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arXiv 1102.0533astro-ph.SR
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银河系中的宽双星--统计方法

Wide Binary Stars in the Galactic Field - A Statistical Approach

Marco Longhitano

摘要:

本论文主要研究银河系中宽双星系统的统计特性。在本研究中,我们选择了一个均匀的样本,覆盖约675平方度的方向的NGP。它包含近670,000颗MS恒星,视星等在15至20.5等之间,光谱类别晚于G5。数据来自SDSS。我们构造的两点关联函数(2 PCF)的角间距在2和30 arcsec之间。由此产生的聚类信号建模的Wasserman-Weinberg技术的装置。我们证明了半长轴的分布符合正则Oepik定律,并推断太阳附近约有10%的恒星属于WB系统。为了减少噪声从光学对,并增加在较大的分离的分析的灵敏度,我们包括距离信息从光度计视差。引入一种新的加权程序的基础上的结合概率的双星,我们推断的颜色和质量比的分布,这是仔细校正观测的选择效应。统计上考虑了大约4,000个WBs,其组成部分的质量在0.2到0.85太阳质量之间。我们发现WB的颜色分布与单场星的颜色分布一致。然而,与随机配对的场星相比,质量差超过0.5太阳质量的对似乎系统性地代表不足。我们的研究结果与先前的研究基本一致,但直接比较很困难,而且往往是不可能的。本文提出的新方法可以看作是对普通自行研究的补充,也是研究银河系引力场中引力带统计特性的一种可行方法。

英文摘要:

This thesis focuses on the statistical properties of wide binary (WB) star systems in the Galactic field. For the present study we select a homogeneous sample covering about 675 square degrees in the direction of the NGP. It contains nearly 670,000 MS stars with apparent magnitudes between 15 and 20.5 mag and spectral classes later than G5. The data were taken from the SDSS. We construct the two-point correlation function (2PCF) for angular separations between 2 and 30 arcsecs. The resulting clustering signal is modeled by means of the Wasserman-Weinberg technique. We show that the distribution of semi-major axis is consistent with the canonical Oepik law and infer that about 10% of all stars in the solar neighbourhood belong to a WB system. To reduce the noise from optical pairs and to increase the sensitivity of the analysis at larger separations, we include distance information from photometric parallaxes. Introducing a novel weighting procedure based on the binding probability of a double star, we infer the distribution of colours and mass ratios, which were carefully corrected for observational selection effects. About 4,000 WBs were taken into account statistically, whose components have masses between 0.2 and 0.85 solar masses. We find that the WB colour distribution is in accord with the colour distribution of single field stars. However, pairs with a mass difference exceeding 0.5 solar masses seem to be systematically underrepresented as compared to a random pairing of field stars. Our results are broadly in agreement with prior studies but a direct comparison is difficult and often impossible. The novel procedure presented in this thesis can be regarded as complementary to common proper motion studies, and constitutes a viable approach to study the statistical properties of WBs in the Galactic field.

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