基于高分辨红外光谱研究核球α元素丰度

The Bulge is one of the most important parts of the Milky Way. The aim of this project is to explore the complex constructure and evolution of the Galactic Bulge, taking the α-element (mainly on Mg and Si) as a probe and based on the APOGEE H-band survey. APOGEE targets focus on red giants which are sensible to NLTE effects. We will carry on the non-local thermodynamic equilibrium (NLTE) analysis to derive the exact α-element abundance of globular clusters in the Bulge. These clusters will be used to calibrate the Bulge field stars, based on the established Mg and Si atomic models. By comparing the results from ASPCAP with ours, we can calibrate the α-element abundance from ASPCAP for the field stars in the Bulge. We will also calculate a group of atmospheric models with the stellar parameters range of sample stars and derive their NLTE corrections. By interpolating the NLTE corrections of models, we will derive the NLTE corrections for sample stars which will be added to the α-element abundance from ASPCAP, in order to obtain the accurate α-element abundance of Bulge field stars. Combining our results with the current Galactic evolution models, we will investigate the formation and chemical evolution history of the bulge.

核球是银河系最为重要的组成成分之一，为探究核球的复杂结构及演化，本项目以α元素（主要是Mg和Si元素）作为探针，基于APOGEE高分辨率红外H波段大样本巡天数据，研究核球区域恒星的形成和演化历史。APOGEE主要观测目标是红巨星，易受NLTE效应影响。因此，本研究采用已建立的Mg和Si原子模型，首先对挑选出来用于定标的核球区域球状星团样本星进行细致的NLTE丰度分析，将得到的精确α元素丰度与ASPCAP给出的Mg和Si元素丰度进行比较，确定经验的校正公式，从而对pipeline给出的核球区域场星的α元素丰度进行校正；计算一批覆盖样本参数范围的恒星大气模型格点的NLTE改正值，通过插值得到样本星的NLTE改正值，以对核球区域样本星的α元素丰度进行修正，从而得到核球区域样本星可靠的α元素丰度，再结合现有的银河系演化模型，研究银河系核球的形成和化学演化历史。

本项目基于APOGEE高分辨率红外H波段大样本巡天数据，以α元素（主要是Mg和Si元素）作为探针，研究核球区域恒星的形成和演化历史。APOGEE主要观测目标是红巨星，易受NLTE效应影响。因此，本研究采用已建立的Mg和Si原子模型，考虑NLTE效应，得到核球及银盘区域场星的α元素丰度，并将核球区域得到的[Mg/Fe]和[Si/Fe]与银盘这两种元素的丰度值进行比较，结果发现，核球区域的[Mg/Fe]丰度普遍要比银盘区域的高，这表明核球的演化过程远比银盘剧烈。同时，我们还将红外H波段的NLTE效应扩展到Ca和Cu两种元素。