Photometric Survey of Galactic Open Clusters

We present a progress of a long term project to obtain UBVI CCD photometry of open clusters which were little studied before, using the Doyak 1.8 m telecope of Bohyunsan Optical Astronomy Observatory operated by the Korea Astronomical Observatory, in Korea. The primary goals of this project are (1) to make a catalog of UBVI photometry of open clusters, (2) to make an atlas of open clusters, and (3) to survey and monitor variable stars in open clusters.

A density functional theory structures, stabilities, and study on size-dependent electronic properties of bimetallic MnAgm （M=Na, Li; n ＋ m ≤ 7） clusters

The equilibrium geometries, relative stabilities, and electronic properties of MnAgm（M=Na, Li; n ＋ m ≤ 7） as well as pure Agn, Nan, Lin （n ≤ 7） clusters are systematically investigated by means of the density functional theory. The optimized geometries reveal that for 2 ≤ n ≤ 7, there are significant similarities in geometry among pure Agn, Nan, and Lin clusters, and the transitions from planar to three-dimensional configurations occur at n = 7, 7, and 6, respectively. In contrast, the first three-dimensional （3D） structures are observed at n ＋ m = 5 for both NanAgm and LinAgm clusters. When n ＋ m ≥5, a striking feature is that the trigonal bipyramid becomes the main subunit of LinAgm. Furthermore, dramatic odd-even alternative behaviours are obtained in the fragmentation energies, secondorder difference energies, highest occupied and lowest unoccupied molecular orbital energy gaps, and chemical hardness for both pure and doped clusters. The analytic results exhibit that clusters with an even electronic configuration （2, 4, 6） possess the weakest chemical reactivity and more enhanced stability.

The geometry structures and electronic properties of Li_mB_n(m+n=12) clusters

The geometric structures, electronic properties, total and binding energies, harmonic frequencies, the highest occupied molecular orbital to the lowest unoccupied molecular orbital energy gaps, and the vertical ionization potential energies of small LimBn （m＋ n = 12） clusters were investigated by the density functional theory B3LYP with a 6-31 I＋G （2d, 2p） basis set. All the calculations were performed using the Gaussian09 program. For the study of the LimBn clusters, the global minimum of the B 12 cluster was chosen as the starting point and the boron atoms were gradually replaced by Li atoms. The results showed that as the number of Li atoms increased, the stability of the LimBn cluster decreased and the physical and chemical properties became more active. In addition, on average there was a large charge transfer from the Li atoms to the B atoms.

Estimating the Metallicity of Old Star Clusters in M33

Based on the method proposed by Kong et al. and on the multi-color spectrophotometry by Ma et al., we estimate the metallicities of 16 old star clusters in the nearby spiral galaxy M33, ten of which are halo globular clusters. These old clusters are all metal poor, the range of metallicity ([Fe/H]) is from-0.14 to-2.12. In general, our results are consistent with those derived by other methods, such as integrated spectra and photometry, and our study confirms the reliability of the method of Kong et al.

Age and Mass Estimates for 41 Star Clusters in M33

In this second paper of our series, we estimate the age of 41 star clusters, which were detected by Melnick & D'odorico in the nearby spiral galaxy M33, by comparing the integrated photometric measurements with theoretical stellar population synthesis models of Bruzual & Charlot. Also, we calculate the mass of these star clusters using the theoretical M/LV ratio. The results show that, these star clusters formed continuously in M33 from ~ 7 × 106–1010 years and have masses between ~ 103 and 2 × 106M☉. M33 frames were observed as a part of the BATC Multicolor Survey of the sky in 13 intermediate-band filters from 3800 to 10 000?. The relation between age and mass confirms that the sample star cluster masses systematically decrease from the oldest to the youngest.

The LAMOST spectroscopic survey of globular clusters in M31and M33.I.catalog and new identifications

We present a catalog of 908 objects observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope（LAMOST） in fields in the vicinity of M31 and M33, targeted as globular clusters（GCs） and candidates. The targets include known GCs and candidates selected from the literature, as well as new candidates selected from the Sloan Digital Sky Survey（SDSS）. Analysis shows that 356 of them are likely GCs with various confidence levels, while the remaining ones turn out to be background galaxies and quasars, stars and H II regions in M31 or foreground Galactic stars. The 356 likely GCs include 298 bona fide GCs and 26 candidates known in the literature. Three candidates, selected from the Revised Bologna Catalog of M31 GCs and candidates（RBC） and one possible cluster from Johnson et al., are confirmed to be bona fide clusters. We search for new GCs in the halo of the M31 among the new candidates selected from the SDSS photometry. Based on radial velocities yielded by LAMOST spectra and visual examination of the SDSS images, we find 28 objects, 5bona fide and 23 likely GCs. Among the five bona fide GCs, three have been recently discovered independently by others, and the remaining 25 are our new identifications,including two bona fide ones. The newly identified objects fall at projected distances ranging from 13 to 265 kpc from M31. Of the two newly discovered bona fide GCs,one is located near M33, probably a GC belonging to M33. The other bona fide GC falls on the Giant Stream with a projected distance of 78 kpc from M31. Of the 23 newly identified likely GCs, one has a projected distance of about 265 kpc from M31 and could be an intergalactic cluster.

Simulation of old open clusters for UVIT on ASTROSAT

The Ultra Violet Imaging Telescope （UVIT） is one of the payloads on the first Indian multiwavelength satellite ASTROSAT, which is expected to be launched by the Indian Space Research Organisation （ISRO） in the year 2015. We have per- formed simulations of UV studies of old open clusters for the UVIT. The colour mag- nitude diagrams （CMDs） and spatial appearances have been created using 10 filters associated with the FUV channel （130-180 nm） and NUV channel （200-300 nm） that are available for observations on the UVIT, for the three old open clusters M67, NGC 188 and NGC 6791. The CMDs are simulated for different filter combinations, and they are used to identify the loci of various evolutionary sequences, white dwarfs, blue stragglers, red giants, subgiants, turn off stars and the main sequence of the clus- ters. The present work helps in identifying a potential area of study in the case of these three old open clusters by considering the availability of filters and the detection limits of the instrument. We also recommend filter combinations, which can be used to detect and study the above mentioned evolutionary stages. The simulations and the results presented here are essential for the optimal use of the UVIT for studies of old open clusters.

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.

Multicolor photometric study of M31 globular clusters

We present the photometry of 30 globular clusters （GCs） and GC candidates in 15 intermediate-band filters covering the wavelength region from - 3000 to 10000A using the archival CCD images of M31 observed as part of the Beijing - Arizona - Taiwan - Connecticut （BATC） Multicolor Sky Survey. We transform these intermediate-band photometric data into the photometry in the standard U BV RI broadbands. These M31 GC candidates are selected from the Revised Bologna Catalog （RBC V.3.5）, and most of these candidates do not have any photometric data. Therefore, the presented photometric data are a supplement to the RBC V.3.5. We find that 4 out of 61 GCs and GC candidates in RBC V.3.5 do not show any signal on the BATC images at their locations. By applying a linear fit of the distribution in the color-magnitude diagram of blue GCs and GC candidates using data from the RBC V.3.5, in this study, we find the ＂blue-tilt＂ of blue M31 GCs with a high confidence at 99.95% or 3.47cr for the confirmed GCs, and 〉 99.99% or 4.87e for GCs and GC candidates.

2MASS photometry and age estimation of the globular clusters in the outer halo of M31

We present the first photometric results in J, H and Ks from 2MASS （Two Micron All Sky Survey） imaging of 10 classical globular clusters （GCs） in the far outer regions of M31. Combined with the V and I photometric data from previous literature, we constructed a color-color diagram between J - Ks and V - Ⅰ. By comparing the integrated photometric measurements with evolutionary models, we estimate the ages of these clusters. The results showed that all of these clusters are older than 3 × 109 yr, and among them four are older than 10 Gyr and the other six have intermediate ages between 3 - 8 Gyr. The masses for these outer-halo GCs are from 7.0 × 104 M to 1.02 × 10^6 M. We argued that GC2 and GC3, whose ages, metallicities and distance moduli are almost the same, were accreted from the same satellite galaxy, if they did not form in situ. The statistical results show that the ages and metallicities of these 10 M31 outer-halo GCs do not vary with projected radial position, and a relationship between age and metallicity does not exist.

Positions and Spectral Energy Distributions of 41 Star Clusters in M33

We present accurate positions and multi-color photometry for 41 star clusters detected by Melnick & D'odorico in the nearby spiral galaxy M33 as a part of the BATC Color Survey of the sky in 13 intermediate-band filters from 3800 to 10 000 A. The coordinates of the clusters are found from the HST Guide Star Catalog. By aperture photometry, we obtain the spectral energy distributions of the clusters. Using the relations between the BATC intermediate-band system and UBVRI broadband system, we derive their V magnitudes and B - V colors and find that most of them are blue, which is consistent with previous findings.

一种M-ary扩频信号扩频序列集估计方法

针对M-ary扩频信号的扩频序列集估计问题,提出一种基于序贯相关检测的扩频码集估计方法。首先,对同步信号样点进行划分,并利用所分向量间的相关特性,通过迭代操作得到码集中某一个元素的估计;然后,将对应于该元素的样点向量从接收信号向量集合中剔除,并重复上述步骤,以序贯的方式得到扩频码集的一个估计;最后,利用原始信号对该码集的各个元素进行检验,剔除码集中的虚假元素从而得到最终估计结果。该方法可以实现M-ary扩频信号的扩频序列集估计,并且不受扩频码集类型的限制,由于避免了二维搜索以及K均值聚类的迭代操作,文中方法具有比文献方法更快的计算速度。

A density functional theory study on size-dependent structures,stabilities,and electronic properties of bimetallic M_nAg_m(M=Na,Li;n + m≤7) clusters

The equilibrium geometries,relative stabilities,and electronic properties of Mn Agm(M=Na,Li;n + m ≤ 7) as well as pure Ag n,Na n,Li n(n ≤ 7) clusters are systematically investigated by means of the density functional theory.The optimized geometries reveal that for 2 ≤ n ≤ 7,there are significant similarities in geometry among pure Ag n,Na n,and Li n clusters,and the transitions from planar to three-dimensional configurations occur at n = 7,7,and 6,respectively.In contrast,the first three-dimensional(3D) structures are observed at n + m = 5 for both Na n Ag m and Li n Ag m clusters.When n + m ≥ 5,a striking feature is that the trigonal bipyramid becomes the main subunit of Li n Ag m.Furthermore,dramatic odd-even alternative behaviours are obtained in the fragmentation energies,secondorder difference energies,highest occupied and lowest unoccupied molecular orbital energy gaps,and chemical hardness for both pure and doped clusters.The analytic results exhibit that clusters with an even electronic configuration(2,4,6) possess the weakest chemical reactivity and more enhanced stability.

Simulated annealing spectral clustering algorithm for image segmentation

The similarity measure is crucial to the performance of spectral clustering. The Gaussian kernel function based on the Euclidean distance is usual y adopted as the similarity measure. However, the Euclidean distance measure cannot ful y reveal the complex distribution data, and the result of spectral clustering is very sensitive to the scaling parameter. To solve these problems, a new manifold distance measure and a novel simulated anneal-ing spectral clustering （SASC） algorithm based on the manifold distance measure are proposed. The simulated annealing based on genetic algorithm （SAGA）, characterized by its rapid convergence to the global optimum, is used to cluster the sample points in the spectral mapping space. The proposed algorithm can not only reflect local and global consistency better, but also reduce the sensitivity of spectral clustering to the kernel parameter, which improves the algorithm’s clustering performance. To efficiently apply the algorithm to image segmentation, the Nystrom method is used to reduce the computation complexity. Experimental results show that compared with traditional clustering algorithms and those popular spectral clustering algorithms, the proposed algorithm can achieve better clustering performances on several synthetic datasets, texture images and real images.

Novel robust approach for constructing Mamdani-type fuzzy system based on PRM and subtractive clustering algorithm

A novel approach for constructing robust Mamdani fuzzy system was proposed, which consisted of an efficiency robust estimator(partial robust M-regression, PRM) in the parameter learning phase of the initial fuzzy system, and an improved subtractive clustering algorithm in the fuzzy-rule-selecting phase. The weights obtained in PRM, which gives protection against noise and outliers, were incorporated into the potential measure of the subtractive cluster algorithm to enhance the robustness of the fuzzy rule cluster process, and a compact Mamdani-type fuzzy system was established after the parameters in the consequent parts of rules were re-estimated by partial least squares(PLS). The main characteristics of the new approach were its simplicity and ability to construct fuzzy system fast and robustly. Simulation and experiment results show that the proposed approach can achieve satisfactory results in various kinds of data domains with noise and outliers. Compared with D-SVD and ARRBFN, the proposed approach yields much fewer rules and less RMSE values.

p-capture reaction cycles in rotating massive stars and their impact on elemental abundances in globular cluster stars: A case study of O, Na and Al

Elemental abundance patterns of globular cluster stars can provide important clues for understanding cluster formation and early chemical evolution.The origin of the abundance patterns,however,still remains poorly understood.We have studied the impact of p-capture reaction cycles on the abundances of oxygen,sodium and aluminium considering nuclear reaction cycles of carbon-nitrogenoxygen-fluorine,neon-sodium and magnesium-aluminium in massive stars in stellar conditions of temperature range 2×107to 10×107K and typical density of 102gm cc-1.We have estimated abundances of oxygen,sodium and aluminium with respect to Fe,which are then assumed to be ejected from those stars because of rotation reaching a critical limit.These ejected abundances of elements are then compared with their counterparts that have been observed in some metal-poor evolved stars,mainly giants and red giants,of globular clusters M3,M4,M13 and NGC 6752.We observe an excellent agreement with[O/Fe]between the estimated and observed abundance values for globular clusters M3 and M4 with a correlation coefficient above 0.9 and a strong linear correlation for the remaining two clusters with a correlation coefficient above 0.7.The estimated[Na/Fe]is found to have a correlation coefficient above 0.7,thus implying a strong correlation for all four globular clusters.As far as[Al/Fe]is concerned,it also shows a strong correlation between the estimated abundance and the observed abundance for globular clusters M13 and NGC 6752,since here also the correlation coefficient is above 0.7 whereas for globular cluster M4 there is a moderate correlation found with a correlation coefficient above 0.6.Possible sources of these discrepancies are discussed.

A proper motion study of the globular cluster M12(NGC 6218)

Using astrometric techniques developed by Anderson et al., we determine proper motions （PMs） in the ~ 14.60 × 16.53 arcmin^2 area of the kinematically ＂thick-disk＂ globular cluster M 12. The cluster＇s proximity and sparse nature makes it a suitable target for ground-based telescopes. Archive images with time gap of ~ 11.1 years were observed with the wide-field imager （WFI） mosaic cam-era mounted on the ESO 2.2m telescope. The median value of PM error in both components is 0.7masyr^-1 for the stars having V ≤ 20mag. PMs are used to determine membership probabil-ities and to separate field stars from the cluster sample. In electronic form, a membership catalog of 3725 stars with precise coordinates, PMs and BVRI photometry is being provided. One of the possible applications of the catalog is demonstrated by gathering the membership information of the variable stars, blue stragglers and X-ray sources reported earlier in the cluster＇s region.

An application of the k-th nearest neighbor method to open cluster membership determination

We introduce a non-parametric method for open cluster membership determination in threedimensional（3D） velocity space（proper motion and radial velocity）. Clean 3D cluster members can be obtained by statistically analyzing the Euclidean distance between each star and its k-th nearest neighbor in3 D velocity space. We use 513 sample stars in the direction of open cluster M67 to construct a 3D velocity space and test our method; 291 3D cluster members are obtained. The color-magnitude diagram, proper motions, radial velocities and spatial distribution of these 3D cluster members demonstrate the effectiveness of our method. From the 291 3D cluster members, the mean radial velocity and absolute proper motion of M67 are Vr = ＋33.46 ± 0.05 km s-1and（PMRA, PMDEC） =（-7.64 ± 0.07,-5.98 ± 0.07） mas yr-1,respectively. In addition, we use 640 sample stars with precise proper motions and radial velocities in the direction of open cluster NGC 188 to test our method. The test results also show that our method is effective.

Examining the M67 Classification as an Open Cluster

The cluster M67 (= NGC 2682) in Cancer is a rich stellar cluster, usually classified as an open cluster. Using our own observations with the 0.4 m telescope, we show that M67 is a tight group of about 1200 stars. The actual radius of the cluster is about 3.1 pc and the average mass of a star in the system is about . We also show that the ratio of the mean kinetic energy of the cluster to its mean gravitational potential energy , while the value predicted by the virial theorem is equal to . So the system is a gravitationally bound. This value of is considered as an evidence of quasi-stability of the cluster and allows us to use the Chandrasekhar-Spitzer relaxation time for M67 Myr as a characteristic dynamical relaxation time of the system. As the cluster is almost twice older its half-life time , it is argued that M67 was in the past (about 4 Gyr ago, close to its forma-tion) a relatively small ( stars) globular cluster, but got “open cluster” shape due to the dynamical evapora-tion of the majority of its stars.

Metal abundance and kinematical properties of the M81 globular cluster system

We present metal abundance properties of 144 globular clusters associated with M81. These globulars represent the largest globular cluster sample in M81 till now. Our main results are： the distribution of metallicities is bimodal, with metallicity peaks at [Fe/H] -1.51 and -0.58, and the metal-poor globular clusters tend to be less spatially concentrated than the metal-rich ones; the metal-rich globular clusters in M81 do not demonstrate a centrally concentrated spatial distribution like the metalrich ones in M31 do; like our Galaxy and M31, the globular clusters in M81 have a small radial metallicity gradient. These results are consistent with those obtained from a small sample of M81 globular clusters. In addition, this paper shows that there is evidence that a strong rotation of the M81 globular cluster system around the minor axis exists, and that rotation is present in the metal-rich globular cluster subsample, but the metal-poor globular cluster subsample shows no evidence of rotation. The most significant difference between the rotation of the metal-rich and metal-poor globular clusters occurs at intermediate projected galactocentric radii. Our results confirm the conclusion of Schroder et al. that M81＇s metal-rich globular clusters at intermediate projected radii are associated with a thick disk of M81.