麦哲伦星云是离我们银河系最近的星系，也是我们银河系的卫星星系。麦哲伦星云的低金属丰度环境和离我们较近的距离非常有利于恒星、星团、行星状星云和星系相互作用等科研目标的研究，这些因素使得它成为我们感兴趣的目标天体系统。 VISTA survey of Magellanic Clouds system（VMC）巡天是欧洲南方天文台针对麦哲伦星云的巡天项目，它提供了近红外Y、J、Ks三个波段的观测图像。观测图像覆盖了大小麦哲伦星云的主要区域、它们相互连接的部分以及部分星流区域。这是目前对麦哲伦星云的巡天范围最广、测光深度较深的观测图像。 作为VMC巡天项目的重要组成部分，巡天数据由VISTA巡天数据处理系统（pipeline）提供，它对原始观测图像进行处理，包括点源的目标提取、测光，并提供最终源表。 由于巡天数据处理系统（pipeline）基于通常科研目标设计，并不针对较暗的源。很多研究要求较精确的暗端数据，数据在一定完备度上有更低的下限，而巡天数据处理系统的处理结果并无法满足这一要求。针对这个问题，我们选择了VMC已完成的巡天区域，通过对原始数据处理，合并多个时期的巡天数据，手动进行PSF 测光，获得了我们最新的源表，进而进行分析，对整个数据在暗端的表现进行了详细描述，最终提供了一套针对暗端天体目标研究所需的数据处理方法。我们的结果描述包括： 1. 研究区域的点扩散函数无系统性变化。 2. 孔径测光与点扩散函数测光在处理VMC巡天数据时的表现以及它们对暗源的区别。 3. 新源表跟pipeline的区别主要体现在测光精度更高，在暗端有效源的数目高出至少30$\%$（取决于波段、观测区域） 4. 随位置变化的完备性曲线。 5. 不同恒星密度区域的光度函数。
其他摘要
Magellanic Clouds are the nearest neighbor of our Milky Way. Their low metallicity and distance from us make it to be the interested object for astronomers。 VISTA survey of Magellanic Clouds system（VMC）is one of important survey projects from Europe South Observatory. It provide inferred images which cover most part of Magellanic Clouds with Y, J, Ks bands, including Large Magellanic Cloud, Small Magellanic Cloud, the bridge between them and part of star stream of Magellanic Cloud. As one of important part of VMC project, the VISTA Data Flow System(VISTA) provide the final images and data acquired by VMC project. The products of VISTA includes the original images, pre-precess images, deep images, catalogue of sources in these images with magnitude from aperture photometry. Since the VDFS pipeline was designed for general object, we are not sure if it can provide good enough data for the fainter sources. Some project will be sensitive with the low mass sources and the fainter hand of data from VMC will play important role in the final result so that confirm the behave of fainter hand are crucial for these project. The goal of our work was to make sure if the final result from VDFS are good enough to be used on fainter sources. we perform our own data reduction on the origin images and compare our result with data from VDFS and point the benefit of our processing, result description as bellow: 1. Point Spread Function(PSF) of the images combined from origin images of several epoch don't vary from one region to another. 2. Results description of aperture and PSF photometry. 3. The final result from our data reduction provide higher accuracy than the VDFS's and give larger catalogue in the fainter hand. 4. The completeness of different region in three bands will be provide, cause its importance for defining the fainter limits of observation。 5. Luminosity of our test region with deferent density.
修改评论