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Search for the Metal-weak Thick Disk from the LAMOST DR5

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Research in Astronomy and Astrophysics 2022年第2期22卷 72-85页

作者： Tai-Sheng Yan jian-rong shi Hao Tian Wei Zhang Bo Zhang Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China Key Laboratory of Space Astronomy and Technology National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China Department of Astronomy Beijing Normal UniversityBeijing 100875China

Based on the data release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey(LAMOST DR5)and the Gaia Early Data Release 3(Gaia EDR3),we construct a sample containing 46,109 giant(log g≤3.5 dex)stars with heliocentric distance d≤4 kpc,and the sample is further divided into two groups of the inner(RGC8.34 kpc).The LZdistributions of our program stars in the panels with different[Fe/H]and[α/Fe]suggest that the thick-disk consists of two distinct components with different chemical compositions and kinematic *** the inner region,the metal-weak thick disk(MWTD)significantly contributes when[α/Fe]>+0.2 dex and[Fe/H]-0.8 ***,MWTD clearly appears only when[α/Fe]>+0.2 dex and[Fe/H]<-1.2 dex for the outer region,and its proportion is lower than that of the inner region within the same *** results can be obtained from the V_(φ)*** higher fraction of MWTD in the inner region than that in the outer region implies that MWTD may form in the inner disk,and is observational evidence about the inside-out disk formation scenario.

关键词： stars:abundances stars:atmospheres Galaxy:structure Galaxy:kinematics and dynamics methods:data analysis

NLTE analysis of high-resolution H-band spectra IV:neutral copper

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Research in Astronomy and Astrophysics 2020年第8期20卷 287-297页

作者： Xiao-Dong Xu jian-rong shi Jun-Bo Zhang Ze-Ming Zhou 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

To obtain reliable Cu abundances with the APOGEE H-band spectra,it is important to investigate the non-local thermodynamic equilibrium(NLTE)effects on the formation of the H-band Cu I *** addition,the Cu atomic model needs to be *** on both the high-resolution and high signal-tonoise ratio H-band spectra from the Apache Point Observatory Galactic Evolution Experiment(APOGEE)and optical data,we derived the LTE and NLTE copper abundances of 13 FGK sample stars with the spectral synthesis *** find that the NLTE effects are negligible for the Cu I 16005.7?A line in the IR *** copper abundances within the uncertainties from these two sets of lines have been obtained,which indicates the reliability of our NLTE copper atomic *** note that the[Cu/Fe]ratios increase with increasing metallicity when~–1.4 dex<[Fe/H]<~–0.5 dex,favoring a secondary(metallicity-dependent)copper production.

关键词： line:formation line:profiles stars:abundances stars:atmospheres

The Chemical Composition of the Field Zero-Age Star HD 77407

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Chinese Journal of Astronomy and Astrophysics 2007年第3期7卷 405-414页

作者： Xue-Liang Zhu jian-rong shi Gang Zhao Ji Li Qing-Xiang Nie College of Physics and Electronics Shandong Normal University Jinan 250014 National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 Department of Physics Hebei Normal University Shijiazhuang 050016

High-resolution optical spectra of the zero age star HD77407 are analysed and its Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Co, Ni and Ba contents are determined using spectral synthesis method. The temperature of the star is determined by fitting the Hα line wings. The parameters derived for this star are Teff=5900 K, log g=4.47 and [Fe/H] = ＋0.07. It is found that the derived iron content is slightly higher than what is given in the published literature. This star shows a relative overabundances of Ca and Ba, and underabundances of Na, V and Ni with respect to the solar mix. Activity of the star is indicated by the filled in Hα and Ca Ⅱ triplet line cores. It has been confirmed that our spectroscopic approach yields fairly reliable and consistent results for active stars.

关键词： stars abundances- stars ZAMS - stars individual HD77407

Exploring the spectral information content in the LAMOST medium-resolution survey(MRS)

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Research in Astronomy and Astrophysics 2020年第4期20卷 57-68页

作者： Bo Zhang Chao Liu Chun-Qian Li Li-Cai Deng Tai-Sheng Yan jian-rong shi Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China

Although high-resolution stellar spectra allow us to derive precise stellar labels(effective temperature,metallicity,surface gravity,elemental abundances,etc.)based on resolved atomic lines and molecular bands,low-resolution spectra have been proved to be competitive in determining many stellar labels at comparable *** is useful to consider the spectral information content when assessing the capability of a stellar spectrum in deriving precise stellar *** this work,we quantify the information content brought by the LAMOST-II medium-resolution spectroscopic survey(MRS)using the gradient spectra as well as the coefficients-of-dependence(CODs).In general,the wavelength coverage of the MRS well constrains the stellar labels but the sensitivities of different stellar labels vary with spectral types and metallicity of the stars of ***,this affects the performance of the stellar label determination from the MRS *** applying the SLAM method to the synthetic spectra which mimic the MRS data,we find that the precision of the fundamental stellar parameters Teff,log g and[M/H]are better when combining both the blue and red bands of the *** is especially important for warm stars because the Hαline located in the red part plays a more important role in determining the effective temperature for warm *** blue and red parts together,we are able to reach similar performance to the low-resolution spectra except for warm ***,at[M/H]-2.0 dex,the uncertainties of fundamental stellar labels estimated from MRS are substantially larger than that from low-resolution *** also tested the uncertainties of Teff,log g and[M/H]from MRS data induced from the radial velocity mismatch and find that a mismatch of about 1 km s-1,which is typical for LAMOST MRS data,would not significantly affect the stellar label ***,reference precision limits are calculated using synthetic gradient spectra,according to which we expect a

关键词： methods:data analysis methods:statistical stars:fundamental parameters stars:abundances

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

Preliminary numerical simulation of mirror seeing for the Chinese Future Giant Telescope

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Research in Astronomy and Astrophysics 2016年第6期16卷 123-128页

作者： En-Peng Zhang Xiang-Qun Cui Guo-Ping Li Yong Zhang jian-rong shi Yong-Heng Zhao National Astronomical Observatories Chinese Academy of Sciences Key Laboratory of Optical Astronomy Chinese Academy of Sciences Nanjing Institute of Astronomical Optics and Technology National Astronomical ObservatoriesChinese Academy of Sciences

Mirror seeing will be one of the key factors influencing image quality of an extremely large ground-based optical telescope （ELT）. Computational fluid dynamics （CFD） can be used to estimate the mirror seeing and the effects of ventilation. In this paper, we present a simplified approach to simulation of mirror seeing for the Chinese Future Giant Telescope （CFGT, 30 m in diameter） with the CFD software ANSYS Icepak. We get the FWHM of the image and the distribution of refractive index structure function （CN2） above the mirror. We demonstrate that thermal control and ventilation are effective ways to improve the image quality. Our simulation results agree with those of other authors for the ELT. To reduce the mirror seeing to a level of 0.5＂, the suggested temperature excess of the primary mirror above the ambient air for thermal control of the CFGT is 0 - 2 K according to the present results of weakly forced convection. The limitations of the method are also discussed.

关键词： astronomical instrumentation -- methods numerical -- telescopes

Estimating the mirror seeing for a large optical telescope with a numerical method

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Research in Astronomy and Astrophysics 2018年第5期18卷 131-136页

It is widely accepted that mirror seeing is caused by turbulent fluctuations in the index of air refraction in the vicinity of a telescope mirror. Computational Fluid Dynamics（CFD） is a useful tool to evaluate the effects of mirror seeing. In this paper, we present a numerical method to estimate the mirror seeing for a large optical telescope（～ 4 m） in cases of natural convection with the ANSYS ICEPAK software. We get the FWHM of the image for different inclination angles（i） of the mirror and different temperature differences（△T） between the mirror and ambient air. Our results show that the mirror seeing depends very weakly on i, which agrees with observational data from the Canada-FranceHawaii Telescope. The numerical model can be used to estimate mirror seeing in the case of natural convection although with some limitations. We can determine △T for thermal control of the primary mirror according to the simulation, empirical data and site seeing.

关键词： astronomical instrumentation - methods numerical- telescopes

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

Automatic determination of stellar atmospheric parameters and construction of stellar spectral templates of the Guoshoujing Telescope (LAMOST)

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Research in Astronomy and Astrophysics 2011年第8期11卷 924-946页

作者： Yue Wu A-Li Luo Hai-Ning Li jian-rong shi Philippe Prugniel Yan-Chun Liang Yong-Heng Zhao jian-Nan Zhang Zhong-Rui Bai Peng Wei Wei-Xiang Dong Hao-Tong Zhang jian-Jun Chen National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Universitede Lyon Universite Lyon 1 Villeurbanne F-69622 France CRAL Observatoire de Lyon CNRS UMR 5574 69561 Saint-Genis Laval France Key Laboratory of Optical Astronomy NAOC Chinese Academy of Sciences Graduate University of Chinese Academy of Sciences Beijing 100049 China Shandong University at Weihai Weihai 264209 China

A number of spectroscopic surveys have been carried out or are planned to study the origin of the Milky Way. Their exploitation requires reliable automated methods and softwares to measure the fundamental parameters of the stars. Adopting the ULySS package, we have tested the effect of different resolutions and signal-to- noise ratios （SNR） on the measurement of the stellar atmospheric parameters （effective temperature Teff, surface gravity log g, and metaUicity [Fe/H]）. We show that ULySS is reliable for determining these parameters with medium-resolution spectra （R ～2000）. Then, we applied the method to measure the parameters of 771 stars selected in the commissioning database of the Guoshoujing Telescope （LAMOST）. The results were compared with the SDSS/SEGUE Stellar Parameter Pipeline （SSPP）, and we derived precisions of 167 K, 0.34dex, and 0.16dex for Teff, logg and [Fe/H] respectively. Furthermore, 120 of these stars are selected to construct the primary stellar spectral template library （Version 1.0） of LAMOST, and will be deployed as basic ingredients for the LAMOST automated parametrization pipeline.

关键词： astronomical data bases: atlases -- stars: fundamental parameters techniques: spectroscopic -- surveys