As part of the LAMOST medium-resolution spectroscopic survey,the LAMOST-MRS-O is a non-time domain survey that aims to perform medium-resolution spectral observations for member stars in the open cluster areas.This su...As part of the LAMOST medium-resolution spectroscopic survey,the LAMOST-MRS-O is a non-time domain survey that aims to perform medium-resolution spectral observations for member stars in the open cluster areas.This survey plans to obtain the spectroscopic parameters such as radial velocity and metal abundances of member stars and provide data support for further study on the chemical and dynamical characteristics and evolution of open clusters in combination with Gaia data.We have completed the observations on ten open cluster fields and obtained 235184 medium-resolution spectra of 133792 stars.Based on the data analyzed of LAMOST DR11v1.1,for some clusters of particular concern,it is found that the sampling ratio of members stars with Gmag<15 mag can reach 70%,which indicates that the LAMOST-MRS-O has reached our initial design goal.展开更多
Recent studies have increasingly identified extended main sequence turn-off(e MSTO)phenomena in Galactic open clusters,yet the number of such clusters with sufficient spectroscopic information for member stars remains...Recent studies have increasingly identified extended main sequence turn-off(e MSTO)phenomena in Galactic open clusters,yet the number of such clusters with sufficient spectroscopic information for member stars remains limited.Unlike most studies that rely on fitting isochrones based on color–magnitude diagram(CMD)morphology to account for varying rotational velocities,our approach leverages LAMOST spectral data to compute actual rotational velocity distributions for confirmed cluster members,along with parameters such as metallicity,differential extinction,and rotational inclination,to utilize PARSEC isochrones for fitting the cluster CMDs.We systematically surveyed all known Galactic open clusters and selected 12 clusters where rotational velocity distributions could be reliably calculated for detailed fitting.Our results successfully reproduced the eMSTO phenomenon observed in these clusters.For the majority of clusters,considering only differential extinction and variations in rotational velocity adequately explains the position and morphology of the MSTO.For some intermediate-age clusters,incorporating rotational inclination additionally accounts for the broadening of the MSTO.This study underscores the importance of spectroscopic data in understanding eMSTO phenomena and provides a probable explanation for interpreting the combined effects of differential extinction,rotation,and inclination on the CMDs of Galactic open clusters.展开更多
There may be several internal defects in railway track work that have different shapes and distribution rules,and these defects affect the safety of high-speed trains.Establishing reliable detection models and methods...There may be several internal defects in railway track work that have different shapes and distribution rules,and these defects affect the safety of high-speed trains.Establishing reliable detection models and methods for these internal defects remains a challenging task.To address this challenge,in this study,an intelligent detection method based on a generalization feature cluster is proposed for internal defects of railway tracks.First,the defects are classified and counted according to their shape and location features.Then,generalized features of the internal defects are extracted and formulated based on the maximum difference between different types of defects and the maximum tolerance among same defects’types.Finally,the extracted generalized features are expressed by function constraints,and formulated as generalization feature clusters to classify and identify internal defects in the railway track.Furthermore,to improve the detection reliability and speed,a reduced-dimension method of the generalization feature clusters is presented in this paper.Based on this reduced-dimension feature and strongly constrained generalized features,the K-means clustering algorithm is developed for defect clustering,and good clustering results are achieved.Regarding the defects in the rail head region,the clustering accuracy is over 95%,and the Davies-Bouldin index(DBI)index is negligible,which indicates the validation of the proposed generalization features with strong constraints.Experimental results prove that the accuracy of the proposed method based on generalization feature clusters is up to 97.55%,and the average detection time is 0.12 s/frame,which indicates that it performs well in adaptability,high accuracy,and detection speed under complex working environments.The proposed algorithm can effectively detect internal defects in railway tracks using an established generalization feature cluster model.展开更多
We fit various color–magnitude diagrams(CMDs) of the high-latitude Galactic globular clusters NGC 5024(M53),NGC 5053,NGC 5272(M3),NGC 5466,and NGC 7099(M30) by isochrones from the Dartmouth Stellar Evolution Database...We fit various color–magnitude diagrams(CMDs) of the high-latitude Galactic globular clusters NGC 5024(M53),NGC 5053,NGC 5272(M3),NGC 5466,and NGC 7099(M30) by isochrones from the Dartmouth Stellar Evolution Database and Bag of Stellar Tracks and Isochrones for α–enrichment [α/Fe] = +0.4.For the CMDs,we use data sets from Hubble Space Telescope,Gaia,and other sources utilizing,at least,25 photometric filters for each cluster.We obtain the following characteristics with their statistical uncertainties for NGC 5024,NGC 5053,NGC 5272,NGC 5466,and NGC 7099,respectively:metallicities [Fe/H] =-1.93 ± 0.02,-2.08 ± 0.03,-1.60 ± 0.02,-1.95 ± 0.02,and-2.07 ± 0.04 dex with their systematic uncertainty 0.1 dex;ages 13.00 ± 0.11,12.70 ± 0.11,11.63 ± 0.07,12.15 ± 0.11,and 12.80 ± 0.17 Gyr with their systematic uncertainty 0.8 Gyr;distances(systematic uncertainty added) 18.22 ± 0.06 ± 0.60,16.99 ± 0.06 ± 0.56,10.08 ± 0.04 ± 0.33,15.59 ±0.03 ± 0.51,and 8.29 ± 0.03 ± 0.27 kpc;reddenings E(B-V) = 0.023 ± 0.004,0.017 ± 0.004,0.023 ± 0.004,0.023 ± 0.003,and 0.045 ± 0.002 mag with their systematic uncertainty 0.01 mag;extinctions AV= 0.08 ± 0.01,0.06 ± 0.01,0.08 ± 0.01,0.08 ± 0.01,and 0.16 ± 0.01 mag with their systematic uncertainty 0.03 mag,which suggest the total Galactic extinction AV= 0.08 across the whole Galactic dust to extragalactic objects at the North Galactic Pole.The horizontal branch morphology difference of these clusters is explained by their different metallicity,age,mass-loss efficiency,and loss of low-mass members in the evolution of the core-collapse cluster NGC 7099 and loose clusters NGC 5053 and NGC 5466.展开更多
Recent studies indicate that some Galactic open clusters(OCs)exhibit extended main-sequence turnoff(eMSTO)in their color–magnitude diagrams(CMDs).However,the number of Galactic OCs with eMSTO structures detected so f...Recent studies indicate that some Galactic open clusters(OCs)exhibit extended main-sequence turnoff(eMSTO)in their color–magnitude diagrams(CMDs).However,the number of Galactic OCs with eMSTO structures detected so far is limited,and the reasons for their formation are still unclear.This work identifies 26 Galactic OCs with undiscovered eMSTOs and investigates the causes of these features.Stellar population types and fundamental parameters of cluster samples are acquired using CMD fitting methods.Among them,the results of 11 OCs are reliable as the observed CMDs are well-reproduced.We propose the crucial role of stellar binarity and confirm the importance of stellar rotation in reproducing eMSTO morphologies.The results also show that the impact of age spread is important,as it can adequately explain the structure of young OCs and fit the observed CMDs of intermediate-age OCs better.展开更多
The inner Milky Way disk globular cluster NGC 6362 appears to exhibit tidal tails composed of stars that have proper motions and positions in the color–magnitude diagram similar to those of cluster stars. Because rec...The inner Milky Way disk globular cluster NGC 6362 appears to exhibit tidal tails composed of stars that have proper motions and positions in the color–magnitude diagram similar to those of cluster stars. Because recent results seem also to show that these stars are distributed across the regions least affected by interstellar absorption and reproduce the observed composite star field density map, we carried out a detailed spectroscopic analysis of a number of chemical element abundances of tidal tail star candidates in order to investigate the relationship between them and NGC 6362. From European Southern Observatory's VLT@FLAMES spectra we found that the red giant branch stars selected as the cluster's tidal tail stars neither have overall metallicities nor abundances of Mg, Ca, Sc, Ti, Cr, Ni and Ba similar to the cluster's ones. Moreover, they are mainly alike to stars that belong to the Milky Way thick disk, some of them could be part of the thin disk and a minor percentage could belong to the Milky Way halo star population. On the other hand, since the resulting radial velocities do not exhibit a distribution function similar to that of the cluster's stars, we concluded that looking for kinematic properties similar to those of the cluster would not seem to be as suitable of an approach for selecting the cluster's tidal tail stars as previously thought.展开更多
Binary stars are common in star clusters and galaxies, but the detailed ef- fects of binary evolution are not taken into account in some color-magnitude diagram （CMD） studies. This paper studies the CMDs of twelve g...Binary stars are common in star clusters and galaxies, but the detailed ef- fects of binary evolution are not taken into account in some color-magnitude diagram （CMD） studies. This paper studies the CMDs of twelve globular clusters via binary- star stellar populations. The observational CMDs of the star clusters are compared to those of binary-star populations, and then the stellar metallicities, ages, distances and reddenings of these star clusters are obtained. The paper also tests the different effects of binary and single stars on CMD studies. It is shown that binaries can better fit the observational CMDs of the sample globular clusters compared to single stars. This suggests that the effects of binary evolution should be considered when modeling the CMDs and stellar populations of star clusters and galaxies.展开更多
The red giant branch(RGB)of globular clusters(GCs)is home to some exotic stars,which may provide clues on the formation of multiple stellar populations in GCs.It is well known that binary interactions are responsible ...The red giant branch(RGB)of globular clusters(GCs)is home to some exotic stars,which may provide clues on the formation of multiple stellar populations in GCs.It is well known that binary interactions are responsible for many exotic stars.Thus,it is important to understand what fraction of stars on the RGB of GCs is the result of binary interactions.In this paper,we performed a binary population synthesis study to track the number of post-binary-interaction(post-BI)stars that appear on the RGB,with particular emphasis on the evolved blue straggler stars(E-BSSs).Assuming an initial binary fraction of nearly 50%,we find that about half of the objects on the RGB(called giants)underwent the binary interactions,and that E-BSSs account for around 10%of the giants in our standard simulation.We also compare the properties of post-BI giants that evolved from different channels.We find that the initial orbital period and mass ratio distributions significantly affect the fraction of post-BI giants.Our results imply that the non-standard stars from binary interactions provide a non-negligible contribution to the RGB stars in GCs,which should be considered in future investigations of the origin of multiple stellar populations.展开更多
As groups of coeval stars born from the same molecular cloud,an open cluster(OC)is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way.The release of high-precision Gaia Early Data ...As groups of coeval stars born from the same molecular cloud,an open cluster(OC)is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way.The release of high-precision Gaia Early Data Release 3(Gaia EDR3)and modern machine-learning methods offer unprecedented opportunities to identify OCs.In this study,we extended conventional HDBSCAN(e-HDBSCAN)for searching for new OCs in Gaia EDR3.A pipeline was developed based on the parallel computing technique to blindly search for OCs from Gaia EDR3within Galactic latitudes∣b∣<25°.As a result,we obtained 3787 star clusters,of which 83 new OCs were reported after cross-match and visual inspection.At the same time,the main star cluster parameters are estimated by color-magnitude diagram fitting.The study significantly increases the sample size and physical parameters of OCs in the catalog of OCs.It shows the incompleteness of the census of OCs across our Galaxy.展开更多
The motion of baryonic components of the Milky Way is governed by both luminous and dark matter content of the Galaxy.Thus,the dynamics of Milky Way globular clusters(GCs)can be used as tracers to infer the mass model...The motion of baryonic components of the Milky Way is governed by both luminous and dark matter content of the Galaxy.Thus,the dynamics of Milky Way globular clusters(GCs)can be used as tracers to infer the mass model of the Galaxy up to a large radius.In this work,we apply the directly observable line-of-sight velocities to test if the dynamics of the GC population are consistent with an assumed axisymmetric gravitational potential of the Milky Way.For this,we numerically compute the phase space distribution of the GC population where the orbits are either oriented randomly or co-/counter-rotating with respect to the stellar disk.Then we compare the observed position and line-of-sight velocity distribution of^150 GCs with those of the models.We found that,for the adopted mass model,the co-rotating scenario is the favored model based on various statistical tests.We do the analysis with and without the GCs associated with the progenitors of early merger events.This analysis can be extended in the near future to include precise and copious data to better constrain the Galactic potential up to a large radius.展开更多
We investigate pulsar timing residuals due to the coupling effect of the pulsar transverse acceleration and the Romer delay.The effect is relatively small and usually negligible.Only for pulsars in globular clusters,i...We investigate pulsar timing residuals due to the coupling effect of the pulsar transverse acceleration and the Romer delay.The effect is relatively small and usually negligible.Only for pulsars in globular clusters,it is possibly important.The maximum residual amplitude,which is from the pulsar near the surface of the core of the cluster,is about tens of nanoseconds,and may hardly be identified for most globular clusters currently.However,an intermediate-mass black hole in the center of a cluster can apparently increase the timing residual magnitudes.Particularly for pulsars in the innermost core region,their residual magnitudes may be significant.The high-magnitude residuals,which are above critical lines of each cluster,are strong evidence for the presence of a black hole or dark remnants of comparable total mass in the center of the cluster.We also explored the timing effects of line-of-sight accelerations for the pulsars.The distribution of measured line-of-sight accelerations are simulated with a Monte Carlo method.Two-dimensional Kolmogorov-Smirnov tests are performed to reexamine the consistency of distributions of the simulated and reported data for various values of parameters of the clusters.It is shown that the structure parameters of Terzan 5 can be constrained well by comparing the distribution of measured lineof-sight accelerations with the distributions from Monte Carlo simulations.We find that the cluster has an upper limit on the central black hole/dark remnant mass of~6000 M⊙.展开更多
We study the counts of resolved SZE (Sunyaev-Zel'dovich effect) clusters expected from an interferometric survey in different cosmological models under different conditions. The self-similar universal gas model an...We study the counts of resolved SZE (Sunyaev-Zel'dovich effect) clusters expected from an interferometric survey in different cosmological models under different conditions. The self-similar universal gas model and Press-Schechter mass function are used. We take the observing frequency to be 90 GHz, and consider two dish diameters, 1.2 m and 2.5 m. We calculate the number density of the galaxy clusters dN/(dΩdz) at a high flux limit S<SUB>v</SUB><SUP>lim</SUP>=100 mJy and at a relative low S<SUB>v</SUB><SUP>lim</SUP> =10 mJy. The total numbers of SZE clusters N in two low-Ω<SUB>0</SUB> models are compared. The results show that the influence of the resolved effect depends not only on D, but also on S<SUB>v</SUB><SUP>lim</SUP>: at a given D, the effect is more significant for a high than for a low S<SUB>v</SUB><SUP>lim</SUP>. Also, the resolved effect for a flat universe is more impressive than that for an open universe. For D = 1.2 m and S<SUB>v</SUB><SUP>lim</SUP> =10 mJy, the resolved effect is very weak. Considering the designed interferometers which will be used to survey SZE clusters, we find that the resolved effect is insignificant when estimating the expected yield of the SZE cluster surveys.展开更多
We investigate the mass-temperature relation of clusters for both the spherical NFW halo model and a concentric triaxial halo model. We study the temperature and density distributions of both an isothermal and a polyt...We investigate the mass-temperature relation of clusters for both the spherical NFW halo model and a concentric triaxial halo model. We study the temperature and density distributions of both an isothermal and a polytropic intra-cluster gas in hydrostatic equilibrium. We find that both the uncertainties in the concentration parameter and in the eccentricities (in case of the triaxial halo) lead to a greater scatter in the emission-weighted temperature at a given halo mass for less massive clusters. This may be helpful when determining the intrinsic statistical error of the σ<SUB>8</SUB> normalization of the linear power spectrum from cluster abundance.展开更多
Many evidences show that the Multiple Population(MP)features exist not only in old clusters but also in intermediate-age clusters in the Megallanic Clouds(MCs),which are characterized by star-to-star abundance scatter...Many evidences show that the Multiple Population(MP)features exist not only in old clusters but also in intermediate-age clusters in the Megallanic Clouds(MCs),which are characterized by star-to-star abundance scatter of several elements,including helium(He).The red giant branch bump(RGBB)’s photometric properties are proved to be related to the variation in helium abundances of the member stars in star clusters.We use the"Modules for Experiments in Stellar Astrophysics"(MESA)stellar evolution code to calculate the evolution sequences of stars along the red giant branch(RGB)with changing helium content.Following the RGB sequences,we then generate a luminosity function of the RGB stars within the grid of input helium abundances,which are compared with the observational data of an intermediate-age MC cluster NGC 1978.展开更多
We study the dynamical states of the 30 most massive galaxy clusters in the TNG100 simulation at redshift z = 0 using three types of tracers: stars, dark matter particles and satellite galaxies. If the massive galaxy ...We study the dynamical states of the 30 most massive galaxy clusters in the TNG100 simulation at redshift z = 0 using three types of tracers: stars, dark matter particles and satellite galaxies. If the massive galaxy cluster is spherically symmetric and relaxed, we can obtain the underlying total mass distribution accurately from its dynamical tracers using the spherical Jeans equations. Although the three tracers of clusters have very different number densities, velocity dispersions and anisotropies, they still trace the same total mass profile. We obtain the total mass profiles of clusters using these tracers separately and compare them with the true mass distributions. We find that:(1) the kinematics of dark matter trace the total mass of all clusters well and the mass inferred from dark matter are generally consistent with the true mass profiles with relative deviations smaller than ~ 25% at all radii;(2) stars in ~ 60% massive clusters are approaching equilibrium and the total mass of these clusters inferred from stars have relative deviations smaller than ~50% at all radii. Stellar substructures are rich and the mass inferred from stars tend to be over-estimated in the inner region;and(3) satellite galaxies are unrelaxed in the inner region and become more relaxed as the radius increases. The total mass inferred from satellites are under-estimated in all regions.展开更多
Fitting parametric models to globular clusters’structural profiles has been essential for the study of stellar dynamics.It provides their important structural parameters,such as the concentrations and core radii of t...Fitting parametric models to globular clusters’structural profiles has been essential for the study of stellar dynamics.It provides their important structural parameters,such as the concentrations and core radii of the clusters.However,existing parametric models can apply only to non-collapsing-core clusters in the early relaxation-evolution stage.Hence,a single parametric model cannot provide globular clusters’structural parameters in both the early and late evolution stages.We have recently found an accurate spectral solution for the self-similar orbit-averaged Fokker-Planck(OAFP)equation to model collapsingcore clusters at the late evolution stage.The present work establishes a new parametric model by combining the self-similar OAFP-and polytropic-models.Although it is a single-mass and isotropic model,the new model applies to at least fifty-five Galactic globular clusters with resolved cores in all the evolution stages.As a main result,we show the characteristics of the relaxation times against the concentrations of the clusters.We also affirm that the structures of low-concentration clusters are polytropic in the Milky Way.展开更多
The China Space Station Telescope(CSST)is a 2 m space-based optical-UV telescope.Its primary goal is to carry out a high-resolution photometric imaging survey of a 17,500 square degree sky area using the on board Surv...The China Space Station Telescope(CSST)is a 2 m space-based optical-UV telescope.Its primary goal is to carry out a high-resolution photometric imaging survey of a 17,500 square degree sky area using the on board Survey Camera.With its wide field of view(1.1 square degrees)and a mosaic imager containing 640 million pixels,studying the different populations of stars within star clusters is highly feasible.The aim of this study is to assess the CSST's ability to distinguish between stellar populations with varying helium abundance levels,with the help of Modules for Experiments in Stellar Astrophysics.The results of the CSST's photometry for these different populations are presented by transferring the models into the CSST Survey Camera photometric system.The findings confirm that helium-enriched stellar populations will have unique patterns in the color-magnitude diagrams under the CSST photometric system,compared to normal stellar populations.The CSST,with its filters and wide field of view of the Survey Camera,provides a new avenue for the study of multiple populations in star clusters.展开更多
We present the results of determination of the age,helium mass fraction(Y),metallicity([Fe/H]),and abundances of the elements C,N,O,Na,Mg,Ca,Ti,C and Mn for the Galactic globular cluster NGC 6652.We use its medium-res...We present the results of determination of the age,helium mass fraction(Y),metallicity([Fe/H]),and abundances of the elements C,N,O,Na,Mg,Ca,Ti,C and Mn for the Galactic globular cluster NGC 6652.We use its medium-resolution integrated-light spectrum from the library of Schiavon and our population synthesis method to fulfill this task.We select the evolutionary isochrone and stellar mass function for our analysis,which provide the best approximation to the shapes and intensities of the observed Balmer line profiles.The determined elemental abundances,age and metallicity are characteristic of stellar populations in the Galactic Bulge.展开更多
Radio emission of globular clusters is studied by analyzing the VLA radio survey data of the NVSS and FIRST. We find that 13 clusters have radio sources within their half-mass radii of clusters. Sources detected pr...Radio emission of globular clusters is studied by analyzing the VLA radio survey data of the NVSS and FIRST. We find that 13 clusters have radio sources within their half-mass radii of clusters. Sources detected previously in NGC 7078 and NGC 6440 are identified. Pulsars in NGC 6121, NGC 6440 and NGC 7078 cannot be detected because of the insufficient survey sensitivity and resolution. There may be a pulsar in the core of Terzan 1. The nature of the extended radio source near the core of NGC 6440 remains unclear. In the core of a globular cluster, there may be many neutron stars or an intermediate mass black hole, but this cannot be clarified with the current radio observations.展开更多
We report the results of our search for planet candidates in open clusters and young stellar associations based on the Transiting Exoplanet Survey Satellite(TESS) Objects of Interest Catalog.We find one confirmed plan...We report the results of our search for planet candidates in open clusters and young stellar associations based on the Transiting Exoplanet Survey Satellite(TESS) Objects of Interest Catalog.We find one confirmed planet,one promising candidate,one brown dwarf and three unverified planet candidates in a sample of 1229 open clusters from the second Gaia data release.We discuss individual planet-star systems based on their basic parameters,membership probability and the observation notes from the ExoFOP-TESS website.We also find ten planet candidates(P> 95%) in young stellar associations by using the BANYAN ∑ Multivariate Bayesian Algorithm.Among the ten candidates,five are known planetary systems.We estimate the rotation periods of the host stars using the TESS light curves and estimate their ages based on gyrochronology.Two candidates with periodic variations are likely to be young planets,but their exact memberships to young stellar associations remain unknown.展开更多
基金supported by the National Natural Science Foundation of China(NSFC)through grants 12090040,12090042,and 12073060the National Key R&D Program of China No.2019YFA0405501+2 种基金J.Z.acknowledges the Youth Innovation Promotion Association CASthe Science and Technology Commission of Shanghai Municipality(grant No.22dz1202400)the Program of Shanghai Academic/Technology Research Leader。
文摘As part of the LAMOST medium-resolution spectroscopic survey,the LAMOST-MRS-O is a non-time domain survey that aims to perform medium-resolution spectral observations for member stars in the open cluster areas.This survey plans to obtain the spectroscopic parameters such as radial velocity and metal abundances of member stars and provide data support for further study on the chemical and dynamical characteristics and evolution of open clusters in combination with Gaia data.We have completed the observations on ten open cluster fields and obtained 235184 medium-resolution spectra of 133792 stars.Based on the data analyzed of LAMOST DR11v1.1,for some clusters of particular concern,it is found that the sampling ratio of members stars with Gmag<15 mag can reach 70%,which indicates that the LAMOST-MRS-O has reached our initial design goal.
基金supported by the National Natural Science Foundation of China,No.12261141689。
文摘Recent studies have increasingly identified extended main sequence turn-off(e MSTO)phenomena in Galactic open clusters,yet the number of such clusters with sufficient spectroscopic information for member stars remains limited.Unlike most studies that rely on fitting isochrones based on color–magnitude diagram(CMD)morphology to account for varying rotational velocities,our approach leverages LAMOST spectral data to compute actual rotational velocity distributions for confirmed cluster members,along with parameters such as metallicity,differential extinction,and rotational inclination,to utilize PARSEC isochrones for fitting the cluster CMDs.We systematically surveyed all known Galactic open clusters and selected 12 clusters where rotational velocity distributions could be reliably calculated for detailed fitting.Our results successfully reproduced the eMSTO phenomenon observed in these clusters.For the majority of clusters,considering only differential extinction and variations in rotational velocity adequately explains the position and morphology of the MSTO.For some intermediate-age clusters,incorporating rotational inclination additionally accounts for the broadening of the MSTO.This study underscores the importance of spectroscopic data in understanding eMSTO phenomena and provides a probable explanation for interpreting the combined effects of differential extinction,rotation,and inclination on the CMDs of Galactic open clusters.
基金National Natural Science Foundation of China(Grant No.61573233)Guangdong Provincial Natural Science Foundation of China(Grant No.2018A0303130188)+1 种基金Guangdong Provincial Science and Technology Special Funds Project of China(Grant No.190805145540361)Special Projects in Key Fields of Colleges and Universities in Guangdong Province of China(Grant No.2020ZDZX2005).
文摘There may be several internal defects in railway track work that have different shapes and distribution rules,and these defects affect the safety of high-speed trains.Establishing reliable detection models and methods for these internal defects remains a challenging task.To address this challenge,in this study,an intelligent detection method based on a generalization feature cluster is proposed for internal defects of railway tracks.First,the defects are classified and counted according to their shape and location features.Then,generalized features of the internal defects are extracted and formulated based on the maximum difference between different types of defects and the maximum tolerance among same defects’types.Finally,the extracted generalized features are expressed by function constraints,and formulated as generalization feature clusters to classify and identify internal defects in the railway track.Furthermore,to improve the detection reliability and speed,a reduced-dimension method of the generalization feature clusters is presented in this paper.Based on this reduced-dimension feature and strongly constrained generalized features,the K-means clustering algorithm is developed for defect clustering,and good clustering results are achieved.Regarding the defects in the rail head region,the clustering accuracy is over 95%,and the Davies-Bouldin index(DBI)index is negligible,which indicates the validation of the proposed generalization features with strong constraints.Experimental results prove that the accuracy of the proposed method based on generalization feature clusters is up to 97.55%,and the average detection time is 0.12 s/frame,which indicates that it performs well in adaptability,high accuracy,and detection speed under complex working environments.The proposed algorithm can effectively detect internal defects in railway tracks using an established generalization feature cluster model.
基金financial support from the Russian Science Foundation (grant No.20-72-10052)。
文摘We fit various color–magnitude diagrams(CMDs) of the high-latitude Galactic globular clusters NGC 5024(M53),NGC 5053,NGC 5272(M3),NGC 5466,and NGC 7099(M30) by isochrones from the Dartmouth Stellar Evolution Database and Bag of Stellar Tracks and Isochrones for α–enrichment [α/Fe] = +0.4.For the CMDs,we use data sets from Hubble Space Telescope,Gaia,and other sources utilizing,at least,25 photometric filters for each cluster.We obtain the following characteristics with their statistical uncertainties for NGC 5024,NGC 5053,NGC 5272,NGC 5466,and NGC 7099,respectively:metallicities [Fe/H] =-1.93 ± 0.02,-2.08 ± 0.03,-1.60 ± 0.02,-1.95 ± 0.02,and-2.07 ± 0.04 dex with their systematic uncertainty 0.1 dex;ages 13.00 ± 0.11,12.70 ± 0.11,11.63 ± 0.07,12.15 ± 0.11,and 12.80 ± 0.17 Gyr with their systematic uncertainty 0.8 Gyr;distances(systematic uncertainty added) 18.22 ± 0.06 ± 0.60,16.99 ± 0.06 ± 0.56,10.08 ± 0.04 ± 0.33,15.59 ±0.03 ± 0.51,and 8.29 ± 0.03 ± 0.27 kpc;reddenings E(B-V) = 0.023 ± 0.004,0.017 ± 0.004,0.023 ± 0.004,0.023 ± 0.003,and 0.045 ± 0.002 mag with their systematic uncertainty 0.01 mag;extinctions AV= 0.08 ± 0.01,0.06 ± 0.01,0.08 ± 0.01,0.08 ± 0.01,and 0.16 ± 0.01 mag with their systematic uncertainty 0.03 mag,which suggest the total Galactic extinction AV= 0.08 across the whole Galactic dust to extragalactic objects at the North Galactic Pole.The horizontal branch morphology difference of these clusters is explained by their different metallicity,age,mass-loss efficiency,and loss of low-mass members in the evolution of the core-collapse cluster NGC 7099 and loose clusters NGC 5053 and NGC 5466.
基金supported by Yunnan Academician Workstation of Wang Jingxiu(202005AF150025)China Manned Space Project(NO.CMSCSST-2021-A08)+1 种基金Guanghe project(ghfund202302019167)the Natural Science Foundation of Yunnan Province(No.202201BC070003)。
文摘Recent studies indicate that some Galactic open clusters(OCs)exhibit extended main-sequence turnoff(eMSTO)in their color–magnitude diagrams(CMDs).However,the number of Galactic OCs with eMSTO structures detected so far is limited,and the reasons for their formation are still unclear.This work identifies 26 Galactic OCs with undiscovered eMSTOs and investigates the causes of these features.Stellar population types and fundamental parameters of cluster samples are acquired using CMD fitting methods.Among them,the results of 11 OCs are reliable as the observed CMDs are well-reproduced.We propose the crucial role of stellar binarity and confirm the importance of stellar rotation in reproducing eMSTO morphologies.The results also show that the impact of age spread is important,as it can adequately explain the structure of young OCs and fit the observed CMDs of intermediate-age OCs better.
基金Based on observations collected at the European Southern Observatory under ESO program(s)113.2661.001.
文摘The inner Milky Way disk globular cluster NGC 6362 appears to exhibit tidal tails composed of stars that have proper motions and positions in the color–magnitude diagram similar to those of cluster stars. Because recent results seem also to show that these stars are distributed across the regions least affected by interstellar absorption and reproduce the observed composite star field density map, we carried out a detailed spectroscopic analysis of a number of chemical element abundances of tidal tail star candidates in order to investigate the relationship between them and NGC 6362. From European Southern Observatory's VLT@FLAMES spectra we found that the red giant branch stars selected as the cluster's tidal tail stars neither have overall metallicities nor abundances of Mg, Ca, Sc, Ti, Cr, Ni and Ba similar to the cluster's ones. Moreover, they are mainly alike to stars that belong to the Milky Way thick disk, some of them could be part of the thin disk and a minor percentage could belong to the Milky Way halo star population. On the other hand, since the resulting radial velocities do not exhibit a distribution function similar to that of the cluster's stars, we concluded that looking for kinematic properties similar to those of the cluster would not seem to be as suitable of an approach for selecting the cluster's tidal tail stars as previously thought.
基金supported by the National Natural Science Foundation of China (Grant No. 10963001)Yunnan Science Foundation(2009CD093)the Scientific Research Foundation of Dali University (DYKF2009 No. 1)
文摘Binary stars are common in star clusters and galaxies, but the detailed ef- fects of binary evolution are not taken into account in some color-magnitude diagram （CMD） studies. This paper studies the CMDs of twelve globular clusters via binary- star stellar populations. The observational CMDs of the star clusters are compared to those of binary-star populations, and then the stellar metallicities, ages, distances and reddenings of these star clusters are obtained. The paper also tests the different effects of binary and single stars on CMD studies. It is shown that binaries can better fit the observational CMDs of the sample globular clusters compared to single stars. This suggests that the effects of binary evolution should be considered when modeling the CMDs and stellar populations of star clusters and galaxies.
基金the National Natural Science Foundation of China(Grant Nos.12073070,11733008,11873085,11521303,12073071,11873016,11903075,12003027 and 11973081)the Natural Science Foundation of Yunnan Province(Nos.2017HC018,202001AT070058 and 202001AU070054)+8 种基金Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant Nos.2018076 and 2012048)the Chinese Academy of Sciences(CASKJZDEW-M06-01)for supportsupported by CAS‘Light of West China’Programsupported by the National Key Basic R&D Program of China(2019YFA0405500)the LAMOST Fellow project,funded by China Postdoctoral Science Foundation(Grant Nos.2019M653504 and 2020T130563)Yunnan province postdoctoral Directed culture Foundationthe Cultivation Project for LAMOST Scientific Payoff and Research Achievement of CAMS-CASthe science research grants from the China Manned Space Project(No.CMS-CSST-2021-A08)。
文摘The red giant branch(RGB)of globular clusters(GCs)is home to some exotic stars,which may provide clues on the formation of multiple stellar populations in GCs.It is well known that binary interactions are responsible for many exotic stars.Thus,it is important to understand what fraction of stars on the RGB of GCs is the result of binary interactions.In this paper,we performed a binary population synthesis study to track the number of post-binary-interaction(post-BI)stars that appear on the RGB,with particular emphasis on the evolved blue straggler stars(E-BSSs).Assuming an initial binary fraction of nearly 50%,we find that about half of the objects on the RGB(called giants)underwent the binary interactions,and that E-BSSs account for around 10%of the giants in our standard simulation.We also compare the properties of post-BI giants that evolved from different channels.We find that the initial orbital period and mass ratio distributions significantly affect the fraction of post-BI giants.Our results imply that the non-standard stars from binary interactions provide a non-negligible contribution to the RGB stars in GCs,which should be considered in future investigations of the origin of multiple stellar populations.
基金supported by the National SKA Program of China No.2020SKA0110300Joint Research Fund in Astronomy(U1831204)under cooperative agreement between the National Natural Science Foundation of China(NSFC)+5 种基金the Chinese Academy of Sciences(CAS)the National Key Research and Development Program of China(2018YFA0404603)the NSFC(Nos.11863002 and 11961141001)supported by the Yunnan Academician Workstation of Wang Jingxiu(No.202005AF150025)China Manned Space Project with NO.CMS-CSST-2021-A08Sino-German Cooperation Project(No.GZ 1284)。
文摘As groups of coeval stars born from the same molecular cloud,an open cluster(OC)is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way.The release of high-precision Gaia Early Data Release 3(Gaia EDR3)and modern machine-learning methods offer unprecedented opportunities to identify OCs.In this study,we extended conventional HDBSCAN(e-HDBSCAN)for searching for new OCs in Gaia EDR3.A pipeline was developed based on the parallel computing technique to blindly search for OCs from Gaia EDR3within Galactic latitudes∣b∣<25°.As a result,we obtained 3787 star clusters,of which 83 new OCs were reported after cross-match and visual inspection.At the same time,the main star cluster parameters are estimated by color-magnitude diagram fitting.The study significantly increases the sample size and physical parameters of OCs in the catalog of OCs.It shows the incompleteness of the census of OCs across our Galaxy.
基金the Infosys Foundation through the Infosys Young Investigator grant。
文摘The motion of baryonic components of the Milky Way is governed by both luminous and dark matter content of the Galaxy.Thus,the dynamics of Milky Way globular clusters(GCs)can be used as tracers to infer the mass model of the Galaxy up to a large radius.In this work,we apply the directly observable line-of-sight velocities to test if the dynamics of the GC population are consistent with an assumed axisymmetric gravitational potential of the Milky Way.For this,we numerically compute the phase space distribution of the GC population where the orbits are either oriented randomly or co-/counter-rotating with respect to the stellar disk.Then we compare the observed position and line-of-sight velocity distribution of^150 GCs with those of the models.We found that,for the adopted mass model,the co-rotating scenario is the favored model based on various statistical tests.We do the analysis with and without the GCs associated with the progenitors of early merger events.This analysis can be extended in the near future to include precise and copious data to better constrain the Galactic potential up to a large radius.
基金the National Natural Science Foundation of China(Grant Nos.11803009 and 11603009)the Natural Science Foundation of Fujian Province(Grant Nos.2018J05006,2018J01416 and 2016J05013).
文摘We investigate pulsar timing residuals due to the coupling effect of the pulsar transverse acceleration and the Romer delay.The effect is relatively small and usually negligible.Only for pulsars in globular clusters,it is possibly important.The maximum residual amplitude,which is from the pulsar near the surface of the core of the cluster,is about tens of nanoseconds,and may hardly be identified for most globular clusters currently.However,an intermediate-mass black hole in the center of a cluster can apparently increase the timing residual magnitudes.Particularly for pulsars in the innermost core region,their residual magnitudes may be significant.The high-magnitude residuals,which are above critical lines of each cluster,are strong evidence for the presence of a black hole or dark remnants of comparable total mass in the center of the cluster.We also explored the timing effects of line-of-sight accelerations for the pulsars.The distribution of measured line-of-sight accelerations are simulated with a Monte Carlo method.Two-dimensional Kolmogorov-Smirnov tests are performed to reexamine the consistency of distributions of the simulated and reported data for various values of parameters of the clusters.It is shown that the structure parameters of Terzan 5 can be constrained well by comparing the distribution of measured lineof-sight accelerations with the distributions from Monte Carlo simulations.We find that the cluster has an upper limit on the central black hole/dark remnant mass of~6000 M⊙.
文摘We study the counts of resolved SZE (Sunyaev-Zel'dovich effect) clusters expected from an interferometric survey in different cosmological models under different conditions. The self-similar universal gas model and Press-Schechter mass function are used. We take the observing frequency to be 90 GHz, and consider two dish diameters, 1.2 m and 2.5 m. We calculate the number density of the galaxy clusters dN/(dΩdz) at a high flux limit S<SUB>v</SUB><SUP>lim</SUP>=100 mJy and at a relative low S<SUB>v</SUB><SUP>lim</SUP> =10 mJy. The total numbers of SZE clusters N in two low-Ω<SUB>0</SUB> models are compared. The results show that the influence of the resolved effect depends not only on D, but also on S<SUB>v</SUB><SUP>lim</SUP>: at a given D, the effect is more significant for a high than for a low S<SUB>v</SUB><SUP>lim</SUP>. Also, the resolved effect for a flat universe is more impressive than that for an open universe. For D = 1.2 m and S<SUB>v</SUB><SUP>lim</SUP> =10 mJy, the resolved effect is very weak. Considering the designed interferometers which will be used to survey SZE clusters, we find that the resolved effect is insignificant when estimating the expected yield of the SZE cluster surveys.
基金Supported by the National Natural Science Foundation of China
文摘We investigate the mass-temperature relation of clusters for both the spherical NFW halo model and a concentric triaxial halo model. We study the temperature and density distributions of both an isothermal and a polytropic intra-cluster gas in hydrostatic equilibrium. We find that both the uncertainties in the concentration parameter and in the eccentricities (in case of the triaxial halo) lead to a greater scatter in the emission-weighted temperature at a given halo mass for less massive clusters. This may be helpful when determining the intrinsic statistical error of the σ<SUB>8</SUB> normalization of the linear power spectrum from cluster abundance.
基金support through Grant Nos.11633005 and 12073090the National Key R&D Program of China(Grant No.2020YFC2201400)。
文摘Many evidences show that the Multiple Population(MP)features exist not only in old clusters but also in intermediate-age clusters in the Megallanic Clouds(MCs),which are characterized by star-to-star abundance scatter of several elements,including helium(He).The red giant branch bump(RGBB)’s photometric properties are proved to be related to the variation in helium abundances of the member stars in star clusters.We use the"Modules for Experiments in Stellar Astrophysics"(MESA)stellar evolution code to calculate the evolution sequences of stars along the red giant branch(RGB)with changing helium content.Following the RGB sequences,we then generate a luminosity function of the RGB stars within the grid of input helium abundances,which are compared with the observational data of an intermediate-age MC cluster NGC 1978.
基金partly supported by the National Key Research and Development Program of China(No.2018YFA0404501)the National Natural Science Foundation of China(Grant Nos.11821303,11761131004 and 11761141012)。
文摘We study the dynamical states of the 30 most massive galaxy clusters in the TNG100 simulation at redshift z = 0 using three types of tracers: stars, dark matter particles and satellite galaxies. If the massive galaxy cluster is spherically symmetric and relaxed, we can obtain the underlying total mass distribution accurately from its dynamical tracers using the spherical Jeans equations. Although the three tracers of clusters have very different number densities, velocity dispersions and anisotropies, they still trace the same total mass profile. We obtain the total mass profiles of clusters using these tracers separately and compare them with the true mass distributions. We find that:(1) the kinematics of dark matter trace the total mass of all clusters well and the mass inferred from dark matter are generally consistent with the true mass profiles with relative deviations smaller than ~ 25% at all radii;(2) stars in ~ 60% massive clusters are approaching equilibrium and the total mass of these clusters inferred from stars have relative deviations smaller than ~50% at all radii. Stellar substructures are rich and the mass inferred from stars tend to be over-estimated in the inner region;and(3) satellite galaxies are unrelaxed in the inner region and become more relaxed as the radius increases. The total mass inferred from satellites are under-estimated in all regions.
文摘Fitting parametric models to globular clusters’structural profiles has been essential for the study of stellar dynamics.It provides their important structural parameters,such as the concentrations and core radii of the clusters.However,existing parametric models can apply only to non-collapsing-core clusters in the early relaxation-evolution stage.Hence,a single parametric model cannot provide globular clusters’structural parameters in both the early and late evolution stages.We have recently found an accurate spectral solution for the self-similar orbit-averaged Fokker-Planck(OAFP)equation to model collapsingcore clusters at the late evolution stage.The present work establishes a new parametric model by combining the self-similar OAFP-and polytropic-models.Although it is a single-mass and isotropic model,the new model applies to at least fifty-five Galactic globular clusters with resolved cores in all the evolution stages.As a main result,we show the characteristics of the relaxation times against the concentrations of the clusters.We also affirm that the structures of low-concentration clusters are polytropic in the Milky Way.
基金supported in part by China Manned Space Project with NO.CMS-CSST-2021-A08the National Natural Science Foundation of China(NSFC,Grants Nos.12233009,12233013,12073090 and 12003001)。
文摘The China Space Station Telescope(CSST)is a 2 m space-based optical-UV telescope.Its primary goal is to carry out a high-resolution photometric imaging survey of a 17,500 square degree sky area using the on board Survey Camera.With its wide field of view(1.1 square degrees)and a mosaic imager containing 640 million pixels,studying the different populations of stars within star clusters is highly feasible.The aim of this study is to assess the CSST's ability to distinguish between stellar populations with varying helium abundance levels,with the help of Modules for Experiments in Stellar Astrophysics.The results of the CSST's photometry for these different populations are presented by transferring the models into the CSST Survey Camera photometric system.The findings confirm that helium-enriched stellar populations will have unique patterns in the color-magnitude diagrams under the CSST photometric system,compared to normal stellar populations.The CSST,with its filters and wide field of view of the Survey Camera,provides a new avenue for the study of multiple populations in star clusters.
文摘We present the results of determination of the age,helium mass fraction(Y),metallicity([Fe/H]),and abundances of the elements C,N,O,Na,Mg,Ca,Ti,C and Mn for the Galactic globular cluster NGC 6652.We use its medium-resolution integrated-light spectrum from the library of Schiavon and our population synthesis method to fulfill this task.We select the evolutionary isochrone and stellar mass function for our analysis,which provide the best approximation to the shapes and intensities of the observed Balmer line profiles.The determined elemental abundances,age and metallicity are characteristic of stellar populations in the Galactic Bulge.
文摘Radio emission of globular clusters is studied by analyzing the VLA radio survey data of the NVSS and FIRST. We find that 13 clusters have radio sources within their half-mass radii of clusters. Sources detected previously in NGC 7078 and NGC 6440 are identified. Pulsars in NGC 6121, NGC 6440 and NGC 7078 cannot be detected because of the insufficient survey sensitivity and resolution. There may be a pulsar in the core of Terzan 1. The nature of the extended radio source near the core of NGC 6440 remains unclear. In the core of a globular cluster, there may be many neutron stars or an intermediate mass black hole, but this cannot be clarified with the current radio observations.
基金partly supported by the National Science Foundation of China (Grant No. 12133005)。
文摘We report the results of our search for planet candidates in open clusters and young stellar associations based on the Transiting Exoplanet Survey Satellite(TESS) Objects of Interest Catalog.We find one confirmed planet,one promising candidate,one brown dwarf and three unverified planet candidates in a sample of 1229 open clusters from the second Gaia data release.We discuss individual planet-star systems based on their basic parameters,membership probability and the observation notes from the ExoFOP-TESS website.We also find ten planet candidates(P> 95%) in young stellar associations by using the BANYAN ∑ Multivariate Bayesian Algorithm.Among the ten candidates,five are known planetary systems.We estimate the rotation periods of the host stars using the TESS light curves and estimate their ages based on gyrochronology.Two candidates with periodic variations are likely to be young planets,but their exact memberships to young stellar associations remain unknown.
