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Performance and sensitivity of Low Resolution Spectrographs

for LAMOST

Zhu Yongtian, Hou Yonghui, Hu Zhongwen

Wang Lei, Wang Jianing

San Diego, 27 June, 2010

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Outline• Brief introduction

--LAMOST

--LRSs

• Test results

-- Image quality

-- Throughout

--Wavelength coverage and resolution

• Some results in early commissioning observation

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LAMOST

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Specification of LAMOST

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

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Specification of

Low Resolution Spectrograph

There are 16 LRS spectrographs

•250 fibers for each spectrograph

•Wavelength coverage 370nm~900nm

•Resolution expected 1000~10000

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The optical layout of the LAMOST-LRS

R1000/2000R5000/10000

R5000/10000

R1000/2000

Blue band(370~590nm)

Red band (570~900nm)

Yongtian Zhu, Zhongwen Hu, Qingfeng Zhang, et al. Proc. SPIE 6269(2006)

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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

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In laboratoryin Xinglong Station

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VPH Grating sets of LAMOST-LRS

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VPHG

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VPH gratings wavefront quality

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Resolution powers

•Low-resolution mode

•Medium-resolution mode

•3700 – 9000 Å R ~ 1000 / 2000

•5100 – 5500 Å 8300 – 8900 Å

•R ~ 5000 / 10000

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32 CCD Detectors

•E2V / England •Chinese Company

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Image quality of blue band for low resolution configurationR=1000

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

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Image quality for medium resolution configuration (R=5000)

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Image quality

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Image quality (with 1.6″slit)

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

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Throughput

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

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Wavelength coverage and resolution

• CCD can cover about 348nm(red band),234nm (blue band)

• The wavelength range: 365-599nm (blue band)

• 565-913nm(red band)

• The resolution at central wavelength:

• 1100 (at 740nm), 1040 (at 480nm)

• The 1D spectrum of arc lamp

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The twilight sky spectra obtained by LAMOST

Blue band Red band

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Some observation results during the early commissioning phase (in the winter 2009)

• A very bright i = 16.44 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)

• ……………………………………

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A very bright i = 16.44 quasar in the ‘redshift desert’ discovered by LAMOST (z=2.427)

• Left panel: The LAMOST spectrum of SDSS J085543.40-001517.7. Right panel: The spectrum of SDSS J085543.40-001517.7 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. 2010 accepted by RAA

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Eight new quasars • 8 new quasars

( 2 quasars in the redshift desert)

• i magnitudes: 16.24 to 19.10

• z (redshift)

0.898 to 2.773

Xue-Bing Wu, Zhendong Jia, Zhaoyu Chen et al. 2010 accepted by RAA

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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. 2010 accepted by RAA

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Thank You！

ytzhu@niaot.ac.cn