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The Observations of LAMOST
Jianrong Shi
NAOC
1/7 2014
The Observation of LAMOST
Jianrong Shi
(NAOC)
Overview
The structure of LAMOST
The observation preparation
How to select the plate
The results from one year Pilot and two year
standard surveys
Structure of LAMOST
MA mirror
4000
Fiber
Positio
ning
5.72m×4.4m
4000
Fibers
MB mirror
6.67 m×6.05m
16
Spectrograph
s
32 CCDs
Characteristics of LAMOST
 A horizontal meridian reflecting Schmidt telescope with an
active correcting plate
 large field of view (5 deg) + large aperture (4m)
Active optics on thin-mirror & segmented mirrors
 4000 optical fibers on focal surface
Parallel controllable fiber positioning
The observation preparation
Focus the MB ( Shack-Hartman MA) ~5mintues
Focus the MA and four guiding stars (center star V <
8 mag. ) ~25mintues
Moving the fibers to the accurate positions (9mintues)
(Which can be done during the focus)
MB 6.67m×6.05m Focal length 20m 37sub-mirrors
Segmented Active optics for
37 sub-mirrors of MB
8
MA 5.72 m×4.4m (24 sub-mirrors)
Segmented and thin
mirror active optics for
24 sub-mirrors of MA
10
4000 fiber positioning units (1.75m)
Guiding
S-H
sensor
CCDs
for MA
11
4000 fiber positioning units
The site conditions
The statistics of the number of hours of BATC
observations per night from 2004-01-01 to 2007-0930. The dashed line shows the theoretical available
time.
Sky brightness
The sky brightness in V band obtained from BATC
Polaris monitor data, as a function of time from 1995 to
2011.
Telescope
Declination
-10o
60o
90o
Effective aperture
4.9m
4.2m
3.6m
Field of view
5 degree
3 degree
Seeing: 3-5 arcsec (dome + site)
Site seeing: < 2 arcsec ; Fiber size: 3.3 arcsec
has a field of view as large as 20 square degrees,
the effective aperture varies from 3.6 to 4.9 meters
in diameter (depending on the pointing). Enables it
to take 4000 spectra in a single exposure at
resolution R = 1800.
Seeing
Comparing the seeing from guide star and DIMM
during Pilot Survey (Oct. 24, 2011- Match 30, 2012 )
Throughpot (Oct. 1 2011)
Signal to Noise Ratio
Signal to Noise Ratio
Signal to Noise Ratio
Signal to Noise Ratio
Signal to Noise Ratio
Throughpot (Oct. 1 2011)
Throughpot (Oct. 2 2011)
How to select the Plate
Observational conditions: (240m)
weather, Moon phase, left time and seeing etc.
VB(9.0<r<14.0) 3*10m
B (14.0<r<16.3) 3*20m – 3*25m
M(16.3<r<17.8) 3*30m
F(17.8<r<18.5) 3*30m
readout ~ 8m
Wish to observe two B plates and more VB plates
the image
The results from pilot survey
Spectra with S/N>10（g or i band）
spectra
plate success ratio
pilot:
597,032
397
45.6%
First year: 1,191,414
768
57.9%
Second year:1,207,119
697
64%
success ratio: the ratio of the Spectra with S/N>10
to all the selected targets
Observed time: 914h, 1278h and 1356h
The reason for the less plates
during the second year
Increase the time for foucs MB、B plate from
20 -25 minutes, added one lamp observation
and more M plates observed
LSS-GAC
DR1 B：76 M：30 F：4
DR2 B：75 M：44
The instrumental fail rate (The ratio of the
lost time due to the instrumental problem to
the observation time)
Pilot: 12.5% first：5.3% second：4.4%
Thank You！