Performance and sensitivity of Low Resolution Spectrographs for LAMOST Zhu Yongtian, Hou Yonghui, Hu Zhongwen Wang Lei, Wang Jianing San Diego, 27 June, 2010

Outline Brief introduction --LAMOST --LRSs Test results -- Image quality -- Throughout --Wavelength coverage and resolution Some results in early commissioning observation

LAMOST

Specification of LAMOST  Effective aperture: D = 4m  Focal ratio: F#= 5  field of view : 5 degrees  Number of Fibers : 4000  FRD: f/5→f/4  Fiber core diameter: 320micons or 3.3″

Specification of Low Resolution Spectrograph  There are 16 LRS spectrographs 250 fibers for each spectrograph Wavelength coverage 370nm~900nm Resolution expected 1000~10000

The optical layout of the LAMOST-LRS R1000/2000 R5000/10000 R1000/2000 Blue band(370~590nm) Red band (570~900nm) Yongtian Zhu, Zhongwen Hu, Qingfeng Zhang, et al. Proc. SPIE 6269(2006)

Spectrograph Parameters 16 low resolution spectrographs (LRSs) for LAMOST 250 fibers(3.3 arcsecs) / Each spectrograph The fibers are separated by 578μm center to center along the 144 mm height arc slit F/4 Schmidt collimator A dichroic beam-splitter 4 VPH gratings/LRS (low, and medium dispersion respectively) 2 articulating red and blue F/1.3 Schmidt cameras field lens Corrector mirrors 4096×4136 EEV CCD 12μm square pixel size

In laboratory in Xinglong Station

VPH Grating sets of LAMOST-LRS

VPHG

VPH gratings wavefront quality

Resolution powers Low-resolution mode Medium-resolution mode 3700 – 9000 Å R ~ 1000 / – 5500 Å  8300 – 8900 Å R ~ 5000 / 10000

32 CCD Detectors E2V / England Chinese Company

Image quality of blue band for low resolution configuration R=1000

Image quality of red band for low resolution configuration (R=1000)

Image quality for medium resolution configuration (R=5000)

Image quality

Image quality (with 1.6″slit) two dimensional spectra of arc lamp (with 1.6″slit)

Throughput Throughput of LAMOST-LRS without considering the CCD quantum efficiency and fiber transmission loss

Wavelength coverage and resolution CCD can cover about 348nm(red band),234nm (blue band) The wavelength range: nm (blue band) nm(red band) The resolution at central wavelength: 1100 (at 740nm), 1040 (at 480nm) The 1D spectrum of arc lamp

The twilight sky spectra obtained by LAMOST Blue band Red band

Some observation results during the early commissioning phase (in the winter 2009) A very bright i = quasar in the ‘redshift desert’ discovered by LAMOST (Xue-Bing Wu1, Zhaoyu Chen1, Zhendong Jia et al.)(2010) Eight new quasars discovered by LAMOST in one extragalatic field (Xue- Bing Wu, Zhendong Jia, Zhaoyu Chen et al.) (2010) LAMOST Discovers Quasars Behind the Andromeda Galaxy(Zhi-Ying Huo, Xiao-Wei Liu, Hai-Bo Yuan et al.)(2010) Detection of New Candidates of Metal-poor Stars with LAMOST Commissioning Data (H.-N. Li, G. Zhao, N. Christlieb) (2010) LAMOST Discovers New Planetary Nebulae in the Outskirts of the Andromeda Galaxy (Hai-Bo Yuan, Xiao-Wei Liu, Zhi-Ying Huo ) (2010) ……………………………………

A very bright i = quasar in the ‘redshift desert’ discovered by LAMOST (z=2.427) Left panel: The LAMOST spectrum of SDSS J Right panel: The spectrum of SDSS J taken by the NAOC/Xinglong 2.16m telescope. The scaled SDSS composite quasar spectrum (in red color) is shown for comparison Xue-Bing Wu, Zhaoyu Chen, Zhendong Jia et al accepted by RAA

Eight new quasars 8 new quasars ( 2 quasars in the redshift desert) i magnitudes: to z (redshift) to Xue-Bing Wu, Zhendong Jia, Zhaoyu Chen et al accepted by RAA

Detection of New Candidates of Metal-poor Stars with LAMOST only the LAMOST blue arm spectra are shown, and the continuum has not been subtracted. Hai-Bo Yuan, Xiao-Wei Liu, Zhi-Ying Huo, et al accepted by RAA

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