Using the "standard pair" technique of paring stars of almost nil and high extinction but otherwise of almost identical stellar parameters from the Sloan Digital Sky Survey (SDSS), and combing the SDSS, Galaxy Evolution Explore (GALEX), Two Micro All Sky Survey (2MASS) and Wide-field Infrared Survey Explorer (WISE) photometry ranging from the far ultraviolet (UV) to the mid-infrared (mid-IR), we have measured dust reddening in theH − Ks, Ks − W 1 and W 1 − W 2 colors for thousands of Galactic stars. The measurements, together with the E(B − V ) values given by Schlegel et al. (1998), allow us to derive the observed, model-free reddening coefficients for those colors. The results are compared with previous measurements and the predictions of a variety of Galactic reddening laws. We find that 1) The dust reddening map of Schlegel et al. (1998) over-estimates E(B − V ) by about 14 per cent, consistent with the recent work of Schlafly et al. (2010) and Schlafly & Finkbeiner (2011); 2) After accounted for the differences in reddening normalization, the newly deduced reddening coefficients for colors F U V − N U V, N U V − u, u − g, g − r, r − i, i − z, z − J, J − H and H − Ks differ by respectively −1640%, 15.5%, 12.6%, −0.8%, 3.4%, −0.7%, 3.5%, 2.5% and 1.4% from the predictions of Fitzpatrick reddening law (Fitzpatrick 1999) for an assumed total-to-selective extinction ratio R(V ) = 3.1, and by respectively −1730%, 13.0%, 8.1%, 10.0%, 8.0%, −13.5%, −1.7%, −6.7% and −17.1% from the predictions of CCM reddening law (Cardelli et al. 1989); and 3) All the new reddening coefficients, except those for N U V − u and u − g, prefer the R(V ) = 3.1 Fitzpatrick reddening law rather than the R(V ) = 3.1 CCM and O'Donnell (O'Donnell 1994) reddening laws. Using the Ks-band extinction coefficient predicted by the R(V ) = 3.1 Fitzpatrick law and the observed reddening coefficients, we have deduced new extinction coefficients for the F U V, N U V, u, g, r, i, z, J, H, W 1 and W 2 passbands. We recommend that the new reddening and extinction coefficients should be used in the future and an update of the Fitzpatrick reddening law in the UV is probably necessary. We stress however that the F U V -and N U V -band coefficients should be used with caution given their relatively large measurement uncertainties. Finally, potential applications of the "standard pair" technique with the LAMOST Galactic surveys are discussed.

We propose a Stellar Locus OuTlier (SLOT) method to determine the binary fraction of main-sequence stars statistically. The method is sensitive to neither the period nor mass-ratio distributions of binaries, and able to provide model-free estimates of binary fraction for large numbers of stars of different populations in large survey volumes. We have applied the SLOT method to two samples of stars from the SDSS Stripe 82, constructed by combining the re-calibrated SDSS photometric data with respectively the spectroscopic information from the SDSS and LAMOST surveys. For the SDSS spectroscopic sample, we find an average binary fraction for field FGK stars of 41%±2%. The fractions decrease toward late spectral types, and are respectively 44%±5%, 43%±3%, 35% ± 5%, and 28% ± 6% for stars of g − i colors between 0.3 -0.6, 0.6 -0.9, 0.9 -1.2, and 1.2 -1.6 mag. A modest metallicity dependence is also found. The fraction decreases with increasing metallicity. For stars of [Fe/H]between −0.5 -0.0, −1.0 -−0.5, −1.5 -−1.0, and −2.0 -−1.5 dex, the inferred binary fractions are 37% ± 3%, 39% ± 3%, 50% ± 9%, and 53% ± 20%, respectively. We have further divided the sample into stars from the thin disk, the thick disk, the transition zone between them, and the halo. The results suggest that the Galactic thin and thick disks have comparable binary fractions, whereas the Galactic halo contains a significantly larger fraction of binaries. Applying the method to the LAMOST spectroscopic sample yields consistent results. Finally, other potential applications and future work with the method are discussed.

We present a detailed determination and analysis of 3D stellar mass distribution of the Galactic disk for mono-age populations using a sample of 0.93 million main-sequence turn-off and subgiant stars from the LAMOST Galactic Surveys. Our results show (1) all stellar populations younger than 10 Gyr exhibit strong disk flaring, which is accompanied with a dumpy vertical density profile that is best described by a sech n function with index depending on both radius and age; (2) Asymmetries and wave-like oscillations are presented in both the radial and vertical direction, with strength varying with stellar populations; (3) As a contribution by the Local spiral arm, the mid-plane stellar mass density at solar radius but 400-800 pc (3-6 • ) away from the Sun in the azimuthal direction has a value of 0.0594 ± 0.0008 M ⊙ /pc 3 , which is 0.0164 M ⊙ /pc 3 higher than previous estimates at the solar neighborhood. The result causes doubts on the current estimate of local dark matter density; (4) The radial distribution of surface mass density yields a disk scale length evolving from ∼4 kpc for the young to ∼2 kpc for the old populations. The overall population exhibits a disk scale length of 2.48 ± 0.05 kpc, and a total stellar mass of 3.6(±0.1) × 10 10 M ⊙ assuming R ⊙ = 8.0 kpc, and the value becomes 4.1(±0.1) × 10 10 M ⊙ if R ⊙ = 8.3 kpc; (5) The disk has a peak star formation rate (SFR) changing from 6-8 Gyr at the inner to 4-6 Gyr ago at the outer part, indicating an inside-out assemblage history. The 0-1 Gyr population yields a recent disk total SFR of 1.96 ± 0.12 M ⊙ /yr.

Accurate determinations of atmospheric parameters (effective temperature T eff , surface gravity log g and metallicity [Fe/H]) and distances for large complete samples are of vital importance for various Galactic studies. We have developed a photometric method to select red giant stars and estimate their atmospheric parameters from the photometric colors provided by the SkyMapper Southern Survey (SMSS) data release (DR) 1.1, using stars in common with the LAMOST Galactic spectroscopic surveys as a training set. Distances are estimated with two different approaches: one based on the Gaia DR2 parallaxes for nearby (d ≤ 4.5 kpc) bright stars and another based on the absolute magnitudes predicted by intrinsic color (g − i) 0 and photometric metallicity [Fe/H] for distant (d > 4.5 kpc) faint stars. Various tests show that our method is capable of delivering atmospheric parameters with a precision of ∼80 K for T eff , ∼0.18 dex for [Fe/H] and ∼0.35 dex for log g but with a significant systematic error at log g ∼ 2.3. For distances delivered from (g − i) 0 and photometric [Fe/H], our test with the member stars of globular clusters show a median uncertainty of 16 per cent with a negligible zero-point offset. Using this method, atmospheric parameters and distances of nearly one million red giant stars are derived from SMSS DR1.1. Proper motion measurements from Gaia DR2 are available for almost all of the red giant stars, and radial velocity measurements from several large spectroscopic surveys are available for 44 per cent of these. This sample will be accessible online at https://yanghuang0.wixsite.com/yangh/research.

Modern large-scale surveys have allowed the identification of large numbers of white dwarfs. However, these surveys are subject to complicated target selection algorithms, which make it almost impossible to quantify to what extent the observational biases affect the observed populations. The LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope) Spectroscopic Survey of the Galactic anti-center (LSS-GAC) follows a well-defined set of criteria for selecting targets for observations. This advantage over previous surveys has been fully exploited here to identify a small yet wellcharacterised magnitude-limited sample of hydrogen-rich (DA) white dwarfs. We derive preliminary LSS-GAC DA white dwarf luminosity and mass functions. The space density and average formation rate of DA white dwarfs we derive are 0.83±0.16×10 −3 pc −3 and 5.42 ± 0.08 × 10 −13 pc −3 yr −1 , respectively. Additionally, using an existing Monte Carlo population synthesis code we simulate the population of single DA white dwarfs in the Galactic anti-center, under various assumptions. The synthetic populations are passed through the LSS-GAC selection criteria, taking into account all possible observational biases. This allows us to perform a meaningful comparison of the observed and simulated distributions. We find that the LSS-GAC set of criteria is highly efficient in selecting white dwarfs for spectroscopic observations (80-85 per cent) and that, overall, our simulations reproduce well the observed luminosity function. However, they fail at reproducing an excess of massive white dwarfs present in the observed mass function. A plausible explanation for this is that a sizable fraction of massive white dwarfs in the Galaxy are the product of white dwarf-white dwarf mergers.

Using a sample of 96,201 primary red clump stars selected from the LAMOST and Gaia surveys, we investigate the stellar structure of the Galactic disk. The sample stars show two separated sequences of high-[α/Fe] and low-[α/Fe] in the [α/Fe]–[Fe/H] plane. We divide the sample stars into five mono-abundance populations (MAPs) with different ranges of [α/Fe] and [Fe/H], named as the high-[α/Fe], high-[α/Fe] and high-[Fe/H], low-[Fe/H], solar, high-[Fe/H] MAPs, respectively. We present the stellar number density distributions in the R–Z plane, and the scale heights and scale lengths of the individual MAPs by fitting their vertical and radial density profiles. The vertical profiles, the variation trend of scale height with the Galactocentric radius, indicate that there is a clear disk flare in the outer disk both for the low-[α/Fe] and the high-[α/Fe] MAPs. While the radial surface-density profiles show a peak radius of 7 kpc and 8 kpc for the high-[α/Fe] and low-[α/Fe] MAPs, respectively. We also investigate the correlation between the mean rotation velocity and metallicity of the individual MAPs, and find that the mean rotation velocities are well separated and show different trends between the high-[α/Fe] and the low-[α/Fe] MAPs. Finally, we discuss the character of the high-[α/Fe] and high-[Fe/H] MAP and find that it is more similar to the high-[α/Fe] MAP either in the radial and vertical density profiles or in the rotation velocity.

Obtaining measurements of chromospheric and photometric activity of stars with near-solar fundamental parameters and rotation periods is important for a better understanding of solar–stellar connection. We select a sample of 2603 stars with near-solar fundamental parameters from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST)-Kepler field and use LAMOST spectra to measure their chromospheric activity and Kepler light curves to measure their photospheric activity (i.e., the amplitude of the photometric variability). While the rotation periods of 1556 of these stars could not be measured due to the low amplitude of the photometric variability and highly irregular temporal profile of light curves, 254 stars were further identified as having near-solar rotation periods. We show that stars with near-solar rotation periods have chromospheric activities that are systematically higher than stars with undetected rotation periods. Furthermore, while the solar level of photospheric and chromospheric activity appears to be typical for stars with undetected rotation periods, the Sun appears to be less active than most stars with near-solar rotation periods (both in terms of photospheric and chromospheric activity).

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