贫金属富碳天琴RR变星的形成  

Formation of Carbon-Enhanced Metal-Poor RR Lyrae Stars

作　　者：夏晔 张先飞 毕少兰 马旭东 XIA Ye;ZHANG Xian-fei;BI Shao-lan;MA Xu-dong(Department of Astronomy,Beijing Normal University,Beijing 100875)

机构地区：[1]北京师范大学天文系

出　　处：《天文学报》2019年第5期54-61,共8页Acta Astronomica Sinica

基　　金：国家自然科学基金项目(10933002、11703001、11273007)资助

摘　　要：贫金属富碳恒星(Carbon-Enhanced Metal-Poor,CEMP)是研究宇宙早期恒星性质和化学演化的极佳样本,通常认为来自双星.目前发现的贫金属富碳星中有9颗天琴RR变星(RR Lyrae star,RRL),其中至少7颗未表现出任何双星特征.传统双星物质转移模型不足以充分解释贫金属富碳天琴RR变星(CEMP-RR Lyrae)单星的形成.之前研究表明氦白矮星和赫氏空隙星(HG)的并合模型可以解释部分富碳红巨星单星的碳增丰现象,因此贫金属富碳星单星也可能来自氦白矮星和赫氏空隙星的并合模型渠道.通过详细计算的氦白矮星和赫氏空隙星并合模型来检验这一演化渠道,结果表明:该并合模型在后续的演化过程中,其重力加速度、温度、表面碳丰度均能与观测符合较好.由此,氦白矮星和赫氏空隙星并合模型极有可能是贫金属富碳天琴RR变星的形成渠道之一.Carbon-enhanced metal-poor stars(CEMPs)are considered to be related to the first generation of stars,and responsible for the chemical evolution of the early galaxy.More than half of them are in binaries,and could be explained by binary evolution,but the formation channel of them is still not fully understood.Of the hundreds of carbon-enhanced metal-poor stars,there are nine carbon-enhanced metal-poor RR Lyrae stars(CEMP-RR Lyrae)have been identified,and at least seven of them are very likely not binaries.The usual binary star evolution channel is difficult to produce such single star,particularly with enrich of carbon.One way in which such a single star might be formed is after the merger of a helium white dwarf with a Hertzsprung star.We use a stellar evolution code to calculate models of the remnants of the mergers,andfind that the models can reproduce the observed distribution of such carbon-enhanced metal-poor single RR Lyrae stars in terms of their surface temperatures,gravities,and carbon abundances.

关 键 词：恒星:丰度 恒星:变星:天琴RR型星 方法:数据分析 

分 类 号：P144[天文地球—天体物理]