In our previous work,we identified~100,000 metal-poor stars([Fe/H]<-1.0)from the LAMOST Survey.This work estimates their chemical abundances and explores the origin and evolution of the Galactic metal-poor disk.Our...In our previous work,we identified~100,000 metal-poor stars([Fe/H]<-1.0)from the LAMOST Survey.This work estimates their chemical abundances and explores the origin and evolution of the Galactic metal-poor disk.Our chemo-dynamical analysis reveals four main populations within the metal-poor disk:(1)a primordial disk older than 12 Gyr with[Fe/H]>-1.5;(2)debris stars from the progenitor galaxy of Gaia±Sausage±Enceladus(GSE),but now residing in the Galactic disk;(3)the metal-poor tail of the metal-rich,high-αdisk formed10±12 Gyr ago,with metallicity lower limit extending to-2.0;(4)the metal-poor tail of the metal-rich,low-αdisk younger than 8 Gyr,reaching a lower metallicity limit of-1.8.These results reveal the presence of a primordial disk and show that both high-αand low-αdisks reach lower metallicities than previously thought.Analysis of merger debris reveals that Wukong,with extremely low metallicity,likely originates from merger events distinct from GSE.Additionally,three new substructures are identified:ShangGu-1,characterized by unusual[Fe/H]-eccentricity correlations;ShangGu-2,possibly heated disk stars;and ShangGu-3,which can be divided into four subgroups based on differing orbital directions,with two aligning with the previously known Nyx and Nyx-2.展开更多
The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has become a crucial resource in astronomical research,offering a vast amount of spectral data for stars,galaxies,and quasars.This paper presents ...The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has become a crucial resource in astronomical research,offering a vast amount of spectral data for stars,galaxies,and quasars.This paper presents the data processing methods used by LAMOST,focusing on the classification and redshift measurement of large spectral data sets through template matching,as well as the creation of data products.Additionally,this paper details the construction of the Multiple Epoch Catalogs by integrating LAMOST spectral data with photometric data from Gaia and Pan-STARRS,and explains the creation of both low-and medium-resolution data products.展开更多
We aim to investigate the propriety of stellar parameter errors of the official data release of the LAMOST lowresolution spectroscopy(LRS)survey.We diagnose the errors of radial velocity(RV),atmospheric parameters([Fe...We aim to investigate the propriety of stellar parameter errors of the official data release of the LAMOST lowresolution spectroscopy(LRS)survey.We diagnose the errors of radial velocity(RV),atmospheric parameters([Fe/H],Teff,logg)andα-enhancement([α/M])for the latest data release version of DR7,including 6,079,235effective spectra of 4,546,803 stars.Based on the duplicate observational sample and comparing the deviation of multiple measurements to their given errors,we find that,in general,the error of[α/M]is largely underestimated,and the error of RV is slightly overestimated.We define a correction factor k to quantify these misestimations and correct the errors to be expressed as proper internal uncertainties.Using this self-calibration technique,we find that the k-factors significantly vary with the stellar spectral types and the spectral signal-to-noise ratio(S/N).Particularly,we reveal a strange but evident trend between k-factors and error themselves for all five stellar parameters.Larger errors tend to have smaller k-factor values,i.e.,they were more overestimated.After the correction,we recreate and quantify the tight correlations between S/N and errors,for all five parameters,while these correlations have dependence on spectral types.It also suggests that the parameter errors from each spectrum should be corrected individually.Finally,we provide the error correction factors of each derived parameter of each spectrum for the entire LAMOST-LRS DR7 and plan to update them for the later data releases.展开更多
基金supported by the National Natural Science Foundation of China(NSFC,grant Nos.11988101 and12222305)National Key R&D Program of China No.2024YFA1611900Guoshoujing Telescope(the Large Sky Area Multi-Object Fiber Spectroscopic Telescope,LAMOST)is a National Major Scientific Project built by the Chinese Academy of Sciences。
文摘In our previous work,we identified~100,000 metal-poor stars([Fe/H]<-1.0)from the LAMOST Survey.This work estimates their chemical abundances and explores the origin and evolution of the Galactic metal-poor disk.Our chemo-dynamical analysis reveals four main populations within the metal-poor disk:(1)a primordial disk older than 12 Gyr with[Fe/H]>-1.5;(2)debris stars from the progenitor galaxy of Gaia±Sausage±Enceladus(GSE),but now residing in the Galactic disk;(3)the metal-poor tail of the metal-rich,high-αdisk formed10±12 Gyr ago,with metallicity lower limit extending to-2.0;(4)the metal-poor tail of the metal-rich,low-αdisk younger than 8 Gyr,reaching a lower metallicity limit of-1.8.These results reveal the presence of a primordial disk and show that both high-αand low-αdisks reach lower metallicities than previously thought.Analysis of merger debris reveals that Wukong,with extremely low metallicity,likely originates from merger events distinct from GSE.Additionally,three new substructures are identified:ShangGu-1,characterized by unusual[Fe/H]-eccentricity correlations;ShangGu-2,possibly heated disk stars;and ShangGu-3,which can be divided into four subgroups based on differing orbital directions,with two aligning with the previously known Nyx and Nyx-2.
基金supported by the Young Data Scientist Program of the China National Astronomical Data Center。
文摘The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has become a crucial resource in astronomical research,offering a vast amount of spectral data for stars,galaxies,and quasars.This paper presents the data processing methods used by LAMOST,focusing on the classification and redshift measurement of large spectral data sets through template matching,as well as the creation of data products.Additionally,this paper details the construction of the Multiple Epoch Catalogs by integrating LAMOST spectral data with photometric data from Gaia and Pan-STARRS,and explains the creation of both low-and medium-resolution data products.
基金supported by the National Natural Science Foundation of China(NSFC)under grants U2031139 and 12273091the National Key R&D Program of China No.2019YFA0405501+3 种基金the science research grants from the China Manned Space Project with No.CMS-CSST-2021-A08the support of the UCAS Joint PHD Training ProgramNational Major Scientific Project built by the Chinese Academy of Sciencesprovided by the National Development and Reform Commission。
文摘We aim to investigate the propriety of stellar parameter errors of the official data release of the LAMOST lowresolution spectroscopy(LRS)survey.We diagnose the errors of radial velocity(RV),atmospheric parameters([Fe/H],Teff,logg)andα-enhancement([α/M])for the latest data release version of DR7,including 6,079,235effective spectra of 4,546,803 stars.Based on the duplicate observational sample and comparing the deviation of multiple measurements to their given errors,we find that,in general,the error of[α/M]is largely underestimated,and the error of RV is slightly overestimated.We define a correction factor k to quantify these misestimations and correct the errors to be expressed as proper internal uncertainties.Using this self-calibration technique,we find that the k-factors significantly vary with the stellar spectral types and the spectral signal-to-noise ratio(S/N).Particularly,we reveal a strange but evident trend between k-factors and error themselves for all five stellar parameters.Larger errors tend to have smaller k-factor values,i.e.,they were more overestimated.After the correction,we recreate and quantify the tight correlations between S/N and errors,for all five parameters,while these correlations have dependence on spectral types.It also suggests that the parameter errors from each spectrum should be corrected individually.Finally,we provide the error correction factors of each derived parameter of each spectrum for the entire LAMOST-LRS DR7 and plan to update them for the later data releases.
