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Data products of GuoShouJing telescope(LAMOST) pipeline and c
urrent problems
LUO Ali@KIAA
LAMOST Workshop
Outline
• Data products
• Progress and problems of 2d pipeline
• Progress of 1d pipeline
• Commissioning data request.
Formal Data products
• Calibrated 1d spectra
• Catalog
Progress and problems of 2d pipeline
Fiber profile
• Fit fiber profile by flat exposure
• Use this profile within other exposures
• That is:
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Flux extraction
• Profile fitting– Good at working against bad pixels, crosstalk,
etc.– Bad at extracting emission lines
• The function varies at center and edge of profile
• Aperture– Fast extracting– For LAMOST, adjacent fibers are far enough
from each other
Flat extraction
Object extraction
Wavelength calibration
• First, calibrate with arc lamp lines
• Then corrected by sky emission lines
• Problem:– Low S/N at 3600Å– Weak arc lamp lines after 7500Å– Image shifts from arc exposure to object
exposure, so the error could increase to 0.2Å from 0.1Å
Stability of spectrograph
Fiber flat
• Fitting a ‘super-flat’ by all fibers
• Divide ‘super-flat’ to get fiber flat
• Problem:– Flat is not flat enough to correct fiber
throughput– Need to improve field flat
Lamp flat vs. night sky
Night sky vs. twilight flat
Sky subtraction
• n sky fibers, fitting a ‘super-sky’
• Need:– Good extraction– Accurate wavelength calibration– Good flat– Good sky emission line profiles
Flux calibration
• By SDSS standard stars
• Correct observed flux by template
• Telluric correction
• Problem:– Some standard stars get no information– Low S/N
Spectrum combination
• Different exposures
• Blue and red part
• Problem:– Too low S/N at the beginning and end of each
spectrum
Examples
Progress of 1d pipeline• Classification and redshift (rv) measurement depends on
quality of data• Stellar parameters
compare of SSPP and ULySS (interpolate in Elodie)
New version of Elodie-Prugniel et al 2010 in preparation
Validation of ULySS with CFLIB
Comparison of SSPP with high resolution spectra
(Allende Prieto et 2008)
Comparison of ULySS with high resolution spectra
Validation of ULySS with SSPP calibrated result
SSPP(v7.5) & ULySS(v)
Problem: template and calibration
Commissioning data requestLAMOST Commissioning data Application（ Only available during LAMOST commissioning）
Applicant Name(Sign): Date:
Institution:
Email:
Data class (objects, observation date, data amount, original data, 1d spectra, parameters):
Purpose (should announce the data will not be used for other purpose):
Feedback (content and time, science production):
LAMOST opinion
Sign: date:
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