A catalog of early-type emission-line stars and Hα line profiles from LAMOST DR2

We present a catalog including 11 204 spectra of 10 436 early-type emission-line stars from LAMOST DR2, among which 9752 early-type emission-line spectra are newly discovered. For these earlytype emission-line stars, we discuss the morphological and physical properties of their low-resolution spectra. In this spectral sample, the Hα emission profiles display a wide variety of shapes. Based on the Hα line profiles, these spectra are categorized into five distinct classes: single-peak emission, single-peak emission in absorption, double-peak emission, double-peak emission in absorption, and P-Cygni profiles. To better understand what causes the Hα line profiles, we divide these objects into four types from the perspective of physical classification, which include classical Be stars, Herbig Ae/Be stars, close binaries and spectra contaminated by H II regions. The majority of Herbig Ae/Be stars and classical Be stars are identified and separated using a(H-K, K-W1) color-color diagram. We also discuss 31 binary systems that are listed in the SIMBAD on-line catalog and identify 3600 spectra contaminated by H II regions after cross-matching with positions in the Dubout-Crillon catalog. A statistical analysis of line profiles versus classifications is then conducted in order to understand the distribution of Hα profiles for each type in our sample. Finally, we also provide a table of 172 spectra with Fe II emission lines and roughly calculate stellar wind velocities for seven spectra with P-Cygni profiles.     

A catalogue of 74 new open clusters found in Gaia Data-Release 2

Based on astrometric data from Gaia Data-Release 2(DR2),we employ an unsupervised machine learning method to blindly search for open star clusters in the Milky Way within the Galactic latitude range of |b|20°.In addition to 2080 known clusters,74 new open cluster candidates are found.In this work,we present the positions,apparent radii,parallaxes,proper motions and member stars of these candidates.Meanwhile,to obtain the physical parameters of each candidate cluster,stellar isochrones are fit to the photometric data.The results show that the apparent radii and the observed proper motion dispersions of these new candidates are consistent with those of open clusters previously identified in Gaia DR2.     

Identifying Carbon stars from the LAMOST pilot survey with the efficient manifold ranking algorithm

Carbon stars are excellent kinematic tracers of galaxies and can serve as a viable standard candle,so it is worthwhile to automatically search for them in a large amount of spectra.In this paper,we apply the efficient manifold ranking algorithm to search for carbon stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) pilot survey,whose performance and robustness are verified comprehensively with four test experiments.Using this algorithm,we find a total of183 carbon stars,and 158 of them are new findings.According to different spectral features,our carbon stars are classified as 58 C-H stars,11 C-H star candidates,56C-R stars,ten C-R star candidates,30 C-N stars,three C-N star candidates,and four C-J stars.There are also ten objects which have no spectral type because of low spectral quality,and a composite spectrum consisting of a white dwarf and a carbon star.Applying the support vector machine algorithm,we obtain the linear optimum classification plane in the J — H versus H — K_s color diagram which can be used to distinguish C-H from C-N stars with their J — H and H — K_s colors.In addition,we identify 18 dwarf carbon stars with their relatively high proper motions,and find three carbon stars with FUV detections likely have optical invisible companions by cross matching with data from the Galaxy Evolution Explorer.In the end,we detect four variable carbon stars with the Northern Sky Variability Survey,the Catalina Sky Survey and the LINEAR variability databases.According to their periods and amplitudes derived by fitting light curves with a sinusoidal function,three of them are likely semiregular variable stars and one is likely a Mira variable star.     

ISO Observations of Symbiotic Stars

A number of symbiotic stars have been observed with ISO. In addition to a number of emission lines, SWS observations of the symbiotic novae RR Tel and V1016 Cyg reveal prominent, broad 10 & 18 μm silicate dust features. The 10 μm features are similar to the crystalline silicate profiles seen in classical novae. There is some evidence that the silicate brightness in V1016 Cyg varies with Mira-component phase. However, the silicate feature in RR Tel also showed some variation even though observations were made at very similar Mira-component phases. PHT observations of S-type symbiotic stars show the IR emission to be dominated by the red-giant component. However, an excess in the PHT-P filters from 10 to 15 μm is evident in all the stars, and there may be a broad 3.2 μm absorption feature or a broad 3.8 μm emission feature. At this time we have no adequate physical explanations for any of these features. This revised version was published online in August 2006 with corrections to the Cover Date.     

The first data release of LAMOST low-resolution single-epoch spectra

LAMOST Data Release 5,covering~17 000 deg~2from-10?to 80?in declination,contains 9million co-added low-resolution spectra of celestial objects,each spectrum combined from repeat exposure of two to tens of times during Oct 2011 to Jun 2017.In this paper,we present the spectra of individual exposures for all the objects in LAMOST Data Release 5.For each spectrum,the equivalent width of 60lines from 11 different elements are calculated with a new method combining the actual line core and fitted line wings.For stars earlier than F type,the Balmer lines are fitted with both emission and absorption profiles once two components are detected.Radial velocity of each individual exposure is measured by minimizingχ~2between the spectrum and its best template.The database for equivalent widths of spectral lines and radial velocities of individual spectra are available online.Radial velocity uncertainties with different stellar type and signal-to-noise ratio are quantified by comparing different exposure of the same objects.We notice that the radial velocity uncertainty depends on the time lag between observations.For stars observed in the same day and with signal-to-noise ratio higher than 20,the radial velocity uncertainty is below 5 km s~(-1),and increases to 10 km s~(-1)for stars observed in different nights.     

A WISE view of IRAS debris disks: revising the dust properties

Debris disks around stars are considered as components of planetary systems.Constraining the dust properties of these disks can give crucial information to formation and evolution of planetary systems.As an all-sky survey,InfRared Astronomical Satellite(IRAS)gave great contribution to the debris disk searching which discovered the first debris disk host star(Vega).The IRAS-detected debris disk sample published by Rhee(Rhee et al.2007)contains 146 stars with detailed information of dust properties.While the dust properties of 45 of them still cannot be determined due to the limitations with the IRAS database(have IRAS detection at 60μm only).Therefore,using more sensitivity data of Wide-.field Infrared Survey Explorer(WISE),we can better characterize the sample stars:for the stars with IRAS detection at 60μm only,we refit the excessive flux densities and obtain the dust temperatures and fractional luminosities;while for the remaining stars with multi-bands IRAS detections,the dust properties are revised which show that the dust temperatures were overestimated in the high temperature band before.Moreover,we identify 17 stars with excesses at the WISE 22μm which have smaller distribution of distance from Earth and higher fractional luminosities than the other stars without mid-infrared excess emission.Among them,15 stars can be found in previous works.     

LASPM:the LAMOST stellar parameter pipeline for M-type stars and application to the sixth and seventh data release(DR6 and DR7)

The molecular-rich atmospheres of M type stars complicate our understanding to their atmospheric properties.Recently,great progress has been made in atmospheric modeling of M-type stars,and we take advantage of the updated BT-Settl model grid to develop a pipeline LAS PM to measure atmospheric parameters(T_(eff),log g,[M/H]) of M-type stars from low-resolution spectra.The pipeline was applied to the sixth and seventh data release(DR6 DR7) of Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST),which released atmospheric parameters for 610419 and 680 185 Mtype spectra,respectively.The key algorithm is to find the best-matching for templates in the synthetic spectral library for an observed spectrum,and then minimizing χ~2 through a linear combination of five best-matching templates.The intrinsic precisions of the parameters were estimated by using the multiple epoch observations for the same stars,which are 118 K,0.20 dex,0.29 dex for T_(eff),log g,and [M/H]respectively.The Teff and log g are consistent with the spectral and luminosity classifications by LAMOST 1D pipeline,and the loci of giants and dwarfs both on spectral index and color-magnitude diagrams show the validity.The metallicities of LASPM are also checked with the selected members of four open clusters(NGC 2632,Melotte 22,ASCC_16,and ASCC_19),which are consistent without any bias.Comparing the results between LASPM and the APOGEE Stellar Parameter and Chemical Abundance Pipeline(ASPCAP),there is a scatter of 73 K,0.22 dex,0.21 dex for T_(eff),log g,and [M/H],respectively.     

Astrometric calibration of the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center （XSTPS-GAC）

We present astrometric calibration of the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center(XSTPS-GAC). XSTPS-GAC is the photometric part of the Digital Sky Survey of the Galactic Anti-center(DSS-GAC),which is a photometric and spectroscopic sky survey, in combination with LAMOST.In order to select an astrometric reference catalog, we made comparisons between the four widely used astrometric catalogs, GSC2.3, USNO-B1.0, UCAC3 and PPMXL.PPMXL shows relatively small systematic errors in positions and more homogeneous proper motion distributions toward the Galactic Anti-center(GAC), and was selected as the reference catalog. Based on the high quality and bright reference stars that were picked out from PPMXL, we performed a 4th-order polynomial fitting in image units,to construct the transformation relation between coordinates used by XSTPS-GAC and standard coordinates, and to simultaneously correct the image distortions in the CCD. Then we applied the derived relation to all sources to obtain their mean celestial coordinates based on the International Celestial Reference System. For bright point sources with r 17.0 mag, the accuracy of astrometric calibration could reach about80 mas for each of the g, r, i bands, with systematic errors being less than 10 mas. But for the faint sources at the brightness limit of the survey, which was r ～ 19.0 mag, the accuracy can still reach 200 mas. After combining all observations, the final weighted average coordinates could reach an accuracy of less than 70 mas for bright stars. For faint stars, the rms residuals of weighted coordinates decrease to ～ 110 mas. The final combined XSTPS-GAC coordinates show a good consistency with the Sloan Digital Sky Survey.     

Astrometric calibration of the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center(XSTPS-GAC)

We present astrometric calibration of the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center(XSTPS-GAC). XSTPS-GAC is the photometric part of the Digital Sky Survey of the Galactic Anti-center(DSS-GAC),which is a photometric and spectroscopic sky survey, in combination with LAMOST.In order to select an astrometric reference catalog, we made comparisons between the four widely used astrometric catalogs, GSC2.3, USNO-B1.0, UCAC3 and PPMXL.PPMXL shows relatively small systematic errors in positions and more homogeneous proper motion distributions toward the Galactic Anti-center(GAC), and was selected as the reference catalog. Based on the high quality and bright reference stars that were picked out from PPMXL, we performed a 4th-order polynomial fitting in image units,to construct the transformation relation between coordinates used by XSTPS-GAC and standard coordinates, and to simultaneously correct the image distortions in the CCD. Then we applied the derived relation to all sources to obtain their mean celestial coordinates based on the International Celestial Reference System. For bright point sources with r 17.0 mag, the accuracy of astrometric calibration could reach about80 mas for each of the g, r, i bands, with systematic errors being less than 10 mas. But for the faint sources at the brightness limit of the survey, which was r ～ 19.0 mag, the accuracy can still reach 200 mas. After combining all observations, the final weighted average coordinates could reach an accuracy of less than 70 mas for bright stars. For faint stars, the rms residuals of weighted coordinates decrease to ～ 110 mas. The final combined XSTPS-GAC coordinates show a good consistency with the Sloan Digital Sky Survey.     

A comparison of stellar atmospheric parameters from the LAMOST and APOGEE datasets

We have compared stellar parameters, including temperature, gravity and metallicity, for common stars in the LAMOST DR2 and SDSS DR12/APOGEE datasets. It is found that the LAMOST dataset provides a more well-defined red clump feature than the APOGEE dataset in the Teff versus log g diagram. With this advantage, we have separated red clump stars from red giant stars, and attempt to establish calibrations between the two datasets for the two groups of stars. The results show that there is a good consistency in temperature with a calibration close to the one-to-one line, and we can establish a satisfactory metallicity calibration of[Fe/H]APOGEE= 1.18[Fe/H]LAMOST + 0.11 with a scatter of ～ 0.08 dex for both the red clump and red giant branch samples. For gravity, there is no correlation for red clump stars between the two datasets, and scatters around the calibrations of red giant stars are substantial. We found two main sources of scatter in log g for red giant stars. One is a group of stars with 0.00253 × Teff- 8.67 log g 2.6 located in the forbidden region, and the other is the contaminated red clump stars, which could be picked out from the unmatched region where stellar metallicity is not consistent with position in the Teff versus log g diagram. After excluding stars in these two regions,we have established two calibrations for red giant stars, log g APOGEE = 0.000615 ×Teff,LAMOST+ 0.697 × log g LAMOST- 2.208(σ = 0.150) for [Fe/H] -1 and log gAPOGEE= 0.000874×Teff,LAMOST+0.588×log g LAMOST-3.117(σ = 0.167)for [Fe/H] -1. The calibrations are valid for stars with Teff = 3800- 5400 K and log g = 0- 3.8 dex, and are useful in work aiming to combine the LAMOST and APOGEE datasets in a future study. In addition, we find that an SVM method based on asteroseismic log g is a good way to greatly improve the accuracy of gravity for these two regions, at least in the LAMOST dataset.     

Cataclysmic variables based on the stellar spectral survey LAMOST DR3

Big data in the form of stellar spectra from the spectroscopic survey associated with the Large Sky Area Multi-object Fiber Spectroscopic Telescope(LAMOST) are important for studying properties of cataclysmic variables(CVs). By cross matching the catalogs of CVs compiled with LAMOST DR3,acquired from October 2011 to July 2015, we obtained the first spectroscopic catalog for CVs observed by LAMOST with high signal to noise ratio, above 8. By integrating line profiles, their equivalent widths(EWs) of the Hα, Hβ, Hγ and Hδ, as well as He I 5876 and 6678 A? lines, were calculated. There were74 stellar spectra from 48 known CVs and three spectra from three new CV candidates. At the same time, we also collected their previously published EWs. Thirty-three objects had repeated spectra and30 stars showed spectral variability in the Hα line. Moreover, we carried out photometric follow-up studies for five CVs(UU Aqr, TT Tri, PX And, BP Lyn and RW Tri). We obtained nine new light curves and revised their linear ephemerides. For RW Tri, there is a possible oscillation with an amplitude of0.0031(2) days and a period of 47.6±0.4 years, which might be caused by a third body(brown dwarf)or magnetic activity cycle.     

The Status of ROSAT X-ray Active Young Stars toward Taurus-Auriga

We present an astrometric study of the candidates of T Tauri stars (TTS)and non-TTS X-ray sources around Tau-Aur, based on the Hipparcos Catalogue andthe ACT Reference Catalogue. The ROSAT selected X-ray sources are found to bea mixed population. A few of them are associated with the Tau-Aur or Orion StarForming Regions (SFR). Some, with distances similar to that of Tau-Aur but withdiscrepant proper motions, are probable or sure Pleiades super-cluster members orother late type young active stars with unresolved nature, more likely to originatein rapidly moving cloudlets, or else having originated from different sites other thanTau-Aur and moved to the present locations. A good many of the non-TTS X-raysources are considered as Hyades cluster members. Some TTS candidates could beforeground pre-main sequence stars or actually young dwarfs not yet depleted oftheir Lithium. Under the hypothesis that the sources we studied are representativeof the ROSAT selected TTS candidates discovered in the outskirts of     

A search for Mg-poor stars using LAMOST survey data

Most Galactic metal-poor stars exhibit enhanced α-abundances(e.g.[Mg/Fe] ～ +0.4) according to previous studies of stellar chemical compositions.However, a handful of metal-poor stars with large deficiencies in Mg(e.g. [Mg/Fe]～-0.2) show severe departures from this α-enhancement trend. The sub-solar[Mg/Fe] ratios of these anomalous stars indicate that they possess different chemical enrichment histories than the majority of Galactic metal-poor stars. In previous work,we presented a method to select Mg-poor metal-poor stars from low-resolution SDSS spectra based on a spectral matching technique. In this paper, a similar method is applied to low-resolution(R ～ 1800) LAMOST spectra. Stellar [Mg/Fe] abundances are determined by using stellar parameters delivered by the LAMOST Data Release2 catalog. From a sample of ～ 60 000 stars with atmospheric parameters in the range Teff = [5500, 6500] K and [Fe/H] = [-2.4, +0.5], we select 15 candidate Mg-poor metal-poor stars.     

Quasars in the Galactic Anti-Center Area from LAMOST DR3

We present a sample of quasars discovered in an area near the Galactic Anti-Center covering150?≤ l ≤ 210?and |b| ≤ 30?,based on LAMOST Data Release 3(DR3).This sample contains 151 spectroscopically confirmed quasars.Among them 80 are newly discovered with LAMOST.All these quasars are very bright,with i magnitudes peaking around 17.5 mag.All the new quasars were discovered serendipitously from objects that were originally targeted with LAMOST as stars having bluer colors,except for a few candidates targeted as variable,young stellar objects.This bright quasar sample at low Galactic latitudes will help fill the gap in the spatial distribution of known quasars near the Galactic disk that are used to construct an astrometric reference frame for the purpose of accurate proper motion measurements that can be applied to,for example,Gaia.They are also excellent tracers to probe the kinematics and chemistry of the interstellar medium in the Milky Way disk and halo via absorption line spectroscopy.     

An Update of the Catalog of Radial Velocity Standard Stars from the APOGEE DR17

We present an updated catalog of 46,753 radial velocity(RV) standard stars selected from the APOGEE DR17.These stars cover the Northern and Southern Hemispheres almost evenly,with 62% being red giants and 38%being main sequence stars.These RV standard stars are stable on a baseline longer than 200 days(with 54% longer than one year and 10% longer than five years) with a median stability better than 215 m s^-1.The average number of observations of those stars is 5 and each observation i...     

X-ray activity from different types of stars

X-ray emission is an important indicator of stellar activity. In this paper, we study stellar Xray activity using the XMM-Newton and LAMOST data for different types of stars. We provide a sample including 1259 X-ray-emitting stars, of which 1090 have accurate stellar parameter estimations. Our sample size is much larger than those used in previous works. We find a bimodal distribution of the X-ray to optical flux ratio(log(fX/fV)) for G and K stars. We interpret that this bimodality is due to two subpopulations with different coronal heating rates. Furthermore, using the full widths at half maxima calculated from Hα and Hβ lines, we show that these stars in the inactive peaks have smaller rotational velocities. This is consistent with the magnetic dynamo theory that presumes stars with low rotational velocities have low levels of stellar activity. We also examine the correlation between log(fX/fV) and luminosity of the excess emission in the Hα line, and find a tight relation between the coronal and chromospheric activity indicators.     

The discovery of 64 luminous infrared galaxies in the LAMOST Complete Spectroscopic Survey of Pointing Area at the Southern Galactic Cap

We report the discovery of 64 luminous infrared galaxies, based on new observations of 20 square degrees from the LAMOST Complete Spectroscopic Survey of Pointing Area at the Southern Galactic Cap and the WISE 22 μm catalog from the AllW ISE Data Release. Half of them are classified as late-type spirals and the others are classified as peculiar/compact galaxies. The peculiar/compact galaxies tend to exhibit higher luminosities and lower stellar masses. We also separate AGNs from HII galaxies in a simple way by examining LAMOST spectra. Those cases show that host AGNs are easily distinguished from others in the mid-infrared color-color diagrams.     

Candidate members of star clusters from LAMOST DR2

In this work, we provide 2189 photometrically- and kinematically-selected candidate members of 24 star clusters from the LAMOST DR2 catalog. We perform two-step membership identification: selection along the stellar track in the colormagnitude diagram, i.e., photometric identification, and selection from the distribution of radial velocities, i.e. the kinematic identification. We find that the radial velocities from the LAMOST data are very helpful in the membership identification. The mean probability of membership is 40% for the sample selected with radial velocity. With these 24 star clusters, we investigate the performance of the radial velocity and metallicity estimated with the LAMOST pipeline. We find that the systematic offsets in radial velocity and metallicity are 0.85 ± 1.26 km s-1and-0.08 ± 0.04 dex, with dispersions of 5.47+1.16-0.71 km s-1and 0.13+0.04-0.02 dex, respectively. Finally, we propose that the photometrically-selected candidate members of the clusters covered by the LAMOST footprint should be assigned higher priority so that more candidate stars can be observed.     

The Preliminary Statistical Analysis of LAMOST DR8 Low Resolution AFGK Stars

We download the Large sky Area Multi-Object fiber Spectroscopic Telescope Data Release 8(LAMOST DR8)low resolution catalog for 6,478,063 AFGK type stars and plot the figures of effective temperature,gravitational acceleration and metal abundance.Some small and medium mass stars are evolved from pre-main sequence or main sequence stage to planetary nebula stage or white dwarf stage by the stellar evolution code MESA.We analyze the observed statistical data and model calculation results,and then o...     

Fixing the reference frame for PPMXL proper motions using extragalactic sources

We quantify and correct systematic errors in PPMXL proper motions using extragalactic sources from the first two LAMOST data releases and the Ve`ron-Cetty Ve`ron Catalog of Quasars. Although the majority of the sources are from the Ve`ron catalog, LAMOST makes important contributions in regions that are not well-sampled by previous catalogs, particularly at low Galactic latitudes and in the south Galactic cap. We show that quasars in PPMXL have measurable and significant proper motions,which reflect the systematic zero-point offsets present in the catalog. We confirm the global proper motion shifts seen by Wu et al., and additionally find smaller-scale fluctuations of the QSO-derived corrections to an absolute frame. We average the proper motions of 158 106 extragalactic objects in bins of 3?× 3?and present a table of proper motion corrections.