摘要
红团簇巨星(red clump giant)被理论和观测证明是非常理想的标准烛光,可以用来精确测量天体的距离.利用2MASS星表(the two micron all sky survey)提供的近红外测光数据和UCAC4天体测量星表(the fourth U.S.naval observatory CCD astrograph catalog)提供的自行等数据分析了疏散星团M67,结合自行、颜色-星等图、高精度视向速度和金属丰度,能够辨认出7颗红团簇巨星是M67的成员星.这7颗红团簇巨星的视向速度、金属丰度以及KS星等值高度一致.基于这7颗红团簇巨星计算得到M67的绝对距离模数为9.48±0.04 mag(或表示成距离787±15 pc),比基于主序拟合法得到的距离明显偏小.分析显示有1颗红团簇巨星以18±10 km/s的速度相对于星团核心运动,原因可能是星团内部动力学演化导致能量均分,小质量恒星在碰撞中获得了更高的速度,从星团中逃逸.
2MASS （the two micron all sky survey） near-infrared data and UCAC4 （the fourth U.S. naval observatory CCD astrograph catalog） data have been used to analyze the old open cluster M67. Seven red clump giants are found in the color-magnitude diagram, and all can be identified as membership by their accurate radial velocities and metallcities. Using the seven red clump giants, the absolute distance modulus of M67 is determined to be 9.48±0.04 mag （787±15 pc）, which is significantly lower than the values derived based on main-sequence fitting. Reasons for this discrepancy are discussed. In addition, a systematic analysis of positions and proper motions of the red clump giants reveals that one is escaping from M67 at a speed of 18±10 km/s. One possible explanation is that internal dynamical relaxation of M67 led to mass segregation; energy equipartition has brought to a redistribution of the stars within the cluster; massive stars would preferentially sink towards the center of the cluster; while low mass stars populate the cluster halo. Low mass stars with higher velocities would evaporate from the cluster halo.
出处
《科学通报》
EI
CAS
CSCD
北大核心
2013年第27期2790-2794,共5页
Chinese Science Bulletin
基金
国家自然科学基金(61063021)
常州大学校基金(ZMF1002121)资助
