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题名	白矮主序双星的寻找与观测的研究
作者	刘成
学位类别	硕士
答辩日期	2011-05
授予单位	中国科学院研究生院（云南天文台）
授予地点	北京
导师	李立芳
关键词	双星 分光观测 白矮星 密近双星
其他题名	Identifying and Observing White dwarf-Main Sequence Binaries within the Sloan Digital Sky Survey
学位专业	天体物理
中文摘要	密近双星演化过程中遇到的三个基本问题：（1）双星演化时涉及的物质交流不稳定性判据；（2）公共包层的形成与演化；（3）角动量损失过程。这些基本问题决定了双星演化的最终结局。虽然理论模型在描述公共包层演化和角动量损失过程方面取得了很大进展，但是一方面这些理论模型结果还不能完全描述这些过程，另一方面这些理论模型非常缺少观测限制。后公共包层双星是一类理想的观测源，完备的观测大样本可以用来限制理论模型。由于短周期的分离白矮-主序双星是后公共包层双星的候选体，且随着SDSS数据的不断释放，这样的系统将不断被丰富。因此，本工作发展了比较普适的颜色选择判据，希望利用这些判据从SDSS释放的数据中寻找到更多的白矮-主序双星，以尽可能的提高样本完备性。 利用白矮星和主序星单星模型，我们构建了分离的各种白矮星加主序星双星模型，并给出了双星模型颜色。根据双星颜色存在的区域，我们分别设计了光学的和近红外的颜色选择准则。利用颜色选择准则，我们从SDSS DR7中找到759 个有光谱的候选体，其中512个被我们证认为白矮-主序双星，另外有4个可能是白矮-主序双星。包括这4个不确定的源，一共有86个双星系统是我们首次发现的。我们结合近红外与光学选择准则（r − i > 0.3；II区），同时从UKIDSS DR5和SDSS DR7中选择候选体并做交叉证认。满足条件的候选体有506个目标天体，其中有13个已经被不同作者发现，10个有光谱的源被证认为是白矮-主序双星，且包含在我们样本中。 对白矮-主序双星光谱，我们使用χ2最小二乘法技术对这些光谱做拟合。除了在光谱拟合程序中给出了两个子星的基本参量，如有效温度、重力加速度、质量和金属丰度，我们还计算了两个子星到地球的距离以及白矮星的冷却年龄。通过对白矮星冷却年龄分布的分析，我们发现白矮星的平均冷却年龄为t ∼ 4.33 × 108年，且有∼ 12%的白矮-主序双星在形成后已经历了∼ 1.2 × 109年的演化。相对于目前的后公共包层双星样本，我们的样本中包含更多冷的年老白矮星双星，且在各个年龄段分布比较均匀。我们接下来的工作，就是要从相对完备的候选体中寻找到短周期的后公共包层双星。
英文摘要	Criterion of dynamically unstable mass transfer, common envelope (CE) evolution and angular momentum loss (AML) are three basic problems in close binary evolution. Solving these problems could help us to understand the formation of various related objects. However, CE evolution and the AML have been mainly developed in theoretical studies. Theoretical results can’t describe the CE phase and AML completely, and there are rare stringent observational constraint on the theoretical studies. The ideal sample of detached post common envelope binaries (PCEBs) provides a observational constraint on the CE evolution and AML in close binary. Short period white dwarf-main sequence (WDMS) binaries are candidates of the PCEBs, and the Sloan Digital Sky Survey (SDSS) offers the possibility of dramatically increasing the number of the WDMS binaries. So, we have developed a color selection criteria to diagnose the WDMS from SDSS, and hoped that completeness of the WDMS binary sample will be improved. Using the single white dwarf and main sequence models, we constructed a detached binary model consisting of a white dwarf plus a main sequence, and obtained model colors of this binary system. According to the model colors areas, we designed optical and near-infrared color selection criteria. Using the colorcriteria, 759 targets which have been observed spectroscopically were selected from the SDSS DR7. Among these, 512 objects are WDMS and 4 objects are WDMS candidates. Of these 516 WDMS and candidates, 86 have not been published so far. Combining the near-infrared with optical color-criteria (r−i > 0.3; II region), we have found 506 targets are the WDMS candidates from UKIRT Infrared Sky Survey (UKIDSS) DR5 cross-matched with the SDSS DR7. Of these 506 candidates, 13 have been identified as the WDMS binaries. By fitting the combined spectrum of the WDMS binaries using a χ2 minimizationtechnique, we derived independent parameter estimates, such as effective temperature, surface gravity, mass, and metallicity, for its components. Furthermore, we independently estimated the distances of the white dwarf and secondary star from us and determined the cooling age of white dwarf in our fitting procedure. According to the distribution of the cooling ages, we found that the mean cooling age t of white dwarf is ∼ 4.33×108 years, and the evolution of∼ 12% WDMS binaries have gone thought about 1.2 × 109 years. So, comparing with the current PCEBs sample, our sample is more extended and contains cooler and older white dwarf binaries. The sample also is uniform distribution. Accordingly, we provide a relatively complete candidate sample for identifying the short period PCEBs.
语种	中文
学科主题	天文学
内容类型	学位论文
源URL	[http://ir.ynao.ac.cn/handle/114a53/4664]
专题	云南天文台_大样本恒星演化研究组
推荐引用方式 GB/T 7714	刘成. 白矮主序双星的寻找与观测的研究[D]. 北京. 中国科学院研究生院（云南天文台）. 2011.

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