基于LAMOST的贫alpha晕族恒星搜寻与分析

The majority of metal-poor Galactic halo stars appear to have chemical abundance that are enhanced by alpha-elements at the early stage of the Galaxy. A few striking exceptions that show severe departures from the general enhanced alpha-element chemical abundance trends of the halo have been discovered in recent years. These stars may have a chemical enrichment history different from majority of the halo. Similarly low-alpha abundances are also displayed by the satellite dwarf spheroidal (dSph) galaxies, suggesting that the alpha-poor stars may have originated from dSph galaxies. Since we know almost nothing about the occurrence frequency of alpha-poor stars and their origin, more detection of such stars will be very helpful to improve our understanding. In this project, a large-scale search of alpha-poor stars based on LAMOST survey may significantly increase the size of the alpha-poor sample and the follow-up high-resolution spectroscopic analysis will be performed for research on their abundance pattern and origin.

大部分贫金属晕族恒星具有增丰的alpha元素丰度，但多项研究在银晕中发现了一些不符合这一增丰趋势的异常恒星，它们表现出明显偏低的[α/Fe]，表明这类贫alpha恒星具有不同于大部分晕族恒星的化学增丰史。类似具有偏低[α/Fe]的恒星在银河系近邻矮星系中普遍存在，目前普遍认为银晕中的贫alpha恒星源自银河系的近邻矮星系。由于目前发现的贫alpha恒星数量较少，我们对这类恒星的形成机制和其在银河系中所占比例仍知之甚少，为了对它们展开更为全面和深入的研究，亟需在银河系内发现更多的贫alpha恒星。本项目旨在利用LAMOST光谱巡天数据开展对贫alpha恒星的大规模搜寻，扩大贫alpha恒星的样本规模，并利用后续的高分辨率光谱分析研究其丰度特征和形成机制。

银河系晕中的贫金属星普遍具有增丰的alpha元素（镁、硅、钙、钛等）丰度，然而观测发现银晕中存在少量alpha元素丰度异常偏低的贫金属星，这类贫alpha恒星偏离银河系晕族恒星的丰度分布趋势，显示它们经历了特殊的化学增丰过程。由于已知的贫alpha晕星的数量极少,一直以来我们对这类恒星的起源和形成机制知之甚少。本项目基于LAMOST光谱巡天项目开展了对贫alpha晕族恒星的大规模搜寻，新发现了上百颗贫alpha晕星，极大地扩展了该类恒星的样本规模，并利用昴星团望远镜对贫alpha晕星进行了高分辨率光谱观测，明确了它们起源自被银河系瓦解的矮星系。矮星系相对较慢的化学演化过程导致了贫alpha恒星具有异常偏低的alpha元素丰度。