New Variable Stars Discovered as By-product of the Beijing Astronomical Observatory Supernova Survey

The Beijing Astronomical Observatory (BAO) 0.6 m telescope has been used for nearby supernova survey in more than 3000 fields, covering a total area of 235 deg2. More than 260000 CCD images have been collected since April 1996, with 45 supernovae discovered. We searched for variables in about 90000 images taken during 1996-1998. For the fields in which long period variables (LPVs) were discovered, we reduced further images taken from 1999 to 2000, for the period estimation. Among the 280000 stars selected from the survey fields, i.e., brighter than 18 mag, we discovered seven new LPVs and reconfirmed three known LPVs. Additionally, we found 146 variable star candidates, and reconfirmed about 20 previously known or suspected objects.

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST)

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) is a special reflecting Schmidt telescope. LAMOST’s special design allows both a large aperture (effective aperture of 3.6 m–4.9 m) and a wide field of view (FOV) (5°). It has an innovative active reflecting Schmidt configuration which continuously changes the mirror’s surface that adjusts during the observation process and combines thin deformable mirror active optics with segmented active optics. Its primary mirror (6.67m×6.05 m) and active Schmidt mirror (5.74m×4.40 m) are both segmented, and composed of 37 and 24 hexagonal sub-mirrors respectively. By using a parallel controllable fiber positioning technique, the focal surface of 1.75 m in diameter can accommodate 4000 optical fibers. Also, LAMOST has 16 spectrographs with 32 CCD cameras. LAMOST will be the telescope with the highest rate of spectral acquisition. As a national large scientific project, the LAMOST project was formally proposed in 1996, and approved by the Chinese government in 1997. The construction started in 2001, was completed in 2008 and passed the official acceptance in June 2009. The LAMOST pilot survey was started in October 2011 and the spectroscopic survey will launch in September 2012. Up to now, LAMOST has released more than 480 000 spectra of objects. LAMOST will make an important contribution to the study of the large-scale structure of the Universe, structure and evolution of the Galaxy, and cross-identification of multiwaveband properties in celestial objects.

Blind search for 21-cm absorption systems using a new generation of Chinese radio telescopes

Neutral hydrogen clouds are known to exist in the Universe, however their spatial distributions and physical properties are poorly understood. Such missing information can be studied by the new generation of Chinese radio telescopes through a blind search of 21-cm absorption systems. We forecast the capabilities of surveys of 21-cm absorption systems by two representative radio telescopes in China - the Five-hundred-meter Aperture Spherical radio Telescope （FAST） and Tianlai 21-cm cosmology experiment （Tianlai）. Facilitated by either the high sensitivity （FAST） or wide field of view （Tianlai） of these telescopes, more than a thousand 21-cm absorption systems can be discovered in a few years, representing orders of magnitude improvement over the cumulative discoveries in the past half a century.

The LEGUE disk targets for LAMOST's pilot survey

We describe the target selection algorithm for the low latitude disk por- tion of the LAMOST Pilot Survey, which aims to test systems in preparation for the LAMOST spectroscopic survey. We use the PPMXL astrometric catalog, which provides positions, proper motions, B/R/I magnitudes （mostly） from USNO-B and d/H/Ks from the Two Micron All Sky Survey （2MASS） as well. We chose eight plates along the Galactic plane, in the region 0° 〈 α° 〈 67° and 42° 〈 δ 〈 59°, which cover 22 known open clusters with a range of ages. Adjacent plates may have some small overlapping area. Each plate covers an area of 2.5° in radius, with its cen- tral star （for the Shack-Hartmann guider） brighter than 8th magnitude. For each plate, we create an input catalog in the magnitude range 11.3 〈 Imag 〈 16.3 and Bmag available from PPMXL. The stars are selected to satisfy the requirements of the fiber positioning system and have a uniform distribution in the I vs. B - I color-magnitude diagram. Our final input catalog consists of 12 000 objects on each of eight plates that are observable during the winter observing season from the Xinglong Station of the National Astronomical Observatory of China.

Mapping the Milky Way with LAMOSTⅠ:method and overview

We present a statistical method to derive the stellar density profiles of the Milky Way from spectroscopic survey data, taking into account selection effects. We assume the selection function, which can be altered during observations and data reductions, of the spectroscopic survey is based on photometric colors and magnitude. Then the underlying selection function for a line-of-sight can be recovered well by comparing the distribution of the spectroscopic stars in a color-magnitude plane with that of the photometric dataset. Subsequently, the stellar density profile along a line-of-sight can be derived from the spectroscopically measured stellar density profile multiplied by the selection function. The method is validated using Galaxia mock data with two different selection functions. We demonstrate that the derived stellar density profiles reconstruct the true ones well not only for the full set of targets, but also for sub-populations selected from the full dataset. Finally, the method is applied to map the density pro- files for the Galactic disk and halo, using the LAMOST RGB stars. The Galactic disk extends to about R = 19 kpc, where the disk still contributes about 10% to the total stellar surface density. Beyond this radius, the disk smoothly transitions to the halo without any truncation, bending or breaking. Moreover, no over-density corresponding to the Monoceros ring is found in the Galactic anti-center direction. The disk shows moderate north-south asymmetry at radii larger than 12 kpc. On the other hand, the R-Z tomographic map directly shows that the stellar halo is substantially oblate within a Galactocentric radius of 20 kpc and gradually becomes nearly spherical beyond 30 kpc.

Astronomical data fusion tool based on PostgreSQL

With the application of advanced astronomical technologies, equipments and methods all over the world, astronomical observations cover the range from radio, infrared, visible light, ultraviolet, X-ray and gamma-ray bands, and enter into the era of full wavelength astronomy. How to effectively integrate data from different ground- and space-based observation equipments, different observers, different bands and different observation times, requires data fusion technology. In this paper we introduce a cross-match tool that is developed in the Python language, is based on the PostgreSQL database and uses Q3C as the core index, facilitating the cross-match work of massive astronomical data. It provides four different cross- match functions, namely： （I） cross-match of the custom error range; （II） cross-match of catalog errors; （III） cross-match based on the elliptic error range; （IV） cross-match of the nearest neighbor algorithm. The resulting cross-matched set provides a good foundation for subsequent data mining and statistics based on multiwavelength data. The most advantageous aspect of this tool is a user-oriented tool applied locally by users. By means of this tool, users can easily create their own databases, manage their own data and cross- match databases according to their requirements. In addition, this tool is also able to transfer data from one database into another database. More importantly, it is easy to get started with the tool and it can be used by astronomers without writing any code.

The site conditions of the Guo Shou Jing Telescope

The weather at the Xinglong Observing Station, where the Guo Shou Jing Telescope （GSJT） is located, is strongly affected by the monsoon climate in north- east China. The LAMOST survey strategy is constrained by these weather patterns. We present statistics on observing hours from 2004 to 2007, and the sky brightness, seeing, and sky transparency from 1995 to 2011 at the site. We investigate effects of the site conditions on the survey plan. Operable hours each month show a strong cor- relation with season： on average there are eight operable hours per night available in December, but only one-two hours in July and August. The seeing and the sky trans- parency also vary with season. Although the seeing is worse in windy winters, and the atmospheric extinction is worse in the spring and summer, the site is adequate for the proposed scientific program of the LAMOST survey. With a Monte Carlo simulation using historical data on the site condition, we find that the available observation hours constrain the survey footprint from 22h to 16h in right ascension; the sky brightness allows LAMOST to obtain a limiting magnitude of V = 19.5 mag with S/N= 10.

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.