这是一篇关于低质量星和褐矮星的巡天探测的硕士论文。褐矮星是质量介于最小质量恒星和最大质量行星之间的一类新发现的天体。褐矮星早期会发生短暂的氢-氘核反应，最大质量褐矮星早期也会有短暂的氢-氢核反应，核反应停止后褐矮星进入漫长的冷却阶段。褐矮星温度与恒星相比非常的低，其辐射主要集中在近红外波段。第一颗 L型矮星是1988年才发现的，而目前正式发现的褐矮星大约只有一千颗。本文综述了褐矮星的研究历史、观测特性以及褐矮星的探测方法，并详细介绍了本人在攻读硕士学位期间在褐矮星巡天探测方面的所做的研究工作。 我们对已发现的 L 和 T 型矮星的 Sloan 数字巡天 (SDSS) 和两微米全天巡天 (2MASS) 的测光数据进行了全面的分析研究，得出了用于从SDSS 和 2MASS巡天数据库中筛选极冷矮星的颜色和星等限制条件。并利用这个条件从 SDSS和 2MASS 巡天数据库中筛选出了180颗左右的极冷矮星候选体，我们通过SDSS 光谱证认了其中36颗 M 和 L型矮星，又利用英国近红外望远镜深场巡天 (UKIDSS)测光数据交叉证认了21颗 L 型矮星，我们还给出这些新 M 和 L型矮星基于 SDSS, UKIDSS 和 2MASS的自行数据。为了确定没有光谱天体的光谱型，我们给出了比先前更为准确的颜色-光谱型关系。第四章详细介绍了上述工作内容。本文第四章的内容是本人一篇科研论文的翻译。 在新近的工作中，我们利用上述方法得到了更大数量的极冷矮星候选体。我们将对这些天体的 SDSS, UKIDSS 和 2MASS的测光和天体测量数据进行分析和研究。另外在这些数据中有三十个天体在 SDSS 或 UKIDSS图象中显示为双星系统，我们将利用丽江2.4米望远镜对他们进行进一步的观测研究。我们在本文第五章中对新近的工作做了一个简单的介绍.
其他摘要
This master's thesis is about large area surveys of low mass stars and brown dwarfs. Brown dwarfs occupy the mass range between the lowest mass stars and the highest mass planets, they have masses too small to be stars, but too large to be planets. The central temperature of a brown dwarf is not high enough to achieve stable hydrogen burning like a star, but all brown dwarfs will undergo short periods of primordial deuterium burning very early in their evolution. Around 1000 brown dwarfs were found since the first discovery of an L dwarf (GD165 B) in 1988. In this thesis I first give an introduction to the research history, observational properties and the detect methods of brown dwarfs. Then I describe my research work on identifying ultra-cool dwarfs with large area surveys. We made a study of the color-color and color-apparent magnitude relationships of known L and T dwarfs based on the data from the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS). Based on our parameterization study we gave the new selection criteria for ultra-cool dwarfs. We found around 180 new ultra-cool dwarf candidates from SDSS and 2MASS. 36 of these objects are M9 and L dwarfs by their SDSS spectra. 21 L objects are crossed identified in the UKIRT Infrared Deep Sky Survey (UKIDSS), which are L dwarfs by the SDSS and 2MASS colors-spectral type relationships developed by us. I give more details about my research work in Chapter 4. Chapter 4 is translate from a paper of mine. We found more ultra-cool dwarf candidates from the SDSS in the latest work. And we will do more study on their photometric and astrometric data form the SDSS, UKIDSS and 2MASS. Thirty of our objects are brown dwarf binary candidates by their SDSS and UKIDSS images, and we will give more observation on them with the Lijiang 2.4m Telescope. I gave an introduction to the latest work in Chapter 5.
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