成员判定是疏散星团研究中最关键的一步,成员判定的好坏直接影响对星团基本参数的估计.首次利用数据挖掘技术中的DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法对疏散星团NGC 6791和M67(NGC 2682)分别...成员判定是疏散星团研究中最关键的一步,成员判定的好坏直接影响对星团基本参数的估计.首次利用数据挖掘技术中的DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法对疏散星团NGC 6791和M67(NGC 2682)分别进行了成员判定,结果表明DBSCAN聚类算法能很有效地剔除场星污染.得到的NGC6791成员星的颜色-星等图上主序清晰并呈现明显的双重主序结构,这表明NGC 6791可能有更复杂的恒星形成与演化历史.对M67的分析表明出现了质量分层现象,并且星团的核心和外围两部分有明显的相对运动.对NGC 6791和M67的分析均表明DBSCAN聚类算法是一种有效的成员判定方法,有传统成员判定方法不具备的一些优点.展开更多
We present metallicities and radial velocities for five old open clusters （NGC 6791, NGC 2420, NGC 2682, NGC 2158, and NGC 7789） using data from the seventh public data release of the Sloan Digital Sky Survey （SDSS...We present metallicities and radial velocities for five old open clusters （NGC 6791, NGC 2420, NGC 2682, NGC 2158, and NGC 7789） using data from the seventh public data release of the Sloan Digital Sky Survey （SDSS）, which includes the directed stellar program SEGUE： Sloan Extension For Galactic Understanding and Exploration. The radial velocities are used to calculate cluster membership probabilities for stars in each cluster region. NGC 6791, NGC 2420, NGC 2682, NGC 2158 and NGC 7789 are found to have mean metallicities [Fe/H]= ＋0.08 ± 0.09, -0.38± 0.11, -0.08±0.05, -0.41 ±0.13 and -0.19 ± 0.13 dex （s.d.）, respectively. The mean radial velocities for NGC 6791, NGC 2420, NGC 2682, NGC 2158 and NGC 7789 are Vr = -45.9 ± 0.2, ＋76.1 ± 0.2, ＋35.0 ± 0.2, ＋26.9 ± 0.2 and -48.2± 0.2 km s^-1（s.e.m.）, respectively. We have compared our results with the values from literatures, and found that our metallicity of NGC 6791 is significantly underestimated （by about 0.3 dex） and our radial velocities of the open clusters agree well with the values derived using high-resolution spectroscopy.展开更多
The Ultra Violet Imaging Telescope （UVIT） is one of the payloads on the first Indian multiwavelength satellite ASTROSAT, which is expected to be launched by the Indian Space Research Organisation （ISRO） in the yea...The Ultra Violet Imaging Telescope （UVIT） is one of the payloads on the first Indian multiwavelength satellite ASTROSAT, which is expected to be launched by the Indian Space Research Organisation （ISRO） in the year 2015. We have per- formed simulations of UV studies of old open clusters for the UVIT. The colour mag- nitude diagrams （CMDs） and spatial appearances have been created using 10 filters associated with the FUV channel （130-180 nm） and NUV channel （200-300 nm） that are available for observations on the UVIT, for the three old open clusters M67, NGC 188 and NGC 6791. The CMDs are simulated for different filter combinations, and they are used to identify the loci of various evolutionary sequences, white dwarfs, blue stragglers, red giants, subgiants, turn off stars and the main sequence of the clus- ters. The present work helps in identifying a potential area of study in the case of these three old open clusters by considering the availability of filters and the detection limits of the instrument. We also recommend filter combinations, which can be used to detect and study the above mentioned evolutionary stages. The simulations and the results presented here are essential for the optimal use of the UVIT for studies of old open clusters.展开更多
基金funded by the National Natural Science Foundation of China(Grant No.10773021)the Key Project No.10833005+1 种基金the Group Innovation Project No.10821302the 973 program with NKBRSFG 2007CB815403
文摘We present metallicities and radial velocities for five old open clusters （NGC 6791, NGC 2420, NGC 2682, NGC 2158, and NGC 7789） using data from the seventh public data release of the Sloan Digital Sky Survey （SDSS）, which includes the directed stellar program SEGUE： Sloan Extension For Galactic Understanding and Exploration. The radial velocities are used to calculate cluster membership probabilities for stars in each cluster region. NGC 6791, NGC 2420, NGC 2682, NGC 2158 and NGC 7789 are found to have mean metallicities [Fe/H]= ＋0.08 ± 0.09, -0.38± 0.11, -0.08±0.05, -0.41 ±0.13 and -0.19 ± 0.13 dex （s.d.）, respectively. The mean radial velocities for NGC 6791, NGC 2420, NGC 2682, NGC 2158 and NGC 7789 are Vr = -45.9 ± 0.2, ＋76.1 ± 0.2, ＋35.0 ± 0.2, ＋26.9 ± 0.2 and -48.2± 0.2 km s^-1（s.e.m.）, respectively. We have compared our results with the values from literatures, and found that our metallicity of NGC 6791 is significantly underestimated （by about 0.3 dex） and our radial velocities of the open clusters agree well with the values derived using high-resolution spectroscopy.
文摘The Ultra Violet Imaging Telescope （UVIT） is one of the payloads on the first Indian multiwavelength satellite ASTROSAT, which is expected to be launched by the Indian Space Research Organisation （ISRO） in the year 2015. We have per- formed simulations of UV studies of old open clusters for the UVIT. The colour mag- nitude diagrams （CMDs） and spatial appearances have been created using 10 filters associated with the FUV channel （130-180 nm） and NUV channel （200-300 nm） that are available for observations on the UVIT, for the three old open clusters M67, NGC 188 and NGC 6791. The CMDs are simulated for different filter combinations, and they are used to identify the loci of various evolutionary sequences, white dwarfs, blue stragglers, red giants, subgiants, turn off stars and the main sequence of the clus- ters. The present work helps in identifying a potential area of study in the case of these three old open clusters by considering the availability of filters and the detection limits of the instrument. We also recommend filter combinations, which can be used to detect and study the above mentioned evolutionary stages. The simulations and the results presented here are essential for the optimal use of the UVIT for studies of old open clusters.
