Discovery of high-velocity EHB stars in the globular cluster ωCentauri(NGC 5139)  

作　　者：Xin-Hua Gao Shou-Kun Xu Li Chen 

机构地区：[1]School of Information Science and Engineering,Changzhou University [2]Shanghai Astronomical Observatory,Chinese Academy of Sciences

出　　处：《Research in Astronomy and Astrophysics》2015年第10期1639-1646,共8页天文和天体物理学研究（英文版）

基　　金：supported by the National Natural Science Foundation of China(NSFC,Grant No.11403004);the School Foundation of Changzhou University(ZMF1002121);support by the 973 Program(2014CB845702);the Strategic Priority Research Program The Emergence of Cosmological Structures of the Chinese Academy of Sciences(CAS;grant XDB09010100);by the NSFC(No.11373054)

摘　　要：Abstract We report the discovery of 45 high-velocity extreme horizontal branch （EHB） stars in the globular cluster Omega Centauri （NGC 5139）. The tangential ve- locities of these EHB stars are determined to be in the range 93-313 km s^-1, with an average uncertainty of -27 km s^-1. The central escape velocity of the cluster is determined to be in the range 60~105 km s^-1. These EHB stars are significantly more concentrated toward the cluster core compared with other cluster members. The formation mechanisms of these EHB stars are discussed. Our conclusions can be sum- marized as follows： （1） A comparison of the tangential velocities of these EHB stars to the central escape velocity of the cluster shows that most if not all of these EHB stars are unbound to the cluster; （2） These EHB stars obtained high velocities in the central cluster region no longer than - 1 Myr ago and may be subsequently ejected from the cluster in the next -1 Myr; （3） If the progenitors of these EHB stars were single stars, then they may have experienced a fast mass-loss process. If the progen- itors were in close binaries, then they may have formed through disruptions by the intermediate-mass black hole in the cluster center.Abstract We report the discovery of 45 high-velocity extreme horizontal branch （EHB） stars in the globular cluster Omega Centauri （NGC 5139）. The tangential ve- locities of these EHB stars are determined to be in the range 93-313 km s^-1, with an average uncertainty of -27 km s^-1. The central escape velocity of the cluster is determined to be in the range 60~105 km s^-1. These EHB stars are significantly more concentrated toward the cluster core compared with other cluster members. The formation mechanisms of these EHB stars are discussed. Our conclusions can be sum- marized as follows： （1） A comparison of the tangential velocities of these EHB stars to the central escape velocity of the cluster shows that most if not all of these EHB stars are unbound to the cluster; （2） These EHB stars obtained high velocities in the central cluster region no longer than - 1 Myr ago and may be subsequently ejected from the cluster in the next -1 Myr; （3） If the progenitors of these EHB stars were single stars, then they may have experienced a fast mass-loss process. If the progen- itors were in close binaries, then they may have formed through disruptions by the intermediate-mass black hole in the cluster center.

关 键 词：Galaxy： globular clusters： individual： ω Cen （NGC 5139） -- stars：Hertzsprung-Russell and C-M diagrams -- stars： kinematics and dynamics -- stars：binaries （including multiple）： close 

分 类 号：P154.12[天文地球—天文学] V435[航空宇航科学与技术—航空宇航推进理论与工程]