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Information from the Kinematics of F and G Stars in the Solar Neighborhood

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chinese Journal of Astronomy and Astrophysics 2002年第5期2卷 419-428页

作者： yu-qin chen, gang zhao and Jian-Rong Shinational astronomical observatories, chinese academy of sciences, beijing 100012 national astronomical observatories Chinese Academy of Sciences Beijing 100012

We have calculated the orbital parameters for 90 stars in chen et al. and updated the kinematic data for stars in Edvardsson et al. by using the accurate Hipparcos parallaxes and proper motions, and recalculated the α-element abundances in Edvardsson et al. in a way consistent with chen et al. The two sets of data are combined in a study of stellar populations and characteristics of F & G stars in the solar neighborhood. We confirm the result of chen et al. that a distinguishable group of stars may belong to the thick disk rather than the thin disk. The ages for the stars are determined using the theoretical isochrones of VandenBerg et al. The age-metallicity relation is investigated for different subgroups according to distance from the sun and galactic orbital parameters. It is found that a mixing of stars with different orbital parameters significantly affect the age-metallicity relation for the disk. Stars with orbits confined to the solar circle all have metallicities [Fe/H] > -0.3 irrespective of their distances from the sun or from the Galactic plane.

关键词： stars: kinematics - Galaxy: evolution - Galaxy: solar neighborhood

Equivalent Widths of 15 Extrasolar-Planet Host Stars

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chinese Journal of Astronomy and Astrophysics 2002年第4期2卷 377-390页

作者： gang zhao, yu-qin chen and Hong-Mei Qiunational astronomical observatories, chinese academy of sciences, beijing 100012 national astronomical observatories CAS NAOC Beijing 100012 China

We present the equivalent widths of 15 extrasolar-planet host stars. These data were based on the high-resolution, high signal-to-noise ratio spectra obtained with the 2.16m telescope at Xinglong station. The error in the Xinglong equivalent width is estimated by a comparison of these data with those given in previous studies of common stars.

关键词： stars: planetary systems - stars: late-type

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

Partitioning the Galactic halo with Gaussian Mixture Models

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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

An Analysis of the Condensation Temperature of Elements of Extrasolar Planetary Systems

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chinese Journal of Astronomy and Astrophysics 2005年第6期5卷 619-626页

作者： Cong Huang gang zhao Hua-Wei Zhang yu-qin chen Department of Astronomy Peking University Beijing 100871 national astronomical observatories Chinese Academy of Sciences Beijing 100012

Using high signal-to-noise ratio spectra of extrasolar planet-hosting stars, we obtained the atmospheric parameters, accurate metallicities and the differential abundance for 15 elements （C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Ni and Ba）. In a search for possible signatures of metal-rich material accreting onto the parent stars, we found that, for a given element, there is no significant trend of increasing [X/H] with increasing condensation temperature To. In our sample of planet-harboring stars, the volatile and refractory elements behave similarly, and we can not confirm if there exists any significant dependence on the condensation temperature Tc.

关键词： planetary systems - stars abundance - stars late-type

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

Stellar Abundance and Galactic Chemical Evolution through LAMOST Spectroscopic Survey

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chinese Journal of Astronomy and Astrophysics 2006年第3期6卷 265-280页

作者： gang zhao yu-qin chen Jian-Rong Shi Yan-Chun Liang Jin-Liang Hou Li chen Hua-Wei Zhang Ai-Gen Li national astronomical observatories Chinese Academy of Sciences Beijing 100012 Shanghai astronomical Observatory Chinese Academy of Sciences Shanghai 200030 Department of Astronomy School of Physics Peking University Beijing 100871 Department of Physics and Astronomy University of Missouri Columbia MO 65211 USA

A project of a spectroscopic survey of Galactic structure and evolution with a Large sky Area Multi-Object fiber Spectroscopic Telescope （LAMOST） is presented. The spectroscopic survey consists of two observational modes for various targets in our Galaxy. One is a major survey of the Milky Way aimed at a systematic study of the stellar abundance and Galactic chemical evolution through low resolution （R = 1000 2000） spectroscopy. Another is a follow-up observation with medium resolution （R = 10000） spectrographs aimed at detailed studies of the selected stars with different chemical composition, kinematics and dynamics.

关键词： techniques: spectroscopic - stars: abundances - Galaxy: structure - Galaxy:abundances - Galaxy: kinematics and dynamics - Galaxy: evolution

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

Chemical abundance analysis of 19 barium stars

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Research in Astronomy and Astrophysics 2016年第1期16卷 159-174页

作者： Guo-Chao Yang Yan-Chun Liang Monique Spite yu-qin chen gang zhao Bo Zhang Guo-qing Liu yu-Juan Liu Nian Liu Li-Cai Deng Francois Spite Vanessa Hill Cai-Xia Zhang College of Physics and Information Engineering Hebei Normal University Shijiazhuang 050024 China Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China University of chinese academy of sciences Beijing 100049 China GEPI Observatoire de Paris-Meudon 92195 Meudon France Physics Department and Tsinghua Center for Astrophysics Tsinghua University Beijing 100084 China Astronomy Department Beijing Normal University Beijing 100875 China Department of Physics Shijiazhuang University Shijiazhuang 050035 China

We aim at deriving accurate atmospheric parameters and chemical abundances of 19 barium（Ba） stars, including both strong and mild Ba stars, based on the high signal-to-noise ratio and high resolution Echelle spectra obtained from the 2.16 m telescope at Xinglong station of national astronomical observatories, chinese academy of sciences. The chemical abundances of the sample stars were obtained from an LTE, plane-parallel and line-blanketed atmospheric model by inputting the atmospheric parameters（effective temperatures Teff, surface gravities log g, metallicity [Fe/H] and microturbulence velocity ξt） and equivalent widths of stellar absorption lines. These samples of Ba stars are giants as indicated by atmospheric parameters, metallicities and kinematic analysis about UVW velocity. Chemical abundances of 17 elements were obtained for these Ba stars. Their Na, Al, α- and iron-peak elements（O, Na, Mg, Al, Si, Ca,Sc, Ti, V, Cr, Mn, Ni） are similar to the solar abundances. Our samples of Ba stars show obvious overabundances of neutron-capture（n-capture） process elements relative to the Sun. Their median abundances of[Ba/Fe], [La/Fe] and [Eu/Fe] are 0.54, 0.65 and 0.40, respectively. The Y I and Zr I abundances are lower than Ba, La and Eu, but higher than the α- and iron-peak elements for the strong Ba stars and similar to the iron-peak elements for the mild stars. There exists a positive correlation between Ba intensity and [Ba/Fe].For the n-capture elements（Y, Zr, Ba, La）, there is an anti-correlation between their [X/Fe] and [Fe/H]. We identify nine of our sample stars as strong Ba stars with [Ba/Fe]〉0.6 where seven of them have Ba intensity Ba=2-5, one has Ba=1.5 and another one has Ba=1.0. The remaining ten stars are classified as mild Ba stars with 0.17〈[Ba/Fe]〈0.54.

关键词： methods: observational - stars: abundances - stars: atmospheres - stars: chemically peculiar- stars: kinematics and dynamics - stars: late-type