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Galactic halo age estimated from LAMOST DR4 and Gaia DR1

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Research in Astronomy and Astrophysics 2019年第1期19卷 87-94页

作者： Jin-Cheng Guo Hua-Wei Zhang Yang Huang Xiao-Wei Liu Ji-Feng Liu Mao-Sheng Xiang Bing-Qiu Chen Hai-Bo Yuan zhi-Jia Tian zhi-ying huo Chun Wang Department of Astronomy Peking University Kavli Institute for Astronomy and Astrophysics Peking University Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of Sciences South-Western Institute for Astronomy Research Yunnan University Department of Astronomy Beijing Normal University

The stellar halo is one of the major components in the Milky Way. Research on its age can provide critical constraints on the origin of the stellar halo and further on the formation of our *** far, different approaches and samples have been used to estimate the age of the Galactic halo. In our previous paper, we carefully selected 63 field halo turn-off stars within 1 kpc from the literature using a kinematic approach, then estimated the age of the halo. In this following work, we not only update the data from LAMOST DR4 and Gaia DR1, but also try a different method to select a clean halo sample by combining the metallicity and orbital parameters. Then we compare this halo turn-off sample with the GARSTEC model in the B-V vs. metallicity plane. After Monte Carlo simulations are performed, the age is estimated to be 10.5±1.4 Gyr, highly consistent with our previous result and other studies. However,due to the limited common sources between LAMOST DR4 and Gaia DR1, the final sample in this paper is still quite small. The estimated age will be more robust with the much larger Gaia DR2.

关键词： galaxies:halos Galaxy:evolution stars:kinematics and dynamics

The LAMOST survey of background quasars in the vicinity of M31 and M33–Ⅲ.results from the 2013 regular survey

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Research in Astronomy and Astrophysics 2015年第8期15卷 1438-1448页

作者： zhi-ying huo Xiao-Wei Liu Mao-Sheng Xiang Jian-Rong Shi Hai-Bo Yuan Yang Huang Yong Zhang Yong-Hui Hou Yue-Fei Wang Ming Yang National Astronomical Observatories Chinese Academy of Sciences Department of Astronomy Peking University Kavli Institute for Astronomy and Astrophysics Peking University Nanjing Institute of Astronomical Optics & Technology Chinese Academy of Sciences

In this work, we report new quasars discovered in fields in the vicinity of the Andromeda（M31） and Triangulum（M33） galaxies with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope（LAMOST, also called the Guo Shou Jing Telescope） during the 2013 observational season, the second year of the regular survey. In total, 1330 new quasars are discovered in an area of ～133 deg2 around M31and M33. With i magnitudes ranging from 14.79 to 20.0 and redshifts from 0.08 to4.85, the 1330 new quasars represent a significant increase in the number of identified quasars in fields in the vicinity of M31 and M33. Up to now, there have been a total of 1870 quasars discovered by LAMOST in this area. The much enlarged sample of known quasars in this area can potentially be utilized to construct a precise astrometric reference frame for the measurement of minute proper motions of M31, M33 and their associated substructures, which are vital for understanding the formation and evolution of M31, M33 and the Local Group of galaxies. Moreover, in the sample,there are a total of 45, 98 and 225 quasars with i magnitudes brighter than 17.0, 17.5and 18.0 respectively. In the aforementioned brightness bins, 15, 35 and 84 quasars are reported here for the first time, and 6, 21 and 81 are reported in our pervious work. In addition, 0, 1 and 6 are from the Sloan Digital Sky Survey and 24, 41 and 54 are from the NED database. These bright quasars provide an invaluable sample to study the kinematics and chemistry of the interstellar/intergalactic medium of the Local Group.

关键词： galaxies: individual(M31 M33)—quasars: general—quasars: emission lines

The evolution of stellar metallicity gradients of the Milky Way disk from LSS-GAC main sequence turn-off stars: a two-phase disk formation history?

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Research in Astronomy and Astrophysics 2015年第8期15卷 1209-1239页

作者： Mao-Sheng Xiang Xiao-Wei Liu Hai-Bo Yuan Yang Huang Chun Wang Juan-Juan Ren Bing-Qiu Chen Ning-Chen Sun Hua-Wei Zhang zhi-ying huo Alberto Rebassa-Mansergas Department of Astronomy Peking University Kavli Institute for Astronomy and Astrophysics Peking University National Astronomical Observatories Chinese Academy of Sciences

Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk. We use 297 042 main sequence turn-off stars selected from the LAMOST Spectroscopic Survey of the Galactic Anticenter（LSS-GAC） to determine the radial and vertical gradients of stellar metallicity,△[Fe/H]/△R and △[Fe/H]/△｜Z ｜ of the Milky Way disk in the direction of the anticenter. We determine ages of those turn-off stars by isochrone fitting and measure the temporal variations of metallicity gradients. We have carried out a detailed analysis of the selection effects resulting from the selection, observation and data reduction of LSS-GAC targets and the potential biases of a magnitude limited sample on the determinations of metallicity gradients. Our results show that the gradients, both in the radial and vertical directions, exhibit significant spatial and temporal variations. The radial gradients yielded by stars with the oldest ages（ 11 Gyr） are essentially zero at all heights from the disk midplane, while those given by younger stars are always negative. The vertical gradients deduced from stars with the oldest ages（ 11 Gyr）are negative and only show very weak variations with Galactocentric distance in the disk plane, R, while those yielded by younger stars show strong variations with *** being essentially flat at the earliest epochs of disk formation, the radial gradients steepen as age decreases, reaching a maximum（steepest） at age 7–8 Gyr, and then they flatten again. Similar temporal trends are also found for the vertical gradients. We infer that the assembly of the Milky Way disk may have experienced at least two distinct phases. The earlier phase is probably related to a slow, pressure-supported collapse of gas, when the gas settles down to the disk mainly in the vertical direction. In the later phase, there are significant radial flows

关键词： Galaxy: abundances—Galaxy: disk—Galaxy: evolution – Galaxy: formation—techniques: spectroscopic

New open cluster candidates discovered in the XSTPS-GAC survey

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Research in Astronomy and Astrophysics 2018年第3期18卷 77-90页

作者： Jin-Cheng Guo Hua-Wei Zhang Hui-Hua Zhang Xiao-Wei Liu Hai-Bo Yuan Yang Huang Song Wang Li Chen Hai-Bin Zhao Ji-Feng Liu Bing-Qiu Chen Mao-Sheng Xiang zhi-Jia Tian zhi-ying huo Chun Wang Department of Astronomy Peking University Kavli Institute for Astronomy and Astrophysics Peking University Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of Sciences South-Western Institute for Astronomy Research Yunnan University Department of Astronomy Beijing Normal University Shanghai Astronomical Observatory Chinese Academy of Sciences Purple Mountain Observatory Chinese Academy of Sciences

The Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center（XSTPS-GAC）is a photometric sky survey that covers nearly 6000 deg^2 towards the Galactic Anti-center（GAC） in the g,r,i bands. Half of its survey field is located on the Galactic Anti-center disk,which makes XSTPSGAC highly suitable to search for new open clusters in the GAC region. In this paper,we report new open cluster candidates discovered in this survey,as well as properties of these open cluster candidates,such as age,distance and reddening,derived by isochrone fitting in the color-magnitude diagram（CMD）.These open cluster candidates are stellar density peaks detected in the star density maps by applying the method from Koposov et al. Each candidate is inspected in terms of its true color image composed from three XSTPS-GAC band images. Then its CMD is checked,in order to identify whether the central region stars have a clear isochrone-like trend differing from background stars. The parameters derived from isochrone fitting for these candidates are mainly based on three band photometry of ***,when these new candidates are able to be seen clearly in 2 MASS data,their parameters are also derived based on the 2 MASS（J-H,J） CMD. There are a total of 320 known open clusters rediscovered and 24 new open cluster candidates discovered in this work. Furthermore,the parameters of these new candidates,as well as another 11 previously known open clusters,are properly determined for the first time.

关键词： open clusters and associations general - Galaxy structure - methods data analysis

A catalogue of Hα emission-line point sources in the vicinity fields of M31 and M33 from the LAMOST survey

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Research in Astronomy and Astrophysics 2020年第6期20卷 273-280页

作者： Meng Zhang Bing-Qiu Chen zhi-ying huo Hua-Wei Zhang Mao-Sheng Xiang Hai-Bo Yuan Yang Huang Chun Wang Xiao-Wei Liu Department of Astronomy Peking UniversityBeijing 100871China South-Western Institute for Astronomy Research Yunnan UniversityKunming 650500China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China Department of Astronomy Beijing Normal UniversityBeijing 100875China

We present a catalogue of 3305 Hα emission-line point sources observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) in the vicinity fields of M31 and M33 during September 2011 and January *** catalogue contains 1487 emission-line stars,532 emission-line nebulae including 377 likely planetary nebulae(PNe),83 H Ⅱ region candidates and 20 possible supernova remnants(SNRs) and 1286 unknown *** them,24 PN candidates,19 H Ⅱ region candidates,10 SNR candidates and one symbiotic star candidate are new *** velocities and fluxes estimated from the Hα line and those quantities of seven other major emission lines including Hβ,[O Ⅲ] A4959,[O Ⅲ] A5007,[N Ⅱ] A6548,[N Ⅱ] A6583,[S Ⅱ] A6717 and [S Ⅱ] A6731 lines of all the catalogued sources yielded from the LAMOST spectra are also presented in our *** catalogue is an ideal starting point to study the chemistry properties and kinematics of M 31 and M 33.

关键词： galaxies individual(M 31,M 33)-stars emission-line-planetary nebulae general-H II regions

The LAMOST spectroscopic survey of globular clusters in M31and *** and new identifications

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Research in Astronomy and Astrophysics 2015年第8期15卷 1392-1413页

作者： Bing-Qiu Chen Xiao-Wei Liu Mao-Sheng Xiang Hai-Bo Yuan Yang Huang zhi-ying huo Ning-Chen Sun Chun Wang Juan-Juan Ren Hua-Wei Zhang Alberto Rebassa-Mansergas Ming Yang Yong Zhang Yong-Hui Hou Yue-Fei Wang Department of Astronomy Peking University Kavli Institute for Astronomy and Astrophysics Peking University National Astronomical Observatories Chinese Academy of Sciences Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of Sciences Nanjing Institute of Astronomical Optics & Technology National Astronomical ObservatoriesChinese Academy of Sciences

We present a catalog of 908 objects observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope（LAMOST） in fields in the vicinity of M31 and M33, targeted as globular clusters（GCs） and candidates. The targets include known GCs and candidates selected from the literature, as well as new candidates selected from the Sloan Digital Sky Survey（SDSS）. Analysis shows that 356 of them are likely GCs with various confidence levels, while the remaining ones turn out to be background galaxies and quasars, stars and H II regions in M31 or foreground Galactic stars. The 356 likely GCs include 298 bona fide GCs and 26 candidates known in the literature. Three candidates, selected from the Revised Bologna Catalog of M31 GCs and candidates（RBC） and one possible cluster from Johnson et al., are confirmed to be bona fide clusters. We search for new GCs in the halo of the M31 among the new candidates selected from the SDSS photometry. Based on radial velocities yielded by LAMOST spectra and visual examination of the SDSS images, we find 28 objects, 5bona fide and 23 likely GCs. Among the five bona fide GCs, three have been recently discovered independently by others, and the remaining 25 are our new identifications,including two bona fide ones. The newly identified objects fall at projected distances ranging from 13 to 265 kpc from M31. Of the two newly discovered bona fide GCs,one is located near M33, probably a GC belonging to M33. The other bona fide GC falls on the Giant Stream with a projected distance of 78 kpc from M31. Of the 23 newly identified likely GCs, one has a projected distance of about 265 kpc from M31 and could be an intergalactic cluster.

关键词： galaxies: individual: M31 M33—galaxies: star clusters—galaxies: Local Group

Quasars in the Galactic Anti-Center Area from LAMOST DR3

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Research in Astronomy and Astrophysics 2017年第4期17卷 7-10页

作者： zhi-ying huo Xiao-Wei Liu Jian-Rong Shi Mao-Sheng Xiang Yang Huang Hai-Bo Yuan Jian-Nan Zhang Wei Zhang Jian-Ling Wang Yu-Zhong Wu Zi-Huang Cao Yong Zhang Yong-Hui Hou Yue-Fei Wang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Department of Astronomy Peking University Beijing 100871 China Kavli Institute for Astronomy and Astrophysics Peking University Beijing 100871 China Department of Astronomy Beijing Normal University Beijing 100875 China Nanjing Institute of Astronomical Optics & Technology Chinese Academy of Sciences Nanjing 210042 China

Abstract We present a sample of quasars discovered in an area near the Galactic Anti-Center covering 150°≤l≤ 210° and ｜b｜ ≤ 30°, based on LAMOST Data Release 3 （DR3）. This sample contains 151 spectroscopically confirmed quasars. Among them 80 are newly discovered with LAMOST. All these quasars are very bright, with i magnitudes peaking around 17.5 mag. All the new quasars were discovered serendipitously from objects that were originally targeted with LAMOST as stars having bluer colors, except for a few candidates targeted as variable, young stellar objects. This bright quasar sample at low Galactic latitudes will help fill the gap in the spatial distribution of known quasars near the Galactic disk that are used to construct an astrometric reference frame for the purpose of accurate proper motion measurements that can be applied to, for example, Gala. They are also excellent tracers to probe the kinematics and chemistry of the interstellar medium in the Milky Way disk and halo via absorption line spectroscopy.

关键词： Galaxy: disk -- quasars: emission lines -- reference systems -- proper motions -- ISM:kinematics and dynamics

Binary Star Fractions from the LAMOST DR4

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Research in Astronomy and Astrophysics 2018年第5期18卷 47-58页

作者： zhi-Jia Tian Xiao-Wei Liu Hai-Bo Yuan Bing-Qiu Chen Mao-Sheng Xiang Yang Huang Chun Wang Hua-Wei Zhang Jin-Cheng Guo Juan-Juan Ren zhi-ying huo Yong Yang Meng Zhang Shao-Lan Bi Wu-Ming Yang Kang Liu Xian-Fei Zhang Tan-Da Li Ya-Qian Wu Jing-Hua Zhang Department of Astronomy Peking University Beijing 100871 China Department of Astronomy Beijing Normal University Beijing 100875 China National Astronomical Observatories Chinese Academy of Sciences Beijing 100101 China Department of Astronomy Yunnan University Kunming 650091 China

Stellar systems composed of single, double, triple or higher-order systems are rightfully regarded as the fundamental building blocks of the Milky Way. Binary stars play an important role in formation and evolution of the Galaxy. Through comparing the radial velocity variations from multiepoch observations, we analyze the binary fraction of dwarf stars observed with LAMOST. Effects of different model assumptions, such as orbital period distributions on the estimate of binary fractions,are investigated. The results based on log-normal distribution of orbital periods reproduce the previous complete analyses better than the power-law distribution. We find that the binary fraction increases with Teff and decreases with [Fe/H]. We first investigate the relation between α-elements and binary fraction in such a large sample as provided by LAMOST. The old stars with high [α/Fe] dominate with a higher binary fraction than young stars with low [α/Fe]. At the same mass, earlier forming stars possess a higher binary fraction than newly forming ones, which may be related with evolution of the Galaxy.

关键词： binaries general- binaries spectroscopic - Galaxy stellar content - stars statistics- surveys

On the LSP3 estimates of surface gravity for LAMOST-Kepler stars with asteroseismic measurements

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Research in Astronomy and Astrophysics 2016年第3期16卷 81-90页

作者： Juan-Juan Ren Xiao-Wei Liu Mao-Sheng Xiang Yang Huang Saskia Hekker Chun Wang Hai-Bo Yuan Alberto Rebassa-Mansergas Bing-Qiu Chen Ning-Chen Sun Hua-Wei Zhang zhi-ying huo Wei Zhang Yong Zhang Yong-Hui Hou Yue-Fei Wang Department of Astronomy Peking UniversityBeijing 100871China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China Max-Planck-Institut fiir Sonnensystemforschung Justus-von-Liebig-Weg 337077 GottingenGermany Stellar Astrophysics Centre Department of Physics and AstronomyAarhus UniversityNy Munkegade 1208000 Aarhus CDenmark Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China Nanjing Institute of Astronomical Optics&Technology National Astronomical ObservatoriesChinese Academy of SciencesNanjing 210042China

Asteroseismology allows for deriving precise values of the surface gravity of stars. The accurate asteroseismic determinations now available for the large number of stars in the Kepler fields can be used to check and calibrate surface gravities that are currently being obtained spectroscopically for a huge number of stars targeted by large-scale spectroscopic surveys, such as the on-going Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） Galactic survey. The LAMOST spectral surveys have obtained a large number of stellar spectra in the Kepler fields. Stellar atmospheric parameters of those stars have been determined with the LAMOST Stellar Parameter Pipeline at Peking University （LSP3）, by template matching with the MILES empirical spectral library. In the current work, we compare surface gravities yielded by LSP3 with those of two asteroseismic samples-- the largest Kepler asteroseismic sample and the most accurate Kepler asteroseismic sample. We find that LSP3 surface gravities are in good agreement with asteroseismic values of Hekker et al., with a dispersion of -0.2 dex. Except for a few cases, asteroseismic surface gravities ofHuber et al. and LSP3 spectroscopic values agree for a wide range of surface gravities. However, some patterns in the differences can be identified upon close inspection. Potential ways to further improve the LSP3 spectroscopic estimation of stellar atmospheric parameters in the near future are briefly discussed. The effects of effective temperature and metallicity on asteroseismic determinations of surface gravities for giant stars are also discussed.

关键词： methods: data analysis -- stars: fundamental parameters -- stars: spectroscopic -- stars general -- stars: oscillations