Determining the observation epochs of star catalogs from ancient China using the generalized Hough transform method

Ancient China recorded a wealth of astronomical observations,notably distinguished by the inclusion of empirical measurements of stellar observations.However,determining the precise observational epochs for these datasets poses a formidable challenge.This study employs the generalized Hough transform methodology to analyze two distinct sets of observational data originating from the Song and Yuan dynasties,allowing accurate estimation of the epochs of these stellar observations.This research introduces a novel and systematic approach,offering a scholarly perspective for the analysis of additional datasets within the domain of ancient astronomical catalogs in future investigations.

Systematic differences in position and proper-motion between the PPMX and UCAC3 catalogs

Considered to be extensions of the Hipparcos reference system, PPMX and UCAC3 are two of the most important astrometric catalogs released in current years. Extensive analyses of these two large catalogs have been made in order to determine the local and overall systematic biases. The regional and magnitude dependent differences in stellar position and proper motion are comparable to random errors and are even larger in the northern hemisphere. The global orientation bias vector ε between the two systems is also significant （up to 17 mas）, which shows the overall differences of the PPMX and UCAC3 catalogs and their reference systems. On the other hand, the term for the global rotation vector a; is small （tenths of mas per year）： it is reasonable to believe that the PPMX and UCAC3 reference frames do not rotate with respect to each other. Because of plate dependent and field-to-field errors in the UCAC3 catalog, we suggest that positions and proper motions of UCAC3 stars in the northern hemisphere （δ 〉 -20°） should be used with caution.

The Quasar Candidate Catalogs of DESI Legacy Imaging Survey Data Release 9

Quasars can be used to measure baryon acoustic oscillations at high redshift, which are considered as direct tracers of the most distant large-scale structures in the universe. It is fundamental to select quasars from observations before implementing the above research. This work focuses on creating a catalog of quasar candidates based on photometric data to provide primary priors for further object classification with spectroscopic data in the future, such as the Dark Energy Spectroscopic Instrument(DESI) Survey. We adopt a machine learning algorithm(Random Forest, RF) for quasar identification. The training set includes 651,073 positives and 1,227,172 negatives, in which the photometric information are from DESI Legacy Imaging Surveys(DESI-LIS) and Wide-field Infrared Survey Explore(WISE), and the labels are from a database of spectroscopically confirmed quasars based on Sloan Digital Sky Survey and the Set of Identifications& Measurements and Bibliography for Astronomical Data. The trained RF model is applied to point-like sources in DESI-LIS Data Release 9. To quantify the classifier’s performance, we also inject a testing set into the to-be-applied data.Eventually, we obtained 1,953,932 Grade-A quasar candidates and 22,486,884 Grade-B quasar candidates out of425,540,269 sources(~5.7%). The catalog covers ~99% of quasars in the to-be-applied data by evaluating the completeness of the classification on the testing set. The statistical properties of the candidates agree with that given by the method of color-cut selection. Our catalog can intensely decrease the workload for confirming quasars with the upcoming DESI data by eliminating enormous non-quasars but remaining high completeness. All data in this paper are publicly available online.

Galactic coordinate system based on multi-wavelength catalogs

The currently used Galactic coordinate system（GalC S） is based on the FK5 system at J2000.0, which was transformed from the FK4 system at B1950.0.The limitations and misunderstandings related to this transformed GalC S can be avoided by defining a new GalC S that is directly connected to the International Celestial Reference System（ICRS）. With more data at various wavelengths released by large survey programs, a more appropriate GalC S consistent with features associated with the Milky Way can be established. We try to find the best orientation of the GalC S using data from two all-sky surveys, AKARI and WISE, at six wavelengths between 3.4 μm and 90 μm, and synthesize results obtained at various wavelengths to define an improved GalC S in the framework of the ICRS. The revised GalC S parameters for defining the new GalC S in the ICRS are summarized as：αp= 192.777°, δp= 26.9298°, for the equatorial coordinates of the north Galactic pole and θ = 122.95017° for the position angle of the Galactic center. As one of the Galactic substructures, the Galactic warp exhibits different forms in different GalC Ss that are constructed with various data and methods, which shows the importance of re-defining the GalC S by the relative commission of the International Astronomical Union that can lead to a better understanding of Galactic structure and kinematics.

Differences between magnitudes of Taiwan earthquakes from catalogs of Taiwan and Beijing

Taiwan is a region with very high seismicity where hundreds of earthquakes with ms occurred per year and more than 40 with m≥7 since 1900 due to it is located at the boundary of collision between Eurasian and the Philippine Sea plates.The magnitudes for the same event from these two catalogs of Taiwan and Beijing are different due to diferent data sources selected and different magnitude scales used. To measure sizes of Taiwan events in uniform magnitude scale, the author adopted a catalog of earthquakes with uniform local magnitude scale (Shin, 1993)compiled by Cheng (1996) in compiling a new catalog of Chinese earthquakes. To measure sizes of Taiwan events,we adopted uniform local magnitude scale for events with 5≤M<6. For event with M≥6 we still adopted IASPEI surface wave magnitude scale. Thus the statistic difference between two magnitude values from Taiwan and Beijing in magnitude interval 5≤M<6 reflects difference between Taiwan uniform local magnitode scale and Beijing surface wave magnitude scale. The statistic difference in magnitude interval he6 reflects difference between IASPEI surface wave magnitude scale and Beijing surface wave magnitude scale. Three data sources from "Wang","Cheng" and "Chinese mainland" of Taiwan events with m≥7 are given in this paper, in order to obtain a complete catalog.The statistic result indicates that Taiwan magnitude is slightly larger than Beijing magnitude for 998 events with 5≤M<6. The mean difference is about 0.13 of magnitude unit with deviation 0.32. Similarly, the mean difference is about 0.09 of magnitude unit with deviation 0.23 for 298 eventS with m≥6. We also noted that the difference of magnitude values between Beijing and Taiwan surface wave magnitUdes changed in different time period.Before 1971, most Taiwan magnitude values of the events is larger than Beijing’s. In contrast, most Beijing magnitude values of the events are larger than Taiwan magnitUde values aller 1972. It is probably related to data sources. Three catalogs of events with m≥7 are given in this paper Wang’s catalog (1995) includes 44 events with M≥7, Cheng’s (1996) 39 events and Chinese catalog, before 1911 compiled by Min (1995), 1912-1990 compiled by Wang, et al (1997) and 1991-1998 compiled by Yang, includes 41 events. The variety of these data sources discussed in this paper can be a useful reference for seismologists who use catalog seismic data do their research.However the statistic results and empirical relations presented in this paper can not be used for converting between magnitude scales, since some of them are not the original observation values. In addition, three catalogs of events with M≥ 7 given in this paper can be used for seismicity research comprehensively.

Preliminary Seismic Hazard Assessment in West Africa Based on Incomplete Seismic Catalogs

West Africa is considered a region of low seismicity. However, the monitoring of earthquake activity by local seismic arrays began very early (as early as 1914) in West Africa but seismic catalogs are very incomplete. In 1991, Bertil studied the seismicity of West Africa based on networks of seismic stations in Ivory Coast and neighboring countries. The reference work of Ambraseys and Adams as well as the recent earthquakes given by the international data centres on the seismicity of West Africa were also used for the computations of earthquake hazard parameters. Different earthquake event data have been compiled and homogenised to moment magnitude (Mw). The obtained catalog covers a period of over four centuries (1615-2021) and contains large historical events and recent complete observations. The complete catalog part has been subdivided into four complete subcatalogs with each a level of completeness. The minimum magnitude and the maximum observed magnitude are equal to 2.89 and 6.8 respectively for the whole catalog. The seismic code software developed by Kijko was used to calculate the earthquake hazard parameters. The results give a b value of 0.83 ± 0.08 for the whole period and preliminary seismic hazards curves are also plotted for return periods 25, 50 and 100 years. This is a good and practical example showing that this procedure can be used for seismic hazard assessment in West Africa.

New cross-matching algorithm in large-scale catalogs with ThreadPool technique

We introduce an algorithm to solve the block-edge problem taking advantage of the two different sky splitting functions： HTM and HEALPix. We make the cross-match with the two functions, and then we obtain the union set of the two different sets. We use the ThreadPool technique to speed up the cross-match. In this way improved accuracy can be obtained on the cross-match. Our experiments show that this algorithm has a remarkable performance superiority compared with the previous ones and can be applied to the cross-match between large-scale catalogs. We give some ideas about solving the many-for-one situation occurred in the cross-match.

Low Surface Brightness Galaxies Selected by Different Model Fitting

We present a study of low surface brightness galaxies(LSBGs) selected by fitting the images for all the galaxies inα.40 SDSS DR7 sample with two kinds of single-component models and two kinds of two-component models(disk+bulge):single exponential,single sersic,exponential+deVaucular(exp+deV),and exponential+sérsic(exp+ser).Under the criteria of the B band disk central surface brightness μ_(0,disk)(B)≥22.5 mag arcsec^(-2) and the axis ratio b/a> 0.3,we selected four none-edge-on LSBG samples from each of the models which contain 1105,1038,207,and 75 galaxies,respectively.There are 756 galaxies in common between LSBGs selected by exponential and sersic models,corresponding to 68.42% of LSBGs selected by the exponential model and 72.83% of LSBGs selected by the sersic model,the rest of the discrepancy is due to the difference in obtaining μ_(0) between the exponential and sersic models.Based on the fitting,in the range of 0.5≤n≤1.5,the relation of μ_(0) from two models can be written as μ_(0,sérsic)-μ_(0,exp)=-1.34(n-1).The LSBGs selected by disk+bulge models(LSBG_(2)comps) are more massive than LSBGs selected by single-component models(LSBG_1comp),and also show a larger disk component.Though the bulges in the majority of our LSBG_(2)comps are not prominent,more than 60% of our LSBG_(2)comps will not be selected if we adopt a single-component model only.We also identified 31 giant low surface brightness galaxies(gLSBGs) from LSBG_(2)comps.They are located at the same region in the color-magnitude diagram as other gLSBGs.After we compared different criteria of gLSBGs selection,we find that for gas-rich LSBGs,M_(*)> 10^(10)M_⊙ is the best to distinguish between gLSBGs and normal LSBGs with bulge.

On the Relation Between Symmetry of Radio Galaxies and Their Physical Parameters

Gravity as a fundamental force plays a dominant role in the formation and evolution of cosmic objects and leaves its effect in the emergence of symmetric and asymmetric structures.Thus,analyzing the symmetry criteria allows us to uncover mechanisms behind the gravity interaction and understand the underlying physical processes that contribute to the formation of large-scale structures such as galaxies.We use a segmentation process using intensity thresholding and the k-means clustering algorithm to analyze radio galaxy images.We employ a symmetry criterion and explore the relation between morphological symmetry in radio maps and host galaxy properties.Optical properties(stellar mass,black hole mass,optical size(R_(50)),concentration,stellar mass surface density(μ_(50)),and stellar age)and radio properties(radio flux density,radio luminosity,and radio size)are considered.We found that there is a correlation between symmetry and radio size,indicating larger radio sources have smaller symmetry indices.Therefore,size of radio sources should be considered in any investigation of symmetry.Weak correlations are also observed with other properties,such as R_(50)for FRI galaxies and stellar age.We compare the symmetry differences between FRI and FRII radio galaxies.FRII galaxies show higher symmetry in 1.4 GHz and 150 MHz maps.Investigating the influence of radio source sizes,we discovered that this result is independent of the sizes of radio sources.These findings contribute to our understanding of the morphological properties and analyses of radio galaxies.

New γ-Ray Sources Identified in All-sky Surveys Based on Fermipy's Advanced Algorithm

We employ an efficient method for identifying γ-ray sources across the entire sky,leveraging advanced algorithms from Fermipy,and cleverly utilizing the Galactic diffuse background emission model to partition the entire sky into72 regions,thereby greatly enhancing the efficiency of discovering new sources throughout the sky through multithreaded parallel computing.After confirming the reliability of the new method,we applied it for the first time to analyze data from the Fermi Large Area Telescope(Fermi-LAT)encompassing approximately 15.41 yr of all-sky surveys.Through this analysis,we successfully identified 1379 new sources with significance levels exceeding 4σ,of which 497 sources exhibited higher significance levels exceeding 5σ.Subsequently,we performed a systematic analysis of the spatial extension,spectra,and light variation characteristics of these newly identified sources.We identified 21 extended sources and 23 sources exhibiting spectral curvature above 10 GeV.Additionally,we identified 44 variable sources above 1 GeV.

All-sky Guide Star Catalog for CSST

The China Space Station Telescope(CSST)is a two-meter space telescope with multiple back-end instruments.The Fine Guidance Sensor(FGS)is an essential subsystem of the CSST Precision Image Stability System to ensure the required absolute pointing accuracy and line-of-sight stabilization.In this study,we construct the Main Guide Star Catalog for FGS.To accomplish this,we utilize the information about the FGS and object information from the Gaia Data Release 3.We provide an FGS instrument magnitude and exclude variables,binaries,and high proper motion stars from the catalog to ensure uniform FGS guidance capabilities.Subsequently,we generate a HEALPix index,which provides a hierarchical tessellation of the celestial sphere,and employ the Voronoi algorithm to achieve a homogeneous distribution of stars across the catalog.This distribution ensures adequate coverage and sampling of the sky.The performance of the CSST guide star catalog was assessed by simulating the field of view of the FGS according to the CSST mock survey strategy catalog.The analysis of the results indicates that this catalog provides adequate coverage and accuracy.The catalog's performance meets the FGS requirements,ensuring the functioning of the FGS and its guidance capabilities.

A Cross-matching Service for Data Center of Xinjiang Astronomical Observatory

Cross-matching is a key technique to achieve fusion of multi-band astronomical catalogs. Due to different equipment such as various astronomical telescopes, the existence of measurement errors, and proper motions of the celestial bodies, the same celestial object will have different positions in different catalogs, making it difficult to integrate multi-band or full-band astronomical data. In this study, we propose an online cross-matching method based on pseudo-spherical indexing techniques and develop a service combining with high performance computing system(Taurus) to improve cross-matching efficiency, which is designed for the Data Center of Xinjiang Astronomical Observatory. Specifically, we use Quad Tree Cube to divide the spherical blocks of the celestial object and map the 2D space composed of R.A. and decl. to 1D space and achieve correspondence between real celestial objects and spherical patches. Finally, we verify the performance of the service using Gaia 3 and PPMXL catalogs. Meanwhile, we send the matching results to VO tools-Topcat and Aladin respectively to get visual results. The experimental results show that the service effectively solves the speed bottleneck problem of crossmatching caused by frequent I/O, and significantly improves the retrieval and matching speed of massive astronomical data.

涨套参数化设计方法研究与实现

为了提高零件模型设计的工作效率,在分析比较两种型号涨套结构的基础上,提取了9个尺寸参数和8个特征参数,拟定并实现了分类型、同类型和超级副本三种参数化设计方案。基于涨套的设计方案,指出了参数化设计方案与一般设计方案相比的优点,并对比分析了三种参数化设计方案的特点,指出三种参数化设计方案在实际生产设计中的适用范围。通过CATIA软件中的catalog功能,在以上不同的参数化设计方案的基础上,分别建立了零件库与特征库。

Seismicity patterns before the 2021 Fin (Iran) doublet earthquakes using the region-time-length and time-to-failure methods

Knowledge regarding earthquake hazards and seismicity is crucial for crisis management, and the occurrence of foreshocks, seismic activity patterns, and spatiotemporal variations in seismic activity have been studied. Furthermore, the estimation of the region-time-length (RTL) parameter has been proposed to detect seismic quiescence before the occurrence of a large earthquake. In addition, the time-to-failure method has been used to estimate the time occurrence of large earthquakes. Hence, in this study, to gain deeper insight into seismic activity in the southern Zagros region, we utilized the RTL algorithm to identify the quiescence and activation phases leading to the Fin doublet earthquakes. Temporal variations in the RTL parameter showed two significant anomalies. One corresponded to the occurrence time of the first earthquake (2017-12-12);the other anomaly was associated with the occurrence time of the second event (2021-11-14). Based on a negative value of the RTL parameter observed in the vicinity of the Fin epicenters (2021), seismic quiescence (a decrease in seismicity compared to the preceding background rate) was identified. The spatial distribution of the RTL prognostic parameters confirms the appearance of seismic quiescence surrounding the epicenter of the Fin doublet earthquakes (2021). The time-to-failure method was designed using precursory events that describe the acceleration of the seismic energy release before the mainshock. Using the time-to-failure method for the earthquake catalog, it was possible to estimate both the magnitude and time of failure of the Fin doublet. Hence, the time-tofailure technique can be a useful supplementary method to the RTL algorithm for determining the characteristics of impending earthquakes.

Life Origin in the Milky Way Galaxy: II. Scanning for Habitable Stellar Systems on Behalf of Future Space Missions

The possibility of the life origin in the stellar systems, located at a distance of ~200 pc from the solar system, was investigated. The stars, in the spectrums of which C (carbon), O (oxygen), N (nitrogen), and P (phosphorus) are found, are called DNA-stars. Based on stellar abundances a new method for searching for habitable exoplanets has been developed and a list of 48 DNA-stars in the solar neighborhood, on which life is possible, has been defined. The quota of DNA-stars is equal 1.3% of the total amount of Hypatia Stellar Catalog. Only three DNA-stars out of selected 48 stars belong to the spectral class as our Sun (G2V). The closest to the solar system is the DNA-star with the number HIP 15510, which belongs to the G8V class and is 6 pc away from the solar system. Nine DNA-stars, which have the highest chemical similarity with solar spectrum, were identified. It is identified that one of these nine stars, HIP 24681, has six planets.

图书馆元数据管理与发布平台--eXtensible Catalog功能模块研究

近年来在语义网、开放平台和关联数据等思想的推动下,图书馆逐渐开始将书目数据通过OAI-PMH、关联数据等多种手段发布到互联网上,并与DBpedia等众多的数据和服务紧密融合,形成互联的"数据网络"。在这个过程中将会用到许多元数据处理工具,本文将为研究人员介绍一个集传统图书馆元数据检索、转化和整合为一体的开源元数据管理与发布平台——eXtensible Catalog。

The use of laser ranging to measure space debris

Space debris is a major problem for all the nations that are currently active in space. Adopting high-precision measuring techniques will help produce a reliable and accurate catalog for space debris and collision avoidance. Laser ranging is a kind of real-time measuring technology with high precision for space debris observation. The first space-debris laser-ranging experiment in China was performed at the Shanghai Observatory in July 2008 with a ranging precision of about 60-80 cm. The experi- mental results showed that the return signals from the targets with a range of 900 km were quite strong, with a power of 40W （2J at 20 Hz） using a 10ns pulse width laser at 532 nm wavelength. The performance of the preliminary laser ranging system and the observed results in 2008 and 2010 are also introduced.

Measurements of atmospheric turbulence parameters at Vainu Bappu Observatory using short-exposure CCD images

We report atmospheric turbulence parameters, namely atmospheric seeing, tilt-anisoplanatic angle(θ_0) and coherence time(Τ_0), measured under various sky conditions, at Vainu Bappu Observatory in Kavalur. Bursts of short exposure images of selected stars were recorded with a high-speed, frame-transfer CCD mounted on the Cassegrain focus of a newly commissioned 1.3 m telescope. The estimated median seeing is ≈ 1.85 " at wavelength of ～ 600 nm, the image motion correlation between different pairs of stars is ～44% for θ0≈ 36" and mean Τ_0 is ≈ 2.4 ms. This work was motivated by the design considerations and expected performance of an adaptive optics system that is currently being planned for the telescope.

Test area of the SAGE survey

Sky surveys represent one of the most important efforts to improve developments in astrophysics,especially when using new photometric bands. We are performing the Stellar Abundance and Galactic Evolution(SAGE) survey with a self-designed SAGE photometric system, which is composed of eight photometric bands. The project mainly aims to study the stellar atmospheric parameters of ～0.5 billion stars in ～12 000 deg2 of the northern sky, which mainly focuses on Galactic astronomy, as well as some aspects of extragalactic astronomy. This work introduces the detailed data reduction process of the test field NGC 6791, including the data reduction of single-exposure images and stacked multi-exposure images, and properties of the final catalog.

Random forest algorithm for classification of multiwavelength data

We introduced a decision tree method called Random Forests for multiwavelength data classification. The data were adopted from different databases, including the Sloan Digital Sky Survey （SDSS） Data Release five, USNO, FIRST and ROSAT. We then studied the discrimination of quasars from stars and the classification of quasars, stars and galaxies with the sample from optical and radio bands and with that from optical and X-ray bands. Moreover, feature selection and feature weighting based on Random Forests were investigated. The performances based on different input patterns were compared. The experimental results show that the random forest method is an effective method for astronomical object classification and can be applied to other classification problems faced in astronomy. In addition, Random Forests will show its superiorities due to its own merits, e.g. classification, feature selection, feature weighting as well as outlier detection.