工作做出了展望。更多还原

【Abstract】 A Be/X-ray binary is a system which contains a Be star and a compact star.Be stars’ luminosity class is Ⅲ-Ⅴ,and at some point of their lives they have shown spectral lines in emission.Be stars have circumstellar disks on their equator planes.When the compact stars pass through the periastrons,they can accrete materials from circumstellar disks.The materials fall into the gravitational potential well,at the same time,their gravitational energy turns into the internal energy,and emit outward in X-ray.In optical and infrared bands,Be stars have two main observational characteristics,spectral emission lines and an excess of IR emission.Both emission line and IR excess originate from the circumstellar disk of the Be star.The optical emission variation of Be/X-ray binaries is dominated by Be star’s disk.Our aim is to study the multiwavelength long-term variability of Swift J0243.6+6124,1A 0535+262,and KS 1947+300 before and after giant X-ray outbursts.We have obtained optical spectroscopy and photometry data before,during,and after the X-ray outbursts.The long-term photometric light curve and the equivalent widths of the Hα and He I λ6678 lines were used to monitor the state of the Be star’s circumstellar disk.The Ha line profiles qualitatively show evidence for V/R variability that was accounted for by fitting the Ha spectral line profile with two Gaussian functions.We divided our data into different phases according to the intensity of the X-ray,optical,and infrared emission to more specifically study changes in the sources.In chapter one,we introduced the classification of X-ray binaries,the two kinds of outbursts of transient Be/X-ray binaries,and the optical and infrared characters of Be stars and Be/X-ray binaries.Chapter two introduces the telescopes we use,the databases we utilize,and the observation strategies and data processing.In chapter three,we divide our observations into three phases based on the changes in the observed parameters of Swift J0243.6+6124,bounded by MJD 58180 and MJD 58530.For Swift J0243.6+6124,phase I covers the rise and decay of the giant X-ray outburst that took place in October-November 2017.We interpret phase Ⅱ as the dissipation of the Be star’s equatorial disk and phase Ⅲ as its recovery.The timescale of a complete formation and dissipation process is about 1250 days.The epoch when the dissipation process stopped and the reformation period began is estimated to be around MJD 58530.We find a delay of～100-200 days between the minimum of the optical or infrared intensity and the strength of the Ha line after the X-ray outburst,which may indicate that the dissipation of the disk begins from the inner parts.The motion of the density perturbation inside the disk is prograde,with a V/R quasi-period of about four years.The source shows a positive correlation in the(B-V)color index versus Vband magnitude diagram,which implies that the system is seen at a small or moderate inclination angle.In chapter four,we carry out long-term optical spectroscopic and photometric observations on the Be/X-ray binary 1A 0535+262 from 2010 to 2021.Our observations cover the giant X-ray outburst in 2020 and one month and one year before it.We find that the V-band brightness,the IR-band brightness and the emission intensities of Ha lines change one by one,which possibly is the result of the viscous diffusion of the materials on the Be disk.The motion of the density perturbation inside the disk is retrograde,and the density perturbations in the inner and outer regions of the circumstellar disk are inconsistent in 2021.Periods Ⅰ→Ⅱ→Ⅲ→Ⅳ constitute a cycle in the(B-V)color index vs.Ⅴ-band magnitude diagram.In chapter five,from 2013 to 2021,we monitored KS 1947+300 for eight years with the intermediate dispersion spectrometer,revealing the evolution of the Be star’s disk and its relation with the multiwavelength activities of the source.From 2000 to 2021,the long-term change trend of KS 1947+300 can be divided into two periods,which are demarcated by October 2013.The two groups of type I outbursts at KS 1947+300 generally have no preferred orbital phase,but adjacent outbursts often occur in close phases.According to the time interval of the type I outbursts,it can be concluded that Pburst<N×Porb,so we can infer that the precession sense of its stellar disk is opposite to the sense of the neutron star’s revolution(retrograde).We find two periodic signals,198 days and 193 days,in the light curves of ZTF-g and r bands,respectively,which probably originate from the circumstellar disk of Be star or the orbital motion of the matter around the binaries.The relationship between the(B-V)color index and the V-band magnitude shows that the inclination of KS 1947+300 is small or medium;moreover,the structure of the 2013-2021 circumstellar disk is different from that of the 1990-1991 disk.Chapter six concludes the whole thesis and gives an outlook for future work.更多还原