Isochrone Fitting of Galactic Globular Clusters—Ⅵ.High-latitude Clusters NGC 5024 (M53),NGC 5053,NGC 5272 (M3),NGC 5466,and NGC7099 (M30)

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.

Study of 26 Galactic Open Clusters with Extended Main-sequence Turnoffs

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.

Internal Defects Detection Method of the Railway Track Based on Generalization Features Cluster Under Ultrasonic Images

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.

LISC Catalog of Open ClustersⅢ.83 Newly Found Galactic Disk Open Clusters Using Gaia EDR3

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.

The Study of Helium Variations in Star Clusters Using China Space Station Telescope

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.

Unveiling the Initial Conditions of Open Star Cluster Formation

Open clusters(OCs)are infrequent survivors of embedded clusters gestated in molecular clouds.Up to now,little is known about the initial conditions for the formation of OCs.Here,we studied this issue using high-precision astrometric parameters provided by Gaia data release 3.The statistics show that the peculiar motion velocities of OCs vary slightly from infancy to old age,providing a remarkable opportunity to use OCs to trace their progenitors.Adopting a dynamical method,we derived the masses of the progenitor clumps where OCs were born,which have statistical characteristics comparable to previously known results for clumps observed in the Galaxy.Moreover,the masses of the progenitor clumps of OCs indicate they should be capable of gestating massive O-type stars.In fact,after inspecting the observed OCs and O-type stars,we found that there are many O-type stars in OCs.The destructive stellar feedback from O-type stars may disintegrate the vast majority of embedded clusters,and only those sufficiently dense ones can survive as OCs.

A binary study of color-magnitude diagrams of 12 globular clusters

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.

The fractions of post-binary-interaction stars and evolved blue straggler stars on the red giant branch of globular clusters

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.

Milky Way globular cluster dynamics:are they preferentially co-rotating?

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.

Probing dark contents in globular clusters with timing effects of pulsar acceleration

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⊙.

Evaluating Helium Variations By Modeling Red Giant Branch Bump of Large Magellanic Cluster NGC 1978

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.

Resolved SZE Cluster Count

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 Svlim=100 mJy and at a relative low Svlim =10 mJy. The total numbers of SZE clusters N in two low-Ω0 models are compared. The results show that the influence of the resolved effect depends not only on D, but also on Svlim: at a given D, the effect is more significant for a high than for a low Svlim. Also, the resolved effect for a flat universe is more impressive than that for an open universe. For D = 1.2 m and Svlim =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.

Mass-Temperature Relation of X-ray Clusters in Triaxial Halo

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 σ8 normalization of the linear power spectrum from cluster abundance.

The relaxation of galaxy clusters at redshift z=0 in IllustrisTNG simulation

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.

Self-similar orbit-averaged Fokker-Planck equation for isotropic spherical dense clusters(iii)Application to Galactic globular clusters

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.

Age and chemical composition of the globular cluster NGC 6652

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.

Radio Emission from Globular Clusters

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.

Variable stars in the open cluster NGC 2141

We report the results of a search for variable stars in the open cluster NGC 2141. Ten variable stars are detected, among which nine are new variable stars and they are classified as three short-period W UMa-type eclipsing binaries, two EA- type eclipsing binaries, one EB-type eclipsing binary, one very short-period RS CVn- type eclipsing binary, one d-type RR Lyrae variable star, and one unknown type of variable star. The membership and physical properties are discussed, based on their light curves, positions in the color magnitude diagrams, spatial locations and periods. A known EB-type eclipsing binary is also identified as a blue straggler candidate in the cluster. Furthermore, we find that all eclipsing contact binaries have prominent asymmetric eclipses and display the O＇Connell effect, which increases with a decrease in orbital periods. This suggests that the O＇Connell effect is probably related to the evolution of the orbital period in short period eclipsing binary systems.

A Search for Exoplanets in Open Clusters and Young Associations based on TESS Objects of Interest

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.

Spectroscopic study of globular clusters in the halo of M31 with the Xinglong 2.16 m telescope Ⅱ: dynamics, metallicity and age

In Paper I, we performed spectroscopic observations on 11 confirmed glob- ular clusters （GCs） in M31 with the Xinglong 2.16 m telescope. We mainly focused on the fitting method and the metallicity gradient for the M31 GC sample. Here, we analyze and further discuss the dynamics, metallicity and age, and their distributions, as well as the relationships between these parameters. In our work, eight more con- firmed GCs in the halo of M31 were observed, most of which lack previous spectro- scopic information. These star clusters are located far from the galactic center at a projected radius of ~ 14 to ~ 117 kpc, which is more spatially extended than that in the previous work. Firstly, we measured the Lick absorption-line indices and the ra- dial velocities. Then the ages and metallicity values of [Fe/H] and [a/Fe] were fitted by comparing the observed spectral feature indices and the Single Stellar Population model of Thomas et al. in the Cassisi and Padova stellar evolutionary tracks, respec- tively. Our results show that most of the star clusters in our sample are older than 10 Gyr except B290, which is ~ 5.5 Gyr, and most of them are metal-poor with metallicity [Fe/H] 〈 - 1, suggesting that these clusters were born at the early stage of the galaxy＇s formation. We find that the metallicity gradient for the outer halo clusters with rp 〉 25 kpc may have an insignificant slope of -0.005 ＋ 0.005 dex kpc-1 and if the outliers G001 and H11 are excluded, the slope does not change significantly, with a value of -0.002 ~ 0.003 dex kpc-1. We also find that the metallicity is not a function of age for the GCs with age 〈 7 Gyr, but for the old GCs with age 〉 7 Gyr, there seems to be a trend that the older ones have lower metallicity. Additionally, we plot metallicity distributions with the largest sample of M31 GCs so far and show the bimodality is not significant, and the number of metal-poor and metal-rich groups be- comes comparable. The spatial distributions show that the metal-rich group is more centrally concentrated but the metal-poor group occupies a more extended halo. In ad- dition, the young population is centrally concentrated but the old population is more spatially extended towards the outer halo.