1,368 research outputs found
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 (, , ) based
on color and proper motion from the SDSS DR9 catalog. Three `phase-space
overdensities' are identified in [\textit{V}, ] with
significance levels of 3. %[L, eccentricity], [L,
L], and [V, V].
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} -180 km s) 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
Multi-Level Opinion Dynamics under Bounded Confidence
Opinion dynamics focuses on the opinion evolution in a social community. Recently, some models of continuous opinion dynamics under bounded confidence were proposed by Deffuant and Krause, et al. In the literature, agents were generally assumed to have a homogeneous confidence level. This paper proposes an extended model for a group of agents with heterogeneous confidence levels. First, a social differentiation theory is introduced and a social group is divided into opinion subgroups with distinct confidence levels. Second, a multi-level heterogeneous opinion formation model is formulated under the framework of bounded confidence. Finally, computer simulations are conducted to study the collective opinion evolution, focusing on three key factors: the fractions of heterogeneous agents, the initial opinions, and the group size. The simulation results demonstrate that the number of final opinions depends on the fraction of closeminded agents when the group size and the initial opinions are fixed; the final opinions converge more easily when the initial opinions are closer; and the number of final opinions can be approximately modeled by a linear increasing function of the group size and the increasing rate is the fraction of close-minded agents
White dwarf-main sequence binaries from LAMOST: the DR1 catalogue
Context. White dwarf-main sequence (WDMS) binaries are used to study several
different important open problems in modern astrophysics.
Aims. The Sloan Digital Sky Survey (SDSS) identified the largest catalogue of
WDMS binaries currently known. However, this sample is seriously affected by
selection effects and the population of systems containing cool white dwarfs
and early-type companions is under-represented.Here we search for WDMS binaries
within the spectroscopic data release 1 of the LAMOST (Large sky Area
Multi-Object fiber Spectroscopic Telescope) survey. LAMOST and SDSS follow
different target selection algorithms. Hence, LAMOST WDMS binaries may be drawn
from a different parent population and thus help in overcoming the selection
effects incorporated by SDSS on the current observed population.
Methods. We develop a fast and efficient routine based on the wavelet
transform to identify LAMOST WDMS binaries containing a DA white dwarf and a M
dwarf companion, and apply a decomposition/fitting routine to their LAMOST
spectra to estimate their distances and measure their stellar parameters,
namely the white dwarf effective temperatures, surface gravities and masses,
and the secondary star spectral types.
Results. We identify 121 LAMOST WDMS binaries, 80 of which are new
discoveries, and estimate the sample to be \sim90 per cent complete. The LAMOST
and SDSS WDMS binaries are found to be statistically different. However, this
result is not due to the different target selection criteria of both surveys,
but likely a simple consequence of the different observing conditions. Thus,
the LAMOST population is found at considerably shorter distances (\sim50-450
pc) and is dominated by systems containing early-type companions and hot white
dwarfs. (abridged)Comment: 14 pages, 8 figures, accepted for publication in A&
Revisit of open clusters UPK 39, UPK 41 and PHOC 39 : a new binary open cluster found
We investigate the three open clusters near Aquila Rift cloud, named as UPK
39 (\texttt{c1} hereafter), UPK 41 (\texttt{c2} hereafter) in Sim et al. (2019)
and PHOC 39 (\texttt{c3} hereafter) in Hunt \& Reffert (2021), respectively.
Using photometric passpands, reddening, and extinction from Gaia DR3, we
construct the color-absolute-magnitude diagram (CAMD). Using isochrone fits
their ages are estimated as , and Myr,
respectively. Their proper motions and radial velocities, estimated using data
from Gaia and LAMOST are very similar. From their orbits, relative distances
among them at different times, kinematics, ages, and metallicities, we conclude
that \texttt{c1} and \texttt{c2} are primordial binary open cluster, which are
likely to have been formed at the same time, and \texttt{c3} may capture
\texttt{c1}, \texttt{c2} in the future.Comment: 11 pages, 8 figures, 1 table. Accepted for publication in A
Revisit of Open Clusters Upk 39, Upk 41 and Phoc 39 : A New Binary Open Cluster Found
We investigate the three open clusters near Aquila Rift cloud, named as UPK 39 (c1 hereafter), UPK 41 (c2 hereafter) in Sim et al. (2019) and PHOC 39 (c3 hereafter) in Hunt & Reffert (2021), respectively. Using photometric passpands, reddening, and extinction from Gaia DR3, we construct the color-absolute-magnitude diagram (CAMD). Using isochrone fits their ages are estimated as 6.3 ± 0.9, 8.1 ± 1.4 and 21.8 ± 2.2 Myr, respectively. Their proper motions and radial velocities, estimated using data from Gaia and LAMOST are very similar. From their orbits, relative distances among them at different times, kinematics, ages, and metallicities, we conclude that c1 and c2 are primordial binary open cluster, which are likely to have been formed at the same time, and c3 may capture c1, c2 in the future
Study on the Safety Management of Connected and Autonomous Vehicle Test Roads Based on the Evaluation of Traffic Safety Facilities
More and more connected and autonomous vehicle (CAV) open test roads reconstructed on the basis of traditional roads have appeared in China. However, the management policies vary, which makes the traffic environment complicated. This paper takes CAV test road safety management as the research aim and investigates the open test condition through the evaluation of the traffic safety facilities. Indicators were rigorously screened, then the game theory model was used to determine the combination weight of the indicators, and the set pair analysis was applied to solve the uncertain problems. A case study for the CAV test road network of a city in central China was implemented and the results show, regarding the traffic safety facilities’ condition, among the 20 sections of the city’s CAV test road network, 15% of which are at an excellent level, 75% of which are at a good level and 10% of which are at a moderate level; road signs, guardrail facilities, isolation facilities and road features are the main limiting factors affecting the level of traffic safety facilities. Based on the results, recommendations have been made for the transport management authorities in the aspects of safety management policy-making and facilities maintenance
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