A catalog of more than 43,000 M giant stars has been selected by Li et al.from the ninth data release of LAMOST.Using the data-driven method SLAM,we obtain the stellar parameters(T_(eff),logg,[M/H],[α/M])for all the ...A catalog of more than 43,000 M giant stars has been selected by Li et al.from the ninth data release of LAMOST.Using the data-driven method SLAM,we obtain the stellar parameters(T_(eff),logg,[M/H],[α/M])for all the M giant stars with uncertainties of 57 K,0.25 dex,0.16 dex and 0.06 dex at SNR>100,respectively.With those stellar parameters,we constrain the absolute magnitude in the K-band,which brings distance with relative uncertainties around 25%statistically.Radial velocities are also calculated by applying cross correlation on the spectra between 8000 and 8950?with synthetic spectra from ATLAS9,which covers the CaⅡtriplet.Comparison between our radial velocities and those from APOGEE DR17 and Gaia DR3 shows that our radial velocities have a system offset and dispersion around 1 and 4.6 km s^(-1),respectively.With the distances and radial velocities combining with the astrometric data from Gaia DR3,we calculate the full 6D position and velocity information,which are able to be used for further chemo-dynamic studies on the disk and substructures in the halo,especially the Sagittarius Stream.展开更多
The clarity of nights is the major factor that should be carefully considered for optical/infrared astronomical observatories in site-testing campaigns.Cloud coverage is directly related to the amount of time availabl...The clarity of nights is the major factor that should be carefully considered for optical/infrared astronomical observatories in site-testing campaigns.Cloud coverage is directly related to the amount of time available for scientific observations at observatories.In this article,we report on the results of detailed night-time cloud statistics and continuous observing time derived from ground-based all-sky cameras(ASCs)at the Muztagh-ata site from 2017to 2021.Results obtained from acquisition data show that the proportion of the annual observing time at the Muztagh-ata site is 65%,and the best period with the least cloud coverage and longer continuous observing time is from September to February.We made a comparison of the monthly mean observing nights obtained from our ASC and CLARA data set,and results show that the discrepancy between them may depend on the cloud top heights.On average,this site can provide 175 clear nights and 169 nights with at least 4 hr of continuous observing time per year.展开更多
Site-testing is crucial for achieving the goal of scientific research and analysis of meteorological and optical observing conditions,one of the associated basic tasks.As one of three potential sites to host the 12-me...Site-testing is crucial for achieving the goal of scientific research and analysis of meteorological and optical observing conditions,one of the associated basic tasks.As one of three potential sites to host the 12-meter Large Optical/infrared Telescope(LOT),the Muztagh-ata site,which is located on the Pamir Plateau in Xinjiang,in west China,began its site-testing task in the spring of 2017.In this paper,we firstly start with an introduction to the site and then present a statistical analysis of the ground-level meteorological properties such as air temperature,barometric pressure,relative humidity,and wind speed and direction,recorded by an automatic weather station with standard meteorological sensors for a two-year duration.We also show the monitoring results of sky brightness during this period.展开更多
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 t...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.展开更多
The Large Optical/infrared Telescope(LOT)is a ground-based 12 m diameter optical/infrared telescope which is proposed to be built in the western part of China in the next decade.Based on satellite remote sensing data,...The Large Optical/infrared Telescope(LOT)is a ground-based 12 m diameter optical/infrared telescope which is proposed to be built in the western part of China in the next decade.Based on satellite remote sensing data,along with geographical,logistical and political considerations,three candidate sites were chosen for ground-based astronomical performance monitoring.These sites include:Ali in Tibet,Daocheng in Sichuan and Muztagh-ata in Xinjiang.Up until now,all three sites have continuously collected data for two years.In this paper,we will introduce this site testing campaign,and present its monitoring results obtained during the period between March 2017 and March 2019.展开更多
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-res...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 precision.It is useful to consider the spectral information content when assessing the capability of a stellar spectrum in deriving precise stellar labels.In 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 interest.Consequently,this affects the performance of the stellar label determination from the MRS spectra.By 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 MRS.This 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 stars.With blue and red parts together,we are able to reach similar performance to the low-resolution spectra except for warm stars.However,at[M/H]-2.0 dex,the uncertainties of fundamental stellar labels estimated from MRS are substantially larger than that from low-resolution spectra.We 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 estimates.Finally,reference precision limits are calculated using synthetic gradient spectra,according to which we expect abundances of at least 17 elements to be measured precisely from MRS spectra.展开更多
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 o...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.展开更多
The NASA Kepler mission obtained long-term high-quality photometric observations for a large number of stars in its original field of view from 2009 to 2013.To provide reliable stellar parameters in a homogeneous way,...The NASA Kepler mission obtained long-term high-quality photometric observations for a large number of stars in its original field of view from 2009 to 2013.To provide reliable stellar parameters in a homogeneous way,the LAMOST telescope began to carry out low-resolution spectroscopic observations for as many stars as possible in the Kepler field in 2012.By June 2018,238386 low-resolution spectra with SNRg≥6 had been collected for 155623 stars in the Kepler field,enabling the determination of atmospheric parameters and radial velocities,as well as spectral classification of the target stars.This information has been used by astronomers to carry out research in various fields,including stellar pulsations and asteroseismology,exoplanets,stellar magnetic activity and flares,peculiar stars and the Milky Way,binary stars,etc.We summarize the research progress in these fields where the usage of data from the LAMOST-Kepler(LK)project has played a role.In addition,time-domain medium-resolution spectroscopic observations have been carried out for about 12000 stars in four central plates of the Kepler field since 2018.The currently available results show that the LAMOST-Kepler medium resolution(LKMRS)observations provide qualified data suitable for research in additional science projects including binaries,high-amplitude pulsating stars,etc.As LAMOST is continuing to collect both low-and mediumresolution spectra of stars in the Kepler field,we expect more data to be released continuously and new scientific results to appear based on the LK project data.展开更多
A large ground-based optical/infrared telescope is being planned for a world-class astronomical site in China.The cloud-free night percentage is the primary meteorological consideration for evaluating candidate sites....A large ground-based optical/infrared telescope is being planned for a world-class astronomical site in China.The cloud-free night percentage is the primary meteorological consideration for evaluating candidate sites.The data from GMS and NOAA satellites and the MODIS instrument were utilized in this research,covering the period from 1996 to 2015.Our data analysis benefits from overlapping results from different independent teams as well as a uniform analysis of selected sites using GMS+NOAA data.Although significant ground-based monitoring is needed to validate these findings,we identify three different geographical regions with a high percentage of cloud-free conditions(~83%on average),which is slightly lower than at Mauna Kea and Cerro Armazones(~85%on average)and were chosen for the large international projects TMT and ELT respectively.Our study finds evidence that cloud distributions and the seasonal changes affected by the prevailing westerly winds and summer monsoons reduce the cloud cover in areas influenced by the westerlies.This is consistent with the expectations from climate change models and is suggestive that most of the identified sites will have reduced cloud cover in the future.展开更多
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 e...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.展开更多
The Large sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) general survey is a spectroscopic survey that will eventually cover approximately half of the celestial sphere and collect 10 million spectra of ...The Large sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) general survey is a spectroscopic survey that will eventually cover approximately half of the celestial sphere and collect 10 million spectra of stars, galaxies and QSOs. Objects in both the pilot survey and the first year regular survey are included in the LAMOST DR1. The pilot survey started in October 2011 and ended in June 2012, and the data have been released to the public as the LAMOST Pilot Data Release in August 2012. The regular survey started in September 2012, and completed its first year of operation in June 2013. The LAMOST DR1 includes a total of 1202 plates containing 2 955 336 spectra, of which 1 790 879 spectra have observed signalto-noise ratio(SNR) ≥ 10. All data with SNR ≥ 2 are formally released as LAMOST DR1 under the LAMOST data policy. This data release contains a total of 2 204 696 spectra, of which 1 944 329 are stellar spectra, 12 082 are galaxy spectra and 5017 are quasars. The DR1 not only includes spectra, but also three stellar catalogs with measured parameters: late A,FGK-type stars with high quality spectra(1 061 918 entries), A-type stars(100 073 entries), and M-type stars(121 522 entries). This paper introduces the survey design, the observational and instrumental limitations, data reduction and analysis, and some caveats. A description of the FITS structure of spectral files and parameter catalogs is also provided.展开更多
Radio stars have attracted astronomers' attention for several decades. To better understand the physics behind stellar radio emissions, it is important to study their optical behaviors. The LAMOST survey provides a l...Radio stars have attracted astronomers' attention for several decades. To better understand the physics behind stellar radio emissions, it is important to study their optical behaviors. The LAMOST survey provides a large database for researching stellar spectroscopic properties of radio stars. In this work, we concentrate on their spectroscopic properties and infer physical properties from their spectra, such as stellar activity and variability. We mined big data from the LAMOST spectral survey Data Release 2 (DR2), published on 2016 June 30, by cross-matching them with radio stars from FIRST and other surveys. We obtained 783 good stellar spectra with high signal to noise ratio for 659 stars. The criteria for selection were positional coincidence within 1.5" and LAMOST objects classified as stars. We calculated the equivalent widths (EWs) of the Ca II H&K, HS, H'7, H/3, Ha and Ca II IRT lines by integrating the line profiles. Using the EWs of the Ha line, we detected 147 active stellar spectra of 89 objects having emissions above the Ha continuum. There were also 36 objects with repeated spectra, 28 of which showed chromospheric activity variability. Furthermore, we found 14 radio stars emitting noticeably in the Ca II IRT lines. The low value of the EWs542/EWsags ratio for these 14 radio stars possibly alludes to chromospheric plage regions.展开更多
This paper describes the data release of the LAMOST pilot survey, which includes data reduction, calibration, spectral analysis, data products and data access. The accuracy of the released data and the information abo...This paper describes the data release of the LAMOST pilot survey, which includes data reduction, calibration, spectral analysis, data products and data access. The accuracy of the released data and the information about the FITS headers of spectra are also introduced. The released data set includes 319 000 spectra and a catalog of these objects.展开更多
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 ...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.展开更多
We present optical luminosity functions(LFs) of galaxies in the0.1 g,0.1 r,0.1 i bands, calculated using data in40 deg2 sky area of the LAMOST Complete Spectroscopic Survey of Pointing Area(LaCoSSPAr) in the Southern ...We present optical luminosity functions(LFs) of galaxies in the0.1 g,0.1 r,0.1 i bands, calculated using data in40 deg2 sky area of the LAMOST Complete Spectroscopic Survey of Pointing Area(LaCoSSPAr) in the Southern Galactic Cap. Redshifts for galaxies brighter than r = 18.1 were obtained mainly with LAMOST. In each band, LFs derived using both parametric and non-parametric maximum likelihood methods agree well with each other. In the0.1 r band, our fitting parameters of the Schechter function are φ*=(1.65 ± 0.36) × 10-2 h3 Mpc-3, M*=-20.69 ± 0.06 mag and α =-1.12 ± 0.08,which agree with previous studies. Separate LFs are also derived for emission line galaxies and absorption line galaxies. The LFs of absorption line galaxies show a dip at0.1 r 18.5 and can be fitted well by a double-Gaussian function, suggesting a bimodality in passive galaxies.展开更多
The [α/Fe] ratios in stars are good tracers to probe the formation history of stellar populations and the chemical evolution of the Galaxy. The spectroscopic survey of LAMOST provides a good opportunity to determine ...The [α/Fe] ratios in stars are good tracers to probe the formation history of stellar populations and the chemical evolution of the Galaxy. The spectroscopic survey of LAMOST provides a good opportunity to determine [α/Fe] of millions of stars in the Galaxy. We present a method of measuring the [α/Fe]ratios from LAMOST spectra using the template-matching technique of the LSP3 pipeline. We use three test samples of stars selected from the ELODIE and MILES libraries, as well as the LEGUE survey to validate our method. Based on the test results, we conclude that our method is valid for measuring [α/Fe]from low-resolution spectra acquired by the LAMOST survey. Within the range of the stellar parameters Teff= [5000, 7500] K, log g = [1.0, 5.0] dex and [Fe/H]= [onsistent with values derived from high-resolution spectra,-1.5, +0.5] dex, our [α/Fe] measurements are c and the accuracy of our [α/Fe] measurements from LAMOST spectra is better than 0.1 dex with spectral signal-to-noise higher than 20.展开更多
From Oct.2019 to Apr.2020,LAMOST performed a time-domain(TD)spectroscopic survey of four K2 plates with both low-and medium-resolution observations.The low-resolution spectroscopic survey acquired 282 exposures(≈46.6...From Oct.2019 to Apr.2020,LAMOST performed a time-domain(TD)spectroscopic survey of four K2 plates with both low-and medium-resolution observations.The low-resolution spectroscopic survey acquired 282 exposures(≈46.6 h)over 25 nights,yielding a total of about 767000 spectra,and the medium-resolution survey took 177 exposures(≈49.1 h)over 27 nights,collecting about 478000 spectra.More than 70%/50%of low-resolution/medium-resolution spectra have signal-to-noise ratio higher than 10.We determine stellar parameters(e.g.,Teff,log g,[Fe/H])and radial velocity(RV)with different methods,including LASP,DD-Payne and SLAM.In general,these parameter estimations from different methods show good agreement,and the stellar parameter values are consistent with those of APOGEE.We use the Gaia DR2 RV values to calculate a median RV zero point(RVZP)for each spectrograph exposure by exposure,and the RVZP-corrected RVs agree well with the APOGEE data.The stellar evolutionary and spectroscopic masses are estimated based on the stellar parameters,multi-band magnitudes,distances and extinction values.Finally,we construct a binary catalog including about 2700 candidates by analyzing their light curves,fitting the RV data,calculating the binarity parameters from medium-resolution spectra and cross-matching the spatially resolved binary catalog from Gaia EDR3.The LAMOST TD survey is expected to represent a breakthrough in various scientific topics,such as binary systems,stellar activity,stellar pulsation,etc.展开更多
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)st...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(RGC<8.34 kpc)and outer region(RGC>8.34 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 properties.For the inner region,the metal-weak thick disk(MWTD)significantly contributes when[α/Fe]>+0.2 dex and[Fe/H]<-0.8 dex,while the canonical thick-disk(TD)dominates when[Fe/H]>-0.8 dex.However,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 metallicity.Similar results can be obtained from the V_(φ)distribution.The 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.展开更多
Two Li-rich candidates,TYC 1338-1410-1 and TYC 2825-596-1,were observed by the new high-resolution echelle spectrograph,LAMOST/HRS.Based on their high-resolution and high-signal-tonoise ratio(SNR)spectra,we derived st...Two Li-rich candidates,TYC 1338-1410-1 and TYC 2825-596-1,were observed by the new high-resolution echelle spectrograph,LAMOST/HRS.Based on their high-resolution and high-signal-tonoise ratio(SNR)spectra,we derived stellar parameters and abundances of 14 important elements for the two candidates.The stellar parameters and lithium abundances indicate that they are Li-rich K-type giants,and having A(Li)NLTE and 2.91 dex,respectively.Our analysis suggests that TYC 1338-1410-1 is probably a red giant branch(RGB)star at the bump stage,while TYC 2825-596-1 is most likely to be a core helium-burning red clump(RC)star.The line profiles of both spectra indicate that the two Li-rich giants are slow rotators and do not show infrared(IR)excess.We conclude that engulfment is not the lithium enrichment mechanism for either star.The enriched lithium of TYC 1338-1410-1 could be created via the Cameron-Fowler mechanism,while the lithium excess in TYC 2825-596-1 could be associated with either non-canonical mixing processes or He-flash.展开更多
We obtained seven spectra of the Be star V423 Aur on 2017 Dec.5 using the LAMOST MediumResolution Spectrograph with exposures from 600 to 1200 seconds.These spectra show the irregular Ha emission line profile variatio...We obtained seven spectra of the Be star V423 Aur on 2017 Dec.5 using the LAMOST MediumResolution Spectrograph with exposures from 600 to 1200 seconds.These spectra show the irregular Ha emission line profile variations(LPVs).In the seven spectra,from the 4 th to 7 th,the left part of Ha profile even shows excess.However,no variation can be seen from the follow-up observation of photometry by 1.26-m telescope and High-Resolution spectra by 2.16-m telescope.According to the High-Resolution spectra,we conclude that it is a B7 V type star with E(B-V)=0.709±0.036 and its vsini is221.8 km s-1.The short-term Ha LPVs could be explained as a result of the transient ejection of matter from rotating disk or shell around V423 Aur.展开更多
基金supported by Beijing Natural Science Foundation with Grant No.1214028the National Natural Science Foundation of China(NSFC)under grant 12103062+7 种基金the NSFC under grant 12273027the NSFC under Grant Nos.12090040,12090044,and 11833006the NSFC with grant No.11835057support from the NSFC(Grant No.12133002)China West Normal University grant 17YC507.the National Key R&D Program of China No.2019YFA0405501supported by the National Key R&D Program of China No.2019YFA0405502Guo 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A catalog of more than 43,000 M giant stars has been selected by Li et al.from the ninth data release of LAMOST.Using the data-driven method SLAM,we obtain the stellar parameters(T_(eff),logg,[M/H],[α/M])for all the M giant stars with uncertainties of 57 K,0.25 dex,0.16 dex and 0.06 dex at SNR>100,respectively.With those stellar parameters,we constrain the absolute magnitude in the K-band,which brings distance with relative uncertainties around 25%statistically.Radial velocities are also calculated by applying cross correlation on the spectra between 8000 and 8950?with synthetic spectra from ATLAS9,which covers the CaⅡtriplet.Comparison between our radial velocities and those from APOGEE DR17 and Gaia DR3 shows that our radial velocities have a system offset and dispersion around 1 and 4.6 km s^(-1),respectively.With the distances and radial velocities combining with the astrometric data from Gaia DR3,we calculate the full 6D position and velocity information,which are able to be used for further chemo-dynamic studies on the disk and substructures in the halo,especially the Sagittarius Stream.
基金supported by the Chinese Academy of Sciences (CAS) “Light of West China”Program (No.2022_XBQNXZ_014)the Xinjiang Natural Science Foundation (Grant No.2022D01A357)+2 种基金the Joint Research Fund in Astronomy under a cooperative agreement between the National Natural Science Foundation of China (NSFC)and the CAS (Grant No.U2031209)the NSFC (Grant Nos.11873081,11603065,and 12073047)resource sharing platform construction project of Xinjiang Uygur Autonomous Region (No.PT2306)。
文摘The clarity of nights is the major factor that should be carefully considered for optical/infrared astronomical observatories in site-testing campaigns.Cloud coverage is directly related to the amount of time available for scientific observations at observatories.In this article,we report on the results of detailed night-time cloud statistics and continuous observing time derived from ground-based all-sky cameras(ASCs)at the Muztagh-ata site from 2017to 2021.Results obtained from acquisition data show that the proportion of the annual observing time at the Muztagh-ata site is 65%,and the best period with the least cloud coverage and longer continuous observing time is from September to February.We made a comparison of the monthly mean observing nights obtained from our ASC and CLARA data set,and results show that the discrepancy between them may depend on the cloud top heights.On average,this site can provide 175 clear nights and 169 nights with at least 4 hr of continuous observing time per year.
基金supported by the National Natural Science Foundation of China(Grant Nos.11873081 and 11603065)the Operation,Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments,budgeted from the Ministry of Finance of China and administered by the Chinese Academy of Sciences。
文摘Site-testing is crucial for achieving the goal of scientific research and analysis of meteorological and optical observing conditions,one of the associated basic tasks.As one of three potential sites to host the 12-meter Large Optical/infrared Telescope(LOT),the Muztagh-ata site,which is located on the Pamir Plateau in Xinjiang,in west China,began its site-testing task in the spring of 2017.In this paper,we firstly start with an introduction to the site and then present a statistical analysis of the ground-level meteorological properties such as air temperature,barometric pressure,relative humidity,and wind speed and direction,recorded by an automatic weather station with standard meteorological sensors for a two-year duration.We also show the monitoring results of sky brightness during this period.
基金the support of the Large Scientific Equipments Repairing Project of Chinese Academy of Sciences:"Cooling Facility and Monitoring instruments for LAMOST Dome Seeing Improvement"
文摘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.
基金supported by the Operation,Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments,budgeted from the Ministry of Finance of China(MOF)and administered by the Chinese Academy of Sciences(CAS)supported by the National Natural Science Foundation of China(Grant No.11873081)。
文摘The Large Optical/infrared Telescope(LOT)is a ground-based 12 m diameter optical/infrared telescope which is proposed to be built in the western part of China in the next decade.Based on satellite remote sensing data,along with geographical,logistical and political considerations,three candidate sites were chosen for ground-based astronomical performance monitoring.These sites include:Ali in Tibet,Daocheng in Sichuan and Muztagh-ata in Xinjiang.Up until now,all three sites have continuously collected data for two years.In this paper,we will introduce this site testing campaign,and present its monitoring results obtained during the period between March 2017 and March 2019.
基金supported by the National Key R&D Program of China(2019YFA0405501)the National Natural Science Foundation of China(Grant No.11835057)。
文摘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 precision.It is useful to consider the spectral information content when assessing the capability of a stellar spectrum in deriving precise stellar labels.In 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 interest.Consequently,this affects the performance of the stellar label determination from the MRS spectra.By 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 MRS.This 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 stars.With blue and red parts together,we are able to reach similar performance to the low-resolution spectra except for warm stars.However,at[M/H]-2.0 dex,the uncertainties of fundamental stellar labels estimated from MRS are substantially larger than that from low-resolution spectra.We 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 estimates.Finally,reference precision limits are calculated using synthetic gradient spectra,according to which we expect abundances of at least 17 elements to be measured precisely from MRS spectra.
基金Supported by the National Natural Science Foundation of China(Grant Nos. 10973021, 10778626 and 10933001)the National Basic Research Development Program of China (Grant No. 2007CB815404)the China Scholarship Council (CSC) (Grant No. 2007104275)
文摘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.
基金the support from the National Natural Science Foundation of China(NSFC,No.11833002)the Beijing Natural Science Foundation(No.1194023)。
文摘The NASA Kepler mission obtained long-term high-quality photometric observations for a large number of stars in its original field of view from 2009 to 2013.To provide reliable stellar parameters in a homogeneous way,the LAMOST telescope began to carry out low-resolution spectroscopic observations for as many stars as possible in the Kepler field in 2012.By June 2018,238386 low-resolution spectra with SNRg≥6 had been collected for 155623 stars in the Kepler field,enabling the determination of atmospheric parameters and radial velocities,as well as spectral classification of the target stars.This information has been used by astronomers to carry out research in various fields,including stellar pulsations and asteroseismology,exoplanets,stellar magnetic activity and flares,peculiar stars and the Milky Way,binary stars,etc.We summarize the research progress in these fields where the usage of data from the LAMOST-Kepler(LK)project has played a role.In addition,time-domain medium-resolution spectroscopic observations have been carried out for about 12000 stars in four central plates of the Kepler field since 2018.The currently available results show that the LAMOST-Kepler medium resolution(LKMRS)observations provide qualified data suitable for research in additional science projects including binaries,high-amplitude pulsating stars,etc.As LAMOST is continuing to collect both low-and mediumresolution spectra of stars in the Kepler field,we expect more data to be released continuously and new scientific results to appear based on the LK project data.
基金partly supported by the Operation,Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments,budgeted from the Ministry of Finance of China(MOF)and administered by the Chinese Academy of Sciences(CAS)supported by the National Natural Science Foundation of China(Grant Nos.11573054,11703065,11603044 and 11873081)+1 种基金support from a CAS PIFIUK STFC grant ST/R006598/1。
文摘A large ground-based optical/infrared telescope is being planned for a world-class astronomical site in China.The cloud-free night percentage is the primary meteorological consideration for evaluating candidate sites.The data from GMS and NOAA satellites and the MODIS instrument were utilized in this research,covering the period from 1996 to 2015.Our data analysis benefits from overlapping results from different independent teams as well as a uniform analysis of selected sites using GMS+NOAA data.Although significant ground-based monitoring is needed to validate these findings,we identify three different geographical regions with a high percentage of cloud-free conditions(~83%on average),which is slightly lower than at Mauna Kea and Cerro Armazones(~85%on average)and were chosen for the large international projects TMT and ELT respectively.Our study finds evidence that cloud distributions and the seasonal changes affected by the prevailing westerly winds and summer monsoons reduce the cloud cover in areas influenced by the westerlies.This is consistent with the expectations from climate change models and is suggestive that most of the identified sites will have reduced cloud cover in the future.
基金support from the Guo Shou Jing Telescope(the Large Sky Area Multi-Object Fiber Spectroscopic Telescope,LAMOST)the Large Scientific Equipments Repairing Project of Chinese Academy of Sciences:"Cooling Facility and Monitoring Instruments for LAMOST Dome Seeing Improvement."supported by National Key Basic Research Program of China Y41J051N01
文摘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.
基金funded by the National Basic Research Program of China (973 Program, 2014CB845700)the National Natural Science Foundation of China (Grant Nos. 11390371)Funding for the project has been provided by the National Development and Reform Commission
文摘The Large sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) general survey is a spectroscopic survey that will eventually cover approximately half of the celestial sphere and collect 10 million spectra of stars, galaxies and QSOs. Objects in both the pilot survey and the first year regular survey are included in the LAMOST DR1. The pilot survey started in October 2011 and ended in June 2012, and the data have been released to the public as the LAMOST Pilot Data Release in August 2012. The regular survey started in September 2012, and completed its first year of operation in June 2013. The LAMOST DR1 includes a total of 1202 plates containing 2 955 336 spectra, of which 1 790 879 spectra have observed signalto-noise ratio(SNR) ≥ 10. All data with SNR ≥ 2 are formally released as LAMOST DR1 under the LAMOST data policy. This data release contains a total of 2 204 696 spectra, of which 1 944 329 are stellar spectra, 12 082 are galaxy spectra and 5017 are quasars. The DR1 not only includes spectra, but also three stellar catalogs with measured parameters: late A,FGK-type stars with high quality spectra(1 061 918 entries), A-type stars(100 073 entries), and M-type stars(121 522 entries). This paper introduces the survey design, the observational and instrumental limitations, data reduction and analysis, and some caveats. A description of the FITS structure of spectral files and parameter catalogs is also provided.
基金supported by the Joint Research Fund in Astronomy (U1631236, U1431114, U1631109 and 11263001)funded by the National Aeronautics and Space Administration and the National Science FoundationNational Major Scientific Project built by CAS
文摘Radio stars have attracted astronomers' attention for several decades. To better understand the physics behind stellar radio emissions, it is important to study their optical behaviors. The LAMOST survey provides a large database for researching stellar spectroscopic properties of radio stars. In this work, we concentrate on their spectroscopic properties and infer physical properties from their spectra, such as stellar activity and variability. We mined big data from the LAMOST spectral survey Data Release 2 (DR2), published on 2016 June 30, by cross-matching them with radio stars from FIRST and other surveys. We obtained 783 good stellar spectra with high signal to noise ratio for 659 stars. The criteria for selection were positional coincidence within 1.5" and LAMOST objects classified as stars. We calculated the equivalent widths (EWs) of the Ca II H&K, HS, H'7, H/3, Ha and Ca II IRT lines by integrating the line profiles. Using the EWs of the Ha line, we detected 147 active stellar spectra of 89 objects having emissions above the Ha continuum. There were also 36 objects with repeated spectra, 28 of which showed chromospheric activity variability. Furthermore, we found 14 radio stars emitting noticeably in the Ca II IRT lines. The low value of the EWs542/EWsags ratio for these 14 radio stars possibly alludes to chromospheric plage regions.
文摘This paper describes the data release of the LAMOST pilot survey, which includes data reduction, calibration, spectral analysis, data products and data access. The accuracy of the released data and the information about the FITS headers of spectra are also introduced. The released data set includes 319 000 spectra and a catalog of these objects.
基金Supported by the National Natural Science Foundation of China.
文摘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.
基金project is supported by the National Key R&D Program of China (2017YFA0402704)the National Natural Science Foundation of China (Grant Nos. 11733006 and U1531245)+2 种基金the National Science Foundation for Young Scientists of China (Grant No. 11603058)the Guo Shou Jing Telescope Spectroscopic Survey Key Projectssupport by the National Natural Science Foundation of China (Y811251N01)
文摘We present optical luminosity functions(LFs) of galaxies in the0.1 g,0.1 r,0.1 i bands, calculated using data in40 deg2 sky area of the LAMOST Complete Spectroscopic Survey of Pointing Area(LaCoSSPAr) in the Southern Galactic Cap. Redshifts for galaxies brighter than r = 18.1 were obtained mainly with LAMOST. In each band, LFs derived using both parametric and non-parametric maximum likelihood methods agree well with each other. In the0.1 r band, our fitting parameters of the Schechter function are φ*=(1.65 ± 0.36) × 10-2 h3 Mpc-3, M*=-20.69 ± 0.06 mag and α =-1.12 ± 0.08,which agree with previous studies. Separate LFs are also derived for emission line galaxies and absorption line galaxies. The LFs of absorption line galaxies show a dip at0.1 r 18.5 and can be fitted well by a double-Gaussian function, suggesting a bimodality in passive galaxies.
基金supported by the National Key Basic Research Program of China(973Program,No.2014CB845700)the National Natural Science Foundation of China(Grant Nos.U1331120,U1431106,U1531118,U1531244 and 11473001)+1 种基金The Guo Shou Jing Telescope(the Large Sky Area MultiObject Fiber Spectroscopic Telescope,LAMOST)is aNational Major Scientific Project built by the Chinese Academy of Sciencesprovided by the National Development and Reform Commission.LAMOST is operated and managed by National Astronomical Observatories,Chinese Academy of Sciences
文摘The [α/Fe] ratios in stars are good tracers to probe the formation history of stellar populations and the chemical evolution of the Galaxy. The spectroscopic survey of LAMOST provides a good opportunity to determine [α/Fe] of millions of stars in the Galaxy. We present a method of measuring the [α/Fe]ratios from LAMOST spectra using the template-matching technique of the LSP3 pipeline. We use three test samples of stars selected from the ELODIE and MILES libraries, as well as the LEGUE survey to validate our method. Based on the test results, we conclude that our method is valid for measuring [α/Fe]from low-resolution spectra acquired by the LAMOST survey. Within the range of the stellar parameters Teff= [5000, 7500] K, log g = [1.0, 5.0] dex and [Fe/H]= [onsistent with values derived from high-resolution spectra,-1.5, +0.5] dex, our [α/Fe] measurements are c and the accuracy of our [α/Fe] measurements from LAMOST spectra is better than 0.1 dex with spectral signal-to-noise higher than 20.
基金the National Natural Science Foundation of China(Grant Nos.11988101,11933004 and 12003050)supported by the National Key Research and Development Program of China(Grant Nos.2019YFA0405000,2019YFA0405504 and 2016YFA0400804)+2 种基金the B-type Strategic Priority Program of the Chinese Academy of Sciences(CAS)under grant number XDB41000000the Youth Innovation Promotion Association of CAS(id.2019057 and 2020060,respectively)the European Research Council(ERC)under the European Union Horizon 2020 research and innovation programme(Cartograph Y GA.804752)。
文摘From Oct.2019 to Apr.2020,LAMOST performed a time-domain(TD)spectroscopic survey of four K2 plates with both low-and medium-resolution observations.The low-resolution spectroscopic survey acquired 282 exposures(≈46.6 h)over 25 nights,yielding a total of about 767000 spectra,and the medium-resolution survey took 177 exposures(≈49.1 h)over 27 nights,collecting about 478000 spectra.More than 70%/50%of low-resolution/medium-resolution spectra have signal-to-noise ratio higher than 10.We determine stellar parameters(e.g.,Teff,log g,[Fe/H])and radial velocity(RV)with different methods,including LASP,DD-Payne and SLAM.In general,these parameter estimations from different methods show good agreement,and the stellar parameter values are consistent with those of APOGEE.We use the Gaia DR2 RV values to calculate a median RV zero point(RVZP)for each spectrograph exposure by exposure,and the RVZP-corrected RVs agree well with the APOGEE data.The stellar evolutionary and spectroscopic masses are estimated based on the stellar parameters,multi-band magnitudes,distances and extinction values.Finally,we construct a binary catalog including about 2700 candidates by analyzing their light curves,fitting the RV data,calculating the binarity parameters from medium-resolution spectra and cross-matching the spatially resolved binary catalog from Gaia EDR3.The LAMOST TD survey is expected to represent a breakthrough in various scientific topics,such as binary systems,stellar activity,stellar pulsation,etc.
基金supported by National Key R&D Program of China No.2019YFA0405500the National Natural Science Foundation of China under Grant Nos.12090040,12090044,11833006,12022304,11973052,11973042 and U1931102+5 种基金supported by Beijing Natural Science Foundation with Grant No.1214028partly supported by National Natural Science Foundation of China with grant No.U2031143supported by the Astronomical Big Data Joint Research Center,co-founded by the National Astronomical Observatories,Chinese Academy of Sciences and Alibaba Cloudpartially supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of SciencesGuo 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 SciencesFunding for the project has been provided by the National Development and Reform Commission。
文摘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(RGC<8.34 kpc)and outer region(RGC>8.34 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 properties.For the inner region,the metal-weak thick disk(MWTD)significantly contributes when[α/Fe]>+0.2 dex and[Fe/H]<-0.8 dex,while the canonical thick-disk(TD)dominates when[Fe/H]>-0.8 dex.However,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 metallicity.Similar results can be obtained from the V_(φ)distribution.The 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.
基金the National Key R&D Program of China(No.2019YFA0405502)the Key Research Program of the Chinese Academy of Sciences under grant No.XDPB09-02+8 种基金the National Natural Science Foundation of China(Grant Nos.11973052,11833006,11473033 and 11603037)the International partnership program’s Key foreign cooperation project,Bureau of International Cooperation,Chinese Academy of Sciences(No.114A32KYSB20160049)supported by the Astronomical Big Data Joint Research Center,co-founded by the National Astronomical Observatories,Chinese Academy of Sciences and Alibaba Cloudpartially supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciencesthe financial support from China Scholarship Council(CSC,No.201604910642)for his study at New Mexico State University in the United States of Americathe supports from Youth Innovation Promotion Association,Chinese Academy of SciencesGuo 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 Commissionthe NASA/IPAC Infrared Science Archive,which is funded by the National Aeronautics and Space Administrationthe Wide-field Infrared Survey Explorer,which is a joint project of the University of California,Los Angeles,and the Jet Propulsion Laboratory/California Institute of Technology,funded by the National Aeronautics and Space Administration。
文摘Two Li-rich candidates,TYC 1338-1410-1 and TYC 2825-596-1,were observed by the new high-resolution echelle spectrograph,LAMOST/HRS.Based on their high-resolution and high-signal-tonoise ratio(SNR)spectra,we derived stellar parameters and abundances of 14 important elements for the two candidates.The stellar parameters and lithium abundances indicate that they are Li-rich K-type giants,and having A(Li)NLTE and 2.91 dex,respectively.Our analysis suggests that TYC 1338-1410-1 is probably a red giant branch(RGB)star at the bump stage,while TYC 2825-596-1 is most likely to be a core helium-burning red clump(RC)star.The line profiles of both spectra indicate that the two Li-rich giants are slow rotators and do not show infrared(IR)excess.We conclude that engulfment is not the lithium enrichment mechanism for either star.The enriched lithium of TYC 1338-1410-1 could be created via the Cameron-Fowler mechanism,while the lithium excess in TYC 2825-596-1 could be associated with either non-canonical mixing processes or He-flash.
基金supported by the National Key R&D Program of China(2017YFA0402704)the National Natural Science Foundation of China(Grant Nos.11733006,11403061,11903048,U1631131,11973060,U1531118,11403037,11225316,11173030,11303038,Y613991N01 and U1531245)+3 种基金the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences,Key Research Program of Frontier Sciences,CAS(Grant No.QYZDY-SSWSLH007)supports from the Science and Technology Development Fund,Macao SAR(file Nos.119/2017/A3,061/2017/A2 and 0007/2019/A)Faculty Research Grants of the Macao University of Science and Technology(No.FRG-19-004-SSI)Guo Shou Jing Telescope(the Large Sky Area MultiObject 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 Commissionpartially supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences.
文摘We obtained seven spectra of the Be star V423 Aur on 2017 Dec.5 using the LAMOST MediumResolution Spectrograph with exposures from 600 to 1200 seconds.These spectra show the irregular Ha emission line profile variations(LPVs).In the seven spectra,from the 4 th to 7 th,the left part of Ha profile even shows excess.However,no variation can be seen from the follow-up observation of photometry by 1.26-m telescope and High-Resolution spectra by 2.16-m telescope.According to the High-Resolution spectra,we conclude that it is a B7 V type star with E(B-V)=0.709±0.036 and its vsini is221.8 km s-1.The short-term Ha LPVs could be explained as a result of the transient ejection of matter from rotating disk or shell around V423 Aur.