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Partitioning the Galactic halo with Gaussian Mixture Models

Research in Astronomy and Astrophysics 2021年第5期21卷 274-286页

作者： Xi-Long Liang Yu-Qin Chen jing-kun zhao Gang zhao School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China CAS Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China

The Galactic halo is supposed to form from merging with nearby dwarf *** order to probe different components of the Galactic halo,we have applied the Gaussian Mixture Models method to a selected sample of metal poor stars with[Fe/H]<−0.7 dex in the APOGEE DR16 catalogue based on four-parameters,metallicity,[Mg/Fe]ratio and spatial velocity(VR,V).Nine groups are identified with four from the halo(group 1,3,4 and 5),one from the thick disk(group 6),one from the thin disk(group 8)and one from dwarf galaxies(group 7)by analyzing their distributions in the([M/H],[Mg/Fe]),(VR,V),(Zmax,eccentricity),(Energy,Lz)and([Mg/Mn],[Al/Fe])*** rest of the two groups are respectively caused by observational effect(group 9)and the cross section component(group 2)between the thin disk and the thick *** is found that in the extremely outer accreted halo(group 1),stars born in the Milky Way cannot be distinguished from those accreted from other galaxies either chemically or *** the intermediate metallicity of−1.6<[Fe/H]<−0.7 dex,the accreted halo is mainly composed of the Gaia-Enceladus-Sausage substructure(group 5),which can be easily distinguished from group 4(the in-situ halo group)in both chemical and kinematic *** stars of group 4 may come from the disk and some disk stars can be scattered to high orbits by resonant effects as shown in the Zmax versus Energy *** also displayed the spatial distribution of main components of the halo and the ratio of accreted components do not show clear relation to the Galactic radius.

关键词： Galaxy:abundances Galaxy:kinematics Galaxy:structure

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Kinematics and activity of M dwarfs in LAMOST DR1

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Research in Astronomy and Astrophysics 2015年第6期15卷 860-870页

作者： Zhen-Ping Yi A-Li Luo jing-kun zhao Yi-Han Song jing-Chang Pan Yong-Heng zhao Yong Zhang Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Shandong University Weihai 264209 China University of Chinese Academy of Sciences Beijing 100049 China Nanjing Institute of Astronomical Optics & Technology National Astronomical Observatories Chinese Academy of Sciences Nanjing 210042 China

We report on the first investigation into kinematics and chromospheric activity of M dwarfs from the Guo Shou jing Telescope （also called the Large Sky Area Multi-Object Fiber Spectroscopic Telescope - LAMOST） data release one （DR1）. The sample comprises 71 304 M dwarfs. Their fundamental parameters such as spectral types, radial velocities, important molecular band indices and magnetic activities are measured. Their distances are determined by a spectroscopic parallax relation. Space motion （U, V, W） and Galactocentric cylindrical coordinates （R, θ, Z） for the M dwarfs are also computed. We examine velocity dispersion as a function of height from the Galactic plane and find that all three components of velocity dispersion in- crease with height as measured with respect to the Galactic plane. The investigation into chromospheric activities along the height from the Galactic plane confirms that M dwarfs closer to the Galactic plane are more likely to be active. We take a pure kinematical approach to select thin disk stars and thick disk stars from our sample, then to investigate the differences in properties between these two populations. Our analysis is in excellent agreement with previous studies and leads to a better understanding of the structure of the Galactic disk.

关键词： stars kinematics -- stars magnetic fields -- stars low-mass, brown dwarfs -- stars fundamental parameters

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Automatic Normalization and Equivalent-Width Measurement of High-Resolution Stellar Spectra

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Chinese Journal of Astronomy and Astrophysics 2006年第6期6卷 689-696页

作者： jing-kun zhao Gang zhao Yu-Qin Chen Jian-Rong Shi Yu-Juan Liu Ju-Yong Zhang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012

It is well known that normalization, radial velocity correction and equivalent-width measurement of high-resolution stellar spectra are time-consuming work. In order to improve the efficiency we present an automatic method for these routines. The continuum is determined by fitting the ＇high points＇ in the spectrum. After continuum normalization, the program automatically searches for the position of the Ha line and obtains a rough radial velocity, then computes an accurate radial velocity by cross-correlation between the given spectrum and the solar spectrum. In this method, the equivalent-width is automatically measured using Gaussian fitting. A comparison between our results and those from traditional analysis shows that the typical error for equivalent width is around 3.8% in our method. Developing such automatic routines does not mean to replace the interactive reduction method： it is just for a quick extraction of information from the spectra, especially those obtained in large sky surveys.

关键词： techniques radial velocities - stars abundances

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The Stellar Abundances and Galactic Evolution Survey:Photonic Passbands and Extinction Coefficients for the u and v Bands

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Research in Astronomy and Astrophysics 2022年第10期22卷 39-48页

作者： Ke-Feng Tan Gang zhao Zhou Fan Wei Wang Hai-Bo Yuan Jie Zheng Chun Li Nan Song jing-kun zhao CAS Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 10049China Chinese Academy of Sciences South America Center for Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China Department of Astronomy Beijing Normal UniversityBeijing 100875China China Science and Technology Museum Beijing 100101China

The Stellar Abundances and Galactic Evolution Survey(SAGES)is a multi-band photometric survey focused on estimation of stellar atmospheric parameters and interstellar *** this paper we have derived photonic passbands for the intermediate-band u and v filters of the SAGES photometric *** derived photonic passbands have been compared with those of the u and v filters of the Stromgren and SkyMapper *** photometry based on the derived photonic passbands could reproduce the observations very *** have also derived observed,model-free extinction coefficients for the SAGES u and v bands(as well as the Pan-STARRS grizy bands)using the“standard pair”*** derived reddening coefficients have been compared with those predicted by the extinction *** of reddening coefficients with effective temperatures and color excesses of B–V given by Schlegel et al.(E(B-V)_(SFD))have been *** obvious trends or significant variations with effective temperatures have been found,but reddening coefficients for all the colors exhibit declining trends with increasing E(B-V)_(SFD),with typical relative variations of twenty-some percent from E(B-V)_(SFD)~0 to 1.

关键词： stars general-(ISM:)dust-extinction-techniques photometric

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Halo stream candidates in the LAMOST DR2

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Research in Astronomy and Astrophysics 2015年第8期15卷 1378-1391页

作者： jing-kun zhao Gang zhao Yu-Qin Chen Ke-Feng Tan Meng-Tian Gao Ming Yang Yong Zhang Yong-Hui Hou Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of Sciences CUG Faculty of Resources China University of GeosciencesWuhan Nanjing Institute of Astronomical Optics & Technology National Astronomical ObservatoriesChinese Academy of Sciences

We have cross-matched the LAMOST DR2 with the WISE, 2MASS and PPMXL catalogs and obtained a sample of 64 819 FGK metal-poor dwarfs with [Fe/H]〈-0.7, distances within 2 kpc from the Sun and reliable kinematics（space velocities,angular momenta and eccentricities）. With a detection strategy for halo streams provided by Klement et al, nine significant ＂phase-space overdensities＂ with stars on very similar orbits are identified from this sample. Among these overdensities, three were previously known and six are new stream candidates. The kinematics and metallicities of these stream candidates are then analyzed; they have typical halo *** have extracted the most probable members of each halo stream according to their angles with respect to the North Galactic Pole and investigate the distribution of the angular momenta to further verify their existences. Detailed study of elemental abundances for these members based on high resolution and high signal-to-noise spectra from follow-up observations in the near future is of high interest to understand the origin of these streams.

关键词： Galaxy: kinematics and dynamics

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A comparison of stellar atmospheric parameters from the LAMOST and APOGEE datasets

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Research in Astronomy and Astrophysics 2015年第8期15卷 1125-1136页

作者： Yu-Qin Chen Gang zhao Chao Liu jing Ren Yun-Peng Jia jing-kun zhao A-Li Luo Yue Wu Yong Zhang Yong-Hui Hou Yue-Fei Wang Ming Yang Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of Sciences Nanjing Institute of Astronomical Optics & Technology National Astronomical ObservatoriesChinese Academy of Sciences

We have compared stellar parameters, including temperature, gravity and metallicity, for common stars in the LAMOST DR2 and SDSS DR12/APOGEE datasets. It is found that the LAMOST dataset provides a more well-defined red clump feature than the APOGEE dataset in the Teff versus log g diagram. With this advantage, we have separated red clump stars from red giant stars, and attempt to establish calibrations between the two datasets for the two groups of stars. The results show that there is a good consistency in temperature with a calibration close to the one-to-one line, and we can establish a satisfactory metallicity calibration of[Fe/H]APOGEE= 1.18[Fe/H]LAMOST ＋ 0.11 with a scatter of ～ 0.08 dex for both the red clump and red giant branch samples. For gravity, there is no correlation for red clump stars between the two datasets, and scatters around the calibrations of red giant stars are substantial. We found two main sources of scatter in log g for red giant stars. One is a group of stars with 0.00253 × Teff- 8.67 〈 log g 〈 2.6 located in the forbidden region, and the other is the contaminated red clump stars, which could be picked out from the unmatched region where stellar metallicity is not consistent with position in the Teff versus log g diagram. After excluding stars in these two regions,we have established two calibrations for red giant stars, log g APOGEE = 0.000615 ×Teff,LAMOST＋ 0.697 × log g LAMOST- 2.208（σ = 0.150） for [Fe/H] 〉-1 and log gAPOGEE= 0.000874×Teff,LAMOST＋0.588×log g LAMOST-3.117（σ = 0.167）for [Fe/H] 〈-1. The calibrations are valid for stars with Teff = 3800- 5400 K and log g = 0- 3.8 dex, and are useful in work aiming to combine the LAMOST and APOGEE datasets in a future study. In addition, we find that an SVM method based on asteroseismic log g is a good way to greatly improve the accuracy of gravity for these two regions, at least in the LAMOST dataset.

关键词： stars: late type—stars: fundamental parameters—stars: atmospheres—stars: abundances

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A modified 3D mean strain energy density criterion for predicting shale mixed-mode Ⅰ/Ⅲ fracture toughness

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第7期16卷 2411-2428页

作者： kun Zheng Chaolin Wang Yu zhao jing Bi Haifeng Liu College of Civil Engineering Guizhou UniversityGuiyang550025China State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China

The fracture toughness of rocks is a critical fracturing parameter in geo-energy exploitation playing a significant role in fracture mechanics and hydraulic *** edge-notched disk bending(ENDB)specimens are employed to measure the entire range of mixed-modeⅠ/Ⅲfracture toughness of Longmaxi *** theoretically interpret the fracture mechanisms,this research first introduces the detailed derivations of three established fracture *** distinguishing the volumetric and distortional strain energy densities,an improved three-dimensional mean strain energy density(MSED)criterion is *** the critical volumetric to distortional MSED ratio decreases,the transition from tensiondominated fracture to shear-dominated fracture is *** results indicate that both peak load and applied energy increase significantly with the transition from pure mode I(i.e.,tension)to pure modeⅢ(i.e.,torsion or tearing)since mode-Ⅲcracking happens in a twisted manner and mode-Ⅰcracking occurs in a coplanar *** macroscopic fracture signatures are consistent with those of triaxial hydraulic *** average ratio of pure mode-Ⅲfracture toughness to pure mode-Ⅰfracture toughness is 0.68,indicating that the obtained mode-Ⅲfracture resistance for a tensionbased loading system is apparent rather than *** to the three mainstream fracture criteria,the present fracture criterion exhibits greater competitiveness and can successfully evaluate and predict mixed-modeⅠ/Ⅲfracture toughness of distinct materials and loading methods.

关键词： Longmaxi shale Hydraulic fracturing Fracture mechanisms Fracture criteria Mixed-modeⅠ/Ⅲfracture toughness Edge-notched disk bending

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High-α-Metal-Rich stars in the LAMOST-MRS survey and its connection with the galactic bulge

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Research in Astronomy and Astrophysics 2021年第6期21卷 424-432页

作者： Hao-Peng Zhang Yu-Qin Chen Gang zhao jing-kun zhao Xi-Long Liang Hai-Ning Li Ya-Qian Wu Ali Luo Rui Wang CAS Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China

We report the detection of a large sample of high-α-metal-rich stars on the low giant branch with 2.60.2 than the comparison *** properties strongly indicate its connection with the outer bar/bulge region at R=3-5 kpc.A tentative interpretation of this special group is that its stars were formed in the X-shaped bar/bulge region,close to its corotation radius,where radial migration is the most intense,and brings them to present locations at 9 kpc and *** eccentricities and slightly outward radial excursions of its stars are consistent with this *** kinematics(cold)and chemistry([α/Fe]~0.1)further support the formation of the instability-driven X-shaped bar/bulge from the thin disk.

关键词： stars:late type stars:abundances stars:fundamental parameters Galaxy:disk Galaxy:evolution Galaxy:structure

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Metallicity calibration for solar type stars based on red spectra

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Research in Astronomy and Astrophysics 2011年第5期11卷 563-576页

作者： jing-kunzhao Gangzhao Yu-QinChen A-LiLuo KeyLaboratoryofOpticalAstronomy NationalAstronomicalObservatoriesChineseAcademyofSciencesBeijing100012China

Based on a high resolution and high signal-to-noise ratio （S/N） spectral analysis of 90 solar-type stars, we have established several new metaUicity calibrations in the Tefr range [5600, 6500] K based on red spectra with the wavelength range of 560-880 nm. The new metallicity calibrations are applied to determine the metallicity of solar analogs selected from Sloan Digital Sky Survey （SDSS） spectra. There is a good consistent result with the adopted value presented in SDSS-DR7 and a small scatter of 0.26 dex for stars with S/N 〉 50 being obtained. This study provides a new reliable way to derive the metallicity for solar-like stars with low resolution spectra. In particular, our calibrations are useful for finding metal-rich stars, which are missing in the SEGUE Stellar Parameter Pipeline.

关键词： techniques: radial velocities - stars: temperatures - stars: abundances

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CaII H&K emission distribution of ～120000 F,G and K stars in LAMOST DR1

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Research in Astronomy and Astrophysics 2015年第8期15卷 1282-1293页

作者： jing-kun zhao Terry D.Oswalt Yu-Qin Chen Jian-Rong Shi Ke-Feng Tan Xiang-Song Fang Gang zhao Ming Yang Yong Zhang Yong-Hui Hou Yue-Fei Wang Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of Sciences Embry-Riddle Aeronautical University 600 S.Clyde Morris Blvd.Daytona Beach FL 32114USA Nanjing Institute of Astronomical Optics & Technology National Astronomical ObservatoriesChinese Academy of Sciences

We present chromospheric activity index SHK measurements for 119 995 F, G and K stars with high signal-to-noise ratio（S/N 〉 80） spectra, extracted from LAMOST DR1 in SDSS g band. The index δS for each of these stars is calculated by the difference between its SHK value and the baseline determined from very inactive stars. The effect of metallicity on measurement of δS varies with stellar Teff. No evident Vaughan-Preston gap appears in our sample. The relation between δS and vertical distance from the Galactic plane is determined for stars with Teff 〈 5500 K. Stars with higher δS tend to be closer to the Galactic plane. Two open clusters in the DR1 sample, M45 and M67, exhibit the expected general trend that δS decays with *** stars with Teff 〉 5500 K, similar δS levels appear in both young and old cluster stars, which supports Pace＇s suggestion that caution should be exercised when deriving the age of a single star by using its chromospheric activity. Finally, we investigate the relation between δS and the kinematics of our sample.

关键词： stars: activity

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