LAMOST Instrument: 4000 Fiber Low Resolution Spectroscopy

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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.     

A Catalog and Statistical Analysis for Magnetic Stars

Magnetic fields are significant in the structure and evolution of stars. We present a comprehensive catalog of 1784known magnetic stars, detailing their identifications, HD numbers, precise locations, spectral types and averaged quadratic effective magnetic fields among other important information. The group comprises 177 O-type stars, 551B-type stars, 520 A-type stars, 91 F-type stars, 53 G-type stars, 61 K-type stars, 31 M-type stars and an additional300 stars whose spectral classification rem...     

Discovery of 2716 hot emission-line stars from LAMOST DR5

We present a catalog of 3339 hot emission-line stars(ELSs)identified from 451695 O,B and A type spectra,provided by LAMOST Data Release 5(DR5).We developed an a...     

Kinematics and activity of M dwarfs in LAMOST DR1

We report on the first investigation into kinematics and chromospheric activity of M dwarfs from the Guo Shou Jing Telescope(also called the Large Sky Area Multi-Object Fiber Spectroscopic Telescope – LAMOST) data release one(DR1).The sample comprises 71 304 M dwarfs. Their fundamental parameters such as spectral types, radial velocities, important molecular band indices and magnetic activities are measured. Their distances are determined by a spectroscopic parallax relation.Space motion(U, V, W) and Galactocentric cylindrical coordinates(R, θ, Z) for the M dwarfs are also computed. We examine velocity dispersion as a function of height from the Galactic plane and find that all three components of velocity dispersion increase with height as measured with respect to the Galactic plane. The investigation into chromospheric activities along the height from the Galactic plane confirms that M dwarfs closer to the Galactic plane are more likely to be active. We take a pure kinematical approach to select thin disk stars and thick disk stars from our sample, then to investigate the differences in properties between these two populations. Our analysis is in excellent agreement with previous studies and leads to a better understanding of the structure of the Galactic disk.     

A catalog of DB white dwarfs from the LAMOST DR5 and construction of templates

In this study, we employ machine learning to build a catalog of DB white dwarfs(DBWDs) from the LAMOST Data Release(DR) 5. Using known DBs from SDSS DR14, we selected samples of highquality DB spectra from the LAMOST database and applied them to train the machine learning process.Following the recognition procedure, we chose 351 DB spectra of 287 objects, 53 of which were new identifications. We then utilized all the DBWD spectra from both SDSS DR14 and LAMOST DR5 to construct DB templates for LAMOST 1 D pipeline reductions. Finally, by applying DB parameter models provided by D. Koester and the distance from Gaia DR2, we calculated the effective temperatures, surface gravities and distributions of the 3 D locations and velocities of all DBWDs.     

Kinematics of Stars from the TGAS (Gaia DR1) Catalogue

Based on the stellar proper motions of the TGAS (Gaia DR1) catalogue, we have analyzed the velocity field of main-sequence stars and red giants from the TGAS catalogue with heliocentric distances up to 1.5 kpc. We have obtained four variants of kinematic parameters corresponding to different methods of calculating the distances from the parallaxes of stars measured with large relative errors. We have established that within the Ogorodnikov–Milne model changing the variant of distances affects significantly only the solar velocity components relative to the chosen centroid of stars, provided that the solution is obtained in narrow ranges of distances (0.1 kpc). The estimates of all the remaining kinematic parameters change little. This allows the Oort coefficients and related Galactic rotation parameters as well as all the remaining Ogorodnikov–Milne model parameters (except for the solar terms) to be reliably estimated irrespective of the parallax measurement accuracy. The main results obtained from main-sequence stars in the range of distances from 0.1 to 1.5 kpc are: A = 16.29 ± 0.06 km s^?1 kpc^?1, B = ?11.90 ± 0.05 km s^?1 kpc^?1, C = ?2.99 ± 0.06 km s^?1 kpc^?1, K = ?4.04 ± 0.16 km s^?1 kpc^?1, and the Galactic rotation period P = 217.41 ± 0.60 Myr. The analogous results obtained from red giants in the range from 0.2 to 1.6 kpc are: the Oort constants A = 13.32 ± 0.09 km s^?1 kpc^?1, B = ?12.71 ± 0.06 km s^?1 kpc^?1, C = ?2.04 ± 0.08 km s^?1 kpc^?1, K = ?2.72 ± 0.19 km s^?1 kpc^?1, and the Galactic rotation period P = 236.03 ± 0.98 Myr. The Galactic rotation velocity gradient along the radius vector (the slope of the Galactic rotation curve) is ?4.32 ± 0.08 km s^?1 kpc^?1 for main-sequence stars and ?0.61 ± 0.11 km s^?1 kpc^?1 for red giants. This suggests that the Galactic rotation velocity determined from main-sequence stars decreases with increasing distance from the Galactic center faster than it does for red giants.     

Early Pre-Main Sequence Evolution of Low Mass Stars

Evolution of the gravitational contraction phase of stars having masses 0.3 < M/M⊙ < 1.5 were studied along with deuterium burning. The equation of state developed by Mihalas et al. (1988) and OPAL opacity tables were used in our investigation. The theoretical time lines were compared with observations. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Statistical Study of the Mass Distribution of Neutron Stars

By reviewing the methods of mass measurements of neutron stars in four different kinds of systems, i.e., the high-mass X-ray binaries (HMXBs), low-mass X-ray binaries (LMXBs), double neutron star systems (DNSs) and neutron star-white dwarf (NS-WD) binary systems, we have collected the orbital parameters of 40 systems. By using the boot-strap method and the Monte-Carlo method, we have rebuilt the likelihood probability curves of the measured masses of 46 neutron stars. The statistical analysis of the simulation results shows that the masses of neutron stars in the X-ray neutron star systems and those in the radio pulsar systems exhibit different distributions. Besides, the Bayes statistics of these four different kind systems yields the most-probable probability density distributions of these four kind systems to be (1.340 ± 0.230)M8, (1, 505 ± 0.125)M8,(1.335 ± 0.055)M8 and (1.495 ± 0.225)M8, respectively. It is noteworthy that the masses of neutron stars in the HMXB and DNS systems are smaller than those in the other two kind systems by approximately 0.16M8. This result is consistent with the theoretical model of the pulsar to be accelerated to the millisecond order of magnitude via accretion of approximately 0.2M8. If the HMXBs and LMXBs are respectively taken to be the precursors of the BNS and NS-WD systems, then the influence of the accretion effect on the masses of neutron stars in the HMXB systems should be exceedingly small. Their mass distributions should be very close to the initial one during the formation of neutron stars. As for the LMXB and NS-WD systems, they should have already under- gone the process of suffcient accretion, hence there arises rather large deviation from the initial mass distribution.     

估计Be星自转的一个统计方法

本文给出了一个统计方法,可以由观测得到的Be星视自转速度U=V sin i,估计出其真自转速度V;本文证实了Be星不是以临界速度旋转的,其真自转速度和临界速度之比为0.7左右。     

Evolution of The Spin Periods of Neutron Stars in Low Mass X-ray Binaries

We present a numerical analysis of the spin evolution of neutron stars in low-mass X-ray binaries, trying to explain the discrepancy in the spin period distribution between observations of millisecond pulsars and theoretical results. In our calculations, we take account of possible effects of radiation pressure and irradiation-induced instability on the structure of the disk, and the evolution of the mass transfer rate, respectively. We report the following results: (1) The radiation pressure in the accretion disk leads to a slight increase of spin periods, and the variation of mass transfer rate caused by the neutron star irradiation can shorten the spin-down phase of evolution. (2) The calculated results of the model combining radiation pressure and irradiation show that the accretion is strongly limited by the radiation pressure in the high mass transfer phase. (3) The accreted mass and fastness parameter can affect the number of systems in the equilibrium state.     

The First Orbits of Six Wide Double Stars in the Solar Neighborhood Based on Gaia DR2 Observations

Astronomy Letters - The apparent motion parameter (AMP) method is designed to determine the orbits of wide pairs of double stars with orbital periods of hundreds and thousands of years. This is a...     

The Spectrum Analysis of Three Chromospherically Active Binary Stars

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Kinematics of the Galaxy from OB Stars with Data from the Gaia DR2 Catalogue

We have selected and analyzed a sample of OB stars with known line-of-sight velocities determined through ground-based observations and with trigonometric parallaxes and propermotions from the Gaia DR2 catalogue. Some of the stars in our sample have distance estimates made from calcium lines. A direct comparison with the trigonometric distance scale has shown that the calcium distance scale should be reduced by 13%. The following parameters of the Galactic rotation curve have been determined from 495 OB stars with relative parallax errors less than 30%: (U, V,W)_⊙ = (8.16, 11.19, 8.55)± (0.48, 0.56, 0.48) km s^?1, Ω₀ = 28.92 ± 0.39 km s^?1 kpc^?1, Ω'₀ = ?4.087 ± 0.083 km s^?1 kpc^?2, and Ω″ ₀ = 0.703 ± 0.067 km s?1 kpc^?3, where the circular velocity of the local standard of rest is V0 = 231 ± 5 km s^?1 (for the adopted R₀ = 8.0 ± 0.15 kpc). The parameters of the Galactic spiral density wave have been found from the series of radial, V_R, residual tangential, ΔV_circ, and vertical, W, velocities of OB stars by applying a periodogram analysis. The amplitudes of the radial, tangential, and vertical velocity perturbations are f_R = 7.1± 0.3 km s^?1, f_θ = 6.5 ± 0.4 km s^?1, and f_W = 4.8± 0.8 km s^?1, respectively; the perturbation wavelengths are λ_R = 3.3 ± 0.1 kpc, λ_θ = 2.3 ± 0.2 kpc, and λ_W = 2.6 ± 0.5 kpc; and the Sun’s radial phase in the spiral density wave is (χ_⊙)_R = ?135? ± 5?, (χ_⊙)θ = ?123? ± 8?, and (χ_⊙)_W = ?132? ± 21? for the adopted four-armed spiral pattern.     

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...     

Kinematics of T Tauri Stars Close to the Sun from the Gaia DR2 Catalogue

Astronomy Letters - The spatial and kinematic properties of a large sample of young T Tauri stars from the solar neighborhood 500 pc in radius have been studied. The following parameters of the...     

The correction of atmospheric dispersion in LAMOST

Atmospheric refraction and dispersion affect the observational quality and efficiency of the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST). In this paper, by both ZEMAX simulation and numerical calculation, the atmospheric dispersion for LAMOST, which will be installed at the latitude 40°.4 and has a 20 m focal length and F5 focal ratio, are calculated for the 0.75 h before and after the transit time. Various types of dispersion prism to be used for correcting the atmospheric dispersion in LAMOST were calculated and analyzed, from which one was finally adopted. The secondary spectrum of the dispersion prism, the residual dispersion during tracking of the telescope and the installation errors of the dispersion prism are investigated.     

LAMOST望远镜的大气色散校正

大气折射与大气色散会影响大视场多目标光纤光谱观测的质量和效率.一个焦距为20m,焦比为F5、位于北纬40.4°的LAMOST望远镜在中天和中天前后0.75小时产生的色散值,用模拟计算得到结果,并用数值计算得到验证.对校正色散可能用的几种色散棱镜进行了计算分析比较,确定了色散棱镜的型式,并分析了色散棱镜的二级光谱以及色散棱镜在望远镜跟踪过程中的残留色散,及色散棱镜的安装误差.     

LAMOST一维光谱提取算法的分析与比较

针对LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope)2维光谱图像数据,对6种抽谱算法进行了分析与比较.比较的算法包括孔径法、轮廓拟合法、直接反卷积方法、基于Tikhonov正则化的反卷积抽谱算法、基于自适应Landweber迭代的反卷积抽谱算法以及基于Richardson-Lucy迭代的反卷积抽谱算法.通过实验对这些算法在信噪比和分辨率两个方面进行了比较,发现基于Tikhonov正则化的反卷积抽谱算法、基于自适应Landweber迭代的反卷积抽谱算法以及基于RichardsonLucy迭代的反卷积抽谱算法是6种算法中最为可靠的3种抽谱算法.最后,对今后的工作进行了展望.