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Observation of high energy and very high emission from Gamma Ray Bursts (GRBs) is crucial to study the gigantic explosion and the underline processes. With a large field-of-view and almost full duty cycle, the Water Cherenkov Detector Array (WCDA), a sub-array of the Large High Altitude Air Shower Observatory (LHAASO), is appropriate to monitor the very high energy emission from unpredictable transients such as GRBs. Nevertheless, the main issue for an extensive air shower array is the high energy threshold which limits the horizon of the detector. To address this issue a new trigger method is developed in this article to lower the energy threshold of WCDA for GRB observation. The proposed method significantly improves the detection efficiency of WCDA for gamma-rays around the GRB direction at 10-300 GeV. The sensitivity of the WCDA for GRB detection with the new trigger method is estimated. The achieved sensitivity of the quarter WCDA array above 10 GeV is comparable with that of Fermi-LAT. The data analysis process and corresponding fluence upper limit for GRB 190719C is presented as an example.

High-precision stellar masses and radii measured directly from binaries can effectively calibrate stellar models. However, such a database containing full spectral types and a large range of metallicity is still not fully established. A continuous effort of data collection and analysis is requested to complete the database. In this work, we provide a catalog containing 184 binaries with independent atmospheric parameters and accurate masses and radii as the benchmark for stellar mass and radius. The catalog contains 56 new detached binaries from the LAMOST medium-resolution spectroscopic survey and 128 detached eclipsing binaries compiled from previous studies. We obtain the orbital solutions of the new detached binaries with uncertainties of masses and radii smaller than 5%. These new samples densify the distribution of metallicity of the high-precision stellar mass library and add nine hot stars with T eff > 8000 K. Comparisons show that these samples agree well with the PARSEC isochrones in T eff–logg–mass–radius–luminosity space. We compare mass and radius estimates from isochrone and spectral energy distribution fitting, respectively, with those from the binary orbital solution. We find that the precision of the stellar-model-dependent mass estimates is >10% and the precision of the radius estimates based on atmospheric parameters is >15%. These give a general view of the uncertainty of the usual approaches to estimate stellar mass and radius.

Large scale spectroscopic surveys such as that using Large-sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) have collected spectra of millions stars in the Milky Way. Utilizing this huge sample of stars to study the assembling history and structure of our Galaxy requires accurate estimates of distance, extinction, age, and mass for individual stars. Combining the parallax constraint from Gaia EDR3 with Bayesian inference, we have estimated the distance and extinction for stars observed in LAMOST DR7, as well as the stellar mass and age for evolved stars in this data release. We validated the accuracies of the stellar parameters by comparing our results against various measurements, including the star-pair technique, asteroseismology, globular clusters, and isochrone fits to main sequence stars and subgiants. This is a valuable catalog of stellar parameters under a Bayesian framework estimated using the data from Gaia EDR3 and LAMOST spectroscopic data. With this data set we explored the stellar population of the Galactic massive substructure Gaia-Sausage-Enceladus (GSE). The kinematically selected members of GSE have a median metallicity of [Fe/H] = −1.29 and a median age of 11.6 Gyr.

{The observatory control system (OCS), a part of automated control of Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST), runs on the CentOS6 platform and implements the communication between modules based on Common Object Request Broker Architecture (CORBA). However, CORBA is complicated and has limited development support; moreover, the official support for CentOS6 has ended. OCS inherently has some shortcomings such as the over-concentration of control and the blocking of device status processing, which hinder the realization of automated observation control of LAMOST. Therefore, this study designs and implements a universal observation control system (UOCS) for optical telescopes. The UOCS takes the device command as the basic execution unit, controls the device execution logic using observation script, controls the observation logic by event-driven messaging, and realizes mutual decoupling between modules via a distributed control mode, thereby ensuring high system robustness. The UOCS performs significantly better than OCS in terms of the observation performance, operator complexity, and communication error. Currently, UOCS is applied to the automated control of some devices and subsystems in LAMOST observation. It will be applied to the automated observation control of Multi-channel Photometric Survey Telescope by 2021., Comment: total have 22 pages and 25 figures

Due to the high complexity of the system and the variety of influencing factors of large astronomical telescopes, the current control system could be improved largely. It’s difficult for traditional automatic control technologies to ensure reliable and highly efficient operation. The key problem is such a system which needs to consider not only the various internal factors but also the various external factors. In addition, some factors are difficult to be digitized. Thus, it’s hard to make mathematical models to represent such complex and dynamic systems. The first goal of this project is to construct a software experimental platform for the intelligentization. The second goal is to develop an intelligent reliability management system, and an optimization system for observation quality. These application systems will be running using the historical data of LAMOST operation. The evaluation of such systems will be based on the simulation of these data.

Dome A in Antarctica has many characteristics that make it an excellent site for astronomical observations, from the optical to the terahertz. Quantitative site testing is still needed to confirm the site's properties. In this paper, we present a statistical analysis of cloud cover and aurora contamination from the Kunlun Cloud and Aurora Monitor (KLCAM). KLCAM is an automatic, unattended all-sky camera aiming for long-term monitoring of the usable observing time and optical sky background at Dome~A. It was installed at Dome~A in January 2017, worked through the austral winter, and collected over 47,000 images over 490 days. A semi-quantitative visual data analysis of cloud cover and auroral contamination was carried out by five individuals. The analysis shows that the night sky was free of cloud for 83 per cent of the time, which ranks Dome~A highly in a comparison with other observatory sites. Although aurorae were detected somewhere on an image for nearly 45 per cent of the time, the strongest auroral emission lines can be filtered out with customized filters., 7 pages, 11 figures, published in MNRAS

In this article, we present a detailed analysis of the statistical properties of seeing for the Muztagh-ata site which is the candidate site for hosting future Chinese Large Optical/infrared Telescope (LOT) project. The measurement was obtained with Differential Image Motion Monitor (DIMM) from April 2017 to November 2018 at different heights during different periods. The median seeing at 11 meters and 6 meters are very close but different significantly from that on the ground. We mainly analyzed the seeing at 11 meters monthly and hourly, having found that the best season for observing was from late autumn to early winter and seeing tended to improve during the night only in autumn. The analysis of the dependence on temperature inversion, wind speed, direction also was made and the best meteorological conditions for seeing is given., 13 pages, 16 figures

Resistive Plate Chambers have largely been used in High Energy Physics and Cosmic Ray research. In view of using this detector for calorimetry applications it is important to know the maximum measurable particle density, or its intrinsic linearity limit, which is tightly related to the dimension of the discharge region. In this paper we report the results of measurements performed at the Beam Test Facility (INFN National Laboratory of Frascati, Italy) where the intrinsic linearity of bakelite RPCs operated in streamer mode has been tested at different impinging particle densities.

The LAMOST spectral survey provides a rich databases for studying stellar spectroscopic properties and chromospheric activity. We cross-matched a total of 105,287 periodic variable stars from several photometric surveys and databases (CSS, LINEAR, Kepler, a recently updated eclipsing star catalogue, ASAS, NSVS, some part of SuperWASP survey, variable stars from the Tsinghua University-NAOC Transient Survey, and other objects from some new references) with four million stellar spectra published in the LAMOST data release 2 (DR2). We found 15,955 spectra for 11,469 stars (including 5398 eclipsing binaries). We calculated their equivalent widths (EWs) of their Hα, Hβ, Hγ, Hδ and Ca ii H lines. Using the Hα line EW, we found 447 spectra with emission above continuum for a total of 316 stars (178 eclipsing binaries). We identified 86 active stars (including 44 eclipsing binaries) with repeated LAMOST spectra. A total of 68 stars (including 34 eclipsing binaries) show chromospheric activity variability. We also found LAMOST spectra of 12 cataclysmic variables, five of which show chromospheric activity variability. We also made photometric follow-up studies of three short period targets (DY CVn, HAT-192-0001481, and LAMOST J164933.24+141255.0) using the Xinglong 60-cm telescope and the SARA 90-cm and 1-m telescopes, and obtained new BVRI CCD light curves. We analyzed these light curves and obtained orbital and starspot parameters. We detected the first flare event with a huge brightness increase of more than about 1.5 magnitudes in R filter in LAMOST J164933.24+141255.0.

An end-to-end calibration method, which is different from the traditional way, has been employed in WFCTA prototype experiment based on N 2 laser. As we known, the calculation of the expected and the observed light fluxes at the front of the aperture of the telescope are crucial in the such method. To calculate predicted light flux accurately, the propagation and scattering of photons in the atmosphere have been considered in detail. In order to get the detector effective areas, which will be used in the transformation of ADC signals to the observed light flux, a ray trace procedure, considering all details of detector response, has been performed for all incident direction of photons in field of view of the detector. By matching the observed and expected light flux at the entrance of the telescope, the overall calibration gains of two telescopes can be obtained. During the test run of the calibration, a overall calibration gain around G = 0 . 38 A D C c o u n t s ∕ p h o t o n and G = 0 . 36 A D C c o u n t s ∕ p h o t o n for WFCT01 and WFCT02 are given, respectively. Furthermore, in view of all uncertainty sources, systematic uncertainties for the calibration have also been estimated. They are around the level of ( − 7 . 3 % , + 7 . 8 % ) . The calibration results achieved by end-to-end method and the traditional way are in consistent at the level of 10%, which is within the range of uncertainties. Since the end-to-end and traditional calibration methods have their own advantages, the performance of the combination of these two calibration methods has also been discussed in the end.

We study the classification and composite spectra of galaxy in the fourth data release (DR4) of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). We select 40,182 spectra of galaxies from LAMOST DR4, which have photometric in- formation but no spectroscopic observations in the Sloan Digital Sky Survey(SDSS). These newly observed spectra are re-calibrated and classified into six classes, i.e. pas- sive, H{\alpha}-weak, star-forming, composite, LINER and Seyfert using the line intensity (H\b{eta}, [OIII]{\lambda}5007, H{\alpha} and [NII]{\lambda}6585). We also study the correlation between spectral classes and morphological types through three parameters: concentration index, (u - r) color, and D4000n index. We calculate composite spectra of high signal-to-noise ra- tio(S/N) for six spectral classes, and using these composites we pick out some features that can differentiate the classes effectively, including H\b{eta}, Fe5015, H{\gamma}A, HK, and Mg2 band etc. In addition, we compare our composite spectra with the SDSS ones and analyse their difference. A galaxy catalogue of 40,182 newly observed spectra (36,601 targets) and the composite spectra of the six classes are available online., Comment: 14 pages, 11 figures

In 2011 ARGO-YBJ experiment has reported a work to study the absolute rigidity scale of the primary cosmic ray particles based on the Moon's shadow observation. Given the progress in high energy hadronic interaction models with LHC data, in cosmic ray chemical composition measurement and in experimental data accumulation, more updates can be researched. This paper aims to further disentangle the composition dependence in absolute-energy-scale calibration by using specific moon-shadow data which mainly is comprised of light component cosmic rays. Results show that, 17% energy scale error is estimated from 3 TeV to 50 TeV. To validate the performance of this technique, the light component cosmic ray spectrum in the same energy region is shown. (C) 2017 Elsevier B.V. All rights reserved.

Astronomy cloud computing environment is a cyber-Infrastructure for Astronomy Research initiated by Chinese Virtual Observatory (China-VO) under funding support from NDRC (National Development and Reform commission) and CAS (Chinese Academy of Sciences). Based on virtualization technology, astronomy cloud computing environment was designed and implemented by China-VO team. It consists of five distributed nodes across the mainland of China. Astronomer can get compuitng and storage resource in this cloud computing environment. Through this environments, astronomer can easily search and analyze astronomical data collected by different telescopes and data centers , and avoid the large scale dataset transportation.

The performance of an interband cascade laser based laser heterodyne radiometer (LHR) is demonstrated in ground-based solar occultation mode. High-resolution (0.0033 cm-1) transmission spectra near 3.53 μm were obtained for simultaneous atmospheric observations of H2O and CH4. Combined with the preprocessed measurement data (acquired at Hefei, China, on June 21th 2016), an optimal estimation method based retrieval algorithm is developed for data retrieval and error analysis. By considering the corrected atmospheric parameters, vertical profiles of H2O and CH4 are retrieved. Finally, the measured total column abundance and XCH4 were calculated to be 1.87 ± 0.02 ppm and 1.88 ± 0.02 ppm, respectively. The interband cascade laser-based laser heterodyne radiometer that is demonstrated in this manuscript has high potential for use in the development of compact, robust, and unattended LHR for spacecraft, airborne or ground-based atmospheric sensing.

Gaia data release 2 (DR2) provides the best non-rotating optical frame aligned with the radio frame (ICRF) thanks to the inclusion of about half-million quasars in the five-parameter astrometric solution. We cross-match with Gaia DR2 the quasars from Large Quasar Astrometric Catalogue, Sloan Digital Sky Survey and LAMOST, obtaining 208,743 new sources (denominated as KQCG), and most of them are fainter than G = 19. Given their crucial diagnostic role for characterizing the properties of the celestial reference frame, we aim to probe more accurately the properties of the reference frame at the faintest magnitudes. Combining them with the quasars already identified in DR2, we estimate the moving mean of parallaxes and proper motions. The features of the proper motion are analyzed by means of vectorial spherical harmonics; the scalar field of parallaxes is expanded into spherical harmonics to investigate their spatial correlation, which reveals an angular scale of systematics of ≈18° with a rms amplitude of 13 μas. The global moving mean of the parallaxes and proper motions are calculated. The amplitude of proper motion bias can be up to ∼10 μas yr−1 in some sky regions for both components, and these biases seem to be related to the patterns of the scanning law. The reference frame exhibits a (−6, −5, −5) ± 1 μas yr−1 spin in the northern hemisphere and a spin of (0, +1, +3) ± 1 μas yr−1 in the southern one, which may be caused by the star contamination. The quadrupolar anisotropy of the proper motion filed is analyzed, where a significant quadrupolar signal (the largest component’s amplitude is up to −15 μas yr−1) is found.

Based on previous site testing and satellite cloud data, Ali, Daocheng and Muztagh-ata have been selected as candidate sites for the Large Optical/Infrared Telescope (LOT) in China. We present the data collection, processing, management and quality analysis for our site testing based on using similar hardware. We analyze meteorological data, seeing, background light, cloud and precipitable water vapor data from 2017 March 10 to 2019 March 10. We also investigated the relative usefulness of our all-sky camera data in comparison to that from the meteorological TERRA satellite data based on a night-by-night comparison of the correlation and consistency between them.We find a 6% discrepancy arising from a wide range of factors.

Site-testing is crucial for achieving the goal of scientific research and analysis of meteorological and optical observing conditions is one of the basic tasks of it. As one of three potential sites to host 12-meter Large Optical/infrared Telescope (LOT), Muztagh-ata site which is located on the Pamirs Plateau in west China's Xinjiang 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, wind speed and direction, recorded by automatic weather station with standard meteorological sensors for two-year long. We also show the monitoring results of sky brightness during this period., 16 pages, 19 figures

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.

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.

Scene-based wavefront sensing currently uses the periodic-correlation algorithm based on fast Fourier transforms. However, when the object scene contains features at the field edges, the performance of the algorithm is poor due to the periodicity of fast Fourier transforms, called wraparound effect. In this paper, we propose an algorithm based on the gradient cross-correlation. Both simulation and experiment results show its dramatic effectiveness against the wraparound effect, and a considerable improvement is obtained in image resolution with closed loop adaptive optics correction.

Quasars are essential for astrometric in the sense that they are spatial stationary because of their large distance from the Sun. The European Space Agency (ESA) space astrometric satellite Gaia is scanning the whole sky with unprecedented accuracy up to a few muas level. However, Gaia's two fields of view observations strategy may introduce a parallax bias in the Gaia catalog. Since it presents no significant parallax, quasar is perfect nature object to detect such bias. More importantly, quasars can be used to construct a Celestial Reference Frame in the optical wavelengths in Gaia mission. In this paper, we compile the most reliable quasars existing in literatures. The final compilation (designated as Known Quasars Catalog for Gaia mission, KQCG) contains 1843850 objects, among of them, 797632 objects are found in Gaia DR1 after cross-identifications. This catalog will be very useful in Gaia mission.

We study the metallicity distribution and kinematic properties of 4,680 A/F/G/K-type giant stars with $|z|>$ 5 kpc selected from the LAMOST spectroscopic survey. The metallicity distribution of giant stars with 5 $, Comment: 8 pages, 8 figures, accepted for publication in ApJ

The radial number density and flattening of the Milky Way's stellar halo is measured with $\mathrm{5351}$ metal-poor ([Fe/H]$, Comment: 16 pages, 24 figures, accepted by MNRAS

Single-exposure spectra in large spectral surveys are valuable for time domain studies such as stellar variability, but there is no available method to eliminate cosmic rays for single-exposure, multi-fiber spectral images. In this paper, we describe a new method to detect and remove cosmic rays in multi-fiber spectroscopic single exposures. Through the use of two-dimensional profile fitting and a noise model that considers the position-dependent errors, we successfully detect as many as 80% of the cosmic rays and correct the cosmic ray polluted pixels to an average accuracy of 97.8%. Multiple tests and comparisons with both simulated data and real LAMOST data show that the method works properly in detection rate, false detection rate, and validity of cosmic ray correction., 23 pages, 9 figures, 1 table

We present a sample of quasars discovered in the area of Galactic Anti-Center (GAC) of $150^{\circ} \leq l \leq 210^{\circ}$ and $|b| \leq 30^{\circ}$, based on the LAMOST Data Release 3 (DR3). The sample contains 151 spectroscopically confirmed quasars. Among them 80 are newly discovered with the LAMOST. All those quasars are very bright, with $i$ magnitudes peaking around 17.5\, mag. All the newly quasars are discovered serendipitously, targeted originally with the LAMOST as stars of bluer colours, except for a few targeted as variable, young stellar object candidates. 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 astrometric reference frame for the purpose of accurate proper motion measurements, for example, Gaia. They are also excellent tracers to probe the kinematics and chemistry of the interstellar medium of the Milky Way disk and halo via absorption line spectroscopy., 4 pages, 1 figure, Accepted for publication in Research in Astronomy and Astrophysics Letter

We present a sample of 48 metal-poor galaxies at $ z < 0.14$ selected from 92,510 galaxies in the LAMOST survey. These galaxies are identified for their detection of the auroral emission line \oiii$\lambda$4363 above $3\sigma$ level, which allows a direct measurement of the electron temperature and the oxygen abundance. The emission line fluxes are corrected for internal dust extinction using Balmer decrement method. With electron temperature derived from \oiii$\lambda\lambda4959,5007/\oiii\lambda4363$ and electron density from $\sii\lambda6731/\sii\lambda6717$, we obtain the oxygen abundances in our sample which range from $\zoh= 7.63$ (0.09 $\Zsun$) to $8.46$ (0.6 $\Zsun$). We find an extremely metal-poor galaxy with $\zoh=7.63 \pm 0.01$. With multiband photometric data from FUV to NIR and $\ha$ measurements, we also determine the stellar masses and star formation rates, based on the spectral energy distribution fitting and $\ha$ luminosity, respectively. We find that our galaxies have low and intermediate stellar masses with $\rm 6.39 \le log(M/M_{\sun})\le 9.27$, and high star formation rates (SFRs) with $\rm -2.18 \le log(SFR/M_{\sun} yr^{-1}) \le 1.95$. We also find that the metallicities of our galaxies are consistent with the local $T_e$-based mass-metallicity relation, while the scatter is about 0.28 dex. Additionally, assuming the coefficient of $\rm \alpha =0.66$, we find most of our galaxies follow the local mass-metallicity-SFR relation, while a scatter about 0.24 dex exists, suggesting the mass-metallicity relation is weakly dependent on SFR for those metal-poor galaxies., Comment: 17 pages, 6 figures, 1 table, accepted to RAA

In this work, we present a catalog of 2651 carbon stars from the fourth Data Release (DR4) of the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST). Using an efficient machine-learning algorithm, we find out these stars from more than seven million spectra. As a by-product, 17 carbon-enhanced metal-poor (CEMP) turnoff star candidates are also reported in this paper, and they are preliminarily identified by their atmospheric parameters. Except for 176 stars that could not be given spectral types, we classify the other 2475 carbon stars into five subtypes including 864 C-H, 226 C-R, 400 C-J, 266 C-N, and 719 barium stars based on a series of spectral features. Furthermore, we divide the C-J stars into three subtypes of CJ( H), C-J(R), C-J(N), and about 90% of them are cool N-type stars as expected from previous literature. Beside spectroscopic classification, we also match these carbon stars to multiple broadband photometries. Using ultraviolet photometry data, we find that 25 carbon stars have FUV detections and they are likely to be in binary systems with compact white dwarf companions., Comment: 72 pages, 23 figures. accepted by ApJS, lal@nao.cas.cn

Virtual Observatory (VO) is a data-intensively online astronomical research and education environment, which takes advantages of advanced information technologies to achieve seamless and global access to astronomical information. AstroCloud is a cyber-infrastructure for astronomy research initiated by Chinese Virtual Observatory (China-VO) project, and also a kind of physical distributed platform which integrates lots of tasks such as telescope access proposal management, data archiving, data quality control, data release and open access, cloud based data processing and analysis. It consists of five application channels, i.e. observation, data, tools, cloud and public and is acting as a full lifecycle management system and gateway for astronomical data and telescopes. Physically, the platform is hosted in six cities currently, i.e. Beijing, Nanjing, Shanghai, Kunming, Lijiang and Urumqi, and serving more than 17 thousand users. Achievements from international Virtual Observatories and Cloud Computing are adopted heavily. In the paper, backgrounds of the project, architecture, Cloud Computing environment, key features of the system, current status and future plans are introduced., Comment: 5 pages, 8 figures, to appear in the Proceedings of "The 3rd International Conference on Wireless Communication and Sensor Network (WCSN 2016)"

Context. Quasars are spatially stationary, and they are essential objects in astrometry when defining reference frames. However, the census of quasars is far from complete. Mid-infared colors can be used to find quasar candidates because AGNs show a peculiar appearance in mid-infrared color, but these methods are incapable of separating quasars from AGNs. Aims. The aim of our study is to use astrometric and mid-infrared methods to select quasars and get a reliable quasar candidates catalog. Methods. We used a near-zero proper motion criterion in conjuction with WISE (all-sky Wide-field Infrared Survey Explorer) [W1-W2] color to select quasar candidates. The [W1-W2] color criterion is defined by the linear boundary of two samples: LAMOST DR5 quasars, which serve as the quasar sample, and LAMOST DR5 stars and galaxies, which serve as the non-quasar sample. The contamination and completeness are evaluated. Results. We present a catalog of 662 753 quasar candidates, with a completeness of about 75% and a reliability of 77.2%., 7 pages, 7 figures, accepted by A&A

Based on the LAMOST survey and Sloan Digital Sky Survey (SDSS), we use low-resolution spectra of 130,043 F/G-type dwarf stars to study the kinematics and metallicity properties of the Galactic disk. Our study shows that the stars with poorer metallicity and larger vertical distance from Galactic plane tend to have larger eccentricity and velocity dispersion. After separating the sample stars into likely thin-disk and thick-disk sub-sample, we find that there exits a negative gradient of rotation velocity $V_{\phi}$ with metallicity [Fe/H] for the likely thin-disk sub-sample, and the thick-disk sub-sample exhibit a larger positive gradient of rotation velocity with metallicity. By comparing with model prediction, we consider the radial migration of stars appears to have influenced on the thin-disk formation. In addition, our results shows that the observed thick-disk stellar orbital eccentricity distribution peaks at low eccentricity ($e \sim 0.2$) and extends to a high eccentricity ($e \sim 0.8$). We compare this result with four thick-disk formation simulated models, and it imply that our result is consistent with gas-rich merger model., Comment: 9 pages, 11 figures, Accepted for publication in MNRAS. arXiv admin note: text overlap with arXiv:1104.3114 by other authors

International audience; We identify 108 M subdwarfs (sdMs) out of more than two hundred thousand M type spectra from the second data release (DR2) of the LAMOST regular survey. This sample, among which 58 members are identified for the first time, includes 33 extreme subdwarfs (esdMs) and 11 ultra subdwarfs (usdMs). The selection is based on the usual ratio of absorption depth of CaH2, CaH3 and TiO5 band systems. We also emphasize the use of the CaH1 band. We provide estimates of spectral subtype (SPT), Le pine metallicity index zeta, effective temperature and [Fe/H]. Both zeta-[Fe/H] and SPT-T-eff figures show reasonable consistency; compared to PHOENIX model spectra, average rounded values of [Fe/H] for sdMs, esdMs and usdMs are respectively -0.5, -1 and -1.5. The photometric distances are estimated, indicating that most sources are located within 500 pc of the Sun and 350 pc of the Galactic disk. Velocities and 3D Galactic motions are also briefly discussed. Among the 108 subdwarfs, seven stars appear to be active with a significant H-alpha emission line. The source LAMOST J104521.52+482823.3 is a white dwarf - M subdwarf binary, while LAMOST J123045.52+410943.8, also active, exhibits carbon features in red.

We select from Paper I a sample of 306 massive star clusters observed with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) in the vicinity fields of M31 and M33 and determine their metallicities, ages and masses. Metallicities and ages are estimated by fitting the observed integrated spectra with stellar synthesis population (SSP) models with a pixel-to-pixel spectral fitting technique. Ages for most young clusters are also derived by fitting the multi-band photometric measurements with model spectral energy distributions (SEDs). The estimated cluster ages span a wide range, from several million years to the age of the universe. The numbers of clusters younger and older than 1 Gyr are respectively 46 and 260. With ages and metallicities determined, cluster masses are then estimated by comparing the multi-band photometric measurements with SSP model SEDs. The derived masses range from $\sim 10^{3}$ to $\sim 10^7$ $M_{\odot}$, peaking at $\sim 10^{4.3}$ and $\sim 10^{5.7}$ $M_{\odot}$ for young ($< 1$ Gyr) and old ($>1$ Gyr) clusters, respectively. Our estimated metallicities, ages and masses are in good agreement with available literature values. Old clusters richer than [Fe/H] $\sim -0.7$ dex have a wide range of ages. Those poorer than [Fe/H] $\sim -0.7$ dex seem to be composed of two groups, as previously found for Galactic GCs -- one of the oldest ages with all values of metallicity down to $\sim -2$ dex and another with metallicity increasing with decreasing age. The old clusters in the inner disk of M\,31 (0 -- 30 kpc) show a clear metallicity gradient measured at $-0.038\pm0.023$ dex/kpc., 22 pages, 18 figures, accepted for publication in the AJ

All of the 14 subfields of the Kepler field have been observed at least once with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, Xinglong Observatory, China) during the 2012-2014 observation seasons. There are 88,628 reduced spectra with SNR$_g$ (signal-to-noise ratio in g band) $\geq$ 6 after the first round (2012-2014) of observations for the LAMOST-Kepler project (LK-project). By adopting the upgraded version of the LAMOST Stellar Parameter pipeline (LASP), we have determined the atmospheric parameters ($T_{\rm eff}$ , $\log g$, and $\rm [Fe/H]$) and heliocentric radial velocity $v_{\rm rad}$ for 51,406 stars with 61,226 spectra. Compared with atmospheric parameters derived from both high-resolution spectroscopy and asteroseismology method for common stars in Huber et al. (2014), an external calibration of LASP atmospheric parameters was made, leading to the determination of external errors for the giants and dwarfs, respectively. Multiple spectroscopic observations for the same objects of the LK-project were used to estimate the internal uncertainties of the atmospheric parameters as a function of SNR$_g$ with the unbiased estimation method. The LASP atmospheric parameters were calibrated based on both the external and internal uncertainties for the giants and dwarfs, respectively. A general statistical analysis of the stellar parameters leads to discovery of 106 candidate metal-poor stars, 9 candidate very metal-poor stars, and 18 candidate high-velocity stars. Fitting formulae were obtained segmentally for both the calibrated atmospheric parameters of the LK-project and the KIC parameters with the common stars. The calibrated atmospheric parameters and radial velocities of the LK-project will be useful for studying stars in the Kepler field., Comment: 53 pages, 21 figures, 5 tables, Accepted for publication by ApJS

The nearly circular (mean eccentricity ~0.06) and coplanar (mean mutual inclination ~3 deg) orbits of the Solar System planets motivated Kant and Laplace to put forth the hypothesis that planets are formed in disks, which has developed into the widely accepted theory of planet formation. Surprisingly, the first several hundred extrasolar planets (mostly Jovian) discovered using the Radial Velocity (RV) technique are commonly on eccentric orbits ( ~ 0.3). This raises a fundamental question: Are the Solar System and its formation special? The Kepler mission has found thousands of transiting planets dominated by sub-Neptunes, but most of their orbital eccentricities remain unknown. By using the precise spectroscopic host star parameters from the LAMOST observations, we measure the eccentricity distributions for a large (698) and homogeneous Kepler planet sample with transit duration statistics. Nearly half of the planets are in systems with single transiting planets (singles), while the other half are multiple-transiting planets (multiples). We find an eccentricity dichotomy: on average, Kepler singles are on eccentric orbits with ~0.3, while the multiples are on nearly circular ( = 0.04^{+0.03}_{-0.04}) and coplanar ( = 1.4^{+0.8}_{-1.1} deg) orbits similar to the Solar System planets. Our results are consistent with previous studies of smaller samples and individual systems. We also show that Kepler multiples and solar system objects follow a common relation ~(1-2)x between mean eccentricities and mutual inclinations. The prevalence of circular orbits and the common relation may imply that the solar system is not so atypical in the galaxy after all., Comment: 2016 PNAS published, see http://www.pnas.org/content/early/2016/09/21/1604692113.abstract

We derive the fraction of substructure in the Galactic halo using a sample of over 10,000 spectroscopically-confirmed halo giant stars from the LAMOST spectroscopic survey. By observing 100 synthetic models along each line of sight with the LAMOST selection function in that sky area, we statistically characterize the expected halo populations. We define as SHARDS (Stellar Halo Accretion Related Debris Structures) any stars in >3-sigma excesses above the model predictions. We find that at least 10% of the Milky Way halo stars from LAMOST are part of SHARDS. By running our algorithm on smooth halos observed with the LAMOST selection function, we show that the LAMOST data contain excess substructure over all Galactocentric radii R_GC < 40 kpc, beyond what is expected due to statistical fluctuations and incomplete sampling of a smooth halo. The level of substructure is consistent with the fraction of stars in SHARDS in model halos created entirely from accreted satellites. This work illustrates the potential of vast spectroscopic surveys with high filling factors over large sky areas to recreate the merging history of the Milky Way., 12 pages, 10 figures; accepted for publication in ApJ

The intraday optical variability of the BL Lacertae object S5 0716+714 is studied using historical light curves. The well-sampled intranight data set is selected. In total, 19 333 data points have been collected over 208 nights. The source exhibits strong variability in the optical band. At a confidence level of 99.9 per cent, for 162 of the 208 nights the source shows intranight variability. The source varies with an increasing rate of 0.043 mag h-1 and a decreasing rate of 0.036 mag h-1 during the observations, with no evident difference between rising and falling parts. The fast variability is found on JD 245 1909, with a decreasing rate of 0.015 mag min-1 over 6 min. The temporal characteristic is studied by using the structure function method. The result shows that the source varies with an 11.5-min time-scale. For this source, the emission size is estimated to be 1.39 x 1014 cm, the mass of the central black hole is estimated to be 107.87 M? and the magnetic field strength is estimated to be 10.6 G.

We present the ultraviolet magnitudes for over three million stars in the LAMOST survey, in which 2,202,116 stars are detected by $GALEX$. For 889,235 undetected stars, we develop a method to estimate their upper limit magnitudes. The distribution of (FUV $-$ NUV) shows that the color declines with increasing effective temperature for stars hotter than 7000 K in our sample, while the trend disappears for the cooler stars due to upper atmosphere emission from the regions higher than their photospheres. For stars with valid stellar parameters, we calculate the UV excesses with synthetic model spectra, and find that the (FUV $-$ NUV) vs. $R'_{\mathrm{FUV}}$ can be fitted with a linear relation and late-type dwarfs tend to have high UV excesses. There are 87,178 and 1,498,103 stars detected more than once in the visit exposures of $GALEX$ in the FUV and NUV, respectively. We make use of the quantified photometric errors to determine statistical properties of the UV variation, including intrinsic variability and the structure function on the timescale of days. The overall occurrence of possible false positives is below 1.3\% in our sample. UV absolute magnitudes are calculated for stars with valid parallaxes, which could serve as a possible reference frame in the NUV. We conclude that the colors related to UV provide good criteria to distinguish between M giants and M dwarfs, and the variability of RR Lyrae stars in our sample is stronger than that of other A and F stars., Comment: ApJS in the press

The Kepler flux, M dwarfs that include flares,the format consist of four columns: BKJD Relative Flux Fit line Flare Flux the Relative flux wil be empty when flares occur, the flares flux will be empty when quiescent flux. the file lamost_obsid is the spectra used in this work, one can use the obsid to download the fits through the following website: http://dr4.lamost.org/

The limitation of the original mountain emulsion chamber experiments is discussed and a way to improve the air shower (AS) core detection at high altitudes by using a hadron calorimeter plus an AS array is presented. In this report the experimental approach is considered to be used to the checking of hadronic interaction models of the forward particle production at 10TeV energy region. Assuming that a KASCADE-like hadron calorimeter is set up at the center of the ARGO array at Yangbajing, a Monte Carlo shows that a low-height interaction and near core AS event sample at 10TeV region can be selected. This sample could provide an almost direct checking on the property of hadron production in the forward region of p-air inelastic interactions.

The ARGO-YBJ experiment has been in stable data taking from November 2007 till February 2013 at the YangBaJing Cosmic Ray Observatory (4300 m a.s.l.). The detector consists of a single layer of Resistive Plate Chambers (RPCs) (6700 m2) operated in streamer mode. The signal pick-up is obtained by means of strips facing one side of the gas volume. The digital readout of the signals, while allows a high space–time resolution in the shower front reconstruction, limits the measurable energy to a few hundred TeV. In order to fully investigate the 1–10 PeV region, an analog readout has been implemented by instrumenting each RPC with two large size electrodes facing the other side of the gas volume. Since December 2009 the RPC charge readout has been in operation on the entire central carpet (∼5800 m2). In this configuration the detector is able to measure the particle density at the core position where it ranges from tens to many thousands of particles per m2. Thus ARGO-YBJ provides a highly detailed image of the charge component at the core of air showers. In this paper we describe the analog readout of RPCs in ARGO-YBJ and discuss both the performance of the system and the physical impact on the EAS measurements. The ARGO-YBJ experiment has been in stable data taking from November 2007 till February 2013 at the YangBaJing Cosmic Ray Observatory (4300 m a.s.l.). The detector consists of a single layer of Resistive Plate Chambers (RPCs) (6700 m2) operated in streamer mode. The signal pick-up is obtained by means of strips facing one side of the gas volume. The digital readout of the signals, while allows a high space-time resolution in the shower front reconstruction, limits the measurable energy to a few hundred TeV. In order to fully investigate the 1-10 PeV region, an analog readout has been implemented by instrumenting each RPC with two large size electrodes facing the other side of the gas volume. Since December 2009 the RPC charge readout has been in operation on the entire central carpet (∼5800 m2). In this configuration the detector is able to measure the particle density at the core position where it ranges from tens to many thousands of particles per m2. Thus ARGO-YBJ provides a highly detailed image of the charge component at the core of air showers. In this paper we describe the analog readout of RPCs in ARGO-YBJ and discuss both the performance of the system and the physical impact on the EAS measurements.

The ARGO-YBJ experiment is a full coverage array of Resistive Plate Chambers (RPCs) with an active area of 5800 m 2 . In order to eliminate the response difference of the charge readout from the RPCs, a calibration procedure is carried out with the iso-gradient method. This method also allows the extension of the absolute calibration with the muon telescope including scintillation detectors to all the RPCs in the array. The overall systematic uncertainty in measurements o10.7%. In general, the method gives results consistent with those from a totally different approach also used in the experiment. The ARGO-YBJ experiment is a full coverage array of Resistive Plate Chambers (RPCs) with an active area of 5800 m2. In order to eliminate the response difference of the charge readout from the RPCs, a calibration procedure is carried out with the iso-gradient method. This method also allows the extension of the absolute calibration with the muon telescope including scintillation detectors to all the RPCs in the array. The overall systematic uncertainty in measurements of the number of particles by the RPCs is 10.7%. In general, the method gives results consistent with those from a totally different approach also used in the experiment.

We present a statistical method to derive the stellar density profiles of the Milky Way from spectroscopic survey data, taking into account selection effects. We assume that the selection function of the spectroscopic survey is based on photometric colors and magnitudes and possibly altered during observations and data reductions. Then the underlying selection function for a line-of-sight can be well recovered by comparing the distribution of the spectroscopic stars in a color-magnitude plane with that of the photometric dataset. Subsequently, the stellar density profile along a line-of-sight can be derived from the spectroscopically measured stellar density profile multiplied by the selection function. The method is validated using Galaxia mock data with two different selection functions. We demonstrate that the derived stellar density profiles well reconstruct the true ones not only for the full targets, but also for the sub-populations selected from the full dataset. Finally, the method is applied to map the density profiles for the Galactic disk and halo, respectively, using the LAMOST RGB stars. The Galactic disk extends to about R=19 kpc, where the disk still contributes about 10% to the total stellar surface density. Beyond this radius, the disk smoothly transitions to the halo without any truncation, bending, or broken. Moreover, no over-density corresponding to the Monoceros ring is found in the Galactic anti-center direction. The disk shows moderate north-south asymmetry at radii larger than 12 kpc. On the other hand, the R-Z tomographic map directly shows that the stellar halo is substantially oblate within a Galactocentric radius of 20 kpc and gradually becomes nearly spherical beyond 30 kpc., Comment: 27 pages, 18 figures, accepted by Research in Astronomy and Astrophysics