Comprehensive stellar population models and the disentanglement of age and metallicity effects
Comprehensive stellar population models and the disentanglement of age and metallicity effects
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DOI：
10.1086/192096
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发表时间：
1994-11
影响因子：
8.7
通讯作者：
G. Worthey
中科院分区：
文献类型：
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作者：
G. Worthey
描述了中型和老年恒星族群的详细模型的构建。输入参数包括金属丰度（-2 小于 (Fe/H) 小于 0.5）、单爆年龄（1.5 至 17 Gyr 之间）和初始质量函数 (IMF) 指数。输出量包括宽带幅度、光谱能量分布、表面亮度波动幅度以及一套 21 个吸收特征指数。这些模型会根据各种可用的观察结果进行检查。对模型输出的检查得出以下结论。 (1) 如果两个群体的百分比变化 delta 年龄/delta Z 大约等于 3/2，则它们在大多数指数中看起来几乎相同。一些指数通过比平常更加丰度敏感（Fe4668、Fe5015、Fe5709 和 Fe5782）或对年龄更加敏感（G4300、H beta 和可能更高阶的巴尔默系）来打破这种简并性。 (2) 目前恒星演化的不确定性与所研究的指数中 IMF 和 Y 的影响具有相同的程度。 (3) 丰度比（如（Mg/Fe））的变化预计在古老恒星族的光谱中很明显。 (4) 预计恒星族的 I 波段通量几乎与金属丰度无关，并且对年龄仅适度敏感。因此，建议将 I 波段用于标准烛光工作或星系中 M/L 的研究。其他结论源于这项工作。 (1) 两个 TiO 指数的模型和观测结果的相互比较似乎表明了星系之间 (V/Ti) 比率的变化，但尚不清楚该观测结果如何与化学富集的标准图景联系起来。 (2) 目前基于综合指数对最富含金属的球状星体的 (Fe/H) 估计可能稍高。 (3)不同作者的群体模型的颜色表现出很大的范围。在太阳金属丰度和 13 Gyr 下，该范围对应于大约 +/- 7 Gyr 的年龄误差。不同作者的模型颜色在不同意义上应用具有较小的不确定性。 (4) 在目前的模型中，颜色的主要误差可能是从恒星大气参数到恒星颜色的转换。 (5) Stellar B - V 难以建模，目前不同作者之间的差距可达 0.2 mag。 (6) 如果恒星通量库中的已知缺陷得到纠正，这项工作在比 U 更红的通带中的总体模型颜色在绝对意义上将精确到大约 0.03 星等。这些更正未在模型输出表中进行。
The construction of detailed models for intermediate and old stellar populations is described. Input parameters include metallicity (-2 less than (Fe/H) less than 0.5), single-burst age (between 1.5 and 17 Gyr), and initial mass function (IMF) exponent. Quantities output include broadband magnitudes, spectral energy distributions, surface brightness fluctuation magnitudes, and a suite of 21 absorption feature indices. The models are checked against a wide variety of available observations. Examinations of model output yield the following conclusions. (1) If the percentage change delta age/delta Z approximately equals 3/2 for two populations, they will appear almost identical in most indices. A few indices break this degeneracy by being either more abundance sensitive (Fe4668, Fe5015, Fe5709, and Fe5782) or more age sensitive (G4300, H beta, and presumably higher order Balmer lines) than usual. (2) Present uncertainties in stellar evolution are of the same magnitude as the effects of IMF and Y in the indices studied. (3) Changes in abundance ratios (like (Mg/Fe)) are predicted to be readily apparent in the spectra of old stellar populations. (4) The I-band flux of a stellar population is predicted to be nearly independent of metallicity and only modestly sensitive to age. The I band is therefore recommended for standard candle work or studies of M/L in galaxies. Other conclusions stem from this work. (1) Intercomparison of models and observations of two TiO indices seem to indicate variation of the (V/Ti) ratio among galaxies, but it is not clear how this observation ties into the standard picture of chemical enrichment. (2) Current estimates of (Fe/H) for the most metal-rich globulars that are based on integrated indices are probably slightly too high. (3) Colors of population models from different authors exhibit a substantial range. At solar metallicity and 13 Gyr, this range corresponds to an age error of roughly +/- 7 Gyr. Model colors from different authors applied in a differential sense have smaller uncertainties. (4) In the present models the dominant error for colors is probably the transformation from stellar atmospheric parameters to stellar colors. (5) Stellar B - V is difficult to model, and current spreads among different authors can reach 0.2 mag. (6) If known defects in the stellar flux library are corrected, the population model colors of this work in passbands redder than U would be accurate to roughly 0.03 mag in an absolute sense. These corrections are not made in the tables of model output.