This paper statistically analyzes the seeing data at the Lenghu site Platform C from 2018 to 2024,during which extensive construction modified the original landscape.The study focuses on the impacts of meteorological ...This paper statistically analyzes the seeing data at the Lenghu site Platform C from 2018 to 2024,during which extensive construction modified the original landscape.The study focuses on the impacts of meteorological factors and building obstructions.The results reveal a progressive degradation in seeing as the monitoring setup passively changed:the median values were 0."76(the original location),0."83 during the Terrace,and 0."99 at the new Dome(temporarily considered the permanent monitoring location).Once the instruments are fully deployed,wind speed and wind direction critically affect seeing quality,with optimal conditions occurring when the wind speed is 2–6 m s^(−1) and the wind direction is between 180°and 270°.However,in 2023 and 2024,the wind speeds decreased,and the prevailing wind direction shifted from southwest to northwest,correlating with poorer seeing.Computational Fluid Dynamics simulations reveal that the construction of the Wide Field Survey Telescope altered the local wind field,increasing turbulence around the Dome,especially when the winds blow from 225°to 255°.In contrast,Platform A,located in a higher and more open area,consistently maintained better seeing,particularly after midnight,likely due to fewer obstructions and lower nocturnal heat release.展开更多
The Large Optical/infrared Telescope of China is a 12 meter diameter ground-based optical/infrared telescope which is proposed to be constructed in the western part of China in favor of its arid climate,and clear,dark...The Large Optical/infrared Telescope of China is a 12 meter diameter ground-based optical/infrared telescope which is proposed to be constructed in the western part of China in favor of its arid climate,and clear,dark nights.A site testing campaign was initiated between November 2016 and March2019 in order to investigate long term astronomical weather conditions in the western part of China,specifically,at three sites:Ali in Tibet,Daocheng in Sichuan and Muztagh-ata in Xinjiang.This is the first attempt to evaluate long term performances of three candidate sites with uniformly calibrated instruments and data collecting/processing methods for a two-year span in China.In this special issue,we present nine papers that describe the whole site testing campaign,including preparation,data collecting/processing methods,instrument set up at three candidate sites as well as detailed statistics for the measurement results from March 2017 to March 2019.展开更多
Large sky Area Multi-Object fiber Spectroscopic Telescope(LAMOST) has completed the observation of nearly 20 million celestial objects,including a class of spectra labeled “Unknown.” Besides low signal-to-noise rati...Large sky Area Multi-Object fiber Spectroscopic Telescope(LAMOST) has completed the observation of nearly 20 million celestial objects,including a class of spectra labeled “Unknown.” Besides low signal-to-noise ratio,these spectra often show some anomalous features that do not work well with current templates.In this paper,a total of 637,889 “Unknown” spectra from LAMOST DR5 are selected,and an unsupervised-based analytical framework of “Unknown” spectra named SA-Frame(Spectra Analysis-Frame) is provided to explore their origins from different perspectives.The SA-Frame is composed of three parts:NAPC-Spec clustering,characterization and origin analysis.First,NAPC-Spec(Nonparametric density clustering algorithm for spectra) characterizes different features in the “unknown” spectrum by adjusting the influence space and divergence distance to minimize the effects of noise and high dimensionality,resulting in 13 types.Second,characteristic extraction and representation of clustering results are carried out based on spectral lines and continuum,where these 13 types are characterized as regular spectra with low S/Ns,splicing problems,suspected galactic emission signals,contamination from city light and un-gregarious type respectively.Third,a preliminary analysis of their origins is made from the characteristics of the observational targets,contamination from the sky,and the working status of the instruments.These results would be valuable for improving the overall data quality of large-scale spectral surveys.展开更多
基金supported by the grant 2023FY101100 of the Ministry of Science and Technology of China(MOST)the key project of the National Natural Science Foundation of China(NSFC,grant No.12233009)the support from the National Natural Science Foundation of China(NSFC,grant Nos.12273064,42222408,12322306,and 12373093).
文摘This paper statistically analyzes the seeing data at the Lenghu site Platform C from 2018 to 2024,during which extensive construction modified the original landscape.The study focuses on the impacts of meteorological factors and building obstructions.The results reveal a progressive degradation in seeing as the monitoring setup passively changed:the median values were 0."76(the original location),0."83 during the Terrace,and 0."99 at the new Dome(temporarily considered the permanent monitoring location).Once the instruments are fully deployed,wind speed and wind direction critically affect seeing quality,with optimal conditions occurring when the wind speed is 2–6 m s^(−1) and the wind direction is between 180°and 270°.However,in 2023 and 2024,the wind speeds decreased,and the prevailing wind direction shifted from southwest to northwest,correlating with poorer seeing.Computational Fluid Dynamics simulations reveal that the construction of the Wide Field Survey Telescope altered the local wind field,increasing turbulence around the Dome,especially when the winds blow from 225°to 255°.In contrast,Platform A,located in a higher and more open area,consistently maintained better seeing,particularly after midnight,likely due to fewer obstructions and lower nocturnal heat release.
基金supported by the Center for Astronomical Mega-Science,Chinese Academy of Sciences(CAMS-CAS)supported by the Operation,Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments,budgeted from the Ministry of Finance of China(MOF)and administrated by the Chinese Academy of Sciences(CAS)supported by the National Natural Science Foundation of China(No.11873081)。
文摘The Large Optical/infrared Telescope of China is a 12 meter diameter ground-based optical/infrared telescope which is proposed to be constructed in the western part of China in favor of its arid climate,and clear,dark nights.A site testing campaign was initiated between November 2016 and March2019 in order to investigate long term astronomical weather conditions in the western part of China,specifically,at three sites:Ali in Tibet,Daocheng in Sichuan and Muztagh-ata in Xinjiang.This is the first attempt to evaluate long term performances of three candidate sites with uniformly calibrated instruments and data collecting/processing methods for a two-year span in China.In this special issue,we present nine papers that describe the whole site testing campaign,including preparation,data collecting/processing methods,instrument set up at three candidate sites as well as detailed statistics for the measurement results from March 2017 to March 2019.
基金supported by the National Natural Science Foundation of China (Grant Nos. U1931209, 62272336)Projects of Science and Technology Cooperation and Exchange of Shanxi Province (Grant Nos. 202204041101037, 202204041101033)+3 种基金the central government guides local science and technology development funds (Grant No. 20201070)The Fundamental Research Program of Shanxi Province (Grant Nos. 20210302123223, 202103021224275)the Ph D Start-up Foundation of Taiyuan University of Science and Technology (20222119)Guo Shou Jing Telescope (the Large sky Area Multi-Object fiber Spectroscopic Telescope, LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission。
文摘Large sky Area Multi-Object fiber Spectroscopic Telescope(LAMOST) has completed the observation of nearly 20 million celestial objects,including a class of spectra labeled “Unknown.” Besides low signal-to-noise ratio,these spectra often show some anomalous features that do not work well with current templates.In this paper,a total of 637,889 “Unknown” spectra from LAMOST DR5 are selected,and an unsupervised-based analytical framework of “Unknown” spectra named SA-Frame(Spectra Analysis-Frame) is provided to explore their origins from different perspectives.The SA-Frame is composed of three parts:NAPC-Spec clustering,characterization and origin analysis.First,NAPC-Spec(Nonparametric density clustering algorithm for spectra) characterizes different features in the “unknown” spectrum by adjusting the influence space and divergence distance to minimize the effects of noise and high dimensionality,resulting in 13 types.Second,characteristic extraction and representation of clustering results are carried out based on spectral lines and continuum,where these 13 types are characterized as regular spectra with low S/Ns,splicing problems,suspected galactic emission signals,contamination from city light and un-gregarious type respectively.Third,a preliminary analysis of their origins is made from the characteristics of the observational targets,contamination from the sky,and the working status of the instruments.These results would be valuable for improving the overall data quality of large-scale spectral surveys.
