Licai Deng

LAMOST spectral survey--An overview

LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) is a Chinese national scientific research facility operated by National Astronomical Observatories, Chinese Academy of Sciences (NAOC). After two years of commissioning beginning in 2009, the telescope, instruments, software systems and operations are nearly ready to begin the main science survey. Through a spectral survey of millions of objects in much of the northern sky, LAMOST will enable research in a number of contemporary cutting edge topics in astrophysics, such as discovery of the first generation stars in the Galaxy, pinning down the formation and evolution history of galaxies — especially the Milky Way and its central massive black hole, and looking for signatures of the distribution of dark matter and possible sub-structures in the Milky Way halo. To maximize the scientific potential of the facility, wide national participation and international collaboration have been emphasized. The survey has two major components: the LAMOST ExtraGAlactic Survey (LEGAS) and the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE). Until LAMOST reaches its full capability, the LEGUE portion of the survey will use the available observing time, starting in 2012. An overview of the LAMOST project and the survey that will be carried out in the next five to six years is presented in this paper. The science plan for the whole LEGUE survey, instrumental specifications, site conditions, and the descriptions of the current on-going pilot survey, including its footprints and target selection algorithm, will be presented as separate papers in this volume.

RINGS AND RADIAL WAVES IN THE DISK OF THE MILKY WAY

We show that in the anticenter region, between Galactic longitudes of

Ring Structure and Warp of NGC 5907: Interaction with Dwarf Galaxies

110^\circ<l<229^\circ

Spatially resolved spectrophotometry of M81: Age, metallicity, and reddening maps

, there is an oscillating asymmetry in the main sequence star counts on either side of the Galactic plane using data from the Sloan Digital Sky Survey. This asymmetry oscillates from more stars in the north at distances of about 2 kpc from the Sun to more stars in the south at 4-6 kpc from the Sun to more stars in the north at distances of 8-10 kpc from the Sun. We also see evidence that there are more stars in the south at distances of 12-16 kpc from the Sun. The three more distant asymmetries form roughly concentric rings around the Galactic center, opening in the direction of the Milky Ways spiral arms. The northern ring, 9 kpc from the Sun, is easily identified with the previously discovered Monoceros Ring. Parts of the southern ring at 14 kpc from the Sun (which we call the TriAnd Ring) have previously been identified as related to the Monoceros Ring and others have been called the Triangulum Andromeda Overdensity. The two nearer oscillations are approximated by a toy model in which the disk plane is offset by of the order 100 pc up and then down at different radii. We also show that the disk is not azimuthally symmetric around the Galactic anticenter and that there could be a correspondence between our observed oscillations and the spiral structure of the Galaxy. Our observations suggest that the TriAnd and Monoceros Rings (which extend to at least 25 kpc from the Galactic center) are primarily the result of disk oscillations.

An anisotropic nonlocal convection theory

The edge-on, nearby spiral galaxy NGC 5907 has long been used as the prototype of a “noninteracting” warped galaxy. We report here the discovery of two interactions with companion dwarf galaxies that substantially change this picture. First, a faint ring structure is discovered around this galaxy that is likely due to the tidal disruption of a companion dwarf spheroidal galaxy. The ring is elliptical in shape with the center of NGC 5907 close to one of the ring’s foci. This suggests that the ring material is in orbit around NGC 5907. No gaseous component to the ring has been detected either with deep Ha images or in Very Large Array H i 21 cm line maps. The visible material in the ring has an integrated luminosity •10 8 L,, and its brightest part has a color . R 2 I » 0.9 All of these properties are consistent with the ring being a tidally disrupted dwarf spheroidal galaxy. Second, we find that NGC 5907 has a dwarf companion galaxy, PGC 54419, which is projected to be only 36.9 kpc from the center of NGC 5907, close in radial velocity ( km s 21 ) to the giant spiral galaxy. This dwarf DV 5 45 is seen at the tip of the H i warp and in the direction of the warp. Hence, NGC 5907 can no longer be considered noninteracting but is obviously interacting with its dwarf companions much as the Milky Way interacts with its dwarf galaxies. These results, coupled with the finding by others that dwarf galaxies tend to be found around giant galaxies, suggest that tidal interaction with companions, even if containing a mere 1% of the mass of the parent galaxy, might be sufficient to excite the warps found in the disks of many large spiral galaxies. Subject headings: galaxies: individual (NGC 5907, PGC 054419) — galaxies: interactions — galaxies: photometry — galaxies: spiral — radio lines: galaxies

Intermediate-band surface photometry of the edge-on galaxy NGC 4565

In this paper we present a multicolor photometric study of the nearby spiral galaxy M81, using images obtained with the Beijing Astronomical Observatory 60/90 cm Schmidt telescope in 13 intermediate-band filters from 3800 to 10000 A. The observations cover the whole area of M81, with a total integration of 51 hr from 1995 to 1997 February. This provides a multicolor map of M81 in pixels of 17 × 17. Using theoretical stellar population synthesis models, we demonstrate that some BATC (Beijing-Arizona-Taiwan-Connecticut Multicolor Sky Survey) colors and color indices can be used to disentangle the age and metallicity effect. We compare in detail the observed properties of M81 with the predictions from population synthesis models and quantify the relative chemical abundance, age, and reddening distributions for different components of M81. We find that the metallicity of M81 is about Z = 0.03, with no significant difference over the whole galaxy. In contrast, an age gradient is found between stellar populations of the central regions and of the bulge and disk regions of M81: the stellar population in its central regions is older than 8 Gyr, while the disk stars are considerably younger (~2 Gyr). We also give the reddening distribution in M81. Some dust lanes are found in the galaxy bulge region, and the reddening in the outer disk is higher than that in the central regions.

Calibration of the BATC Survey: Methodology and Accuracy

We present in this paper an anisotropic nonlocal theory of stellar convection. Following the idea of Rotta, we propose that the correlation of turbulent pressure and velocity gradient tends to make the turbulent velocity isotropic, and we further introduce a convection parameter c(3) to measure the strength of such isotropization. By using such a theory, the structure of the solar convection zone is calculated. Our calculation shows that the radial component dominates in the convectively unstable zone, in which the ratio between the radial component and the horizontal component is w(r)(2)/w(h)(2) = ( 3 + c(3))/2c(3). In the upper overshooting zone, turbulent velocity is almost isotropic ( w(r)(2)/w(h)(2) similar to 0.5) and is independent of c(3), while in the lower overshooting zone, w(r)(2)/w(h)(2) similar to 0.5, and it tends to decrease as c(3) decreases. We also studied the effects of anisotropic convection on the structure and evolution of stars. It is shown that the anisotropy hardly affects the temperature and pressure structure of stars. However, the anisotropy increases with the decrease of c(3); therefore, the effect of overshooting decreases. Thus, the effects of anisotropy of turbulent convection on stellar evolution cannot be neglected.

The K giant stars from the LAMOST survey data I: identification, metallicity, and distance

We present a deep, 42.79 hr image of the nearby, edge-on galaxy NGC 4565 in the Beijing-Arizona-Taipei-Connecticut 6660 Angstrom band using the large-format CCD system on the 0.6 m Schmidt telescope at the Xinglong Station of the National Astronomical Observatories of China. Following the procedures previously developed by our team for the analysis of deep images of galaxies, we obtain a final image that is calibrated to an accuracy of 0.02 mag in zero point and for which we can measure galaxy surface brightness to an accuracy of 0.25 mag at a surface brightness of 27.5 mag arcsec(-2) at 6660 Angstrom, corresponding to a distance of 22 kpc from the center of the disk. The integrated magnitude of NGC 4565 in our filter is m(6660) = 8.99 (=R magnitude of 9.1) to a surface brightness of 28 mag arcsec(-2). We analyze the faint outer parts of this galaxy using a two-dimensional model comprised of three components: an exponential thin disk, an exponential thick disk, and a power-law halo. Combined with a need to provide a cutoff radius for the disk, a total of 12 parameters are included in our model. We determine the best values of our model parameters via 10,000 random initial values, 3700 of which converge to final values. We then plot the chi(2) for each converged fit versus parameter value for each of the 12 parameters. The thin-disk and thick-disk parameters that we determine here are consistent with those of previous studies of this galaxy. However, our very deep image permits a better determination of the power-law fit to the halo, constraining this power law to be between r(-3.2) and r(-4.0), with a best-fit value of r(-3.88). We find the axis ratio of the halo to be 0.44 and its core radius to be 14.4 kpc ( for an adopted distance of 14.5 Mpc). We also agree with others that the bulge of NGC 4565 is fitted well by an exponential luminosity distribution with a scale height similar to that found for the thin disk.

The Binary Fraction of the Young Cluster NGC 1818 in the Large Magellanic Cloud

ABSTRACT We describe in detail the extinction correction procedures used for the Beijing‐Arizona‐Taiwan‐Connecticut Sky Survey (BATC Survey). The survey covers the spectral range 3200–9900 A by utilizing a set of 15 intermediate‐band filters. These filters are specifically designed to exclude most of the bright and variable night‐sky emission lines. We also present extinction coefficients for the filter passbands for typical photometric nights at the Xinglong Observing Station, Beijing Astronomical Observatory (where the observations of the survey are being carried out). Time‐dependent, low‐amplitude (∼1%), nightly extinction variation has been observed. Such variation is demonstrably independent of filter bandpass and air mass, with amplitudes ranging from ∼0.01 to ∼0.03 mag. The variation is plausibly caused by slowly varying (at ∼1%) atmospheric extinction, possibly related to changes in air pressure/temperature/humidity that occur during the night. An iterative fitting scheme has been developed to tak...

Discovery of Super-Li-rich Red Giants in Dwarf Spheroidal Galaxies

We present a support vector machine classifier to identify the K giant stars from the LAMOST survey directly using their spectral line features. The completeness of the identification is about 75% for tests based on LAMOST stellar parameters. The contamination in the identified K giant sample is lower than 2.5%. Applying the classification method to about 2 million LAMOST spectra observed during the pilot survey and the first year survey, we select 298,036 K giant candidates. The metallicities of the sample are also estimated with uncertainty of