解决Local Group以外的恒星星族：MAD对UKS2323-326的观测
Resolving Stellar Populations outside the Local Group: MAD observations of UKS2323-326
摘要：
我们提出了一项研究，旨在推导出在中等年龄的演化恒星星族在矮不规则星系UKS 2323 -326的恒星形成的限制。这些观测也旨在证明在ESO甚大望远镜上实施的多共轭自适应光学演示器（MAD）的科学能力，该演示器作为自适应光学（AO）技术的测试台。我们执行准确的，深测光的领域使用J和Ks波段AO图像的中心区域的星系。近红外（IR）色星等图清楚地显示了渐近巨星分支（AGB）星、红超巨星和红巨星分支（RGB）星的序列，直到RGB尖端以下约1等。光学近红外图，通过结合我们的数据与哈勃太空望远镜的观测，提供了最好的恒星在各个演化阶段的分离。AGB星比RGB尖端亮的数量使我们能够估计中间年龄的恒星形成。假设初始质量函数为Salpeter，我们发现在中等年龄的恒星形成事件中，在观测区域产生了约6 × 10^5 M太阳的恒星。
英文摘要：
We present a study aimed at deriving constraints on star formation at intermediate ages from the evolved stellar populations in the dwarf irregular galaxy UKS2323-326. These observations were also intended to demonstrate the scientific capabilities of the multi-conjugated adaptive optics demonstrator (MAD) implemented at the ESO Very Large Telescope as a test-bench of adaptive optics (AO) techniques. We perform accurate, deep photometry of the field using J and Ks band AO images of the central region of the galaxy. The near-infrared (IR) colour-magnitude diagrams clearly show the sequences of asymptotic giant branch (AGB) stars, red supergiants, and red giant branch (RGB) stars down to ~1 mag below the RGB tip. Optical-near-IR diagrams, obtained by combining our data with Hubble Space Telescope observations, provide the best separation of stars in the various evolutionary stages. The counts of AGB stars brighter than the RGB tip allow us to estimate the star formation at intermediate ages. Assuming a Salpeter initial mass function, we find that the star formation episode at intermediate ages produced ~6x10^5 M_sun of stars in the observed region.
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