稀有天体源分类的k-NN方法：Spitzer/IRAC对棕矮星的光度搜索
A k-NN Method to Classify Rare Astronomical Sources: Photometric Search of Brown Dwarfs with Spitzer/IRAC
摘要：
本文提出了一种基于加权k-NN方法的稀有天文源光度搜索的统计方法。一个度量定义在一个多维的颜色-幅度空间的基础上，只有模板源的光度特性和光度的模板和数据的不确定性，而不需要定义的ad-hoc颜色和幅度削减，可能会偏置的搜索。该度量被定义为两个参数的函数，邻居的数量k和阈值距离D_th，可以优化最大的选择效率和完整性。我们应用的方法来搜索的L和T矮星的斯皮策河外第一次看调查和Bootes领域的斯皮策浅调查，以及搜索附近的恒星周围的亚恒星质量的同伴。在高水平的完整性下，我们确认在第一次观测中至少有两个波段没有发现晚T矮星，而在浅层观测中只有一个（以前由Stern等人在2007年发现）。这一结果与晚T矮星的预期统计数据一致。一个L/早T候选者在第一次调查中被发现，3个在浅层调查中，目前正在进行后续的光谱验证。最后，我们讨论了这种方法在斯皮策暖任务探索科学计划中搜索棕矮星的潜力。
英文摘要：
We present a statistical method for the photometric search of rare astronomical sources based on the weighted k-NN method. A metric is defined in a multi-dimensional color-magnitude space based only on the photometric properties of template sources and the photometric uncertainties of both templates and data, without the need to define ad-hoc color and magnitude cuts which could bias the search. The metric is defined as a function of two parameters, the number of neighbors k and a threshold distance D_th that can be optimized for maximum selection efficiency and completeness. We apply the method to the search of L and T dwarfs in the Spitzer Extragalactic First Look Survey and the Bootes field of the Spitzer Shallow Survey, as well as to the search of sub-stellar mass companions around nearby stars. With high level of completeness, we confirm the absence of late-T dwarfs detected in at least two bands in the First Look Survey, and only one in the Shallow Survey (previously discovered by Stern et al. 2007). This result is in agreement with the expected statistics for late-T dwarfs. One L/early-T candidate is found in the First Look Survey, and 3 in the Shallow Surveys, currently undergoing follow-up spectroscopic verification. Finally, we discuss the potential for brown dwarf searches with this method in the Spitzer warm mission Exploration Science programs.
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