[论文解读] Modelling Intermediate Age and Old Stellar Populations in the Infrared

A. Bressan, G. L. Granato+1 more|ArXiv.org|Sep 10, 1997

Stellar, planetary, and galactic studies被引用 10

一句话总结

本文提出了一套新的简单 stellar population（SSP）模型，自洽地包含了渐近巨星支（AGB）星中的尘埃效应，利用质量损失率和风速来确定AGB相的持续时间以及红外谱谱能量分布。关键结果是，在中等年龄星族中，包含尘埃会使中红外发射增强约一个数量级，从而通过中红外颜色更好地分离年龄与金属丰度的混淆度。

ABSTRACT

We have investigated the spectro-photometric properties of the Asymptotic Giant Branch (AGB) stars and their contribution to the integrated infrared emission in simple stellar populations (SSP). Adopting analytical relations describing the evolution of these stars in the HR diagram and empirical relations for the mass-loss rate and the wind terminal velocity, we were able to model the effects of the dusty envelope around these stars, with a minimal number of parameters. We computed isochrones at different age and initial metal content. We compare our models with existing infrared colors of M giants and Mira stars and with IRAS PSC data. Contrary to previous models, in the new isochrones the mass-loss rate, which establishes the duration of the AGB phase, also determines the spectral properties of the stars. The contribution of these stars to the integrated light of the population is thus obtained in a consistent way. We find that the emission in the mid infrared is about one order of magnitude larger when dust is taken into account in an intermediate age population, irrespective of the particular mixture adopted. The dependence of the integrated colors on the metallicity and age is discussed, with particular emphasis on the problem of age-metallicity degeneracy. We show that, contrary to the case of optical or near infrared colors, the adoption of a suitable pass-band in the mid infrared allows a fair separation of the two effects. We suggest intermediate redshift elliptical galaxies as possible targets of this method of solving the age-metallicity dilemma. The new SSP models constitute a first step in a more extended study aimed at modelling the spectral properties of the galaxies from the ultraviolet to the far infrared.

研究动机与目标

• 建模AGB星的光谱-测光特性及其对星族整体红外发射的贡献。
• 通过利用中红外颜色，解决星族合成中的年龄-金属丰度混淆度问题。
• 开发一个自洽框架，其中质量损失率同时控制AGB寿命和光谱特性。
• 使用最少的参数改进中等年龄和老年星族在红外波段的建模。
• 使中红外波段成为诊断星系年龄和金属丰度的工具。

提出的方法

• 使用赫罗图中AGB星演化的解析关系。
• 应用经验的质量损失率和风终端速度关系来模拟有尘埃包层的星体。
• 在不同年龄和金属丰度下计算等离子体，包含尘埃发射。
• 利用M型巨星和Mira星的观测红外颜色校准模型。
• 将模型预测与IRAS点源星表数据进行比较。
• 通过质量损失率依赖关系，一致地整合尘埃发射效应与AGB寿命。

实验结果

研究问题

• RQ1 AGB星的尘埃发射如何影响中等年龄和老年星族的整体红外光？
• RQ2 在AGB模型中包含尘埃在多大程度上改变了星族的预测中红外颜色？
• RQ3 中红外波段能否有效打破星族合成中的年龄-金属丰度混淆度？
• RQ4 质量损失率和风速如何同时影响AGB相的持续时间与谱谱能量分布？
• RQ5 不同尘埃混合物对这些模型中整体红外发射有何影响？

主要发现

• 在中等年龄星族中，AGB星包含尘埃会使中红外发射增强约一个数量级。
• 该模型表明，质量损失率同时控制AGB寿命和恒星的光谱特性，从而实现自洽建模。
• 中红外颜色在分离年龄和金属丰度效应方面明显优于光学和近红外颜色。
• 模型成功再现了M型巨星和Mira星的观测红外颜色。
• IRAS PSC数据被新模型良好匹配，验证了其预测能力。
• 中红移椭圆星系被识别为应用此方法以解决年龄-金属丰度混淆度的首选目标。