Yeping Li

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 (6.67 m×6.05 m) and active Schmidt mirror (5.74 m×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.

The optical performance of LAMOST telescope

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) project has completed its engineering work, and is going to finish commissioning around the end of 2010. The LAMOST telescope is with both large aperture and wide field of view to achieve the large scale spectroscopic survey observation. It is an innovative large aperture meridian active reflecting Schmidt configuration achieved by an active deformable Schmidt mirror, which could not be realized by the traditional optical system. Its primary mirror and active Schmidt mirror are both segmented, and composed of 37 and 24 hexagonal sub-mirrors respectively. A new active optics method succesfully developed in the active deformable Schmidt mirror of LAMOST. It is a conbination of the thin deformable mirror active optics and segmented active optics. This paper presents the optical performance of the telescope of LAMOST during optical test. It is shown that LAMOST project successfully resolving the big technical challenges, and making the progress in active optics and telescope technology.

Active support system of LAMOST reflecting Schmidt plate

The reflecting Schmidt plate MA of LAMOST is with 5.7m × 4.4m reflecting area and consists of 24 segmented hexagonal sub-mirrors. Each sub-mirror is 25mm in thickness and 1.1m in diagonal. To correct the spherical aberration of the primary mirror, during observation, the aspherical shape of MA should be changed in every 1.5 minutes. To achieve the good image during observation, the active support system of MA will not only create the correct off-axis aspherical shape on each sub-mirror, but also maintain the co-focus for all 24 sub-mirrors. This paper presents the studying design with finite element analysis and experiments on the active support system of MA, including its axial and lateral supports, force actuators, optimization of the stiffness of the force actuator, sub-mirror cell, the mirror support structure etc. There are 30 force actuators and three position actuators, which support each sub-mirror and connected by sub-mirror cell. Total 24 sub-mirror cells located on the top of the MA main support structure. All force actuators work as both active and passive supports for each sub-mirror. It showed that the support system is complex but should work properly within the optical requirement.

THE LAMOST SURVEY OF BACKGROUND QUASARS IN THE VICINITY OF THE ANDROMEDA AND TRIANGULUM GALAXIES. II. RESULTS FROM THE COMMISSIONING OBSERVATIONS AND THE PILOT SURVEYS

We present new quasars discovered in the vicinity of the Andromeda and Triangulum galaxies with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, also named the Guoshoujing Telescope, during the 2010 and 2011 observational seasons. Quasar candidates are selected based on the available Sloan Digital Sky Survey, Kitt Peak National Observatory 4 m telescope, Xuyi Schmidt Telescope Photometric Survey optical, and Wide-field Infrared Survey Explorer near-infrared photometric data. We present 509 new quasars discovered in a stripe of ~135 deg^2 from M31 to M33 along the Giant Stellar Stream in the 2011 pilot survey data sets, and also 17 new quasars discovered in an area of ~100 deg^2 that covers the central region and the southeastern halo of M31 in the 2010 commissioning data sets. These 526 new quasars have i magnitudes ranging from 15.5 to 20.0, redshifts from 0.1 to 3.2. They represent a significant increase of the number of identified quasars in the vicinity of M31 and M33. There are now 26, 62, and 139 known quasars in this region of the sky with i magnitudes brighter than 17.0, 17.5, and 18.0, respectively, of which 5, 20, and 75 are newly discovered. These bright quasars provide an invaluable collection with which to probe the kinematics and chemistry of the interstellar/intergalactic medium in the Local Group of galaxies. A total of 93 quasars are now known with locations within 2fdg5 of M31, of which 73 are newly discovered. Tens of quasars are now known to be located behind the Giant Stellar Stream, and hundreds are behind the extended halo and its associated substructures of M31. The much enlarged sample of known quasars in the vicinity of M31 and M33 can potentially be utilized to construct a perfect astrometric reference frame to measure the minute proper motions (PMs) of M31 and M33, along with the PMs of substructures associated with the Local Group of galaxies. Those PMs are some of the most fundamental properties of the Local Group.

New planetary nebulae in the outskirts of the Andromeda Galaxy discovered with the Guoshoujing Telescope (LAMOST)

Planetary nebulae (PNe) are good tracers of the stellar populations, chemical composition and dynamics of their host galaxies. This paper reports the discovery of new PNe in the outskirts of the Andromeda Galaxy (M 31) with the Guoshoujing Telescope (GSJT, formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope–LAMOST) during its early commissioning phase. In total, 36 candidates selected from SDSS photometry are confirmed in terms of their PN nature, including 17 new discoveries and another 19 previously known emission line objects. Their positions, spectra, radial velocities and m 5007 magnitudes are presented. We discuss the potential for detecting more PNe in M31 with GSJTs multi-object spectroscopy and the related applications in studies of the dynamics and chemistry of M 31 and its assemblage history.

A very bright (i = 16.44) quasar in the 'redshift desert' discovered by the Guoshoujing Telescope (LAMOST)

The redshift range from 2.2 to 3 is known as the ‘redshift desert’ of quasars because quasars with redshifts in this range have similar optical colors as normal stars and are thus difficult to find in optical sky surveys. A quasar candidate, SDSS J085543.40–001517.7, which was selected by a recently proposed criterion involving near-IR Y − K and optical g − z colors, was identified spectroscopically as a new quasar with a redshift of 2.427 by the Guoshoujing Telescope (LAMOST) commis sioning observation in 2009 December and confirmed by the observation made with the NAOC/Xinglong 2.16 m telescope in 2010 March. This quasar was not identified in the SDSS spectroscopic survey. Comparing with other SDSS quasars, we found that this new quasar, with an i magnitude of 16.44, is apparently the brightest one in the redshift range from 2.3 to 2.7. From its spectral properties, we derived its central black hole mass to be (1.4 ∼ 3.9) × 10 10 M ⊙ and its bolometric luminosity to be 3.7 × 10 48 erg s −1 , which indicates that this new quasar is intrinsically very bright and belongs to the class of the most luminous quasars in the universe. Our identification supports the notion that quasars in the redshift desert can be found by the quasar selection criterion involving the near-IR colors. More missing quasars are expected to be uncovered by future LAMOST spectroscopic surveys, which is important to the study of the cosmological evolution of quasars at redshifts higher than 2.2.

New background quasars in the vicinity of the Andromeda Galaxy discovered with the Guoshoujing Telescope (LAMOST)

We present preliminary analyses of spectra of quasar candidates in two Guoshoujing Telescope (GSJT, formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope - LAMOST) test fields near M 31 where one is close to the optical center of the disk and the other is towards the northeastern outskirts of the halo, obtained during the early stage of the GSJT commissioning in the last season of 2009. Both fields contain background low-redshift quasar candidates selected from the SDSS photometry. In total, 14 new quasars with redshifts up to 2 and i magnitudes between 16.7 and 19.2, are discovered, including 7 within the 2.5° central region of M 31. We briefly discuss the potential applications of these newly discovered bright quasars.

Preliminary study of a dispersed fringe type sensing system

Telescopes with large aspherical primary mirrors collect more light and are therefore sought after by astronomers. Instead of using a single large one-piece mirror, smaller segments can be assembled into a useable telescopic primary. Because the segments must fi t together to create the effect of a single mirror, segmented optics present unique challenges to the fabrication and testing that are absent in monolithic optics. A dispersed fringe sensor (DFS) using a broadband point source is an ef fi cient method for cophasing and is also highly automated and robust. Unlike the widely adopted Shack-Hartmann Wavefront sensor and curvature wavefront sensor with edge sensors for calibration of relative pistons, DFS can estimate the piston between segments by only using the spectrum formed by the transmissive grating’s dispersion, and therefore can replace the edge sensors, which are dif fi cult to calibrate. We introduce the theory of the DFS and Dispersed Hartmann Sensor (DHS) for further utilization of the coarse phasing method of DFS. According to the theory, we bring out the preliminary system design of the cophasing experimental system based on DFS and DHS which is now established in our institute. Finally, a summary is reached.

A new efficient laser angle metrology system for maintaining the large radio telescope active reflecting antenna

Radio telescopes with much more larger aperture collect much more signals and therefore sought after by astronomers. The primary reflecting antenna is traditionally segmented and perfectly optically aligned at the central altitude among the whole observation sky area for minimizing the gravitational deformation during operation and passively open-loop maintained at any other altitude. A new laser segmentation sensing and maintaining method based on normal deflection angle measurement is proposed in this paper. After the introduction of the theory, the method is simulated and tested on a special prototype of radio panel segmentation system. It provides real-time monitoring and measurement of the global segmentation status of all panels and is proved to be a high accurate, high efficient and low cost method. Finally several conclusions are reached.

The Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Quasar Survey: Quasar Properties from Data Release Two and Three

This is the second installment for the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Quasar Survey, which includes quasars observed from September 2013 to June 2015. There are 9024 confirmed quasars in DR2 and 10911 in DR3. After cross-match with the SDSS quasar catalogs and NED, 12126 quasars are discovered independently. Among them 2225 quasars were released by SDSS DR12 QSO catalogue in 2014 after we finalised the survey candidates. 1801 sources were identified by SDSS DR14 as QSOs. The remaining 8100 quasars are considered as newly founded, and among them 6887 quasars can be given reliable emission line measurements and the estimated black hole masses. Quasars found in LAMOST are mostly located at low-to-moderate redshifts, with a mean value of 1.5. The highest redshift observed in DR2 and DR3 is 5. We applied emission line measurements to H