标题： 矮星系恒星形成历史推导中包含水平分支星：Carina dSph 显示英文标题

标题： Inclusion of Horizontal Branch stars in the derivation of star formation histories of dwarf galaxies: the Carina dSph

摘要： 我们通过合成建模技术对小麦哲伦星系的水平分支进行了详细分析，一致地考虑了从主序星和红巨星分支光谱观测中确定的恒星形成历史和金属丰度演化。我们发现，一个范围为0.1-0.14 M的综合红巨星分支质量损失值，随着金属丰度增加，能够再现旧水平分支的颜色延伸。然而，仅将质量损失作为自由参数是不足以匹配卡琳娜水平分支的详细形态的。我们探讨了恒星形成历史在合成与观测水平分支之间差异中的作用。我们推导出一个简化的爆发式恒星形成历史，能够再现水平分支恒星计数，并且定性地匹配红巨星和主序星转折区域。这种恒星形成历史由基于主序星转折和红巨星的恒星形成历史中的年龄和[M/H]成分子集组成，包括四个不同强度的恒星形成爆发，分别位于2、5、8.6和11.5 Gyr，平均[M/H]随年龄增加而从\sim -1.7下降到\sim -2.2，并具有0.1 dex的高斯分布。我们提出的恒星形成历史的金属丰度分布函数与使用红外CaT特征并通过CaT-[Fe/H]校准测得的金属丰度分布进行比较，一旦考虑到卡琳娜星样本中测量的[Ca/Fe]丰度范围，该范围会使推导出的[Fe/H]分布偏向于过低的值，两者显示出定性的吻合。总之，我们展示了如何提取和解释卡琳娜水平分支（以及矮星系一般情况）中的信息，以完善仅从红巨星和主序星得到的恒星形成历史。简写 显示英文摘要

摘要： We present a detailed analysis of the Horizontal Branch of the Carina Dwarf Spheroidal Galaxy by means of synthetic modelling techniques, taking consistently into account the star formation history and metallicity evolution as determined from main sequence and red giant branch spectroscopic observations. We found that a range of integrated red giant branch mass loss values of 0.1-0.14 M, increasing with metallicity, is able to reproduce the colour extension of the old Horizontal Branch. However, leaving the mass loss as the only free parameter is not enough to match the detailed morphology of Carina Horizontal Branch. We explored the role played by the star formation history on the discrepancies between synthetic and observed Horizontal Branches. We derived a toy bursty star formation history that reproduces the horizontal branch star counts, and also matches qualitatively the red giant and the turn off regions. This star formation history is made of a subset of age and [M/H] components of the star formation history based on turn off and red giants only, and entails four separate bursts of star formation of different strenghts, centred at 2, 5, 8.6 and 11.5 Gyr, with mean [M/H] decreasing from \sim -1.7 to \sim -2.2 for increasing ages, and a Gaussian spread of 0.1 dex. The comparison between the metallicity distribution function of our star formation history and the one measured from the infrared CaT feature using a CaT-[Fe/H] calibration shows a qualitative agreement, once taken into account the range of [Ca/Fe] abundances measured in a sample of Carina stars, that biases the derived [Fe/H] distribution toward too low values. In conclusion, we have shown how the information contained within the horizontal branch of Carina (and dwarf galaxies in general) can be extracted and interpreted to refine the star formation history derived from red giants and turn off stars only. Abridged