船底座计划VII：用c_UBI指数研究红巨星分支星的年龄-金属丰度简并度
The Carina Project VII: Towards the breaking of the age-metallicity degeneracy of red giant branch stars using the c_UBI index
摘要：
我们提出了一个分析的光度和光谱数据的船底座dSph星系，测试一种新的方法类似于用于解开多个人口在银河系球状星团（GC）。我们发现，一个适当的颜色组合是能够分开的红巨星分支（RGB）的两个主要的隆突人口（老的一个，\sim 12 Gyr，和中间年龄的一个，4-8 Gyr）的显着部分。特别地，c_UBI=（U-B）-（B-I）伪色允许我们沿着RGB的相关部分跟踪两个群体的RGB。我们发现，最老的恒星比中等年龄的恒星具有更多的负c_UBI假色。我们将RGB星的伪色与它们的化学性质相关联，发现铁含量和c_UBI之间存在显著的趋势。属于老星族的恒星系统地比属于中龄星族的恒星更贫金属（[Fe/H]=-2.32 \pm 0.08 dex）（[Fe/H]=-1.82 \pm 0.03 dex）。这为该星系的化学演化历史提供了坚实的证据，我们有一个新的诊断方法，可以让我们打破氢燃烧高级演化阶段的年龄-金属丰度简并性。我们比较了恒星在c_UBI平面上的分布与理论等时线，发现在基于标准重元素分布的理论框架中开发的模型不能达成令人满意的一致。最后，我们讨论了可能的系统性差异时，与多个群体的GC。
英文摘要：
We present an analysis of photometric and spectroscopic data of the Carina dSph galaxy, testing a new approach similar to that used to disentangle multiple populations in Galactic globular clusters (GCs). We show that a proper colour combination is able to separate a significant fraction of the red giant branch (RGB) of the two main Carina populations (the old one, \sim 12 Gyr, and the intermediate-age one, 4-8 Gyr). In particular, the c_UBI=(U-B)-(B-I) pseudo-colour allows us to follow the RGB of both populations along a relevant portion of the RGB. We find that the oldest stars have more negative c_UBI pseudo-colour than intermediate-age ones. We correlate the pseudo-colour of RGB stars with their chemical properties, finding a significant trend between the iron content and the c_UBI. Stars belonging to the old population are systematically more metal poor ([Fe/H]=-2.32\pm0.08 dex) than the intermediate-age ones ([Fe/H]=-1.82\pm0.03 dex). This gives solid evidence on the chemical evolution history of this galaxy, and we have a new diagnostic that can allow us to break the age-metallicity degeneracy of H-burning advanced evolutionary phases. We compared the distribution of stars in the c_UBI plane with theoretical isochrones, finding that no satisfactory agreement can be reached with models developed in a theoretical framework based on standard heavy element distributions. Finally, we discuss possible systematic differences when compared with multiple populations in GCs.
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