Binary Star Fractions from the LAMOST DR4

Stellar systems composed of single, double, triple or higher-order systems are rightfully regarded as the fundamental building blocks of the Milky Way. Binary stars play an important role in formation and evolution of the Galaxy. Through comparing the radial velocity variations from multiepoch observations, we analyze the binary fraction of dwarf stars observed with LAMOST. Effects of different model assumptions, such as orbital period distributions on the estimate of binary fractions,are investigated. The results based on log-normal distribution of orbital periods reproduce the previous complete analyses better than the power-law distribution. We find that the binary fraction increases with Teff and decreases with [Fe/H]. We first investigate the relation between α-elements and binary fraction in such a large sample as provided by LAMOST. The old stars with high [α/Fe] dominate with a higher binary fraction than young stars with low [α/Fe]. At the same mass, earlier forming stars possess a higher binary fraction than newly forming ones, which may be related with evolution of the Galaxy.     

The ORAC‐DR data reduction pipeline

The ORAC‐DR data reduction pipeline has been used by the Joint Astronomy Centre since 1998. Originally developed for an infrared spectrometer and a submillimetre bolometer array, it has since expanded to support twenty instruments from nine different telescopes. By using shared code and a common infrastructure, rapid development of an automated data reduction pipeline for nearly any astronomical data is possible. This paper discusses the infrastructure available to developers and estimates the development timescales expected to reduce data for new instruments using ORAC‐DR. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Halo stream candidates in the LAMOST DR2

We have cross-matched the LAMOST DR2 with the WISE, 2MASS and PPMXL catalogs and obtained a sample of 64 819 FGK metal-poor dwarfs with [Fe/H]-0.7, distances within 2 kpc from the Sun and reliable kinematics(space velocities,angular momenta and eccentricities). With a detection strategy for halo streams provided by Klement et al, nine significant "phase-space overdensities" with stars on very similar orbits are identified from this sample. Among these overdensities, three were previously known and six are new stream candidates. The kinematics and metallicities of these stream candidates are then analyzed; they have typical halo characteristics.We have extracted the most probable members of each halo stream according to their angles with respect to the North Galactic Pole and investigate the distribution of the angular momenta to further verify their existences. Detailed study of elemental abundances for these members based on high resolution and high signal-to-noise spectra from follow-up observations in the near future is of high interest to understand the origin of these streams.     

The neutral interface adjoining theHII region DR21

Observations of C100 and C125 atomic carbon recombination lines were made at the Algonquin Radio Observatory, towards the neutral interface separating theHii region DR21 (at RA=20^h37^m14^s, Dec=+42°0900) from its associated molecular cloud. An analysis of the Cn observations in conjunction with a simple model of a neutral interface enabled the derivation of the following parameters: electron density of 300 cm^–3, electron temperature of 30 K, microturbulent velocity of 2.3 km s^–1, and depth of the neutral interface of 0.01 pc. A single,stimulated emission model is sufficient to reproduce the Cn observations in the wavelength range from 4.6 cm (C100) to 21 cm (C166). All the known Cn data do support a pressure equilibrium between the neutral interface and theHii region, after the usual allowance is made for carbon depletion on grains.     

M-giant star candidates identified in LAMOST DR 1

We perform a discrimination procedure with the spectral index diagram of TiO 5 and Ca H2+Ca H3 to separate M giants from M dwarfs. Using the M giant spectra identified from LAMOST DR1 with high signal-to-noise ratio, we have successfully assembled a set of M giant templates, which show more reliable spectral features. Combining with the M dwarf/subdwarf templates in Zhong et al., we present an extended library of M-type templates which includes not only M dwarfs with a well-defined temperature and metallicity grid but also M giants with subtypes from M0 to M6. Then, the template-fitting algorithm is used to automatically identify and classify M giant stars from LAMOST DR1. The resulting catalog of M giant stars is cross-matched with 2MASS J H Ks and WISE W1/W2 infrared photometry. In addition, we calculated the heliocentric radial velocity of all M giant stars by using the cross-correlation method with the template spectrum in a zero-velocity rest frame.Using the relationship between the absolute infrared magnitude MJ and our classified spectroscopic subtype, we derived the spectroscopic distance of M giants with uncertainties of about 40%. A catalog of 8639 M giants is provided. As an additional result of this analysis, we also present a catalog of 101 690 M dwarfs/subdwarfs which are processed by our classification pipeline.     

Correlation function of quasars from SDSS DR3

We calculate the parameters of the two-point correlation function of quasars w(r) = (r _c /r) ^γ on the basis of the SDSS DR3 data. The correlation functions are first determined from projected distances with the use of a special technique for compiling randomized catalogs. Next the parameters of the spatial correlation function are obtained with the assumption of local isotropy. For the quasars with redshifts z = 0.8–2.1, we obtained the estimates γ = 1.76 ± 0.14, r _c = 6.60 ± 0.85 h ^?1 Mpc in the comoving distance range 2–30 Mpc and γ = 1.90 ± 0.11, r _c = 6.95±0.57 h ^?1 Mpc in the range 2–50 Mpc. These estimates agree, within the limits of errors, with the estimates obtained for the redshifts 0.4 < z < 2.1. The original catalog shows some deficit of pairs with separations less than 1 Mpc.     

The radio and infrared spectrum of DR 21

The radio and infrared spectrum of DR 21 is established over a wide range of frequencies (from 10² to 10⁸ MHz). Two physical processes, free-free emission from the ionized hydrogen at radio wavelengths and reradiation at infrared wavelengths of the original stellar ultraviolet radiation by dust grains have to be considered in the explanation of the derived spectrum. Physical parameters of the object deduced from its radio emission are also presented.     

H2 fluorescence in HH 7 and DR 21

We present evidence for Ly pumping of the Lyman band system of molecular hydrogen in Herbig-Haro 7 and the bipolar outflow DR 21. For this study we have measured several vibrational-rotational emission lines of H₂ whose energy levels are widely spaced and ranging from 6000 (v = 1) to 25000 Kelvin (v = 4). We show that the near-infrared H₂ emission from the shocked gas in HH 7 can be well described by a bow C-type shock. The enhanced emission observed from the higher energy levels (v > 3) can be well modelled by employing the Ly pumping mechanism.In the DR 21 outflow the multi-line study showed that different physical conditions exist in the eastern and western emission lobes. The higher H₂ line ratios measured in the eastern lobe suggests a higher Ly pump rate which may be locally produced in the fast bowshocks. The FUV radiation field emanating from the central HII regions may in addition be exciting the Lyman and Werner bands of H₂ in the molecular lobes.We show that the observed H₂ emission can be interpreted in terms of a simple model consisting of a C-type bowshock, which produces the low excitation H₂ emission, and a FUV radiation field with enough Ly line radiation to produce the high excitation H₂ emission through fluorescence.     

Searching for classical Be stars in LAMOST DR1

We report on searching for Classical B-type emission-line(CBe) stars in the first data release of the Large Sky Area Multi-Object fiber Spectroscopic Telescope(LAMOST; also called the Guo Shou Jing Telescope). A total of 192 objects(including 12 previously known CBes) were identified as CBe candidates with prominent He I λ4387, He I λ4471 and Mg II λ4481 absorption lines, as well as Hβλ4861and Hαλ6563 emission lines. These candidates significantly increase the currently known sample of CBes by about 8%. Most of the CBe candidates are distributed near the Galactic Anti-Center due to the observing strategy used for LAMOST. Only two CBes are in star clusters. These two CBes have ages of 15.8 and 398 Myr, respectively.     

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.     

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.     

Structural Properties of Early-Type Galaxies from the SDSS DR2

Two-dimensional bulge/disk light decomposition with GIM2D in both the r-and g-bands has been applied to a sample of 129 early-type galaxies brighter than 13.5 magnitude in the r-band,selected from the Sloan Digital Sky Survey Data Release 2.Intensity-weighted Fourier coefficient (a4/a) was also derived for each sample galaxy.Our analysis shows that and between bulge and disk scale sizes.Isophotal shape parameter (a4/a) is not correlated with BIT and nB.Both bulge and disk components satisfy a color-magnitude relation.The k space Fundamental Plane analysis shows that galaxies with larger B/T tend to lie tighter and closer to the line of k1 k2=8 (the so-called "zone of avoidance") than the galaxies with smaller B/T.It indicates that existence of the disk component may lead to scatter of the distribution on the Fundamental Plane.Our analysis also shows that k1 k2 correlates with (y-r) color and B/T,but does not correlate with (a4/a) for early-type galaxies.The fitted parameters and other retrieved parameters used in this paper for all sample galaxies are available online.     

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.     

Fundamental Plane of FSRQs from SDSS DR5 Quasar Catalogue

In this work, we explore a sample of 362 flat-spectrum radio quasars (FSRQs) to investigate the jet formation. We find that the fundamental plane for our FSRQs can be expressed as $L_{\rm 5~GHz}\propto M_{\rm bh}^{-0.19}L_{\rm 2~keV}^{1.08}$ . We also find that the 5?GHz luminosities are tightly related to both black hole mass and Eddington ratio, which is established as $L_{\rm 5~GHz}\propto M_{\rm bh}^{0.67}(L_{\rm bol}/ L_{\rm EDD})^{1.32}$ .     

Local standard of rest based on Gaia DR2 catalog

The local standard of rest(LSR) provides a reference framework for studies of Galactic kinematics. Determination of the LSR corresponds to the measurement of solar peculiar motion, which is under debate due to the fact that different methods and samples have been used. Adopting the astrometric data and line-of-sight velocities of main sequence stars from Gaia DR2, we present a detailed analytical study of stellar kinematics in the solar neighborhood. Based on an improved version of the Stromberg relation, we obtain a robust estimation of the solar peculiar motion, which is given by(U☉,V☉,W☉)=(8.63 ± 0.64, 4.76 ± 0.49, 7.26 ± 0.36) km s^-1. The corresponding radial scalelength is yielded as Rd ～ 2.5 kpc. The radial and vertical components of solar peculiar motion are basically consistent with the classical values, while the tangential component is a few km s^-1 smaller than most estimates in literature.