YNAO OpenIR  > 双星与变星研究组
食矮新星的测光分析
Alternative TitleA photometric study of the eclipsing dwarf novae
韩忠涛
Subtype硕士
Thesis Advisor钱声帮
2014-04
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矮新星 激变变星 测光观测
Abstract矮新星是具有频繁爆发现象的激变变星。主星是一颗弱磁白矮星,次星是一颗充满洛希瓣的晚型主序星,物质从次星内拉格朗日点溢出在主星周围形成吸积盘,物质流与吸积盘撞击形成热斑。吸积盘的存在使得矮新星具有复杂的物理变化和观测特征,比如爆发和高低态变化等。对它们进行研究极大的促进我们对吸积盘和物质转移理论的理解。而掩食对确定矮新星中各光源的相对亮度、几何位置和物理结构提供了极好的机会。不仅如此,食极小时刻的变化还反映轨道周期变化的信息,所以对掩食矮新星的研究是重要且有意义的。本文主要对一颗典型的食矮新星样本OY Car进行观测和研究,同时也对矮新星进行了统计分析,获得研究成果如下: 1、对OY Car的轨道周期进行分析,发现其轨道周期长期减小。由于该系统是由小质量星向大质量星转移物质,所以物质转移引起周期增加而不是减小,而引力辐射引起的周期减小率不足以解释观测到的周期减小。最终我们考虑磁滞机制并使用Rappaport et al. (1983)提出的磁滞模型并获得了较好的解释,但是这与激变变星演化的标准化模型是矛盾的。标准化模型认为周期空缺之下的激变变星角动量损失由引力辐射单独推动,所以这个减小有可能是更长周期变化的一部分。然而目前新的观点认为空缺之下的矮新星也可能有很强的磁滞,并且此观点已经得到许多观测证据的支持,我们的结论也是证据之一,这些证据对标准化模型提出了严峻的挑战。除了周期减小,还发现振幅约为27.8秒,周期大概是14年的周期性振荡成分,对其进行分析讨论,认为其最合理的解释是第三天体的光时效应。对第三天体的参数进行计算,发现其极有可能是一颗介于巨行星和褐矮星之间的临界亚恒星天体。 2、对OY Car的食光变曲线进行分析,发现其非爆发态时存在类似磁激变变星和类新星的高低态变化。我们观测到的最高态到最低态的变幅1mag,且从光变曲线中我们获得了如下信息:热斑变大变亮(暗)、吸积盘由内向外扩张、食外活跃的闪烁以及清晰的边界层轮廓。分析结果认为导致高态的主要原因是物质转移率的突然增加和吸积盘不稳定,而低态主要是物质转移率突然降低引起。物质转移率变化的原因目前的黑子理论可以解释的很好,即物质转移率升高是内拉格朗日点附近的耀斑引起,降低则是黑子引起。目前只有极少数的矮新星发现存在高低态变化。 3、观测到OY Car的爆发现象。其中2008年11月28日至2009年1月14日的爆发曲线是一次正常爆发,2009年11月23日和24日的爆发则是处于一次超级爆发的下降过程。将观测结果与AAVSO对OY Car的长期观测结果进行比较,发现在对应时间段我们的观测结果与AAVSO的结果完全一致。 4、对已发布的激变变星表以及在线数据进行搜集,获得了最新的矮新星星表,以此为依据对轨道周期分布以及其他参量进行了统计分析,得到如下一些结论:首先周期频数图显示空缺有消失的趋势,从3小时到2小时有一个渐变的过程,食矮新星的周期分布整体上则与总分布图一致,说明轨道倾角应该是随机均匀分布的;其次对矮新星次星质量与周期的关系进行统计得到与理论计算一致的结果,意味着次星质量-周期关系在矮新星中是普遍适用的;矮新星正常爆发达最大时的亮度与轨道周期之间的关系验证了1987年Warner的统计结果,且我们的统计结果展示出大部分矮新星都很暗弱;最后,对质量比-周期关系以及次星光谱型的统计发现这些关系与目前的理论预测和观测结果相符合。
Other AbstractDwarf novae are erupting cataclysmic variable stars in which a Roche-lobe filling late-type main sequence star(Secondary star) transfers matter to an accretion disc around a white dwarf(Primary star). The gas stream from the secondary feeds material into the disc at a point near its outer rim where a bright spot is formed. The existence of accretion disc makes it have complex physical changes and observed features, including the outburst of the frequent phenomenon and the transitions from a high state to a low state, etc. It will greatly promote the understanding to the theory of the accretion disc and the mass transfer to study these phenomenon. The eclipse provides an excellent opportunity to determine the relative brightness of each light source, geometric position and physical structure. And the times of mid-eclipse also reveals that the orbital period is changing. Therefore, the study of eclipsing dwarf novae is important and meaningful. In the present paper, the photometric observations of a typical eclipsing dwarf novae OY Car are observed and analyzed, and the parameters of the dwarf novae were also studied statistically. Some results are obtained as follows: 1、The orbital period variations of OY Car are analyzed. It is shown that the orbital period of OY Car is decreasing . Since the system consist of a less massive donor star and a more massive gainer star, we would expect the orbital period to increase rather than decrease. Gravitational radiation loss to explain the observed change. The Rappaport et al.(1983) prescription to calculate the orbital period change caused by magnetic braking are found to be able to explain the observed period decrease. However, according to the CV standard model, a donor star should not have magnetic braking. It is therefore possible that the observed downward parabolic change is simply a part of a long-period cyclic variation. On the other hand, recently, a new view that fully convective donors below the period gap are capable of generating significant magnetic fields and can produce MB strong enough。This idea is supported by some observational evidence, and our calculation is consistent with this possibility. These evidences pose a severe challenge to the CV standard model. In addition, a cyclic change with a small amplitude of 27.8s and a period of 14.0 yr is detected. We attempted to interpret the a cyclic change with the light travel-time effect due to an invisible third star in the system. Based on the analysis of the light travel-time effect, we find that the third star may be a critical substellar object between brown dwarf and giant planet. 2、The eclipsing light curves of OY Car are studied, the results reveal that OY Car has the transitions from a high state to a low state in quiescence, which is similar to the magnetic cataclysmic variable and nova-likes. We observed that the magnitude change amplitude between the highest state and the lowest state is about 1mag. From the light curve, we obtained the following information: hot spot is larger than the previous, and brighter(more faint) than before、the expansion of Accretion disk、flicking and the profile of boundary layer. The main reason for the high state is the sudden increase of matter transfer rate and the accretion discs is unstable, and the lower state is mainly caused by mass transfer rate suddenly drops. Starspots theory can well explain the variation of mass transfer, a lower mass transfer rate may be reflect starspots growing near L1 or form elsewhere and drift across it, a higher mass transfer is caused by flare. So far, only a few dwarf novae have been observed to have behavior resembling high or low states. 3、The outburst of the frequent phenomenon have been observed from 28 November 2008 to 14 January 2009, which should be a normal outburst. And the light curves on 23 November 2009 and 24 November 2009 are in the declined stages of a superoutburst. Comparing with the AAVSO's long-term observation result
Subject Area天文学
Pages91
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/5983
Collection双星与变星研究组
Recommended Citation
GB/T 7714
韩忠涛. 食矮新星的测光分析[D]. 北京. 中国科学院研究生院(云南天文台),2014.
Files in This Item:
File Name/Size DocType Version Access License
食矮新星的测光分析.pdf(11325KB)学位论文 开放获取CC BY-NC-SAView Application Full Text
Related Services
Recommend this item
Bookmark
Usage statistics
Export to Endnote
Google Scholar
Similar articles in Google Scholar
[韩忠涛]'s Articles
Baidu academic
Similar articles in Baidu academic
[韩忠涛]'s Articles
Bing Scholar
Similar articles in Bing Scholar
[韩忠涛]'s Articles
Terms of Use
No data!
Social Bookmark/Share
File name: 食矮新星的测光分析.pdf
Format: Adobe PDF
All comments (0)
No comment.
 

Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.