Three Moving Groups Detected in the LAMOST DR1 Archive

We analyze the kinematics of thick disk and halo stars observed by the Large sky Area Multi-Object Fiber Spectroscopic Telescope. We have constructed a sample of 7,993 F, G and K nearby main-sequence stars (\textit{d} $<$ 2 kpc) with estimates of position (x, y, z) and space velocity ($U$, $V$, $W$) based on color and proper motion from the SDSS DR9 catalog. Three `phase-space overdensities' are identified in [\textit{V}, $\sqrt{U^{2}+2V^{2}}$] with significance levels of $\sigma$ $>$ 3. %[L$_{Z}$, eccentricity], [L$_{Z}$, L$_{\bot}$], and [V$_{az}$, V$_{\triangle}E$]. Two of them (Hyades-Pleiades stream, Arcturus-AF06 stream) have been identified previously. We also find evidence for a new stream (centered at \textit{V} $\sim$ -180 km s$^{-1}$) in the halo. The formation mechanisms of these three streams are analyzed. Our results support the hypothesis the Arcturus-AF06 stream and the new stream originated from the debris of a disrupted satellite, while Hyades-Pleiades stream has a dynamical origin.Comment: 7 pages, 5 figure

Stellar Stream Candidates in the Solar Neighborhood Found in the LAMOST DR3 and TGAS

We have cross-matched the LAMOST DR3 with the Gaia DR1 TGAS catalogs and obtained a sample of 166,827 stars with reliable kinematics. A technique based on the wavelet transform was applied to detect significant overdensities in velocity space among five subsamples divided by spatial position. In total, 16 significant overdensities of stars with very similar kinematics were identified. Among these, four are new stream candidates and the rest are previously known groups. Both the U-V velocity and metallicity distributions of the local sample show a clear gap between the Hercules structure and the Hyades-Pleiades structure. The U-V positions of these peaks shift with the spatial position. Following a description of our analysis, we speculate on possible origins of our stream candidates.Comment: 16 pages, 5 figure

Abundance gradients in the galactic disk

The relationship between abundances and orbital parameters for 235 F- and G-type intermediate- and low- mass stars in the Galaxy is analyzed. We found that there are abundance gradients in the thin disk in both radial and vertical directions (-0.116 dex/kpc and -0.309 dex/kpc respectively). The gradients appear to be flatter as the Galaxy evolves. No gradient is found in the thick disk based on 18 thick disk stars. These results indicate that the ELS model is mainly suitable for the evolution of the thin disk, while the SZ model is more suitable for the evolution of the thick disk. Additionally, these results indicate that in-fall and out-flow processes play important roles in the chemical evolution of the Galaxy.Comment: 10 pages, 2 figures. Published in Science in China (Series G) vol 46(1), 200

A Catalog of Moving Group Candidates in The Solar Neighborhood

Based on the kernel estimator and wavelet technique, we have identified 22 moving group candidates in the solar neighborhood from a sample which includes around 14,000 dwarfs and 6000 giants. Six of them were previously known as the Hercules stream, the Sirus-UMa stream, the Hyades stream, the Caster group, the Pleiades stream, and the IC 2391; five of them have also been reported by other authors. 11 moving group candidates, not previously reported in the literature, showprominent structures in dwarf or giant samples.Acatalog of moving group candidates in the solar neighborhood is presented in this work.Comment: 5 pages, 3 figures, accepted for publication in Astrophysical Journal Letter

Evidence for Co-rotation Origin of Super Metal Rich Stars in LAMOST-Gaia: Multiple Ridges with a Similar Slope in phi versus Lz Plane

Super metal-rich (SMR) stars in the solar neighborhood are thought to be born in the inner disk and came to present location by radial migration, which is most intense at the co-rotation resonance (CR) of the Galactic bar. In this work, we show evidence for the CR origin of SMR stars in LAMOST-Gaia by detecting six ridges and undulations in the phi versus Lz space coded by median VR, following a similar slope of -8 km/s kpc/deg. The slope is predicted by Monario et al.'s model for CR of a large and slow Galactic bar. For the first time, we show the variation of angular momentum with azimuths from -10 deg to 20 deg for two outer and broad undulations with negative VR around -18 km/s following this slope. The wave-like pattern with large amplitude outside CR and a wide peak of the second undulations indicate that minor merger of the Sagittarius dwarf galaxy with the disk might play a role besides the significant impact of CR of the Galactic bar.Comment: 5 pages, 3 figures, published in ApJ Lette

Research on reverse logistics location under uncertainty environment based on grey prediction

AbstractThis article constructs reverse logistic network based on uncertain environment, integrates the reverse logistics network and distribution network, and forms a closed network. An optimization model based on cost is established to help intermediate center, manufacturing center and remanufacturing center make location decision. A gray model GM (1, 1) is used to predict the product holdings of the collection points, and then prediction results are carried into the cost optimization model and a solution is got. Finally, an example is given to verify the effectiveness and feasibility of the model