The formation of a blue cluster in the local Universe

It is well known from the Butcher-Oemler effect that galaxies in dense environment are mostly red with little star formation and the fraction of blue galaxies in galaxy groups/clusters also declines rapidly with redshifts.A recent work by Hashimoto et al.reported a local ‘blue cluster’ with a high fraction of blue galaxies(∼0.57),higher than the model predictions.They ascribed this blue cluster to the feeding of gas along a filamentary structure around the cluster.In this work we use group catalog from the Sloan Digital Sky Survey Data Release 7(SDSS DR7) and the state-of-art of semi-analytic model(SAM) to investigate the formation of blue clusters in the local Universe.In total,we find four blue clusters with halo mass ∼10^14 M⊙ at 0.02 <z<0.082,while only the one found by Hashimoto et al.is in a filamentary structure.The SAM predicts that blue clusters have later formation time and most blue satellite galaxies are recently accreted.We conclude that the formation of blue clusters is mainly governed by newly accreted blue satellites,rather than the effect of large-scale environment.

Candidate members of star clusters from LAMOST DR2

In this work, we provide 2189 photometrically- and kinematically-selected candidate members of 24 star clusters from the LAMOST DR2 catalog. We perform two-step membership identification： selection along the stellar track in the colormagnitude diagram, i.e., photometric identification, and selection from the distribution of radial velocities, i.e. the kinematic identification. We find that the radial velocities from the LAMOST data are very helpful in the membership identification. The mean probability of membership is 40% for the sample selected with radial velocity. With these 24 star clusters, we investigate the performance of the radial velocity and metallicity estimated with the LAMOST pipeline. We find that the systematic offsets in radial velocity and metallicity are 0.85 ± 1.26 km s-1and-0.08 ± 0.04 dex, with dispersions of 5.47＋1.16-0.71 km s-1and 0.13＋0.04-0.02 dex, respectively. Finally, we propose that the photometrically-selected candidate members of the clusters covered by the LAMOST footprint should be assigned higher priority so that more candidate stars can be observed.

A cluster-based analysis of propagation characteristics in MIMO relay channels based on wideband measurement

In this paper, the characteristics of clusters induced by a variety of propagation mechanisms in the link from the relay station （RS） to the mobile station （MS） are presented. Based on the results of high resolution channel parameter estimation, an automatic framework integrated with the manual intervention is utilized to perform the cluster identification and tracking. The power proportion and angular spread of clusters are investigated in both the line-of-sight （LOS） and non-line-of-sight （NLOS） scenarios. The measurement results indicate that the channel characteristics of clusters are different from the link from the base station to the MS due to the lower height of the RS antennas.