YNAO OpenIR  > 双星与变星研究组
利用脉动指针探测短周期脉动变星伴星及相关演化探讨
Alternative TitleUsing the Pulsation to Detect the Companions of Short Period Pulsation Variable and the Related Evolution Discussion
李临甲
Subtype博士
Thesis Advisor钱声帮
2015-07-01
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline天体物理
Keyword脉动变星 测光观测 脉动周期 光时轨道效应
Abstract本文的研究对象为短周期脉动变星,包括天琴座RR型星、盾牌座δ型星以及凤凰座SX型星;研究内容则是利用脉动变星本身的脉动作为探测指针来寻找脉动变星的伴星。本文首先将天琴座RR型星作为主要对象,对该领域的研究内容进行了简要综述,包括其数量和分布、作为标准烛光的特性、奥斯特霍夫星群、脉动周期的长期变化以及Blazhko效应等内容;并针对其在观测上极少被发现处于双星系统中进行了探讨。同时,本文还就凤凰座SX型星的物理及演化特性进行了介绍。通过利用Kepler空间望远镜、地面巡天项目以及国内的一些小口径望远镜的测光观测数据,我们采用O-C分析以及其它相应分析方法在对探测短周期脉动变星的伴星方面取得以下研究成果。1、利用Kepler卫星的高精度不间断的,持续大约1470天的Long candence测光数据,在经过谨慎地O-C分析和论证后,我们在21颗非Blazhko RRab变星中发现两颗星FN Lyr和V894 Cyg是存在着小质量的伴星天体的。经过计算,伴星的质量函数分别为f(M)=(3.94±0.82)×10-6和(2.01±0.22)×10-4M⊙。当假设系统轨道倾角是随机分布时,这两个伴星是亚恒星天体(褐矮星或大质量行星)的概率分别是89.4%和59.4%。当轨道倾角为90度时,伴星与脉动主星的最小距离分别是1.03和0.50 AU。此外,它们的轨道周期分别为794.8和1084.4天。将这些轨道参数与含B型亚矮星的双星轨道参数比较,有迹象表明不同的水平分支星是有着不同的演化历史的,而且伴星在其中起着比较重要的影响。此外,我们还就两颗星的脉动周期的长期变化进行了讨论。根据我们的工作,含天琴座RR型星的双星并不是罕见的,至少是在成员天体相距较远的双星中。2、在对剩余的19颗非Blazhko RRab型星的研究中,我们发现其中一些目标的O-C数据可以用抛物线成分来描述,表明其脉动周期存在着线性变化。但是经过分析,其脉动周期变化率的绝对值要大于由演化导致的变化率。同时考虑到Kepler空间望远镜的观测时长较短,只有4年左右,因此得到的周期变化率不能真实反映其脉动周期的长期变化性质。我们认为这些变化可能为周期更长的周期性变化成分的一部分,因此还需要对这些目标进行持续地跟踪观测。此外,还有一些目标的O-C图表现出准周期性或不规则变化,表明了影响脉动周期变化的机制的复杂性。3、在通过收集地面巡天WASP项目数据和利用国内小口径望远镜观测得到多个光度极大时刻,并收集了1961到2013年间所有光度计算时刻数据后,我们采用O-C分析方法,分析了大变幅盾牌座δ型星SZ Lyn的脉动周期及轨道参数;确认了SZ Lyn所在的恒星系统存在着一个1.15±0.25度/年的轨道进动;并通过分析得出脉动主星SZ Lyn的伴星其实是一个密近双星,并且双星就是导致进动的原因。因此SZ Lyn所在的系统其实是一个三星系统。我们还采用依巴谷卫星(Hipparcos)天体测量数据对SZ Lyn进行了天体测量,结果得出SZ Lyn所在的系统轨道倾角为39.5±17.7度,三角视差为2.61±0.98毫角秒(对应的距离为380±140 pc)。此外,我们重新分析了由Bardin&Imbert(1984)[18]给出的SZ Lyn的平均视向速度值,并注意到其在经过开普勒轨道拟合后的残差中还存在一个弱的周期性变化成分。我们认为未来需要高精度的分光观测来确认这一变化成分。4、我们对脉动周期为0.05875天的大变幅凤凰座SX型星DW Psc进行了观测和周期分析后,在其O-C图中发现清晰的严格周期性变化成分,周期为6.08年,O-C值变化振幅为0.0066天。而这一成分可以由光时轨道效应来解释,这便意味着DW Psc是在双星系统中的。通过偏心轨道拟合以及计算,我们得到双星的轨道偏心率为0.4,伴星的质量下限为0.45±0.03 M⊙,两子星的距离为2.7±0.3 AU。经过讨论,我们认为伴星的存在对DW Psc这类星族II的凤凰座SX型星的起源和未来演化有着重要的影响。而我们的对DW Psc的伴星探测工作也使得它变成一个非常有趣并值得深入研究的目标。
Other AbstractIn the present paper, the main objects of study are short period pulsation variables, including RR Lyrae stars, Delta Scuti stars and SX Phe stars, and the contents of the study are using the pulsation to detect the companions of short period pulsation variable. We first give a brief overview of the research in RR Lyrae stars, including the number and distribution, the characteristics as standard candles, the Oosterhoff group, the long term changes of the pulsation period and the Blazhko effect, discuss the observational fact of that RR Lyrae stars are rarely found in binary systems, and then introduce the evolution properties of SX Phe stars. By using the photometric data of Kepler space telescope, ground surveys and our small telescopes, we use the O-C method and other methods to detect the companions of short period pulsation stars, and obtain the results as follow: 1. Long cadence corrected PDC fluxes of FN Lyr(KIC 6936115) and V894 Cyg(KIC 9591503), observed continuously by Kepler mission, spanning over 1470 d are used to determine hundreds of times of maximum and minimum for analysis of O?C residuals. The clear variations in the O?C diagrams are interpreted to be caused by the light-travel-time effect due to additional companions. The mass functions of the companions are f(M)=(3.94 ± 0.82) × 10?6 and (2.01 ± 0.22) × 10?4M⊙. Assuming that the orbital plane inclination follows a random distribution, the companions to both stars can be constrained to be substellar objects(brown dwarf , or giant planet), with 89.4% and 59.4% probability, respectively. Under the assumption that the orbital inclination equals 90?, the distances between the companions and the central RR Lyrae stars at periastron should be 1.03 and 0.50 AU, respectively. In addition, the orbital periods are 794.8 and 1084.4 d for FN Lyr and V894 Cyg, respectively. Comparing these orbital parameters with those of B subdwarf stars in binary systems yields strong hints that horizontal branch stars may have different evolution histories. The long-term pulsation period changes are also discussed. Based on our studies, RR Lyrae stars in binary systems are not rare, at least among binary systems with wider separations. 2. the O?C diagrams of other 19 Non-Blazhko RRab-type stars in Kepler field also show some variations, including the parabolic variations and irregular variations. The parabolic variations mean that the pulsation periods are changing linearly with time. However, the observed β values are slightly larger than those predicted by theoretical models. Considering that the data observed by Kepler are not enough for the research of long term pulsation period, more photometric observations are needed in the future to check the changes. Moreover, the O?C diagrams of some stars show irregular variations or semi-periodic changes, indicating that some unknown mechanism may influence the O?C values. 3. We determine forty-two new times of light maximum from our photometry observations and WASP project, and collect all the times of light maximum observed between 1961 and 2013 to calculate the orbital elements of the SZ Lyn binary system and secular change of the pulsation period with the classical O?C method. We confirm the decrease of longitude of the periastron passage with a rate of (?1.15 ± 0.25)? yr?1, and discuss the causative mechanism. The results show that the precession of the star’s orbit is due to a close binary system, which means that SZ Lyn system is actually a triple star system. We use the Hipparcos Intermediate Astrometric Data to obtain the complete orbital elements of SZ Lyn system and find that the inclination i and parallax are 39.5±17.7? and 2.61±0.98 mas (corresponds to 380±140 pc), respectively. We reanalyze the mean radial velocities of SZ Lyn given by Bardin & Imbert (1984) [6], and notice a weak variation existing in the residuals from a single-Keplerian fit. We suggest that more detailed high-precision spectroscopic observations are definitely needed in the future to check this short periodic change. 4. DW Psc is a high-amplitude SX Phe-type variable with a period of pulsation of 0.05875 days. Using a few newly determined times of maximum light together with those collected from the literature, the changes in the O?C diagram are analyzed. It is discovered that the O?C curve of DW Psc shows a cyclic variation with a period of 6.08 years and a semi-amplitude of 0.0066 days. The periodic variation is analyzed for the light travel time effect, which is due to the presence of a stellar companion (M2 sin i ? 0.45(±0.03)M⊙). The two-component stars in the binary system are orbiting each other in an eccentric orbit (e ~ 0.4) at an orbital separation of about 2.7(±0.3) AU. The detection of a close stellar companion to an SX Phe-type star supports the idea that SX Phe-type pulsating stars are blue stragglers that were formed from the merging of close binaries. The stellar companion has played an important role in the merging of the original binary by removing angular momentum from the central binary during early dynamical interaction or/and late dynamical evolution. After the more massive component in DW Psc evolves into a red giant, the cool close companion should help to remove the giant envelope via possible critical Rochelobe overflow, and the system may be a progenitor of a cataclysmic variable. The detection of a close stellar companion to DW Psc makes it a very interesting system to study in the future.
Subject Area天文学
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/9453
Collection双星与变星研究组
Affiliation中国科学院云南天文台
Recommended Citation
GB/T 7714
李临甲. 利用脉动指针探测短周期脉动变星伴星及相关演化探讨[D]. 北京. 中国科学院研究生院,2015.
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