基于SDSS-DR8及2MASS数据的疏散星团NGC 6791的基本性质研究

利用斯隆数字巡天（SDSS）第8次释放数据（DR8）的恒星光谱数据及2MASS（Two Micro All Sky Survey）近红外点源测光数据研究著名的疏散星团NGC 6791,得到该星团的视向速度与金属丰度分别为V_r=-46.4±0.2 km·s^-1和Fe/H]=0.32±0.11dex.利用星团中红团簇巨星作为理想"标准烛光",结合2MASS近红外点源测光数据计算了该星团的绝对距离模数为（m-M）₀=13.02±0.08 mag或4.02±0.15 kpc.与其他研究者给出的结果进行了比较,金属丰度、视向速度及绝对距离模数都符合得比较好.主要结论有3点:（1）NGC 6791是个极度富金属的星团;（2）在SDSS的光谱分辨能力以内,分离出的87颗团星之间不存在明显的金属丰度差异;（3）得到的距离模数对年龄、金属丰度及尘埃消光不敏感,是一种可靠的间接测量.

A Study on the Fundamental Characteristics of Open Cluster NGC 6791 Based on SDSS-DR8 and 2MASS Data

SDSS-DR8（The Eighth Data Release of Sloan Digital Sky Survey） and 2MASS （Two Micro All Sky Survey） data are used to analyze the fundamental parameters of the open cluster NGC 6791.Using the radial velocities of 274 stars in the region of the cluster, we calculate the membership probability for each star with the maximum likelihood method.Based on the stars with high membership probabilities,we derive a mean radial velocity value V_r = -46.4±0.2 km·s^-1 and a mean metallicity valueFe/H]= 0.32±0.11 dex. Using red clump giants in the cluster as a kind of excellent distance indicator,we derive an absolute distance modulus value（m - M）₀ = 13.02±0.08 mag or distance 4.02±0.15 kpc.We therefore confirm that NGC 6791 is extremely metal-rich,and within the resolution of SDSS spectra,NGC 6791 does not show any evidence of internal spread in metallicity. The radial velocity and metallicity obtained by us are in good agreement with the values reported by other authors based on high-resolution spectra.Our derived absolute distance modulus based on red clump giants is also consistent with the values obtained from main sequence fittings by some authors.