标题： 中紫外窄带指数的演化简单恒星种群 显示英文标题

标题： Mid-UV Narrow-Band Indices of Evolved Simple Stellar Populations

摘要： 我们探讨了选定的中紫外（1900-3200埃）光谱指数的简单星族（SSPs）特性。 我们将高分辨率UVBLUE恒星光谱库纳入演化星族合成代码中，该代码基于最新的Padova等时线。 我们分析了紫外指数相对于年龄和化学组成的变化趋势。 作为对观测数据的首次测试，我们将结果与银河系球状星团的经验中紫外光谱指数进行比较，这些指数由国际紫外探测器（IUE）观测得到。 我们发现合成指数表现出多种特性，其中主要的是大多数指数在年龄大于2 Gyr时具有轻微的年龄敏感性。 然而，对于高金属丰度，两个指数Fe II 2332和Fe II 2402表现出显著不同的模式，在前2 Gyr内急剧增加，之后迅速下降。 这些指数明显标记了年轻（约1 Gyr）且金属丰度高（Z > Z_sun）的恒星种群的存在。 我们补充了银河系球状星团现有的紫外指数的新测量数据，并仔细识别出一个包含十个适合与理论模型比较的子样本。 比较结果显示了一定程度的一致性，特别是指数与金属丰度的强趋势得到了良好再现。 我们还讨论了未来建模中应考虑的主要改进，包括α增强对光谱能量分布的影响等。 显示英文摘要

摘要： We explore the properties of selected mid-ultraviolet (1900-3200 angstrom) spectroscopic indices of simple stellar populations (SSPs). We incorporate the high resolution UVBLUE stellar spectral library into an evolutionary population synthesis code, based on the most recent Padova isochrones. We analyze the trends of UV indices with respect to age and chemical composition. As a first test against observations, we compare our results with the empirical mid-UV spectral indices of Galactic globular clusters, observed with the International Ultraviolet Explorer (IUE). We find that synthetic indices exhibit a variety of properties, the main one being the slight age sensitivity of most of them for ages>2 Gyr. However, for high metallicity, two indices, Fe II 2332 and Fe II 2402, display a remarkably different pattern, with a sharp increase within the first two Gyr and, thereafter, a rapid decline. These indices clearly mark the presence of young (~1 Gyr) metal rich (Z > Z_sun) stellar populations. We complement existing UV indices of Galactic globular clusters with new measurements, and carefully identify a sub-sample of ten indices suitable for comparison with theoretical models. The comparison shows a fair agreement and, in particular, the strong trend of the indices with metallicity is well reproduced. We also discuss the main improvements that should be considered in future modelling concerning, among others, the effects of alpha-enhancement in the spectral energy distributions.