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Automated estimation of stellar fundamental parameters from low resolution spectra: the PLS method

Research in Astronomy and Astrophysics 2009年第6期9卷 712-724页

作者： Jian-Nan Zhang A-li Luo Yong-Heng zhao national astronomical observatories Chinese Academy of Sciences Beijing 100012 China

PLS （Partial Least Squares regression） is introduced into an automatic estimation of fundamental stellar spectral parameters. It extracts the most correlative spectral component to the parameters （Teff, log g and [Fe/H]）, and sets up a linear regression function from spectra to the corresponding parameters. Considering the properties of stellar spectra and the PLS algorithm, we present a piecewise PLS regression method for estimation of stellar parameters, which is composed of one PLS model for Teff, and seven PLS models for log g and [Fe/H] estimation. Its performance is investigated by large experiments on flux calibrated spectra and continuum normalized spectra at different signal-to-noise ratios （SNRs） and resolutions. The results show that the piecewise PLS method is robust for spectra at the medium resolution of 0.23 nm. For low resolution 0.5 nm and 1 nm spectra, it achieves competitive results at higher SNR. Experiments using ELODIE spectra of 0.23 nm resolution illustrate that our piecewise PLS models trained with MILES spectra are efficient for O ～ G stars： for flux calibrated spectra, the systematic offsets are 3.8%, 0.14 dex, and -0.09 dex for Teff, log g and [Fe/H], with error scatters of 5.2%, 0.44 dex and 0.38 dex, respectively; for continuum normalized spectra, the systematic offsets are 3.8%, 0.12dex, and -0.13 dex for Teff, log g and [Fe/H], with error scatters of 5.2%, 0.49 dex and 0.41 dex, respectively. The PLS method is rapid, easy to use and does not rely as strongly on the tightness of a parameter grid of templates to reach high precision as Artificial Neural Networks or minimum distance methods do.

关键词： methods data analysis -- methods statistical -- stars fundamental param- eters (classification, temperatures, metallicity) -- techniques spectroscopic -- surveys

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Sky subtraction for LAMOST

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Research in Astronomy and Astrophysics 2017年第9期17卷 25-38页

作者： Zhong-Rui Bai Hao-Tong Zhang Hai-Long Yuan Guang-Wei li Jian-Jun Chen Ya-Juan Lei Hui-Qin Yang Yi-Qiao Dong gang Wang Yong-Heng zhao 1 University of chinese academy of sciences Beijing 100049China Key Lab for Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China

Sky subtraction is a key technique in data reduction of multi-fiber spectra. Knowledge of characteristics related to the instrument is necessary to determine the method adopted in sky subtraction. In this study, we describe the sky subtraction method designed for the Large sky Area Multi-Object fiber Spectroscopic Telescope （LAMOST） survey. The method has been integrated into the LAMOST 2D Pipeline v2.6 and applied to data from LAMOST DR3 and later. For LAMOST, calibration using sky emission lines is used to alleviate the position-dependent （and thus time-dependent） ,-~ 4% fiber throughput uncertainty and small wavelength instability （0.1/~） during observation. Sky subtraction using principal component analysis （PCA） further reduces 25% of the sky line residual from OH fines in the red part of LAMOST spectra after the master sky spectrum, which is derived from a B-spline fit of 20 sky fibers in each spectrograph. Using this approach, values are adjusted by a sky emission line and subtracted from each fiber. Further analysis shows that our wavelength calibration accuracy is about 4.5 km s-1, and the averages of residuals after sky subtraction are about 3% for sky emission lines and 3% for the continuum region. The relative sky subtraction residuals vary with moonlight background brightness, and can reach as low as 1.5% for regions that have sky emission lines during a dark night. Tests on F stars with both similar sky emission line strength and similar object continuum intensity show that the sky emission line residual of LAMOST is smaller than that of the SDSS survey.

关键词： techniques: spectroscopic -- methods data analysis -- instrumentation spectrographs

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Inter-annual variation of the earth rotation and El Nio

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chinese Science Bulletin 2002年第2期47卷 105-107页

作者： HAN Yanben zhao Juan li Zhian national astronomical Observatory Chinese Academy of SciencesBeijing 100012China Department of Astronomy Beijing Normal UniversityBeijing 100875China

The relationship between the inter-annual variations of the earth rotation, atmospheric angular momentum (AAM), sunspot number and El Ni(?)o is analyzed. The result shows that the inter-annual variation of the earth rotation responds to the variation of AAM and the preg-nancy of El Ni(?)o timely. Generally, the inter-annual compo-nent of the earth rotation will reach zero in a changing proc-ess that increases from the negative to the positive extreme before El Ni(?)o occurs about half year or more. And the solar activity may have certain influence on the appearance of El Ni(?)o. We consider that El Ni(?)o will possibly appear around the end of 2001.

关键词： El Nino inter-annual variation of earth rotation atmospheric angular moment solar activity.

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High Resolution Spectroscopy of Halo Stars in the Near UV and Blue Region I. Spectra in the Wavelength Region 3550-5000 A

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chinese Journal of Astronomy and Astrophysics 2006年第5期6卷 579-587页

作者： V. G. Klochkova gang zhao S. V. Ermakov V. E. Panchuk national astronomical observatories Chinese Academy of Sciences Beijing 100012 Special Astrophysical Observatory Russian Academy of Sciences Nighnij Arkhyz 369167Karachai-Cherkessia Russia

An atlas of high resolution （R = 60 000） CCD-spectra in the wavelength range 3500-5000A is presented for four objects in metallicity range -3.0 〈 [Fe/H] 〈 -0.6, temperature range 4750 〈 Teff 〈 5900K, and surface gravity range 1.6 〈 Igg 〈 5.0. We describe the calibration of the stellar atmospheric parameters using Alonso＇s formula based on the method of infrared flux and outline the determination of the abundances of a total number of 25 chemical elements. An analysis of the abundance determination errors for different chemical elements is carried out, and a method is provided for the observations and reduction of spectral material. Properties of the method of producing an atlas of spectra and line identifications are described.

关键词： stars halo stars - stars G, K-type - stars spectra - stars UV-spectra

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The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST)

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Research in Astronomy and Astrophysics 2012年第9期12卷 1197-1242页

作者： Xiang-Qun Cui Yong-Heng zhao Yao-Quan Chu Guo-Ping li Qi li li-Ping Zhang hong-Jun Su Zheng-Qiu Yao Ya-Nan Wang Xiao-Zheng Xing Xin-Nan li Yong-Tian Zhu gang Wang Bo-Zhong Gu A-li Luo Xin-Qi Xu Zhen-Chao Zhang Gen-Rong liu Hao-Tong Zhang De-Hua Yang Shu-Yun Cao Hai-Yuan Chen Jian-Jun Chen Kun-Xin Chen Ying Chen Jia-Ru Chu Lei Feng Xue-Fei Gong Yong-Hui Hou hong-Zhuan Hu Ning-Sheng Hu Zhong-Wen Hu Lei Jia Fang-Hua Jiang Xiang Jiang Zi-Bo Jiang Ge Jin Ai-Hua li Yan li Ye-Ping li Guan-Qunliu Zhi-gang liu Huo-Ming Shi Zheng-hong Tang Qing-Sheng Tao Xiang-Yan Yuan Chao Zhai Jing Zhang Yan-Xia Zhang Yong Zhang Ming zhao Fang Zhou Guo-Hua Zhou Jie Zhu Si-Cheng Zou national astronomical observatories Chinese Academy of Sciences Beijing 100012 China yzhao @ *** Nanjing Institute of astronomical Optics and Technology National Astronomical ObservatoriesChinese Academy of Sciences Nanjing 210042 China University of Science and Tecfinologyof China Hefei 230026 China Shanghai astronomical Observatory Chinese Academy of Sciences Shanghai 200030 China Institute of Architecture Design and Research Chinese Academy of Sciences Beijing 100190China

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) is a special reflecting Schmidt telescope. LAMOST’s special design allows both a large aperture (effective aperture of 3.6 m–4.9 m) and a wide field of view (FOV) (5°). It has an innovative active reflecting Schmidt configuration which continuously changes the mirror’s surface that adjusts during the observation process and combines thin deformable mirror active optics with segmented active optics. Its primary mirror (6.67m×6.05 m) and active Schmidt mirror (5.74m×4.40 m) are both segmented, and composed of 37 and 24 hexagonal sub-mirrors respectively. By using a parallel controllable fiber positioning technique, the focal surface of 1.75 m in diameter can accommodate 4000 optical fibers. Also, LAMOST has 16 spectrographs with 32 CCD cameras. LAMOST will be the telescope with the highest rate of spectral acquisition. As a national large scientific project, the LAMOST project was formally proposed in 1996, and approved by the chinese government in 1997. The construction started in 2001, was completed in 2008 and passed the official acceptance in June 2009. The LAMOST pilot survey was started in October 2011 and the spectroscopic survey will launch in September 2012. Up to now, LAMOST has released more than 480 000 spectra of objects. LAMOST will make an important contribution to the study of the large-scale structure of the Universe, structure and evolution of the Galaxy, and cross-identification of multiwaveband properties in celestial objects.

关键词： techniques: wide field telescope - active optics - multi fiber - spectroscopy survey - data reduction

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Discovery of 13 New Variable Stars in the Field of the Open Cluster NGC 2168 (M35)

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chinese Journal of Astronomy and Astrophysics 2005年第4期5卷 356-362页

作者： Juei-Hwa Hu Wing-Huen Ip Xiao-bin Zhang zhao-Ji Jiang Jun Ma Xu Zhou Institute of Astronomy National Central University Chung Li 32054 Taiwan national astronomical Observatory Chinese Academy of Sciences Beijing 100012

A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems,one EA type and two EB type eclipsing binaries （one of them could be a W UMa system）, and seven pulsating stars including three candidates of δ Scuti stars.

关键词： open clusters: individual (NGC 2168)-stars: variables (general)-binaries: general

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The diurnal transport of atmospheric water vapor during major dust storms on Mars based on the Mars Climate Database,version 5.3

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Earth and Planetary Physics 2020年第6期4卷 550-564页

作者： Jing li zhao Peng Wu Tao li Xi Zhang Jun Cui Planetary Environmental and Astrobiological Research Laboratory School of Atmospheric SciencesSun Yat-sen UniversityZhuhai Guangdong 519082China chinese academy of sciences Key Laboratory of Geospace Environment School of Earth and Space SciencesUniversity of Science and Technology of ChinaHefei 230026China Department of Earth and Planetary sciences University of California Santa CruzSanta CruzCalifornia 95064USA chinese academy of sciences Key Laboratory of Lunar and Deep Space Exploration National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China chinese academy of sciences Center for Excellence in Comparative Planetology Hefei 230026China

In recent studies of the Martian atmosphere,strong diurnal variation in the dust was discovered in the southern hemisphere during major dust storms,which provides strong evidence that the commonly recognized meridional transport process is driven by thermal *** process,when coupled with deep convection,could be an important part of the short-term atmospheric dynamics of water ***,the potential of this process to alter the horizontal distribution of moist air has not been systematically *** this work,we conducted pre-research on the horizontal transport of water vapor associated with the migrating diurnal tide(DW1)at 50 Pa in the upper troposphere during major dust storms based on the Mars Climate Database(MCD)5.3,a state-of-the-art database for Martian atmospheric research that has been validated as simulating the relevant short-period atmospheric dynamics *** found westward-propagating diurnal patterns in the global water vapor front during nearly all the major dust storms from Martian years(MYs)24 to *** and correlation analyses showed that the diurnal transport of water vapor during global and A-season regional dust storms is dominated by the *** effect of the tidal transport of water vapor varies with the types of dust storms in different *** regional dust storms,the tidal transport induces only limited diurnal motion of the water ***,the horizontal tidal wind tends to increase the abundance of daytime water vapor at mid-to low latitudes during the MY 28 southern summer global dust storm while decreasing it during the MY 25 southern spring global dust *** tidal transport process during these two global dust storms can induce opposite effects on water escape.

关键词： Martian atmosphere thermal tides water vapor dust storms water escape

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Peculiar in-plane velocities in the outer disc of the Milky Way

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Research in Astronomy and Astrophysics 2017年第11期17卷 45-58页

作者： Hai-Jun Tian Chao liu Jun-Chen Wan You-gang Wang Qiao Wang li-Cai Deng Zi-Huang Cao Yong-Hui Hou Yue-Fei Wang Yue Wu Yong-Heng zhao China Three Gorges University Yichang 443002 China Max Planck Institute for Astronomy K6nigstuhl 17 D-69117 Heidelberg Germany Key Laboratory for Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Key Laboratory of Computational Astrophysics National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Nanjing Institute of astronomical Optics & Technology National Astronomical Observatories Chinese Academy of Sciences Nanjing 210042 China

We present the peculiar in-plane velocities derived from LAMOST red clump stars, which are purified and separated by a novel approach into two groups with different ages. The samples are mostly contributed around the Galactic anti-center direction so that we are able to map the radial profiles of the radial and azimuthal velocities in the outer disc. From variations of the in-plane velocities with Galactocentric radius for the younger and older populations, we find that both radial and azimuthal velocities are not axisymmetric at 8 〈 R 〈 14 kpc. The two red clump populations show that the mean radial velocity is negative within R - 9 kpc and positive beyond. This is likely because of the perturbation induced by the rotating bar. The cross-zero radius, R -9 kpc, essentially indicates the rough location of the Outer lindblad Resonance radius. Given the circular speed of 238 km s^-1, the pattern speed of the bar can be approximated as 45 km s^-1 kpc^-1. The young red clump stars show larger mean radial velocity than the old population by about 3km s^-1 between R-9 and 12kpc. This is possibly because the younger population is more sensitive to the perturbation than the older one. The radial profiles of the mean azimuthal velocity for the two populations show an interesting U-shape, i.e. at R 〈 ***, the azimuthal velocity declines with R by about 10km s^-1, while at R 〉 10.5 kpc it increases with R to 240 - 245 km s^-1. It is not clear why the mean azimuthal velocity shows this U-shape along the Galactic anti-center direction. Moreover, the azimuthal velocity for the younger population is slightly larger than that for the older one and the difference moderately declines with R. Beyond R0-12 kpc, the azimuthal velocities for the two populations are indistinguishable.

关键词： Galaxy: disc -- Galaxy: structure -- Galaxy: kinematics and dynamics -- Galaxy: stellar content -- stars: kinematics and dynamics

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Generation of strong magnetic fields with a laser-driven coil

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High Power Laser Science and Engineering 2018年第3期6卷 1-8页

作者： Zhe Zhang Baojun Zhu Yutong li Weiman Jiang Dawei Yuan Huigang Wei Guiyun liang Feilu Wang gang zhao Jiayong Zhong Bo Han Neng Hua Baoqiang Zhu Jianqiang Zhu Chen Wang Zhiheng Fang Jie Zhang beijing national Laboratory of Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China School of Physical sciences University of Chinese Academy of Sciences Beijing 100049 China Collaborative Innovation Center oflFSA (CICIFSA) Shanghai Jiao Tong University Shanghai 200240 China Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Department of Astronomy Beijing Normal University Beijing 100875 China national Laboratory on High Power Laser and Physics Chinese Academy of Sciences Shanghai 201800 China Shanghai Institute of Laser Plasma Shanghai 201800 China Key Laboratory for Laser Plasmas (MoE) and Department of Physics and Astronomy Shanghai Jiao Tong University Shanghai 200240 China

As a promising new way to generate a controllable strong magnetic field, laser-driven magnetic coils have attracted interest in many research fields. In 2013, a kilotesla level magnetic field was achieved at the Gekko XII laser facility with a capacitor-coil target. A similar approach has been adopted in a number of laboratories, with a variety of targets of different shapes. The peak strength of the magnetic field varies from a few tesla to kilotesla, with different spatio- temporal ranges. The differences are determined by the target geometry and the parameters of the incident laser. Here we present a review of the results of recent experimental studies of laser-driven magnetic field generation, as well as a discussion of the diagnostic techniques required for such rapidly changing magnetic fields. As an extension of the magnetic field generation, some applications are discussed.

关键词： lab astrophysics laser-plasma interaction magnetic field plasma astrophysics

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The Qitai radio telescope

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Science China(Physics,Mechanics & Astronomy) 2023年第8期66卷 150-161页

作者： Na Wang Qian Xu Jun Ma Zhiyong liu Qi liu Hailong Zhang Xin Pei Maozheng Chen Richard N.Manchester Kejia Lee Xingwu Zheng Hans J.Kärcher Wulin zhao hongwei li Dongwei li Martin Süss Matthias Reichert Zhongyi Zhu Congsi Wang Mingshuai li Rui li Ning li Guljaina Kazezkhan Wenming Yan gang Wu Lang Cui Ming Zhang Haitao li Xinjiang astronomical Observatory Chinese Academy of SciencesUrumqi 830011China Key Laboratory of Radio Astronomy Chinese Academy of SciencesNanjing 210008China Xinjiang Key Laboratory of Radio Astrophysics Urumqi 830011China Xinjiang Key Laboratory of Microwave Technology Urumqi 830011China Australia Telescope national Facility CSIRO Space and AstronomyEpping 1710Australia Department of Astronomy Peking UniversityBejing 100871China School of Astronomy and Space Science Nanjing UniversityNanjing 210093China Dr.Hans Jirgen Karcher Engineering Office Karben 61184Germany Northwest China Research Institute of Electronic Equipment Xi'an 710065China OHB Digital Connect(MT Mechatronics) Mainz 55130Germany beijing Institute of Architetural Design Beijing 100045China Guangzhou Instiute of Technology Xidian UniversityGuangzhou 510555 China

This study presents a general outline of the Qitai radio telescope(QTT)***,the site of the telescope,is a county of Xinjiang Uygur Autonomous Region of China,located in the east Tianshan Mountains at an elevation of about 1800 *** QTT is a fully steerable,Gregorian-type telescope with a standard parabolic main reflector of 110 m *** QTT has adopted an umbrella support,homology-symmetric lightweight *** main reflector is active so that the deformation caused by gravity can be *** structural design aims to ultimately allow high-sensitivity observations from 150 MHz up to115 *** satisfy the requirements for early scientific goals,the QTTwill be equipped with ultra-wideband receivers and large field-of-view multi-beam receivers.A multi-function signal-processing system based on RFSo C and GPU processor chips will be *** will enable the QTT to operate in pulsar,spectral line,continuum and Very Long Baseline Interferometer(VLBI)observing *** compatibility(EMC)and radio frequency interference(RFI)control techniques are adopted throughout the system *** QTT will form a world-class observational platform for the detection of lowfrequency(nano Hertz)gravitational waves through pulsar timing array(PTA)techniques,pulsar surveys,the discovery of binary black-hole systems,and exploring dark matter and the origin of life in the *** QTT will also play an important role in improving the chinese and international VLBI networks,allowing high-sensitivity and high-resolution observations of the nuclei of distant galaxies and gravitational lensing *** astrometric observations will also contribute to improving the accuracy of the celestial reference ***,the QTT will be able to support future space activities such as planetary exploration in the solar system and to contribute to the search for extraterrestrial intelligence.

关键词： radio telescope radio astronomy observation receiver RFI

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