利用APOGEE的超富金属星研究银盘恒星的径向迁移效应  

Radial Migration of the Galactic Disk Based on Super Metal-rich Stars in the APOGEE Survey

作　　者：曲大铭 陈玉琴[1,2] 张浩鹏 赵刚 Qu Daming;Chen Yuqin;Zhang Haopeng;Zhao Gang(Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100101,China;School of Astronomy and Space Science,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院光学天文重点实验室(国家天文台),北京100101 [2]中国科学院大学天文与空间科学学院,北京100049

出　　处：《天文研究与技术》2020年第3期265-275,共11页Astronomical Research & Technology

基　　金：国家自然科学基金(11988101,11625313,11890694);国家重点研发计划(2019YFA0405500)资助。

摘　　要：从APOGEE DR14巡天数据中选取[Fe/H]>0.2 dex的超富金属星,利用GAIADR2提供的距离和自行以及APOGEE的视向速度计算它们的运动学和轨道参数,探讨银盘恒星的径向迁移效应。研究发现,绝大多数超富金属星经历了径向迁移过程,通过共振(Churning)或模糊(Blurring)效应起作用。发生共振迁移的恒星(即|Rg-Rb|>1 kpc)占总样本数的95.9%,而发生模糊迁移的样本星(即|R-Rg|>1 kpc)占总样本数的50.5%,表明共振迁移在银盘演化中占主导地位。共振迁移距离(|Rg-Rb|集中分布在2~5 kpc)比模糊迁移距离(|R-Rg|集中分布在1~2 kpc)更大。细致分析了共振迁移效应在银河系内盘、太阳邻域和外盘等不同区域的影响,发现外盘的共振径向迁移效应比内盘更剧烈。这些超富金属星的径向迁移特征可以用银河系棒和旋臂共同作用的N体-化学动力学模型解释。由于超富金属星诞生于银河系内盘3~5 kpc处,正好落在棒的共转共振区(4.7 kpc)附近,它们在剧烈的共振共转作用下被加速向外迁移2~5 kpc以后,到达外林德布拉德(1/2本轮频率)共振区(7.5 kpc)附近,在这里它们再次被加速并迁移至外盘(12 kpc以外)。最后证实了APOGEE数据也存在年轻的超富金属星,它们主要是红团簇第二序列的恒星,它们的共振迁移率远大于棒模型预言的理论值,因此需要其它的物理机制来解释。Super metal-rich stars with[Fe/H]>0.2 dex are selected from APOGEE DR14,their kinematical parameters,spatial velocities and orbital parameters are calculated based on Gaia DR2 data.The birth sites are estimated from metallicity and age.It is found that most of super metal-rich stars belong to the thin disk based on their low[α/Fe]ratios and they undergo radial migration with 95.9%stars caused by churning and 50.5%stars by blurring.Migration distances due to churning peak at 2-5 kpc,which is larger than that caused by blurring(with a peak of 1-2 kpc).Thus,churning dominates(over blurring)during the evolution of the Galactic thin disk.It is found that migration distance due to churning increases with guiding radius when the sample is divided into different regions representing the inner disk,solar neighborhood and the outer disk.We propose a reasonable picture to explain these results as follows.Based on the N-body-chemo-dynamical model by Minchev et al,the bar's corotation resonance(at 4.7 kpc)can bring these stars from their birth sites(3-5 kpc)to solar neighborhood of 7-9 kpc.Then some super metal-rich stars are further accelerated at the 2:1 outer Lindblad resonance region(at 7.5 kpc)and migrated outward by 4-8 kpc,reaching the outer disk(10 kpc and beyond).Finally,we confirm the existence of young super metal-rich stars with age less than 1.0 gigayear in the APOGEE data.Since their migration rate is much higher than that predicted by the bar model,other mechanisms of radial migration should be introduced to explain their behaviors.

关 键 词：超富金属星 径向迁移 共转共振 

分 类 号：TN216[电子电信—物理电子学]