The LAMOST 1d Spectroscopic Pipeline

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The LAMOST 1d Spectroscopic Pipeline
The KIAA-Cambridge Joint Workshop on Near-Field
Cosmology and Galactic Archeology

• A-Li LUO
• LAMOST team, NAOC
• 2008/12/3

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Lessons from SDSS

• Three 1d pipelines of SDSS (template based )
• Princeton 1d Fermi 1d SEGUE SSPP
• Have been improving from DR1-gtDR7

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Task of 1D pipeline

• Classification and Identification
• Measurement (z of galaxies and QSOs, rv of stars)
• Stellar parameter estimation
• Special Candidate searching (Supernovae,
  Metal-poor stars, HII ) according to
  requirements of astronomers

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Software Structure
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Production
1. Catalogs 2. Calibrated spectra with analysis
results
AGN
Galaxies Stars QSOs
Starburst
Supernovae Search
Galaxies (z)
Normal galaxies
Emission Line stars
Stars (rv)
H II Identification
O B Stars
QSOs (z)
A F G K Stars
Stellar-Atmospheric- Parameters
Input Catalog
M or later Stars
Unknown
Reflection Nebulae
Multi-Wavelength Identification
Candidate Catalogue
Results
Basic Production
Reference classification
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Comparison between object type and spectral
class in SDSS DR5
-- object type -- spectral class
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Classification algorithm

• Automated Classification by objective methods
  (training by templates, predicting by distance or
  density ), collaborators IA(CAS), BNU,SDU, etc.
• Identified by line measurement

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Identification automatically
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STELLAR ANALYSIS PIPELINE
A, F,G, K type stellar spectra
Continuum Rectification
Sub-grid model spectra Teff100K, logg0.25dex
Fe/H0.25dex
Best fit rough spectra
Rough model spectra grid Teff500K,
logg1.0dex, Fe/H1.0 dex
Cross-correlation
Vrad geo
Cross-correlation
Vrad geo Correction
Best fit spectra
Line index definition H_delta, H_zeta, , CaII
triplet, HK, G band
10-20 km/s
Fe/H C/Fe Teff logg
Optimization of different methods
Line Index Measure
Line index Color index calibration (ANN,
Polynomial)
Color index from Input Catalog
GOOD
BAD
Health Check?
Absolute Magnitude
trash bin
Visual Magnitude
High Resolution Spectra for example. HERES 372
stars (VLT/UVES) R20000
S/N50
distance
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Line Indices

• To determine the local continuum level
• Width selection

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Some lines used in the pipeline

• CaII K line (3933A)
• Balmer lines
• CaII triplet
• Mg I b
• G band and C/Fe
• Colors

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CaII K Fe/H
Relationship between Fe/H and CaII K in
4500K,5000K,5500K,6000K,6500K,7000K and 7500K
respectively (Marcs model synthetic spectra).
Lines (left) and 2 order polynomial (right) are
used to fit the relationships from low to high
temperature.
Relationships between Fe/H and the strength of
CaII K in SDSS/SEGUE (Dr6).
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Balmer lines Teff
Three Balmer lines in Kurucz model spectra
H? (434.0 nm)
Hd (410.2 nm)
H? (388.9 nm)
Fe/H-3.0
Fe/H-2.0
Fe/H-2.0
Fe/H-3.0
Fe/H0
Fe/H0
Fe/H-1.0
Fe/H-1.0

• Hd and H? in CFLIB spectra are obvious
  correlated with Teff.
• Since the resolution of 1 Å FWHM of CFLIB and
  low S/N in the range around H? for half of the
  CFLIB dataset, H? line in 3889 Å is difficult to
  measure.
• Fitting Teff Hd
• Teff 4572.813 546.716Hd - 53.773Hd2
  
• error100-200K

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CaII triplet
Fitting of relationship between CaII triplet and
Teff, Fe/H, and logg respectively, CFLIB
spectra were used as experimental dataset
Relationship between CaII triplet and Fe/H, EW
of all Ca II triplet of SDSS/SEGUE spectra are
plotted in left panel, and Fe/H varies with
CaII triplet when T 5000K, logg 2.0 in right
panel.
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MgI b gravity
(left) SDSS data, (right) ELODIE
data.
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G band C/Fe
Relationship between G band and C/Fe with HES
follow up spectra
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Color Teff
Temperature varies with B-V Color in CFLIB
dataset
For SDSS, in the range -0.3 lt g-r lt1.0, the
following expression provides the effective
temperature with an rms only 2 (100-200K)
(Ivezic et al 2006)
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Structure of the stellar analysis pipeline
Independent compiled module script
Already completed module list
Kurucz model calculation
Continuum fitting (whole range)
ANN Module
Regression module
Spectra synthesize
Continuum fitting (local range)
Interpolation module
Cross correlation
Line index calculation
EW calculation module
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Kurucz model calculation

• Atlas9 Kurucz/Castelli
• LTE
• NewODF
• Intermod an interpolation program to quickly
  generate intermediate models from an initial grid

Spectra Synthesize

• Synthe
• Spectrum Gray

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Test with Elodie library
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Accuracy of the parameters

• Checked with SEGUE dr6 data

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Accuracy of parameters with different SNR
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Thanks !