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Physical Modelling of InstrumentsPhysical Modelling of Instruments
Activities in ESO’s Instrumentation Division
Florian Kerber, Paul Bristow
2
Our PartnersOur Partners
INS, TEC, DMD, LPO, … Instrument Teams (CRIRES, X-shooter …) Space Telescope European Coordinating Facility
(ST-ECF)– M.R. Rosa
Atomic Spectroscopy Group (NIST)– J. Reader, G. Nave, C.J. Sansonetti
CHARMS (NASA, Goddard SFC)– D.B. Leviton, B.J. Frey
3
OutlineOutline
Instrument Modelling - Concept Instrument Modelling - Basics Instrument Modelling - Details Input for the Model Discussion
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Building & Operating an InstrumentBuilding & Operating an Instrument
Science Requirements Optical Design (code V, Zemax) Engineering Expertise Testing and Commissioning
Operation and Data Flow Calibration of Instrument Scientific Data and Archive
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From Concept to ApplicationFrom Concept to Application
M. Rosa: Predictive calibration strategies: The FOS as a case study (1995)
P. Ballester, M. Rosa: Modeling echelle spectrographs (A&AS 126, 563, 1997)
P. Ballester, M. Rosa: Instrument Modelling in Observational Astronomy (ADASS XIII, 2004)
Bristow, Kerber, Rosa: four papers in HST Calibration Workshop, 2006
UVES, SINFONI, FOS, STIS, VLTI, ETC
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Physical ModelPhysical Model
Optical Model (Ray trace)
High quality Input Data
Simulated Data Close loop between Model and Observations
Optimizer Tool (Simulated Annealing)
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STIS-CE Lamp Project STIS-CE Lamp Project
Pt-Ne atlas, Reader et al. (1990) done for GHRS
STIS uses Pt/Cr-Ne lamp Impact of the Cr lines
strongest in the NUV List of > 5000 lines accurate to < 1/1000 nm
Echelle, c 251.3 nm
# of lines: Pt-Ne 258 # of lines: Pt-Ne 258 vs Pt/Cr-Ne 1612
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STISSTIS
9Standard: =(3.3 ± 1.9) STIS Model: =(0.6 ± 1.7)
STIS Science Demo Case: Result STIS Science Demo Case: Result
1 pixel
10-4 nm
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Traditional Wavelength CalibrationTraditional Wavelength Calibration
Data collected for known wavelength source (lamp or sky):– Match observed features to wavelengths of
known features– Fit detector location against wavelength =>
polynomial dispersion solution
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Physical Model ApproachPhysical Model Approach
Essentially same input as the polynomial:– x,y location on detector
– Entrance slit position (ps) & wavelength ()
Require that the model maps:
for all observed features.
€
ps,λ a x,y
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CRIRESCRIRES
950 - 5000 nm Resolution / 100,000 ZnSe pre-disperser prism Echelle 31.6 lines/mm 4 x Aladdin III 1k x1k
InSb array Commissioning June 06
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Model KernelModel Kernel
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Model KernelModel Kernel
Speed– Streamlined (simplistic) description– Fast - suitable for multiple realisations
Spectrograph (CRIRES - cold part only)– Tips and tilts of principal components– Dispersive behaviour of prism and grating– Detector layout
This is not a full optical model
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Operating Modes (foreseen)Operating Modes (foreseen)
1. General optimisation (calibration scientist, offline)
2. Grating & prism optimisation (automatic)
3. Data reduction (pipeline)
4. Data simulation (interactive, offline)
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Operating Modes (foreseen)Operating Modes (foreseen)
1. General optimisation (calibration scientist, offline)
2. Grating & prism optimisation (automatic)
3. Data reduction (pipeline)
4. Data simulation (interactive, offline)
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Operating Modes (foreseen)Operating Modes (foreseen)
1. General optimisation (calibration scientist, offline)
2. Grating & prism optimisation (automatic)
3. Data reduction (pipeline)
4. Data simulation (interactive, offline)
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Operating Modes (foreseen)Operating Modes (foreseen)
1. General optimisation (calibration scientist, offline)
2. Grating & prism optimisation (automatic)
3. Data reduction (pipeline)
4. Data simulation (interactive, offline)
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Simulated Stellar SpectrumSimulated Stellar Spectrum
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Optimisation StrategyOptimisation Strategy
Take limits from design and construction One order/mode - rich spectra
– Optimise detector layout
Multiple order/modes (detector layout fixed)– Optimise all except prism/grating
All order/modes (all parameters fixed except prism/grating)– Optimise prism/grating settings for each mode
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Near IR Wavelength StandardsNear IR Wavelength Standards
1270–1290 nm
Th-Ar
Ne
Kr
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Th-Ar lamp:Visible and Near IRTh-Ar lamp:Visible and Near IR
Established standard source in Visual– Palmer & Engleman (1983) 278 - 1000 nm– FEROS, FLAMES, HARPS, UVES, Xshooter
Cryogenic High Resolution Echelle Spectrometer (CRIRES) at VLT– 950 - 5000 nm, Resolution ~100,000– Project to establish wavelength standards (NIST)– UV/VIS/IR 2 m Fourier Transform Spectrometer (FTS)
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Measurements with FTS at ESOMeasurements with FTS at ESO
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Spectrum - Operating CurrentSpectrum - Operating Current
0
1
2
3
4
5
6
7
8
2 6 10 14 18 22
Lamp operating current [mA]
Intensity [normalised to 10 mA]
ArgonThorium
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Th-Ar in the near IR: SummaryTh-Ar in the near IR: Summary
• > 2000 lines as wavelength standards in the range 900 - 4500 nm
• insight into the properties of Th-Ar lamps, variation of the spectral output/continuum as a function of current
• Th-Ar hollow cathode lamps - a standard source for wavelength calibration for near IR astronomy
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CRIRES pre-disperser prism - ZnSeCRIRES pre-disperser prism - ZnSe
n(,T)from CHARMS, (GSFC, NASA)
Leviton & Frey, 2004
31Wavelength [nm]1124 1138
Measured line shifts Physical Model
– Th-Ar line list– n(,T) & dn/dT of
ZnSe
ZnSe Prism: Temperature 73 - 77 KZnSe Prism: Temperature 73 - 77 K
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Location of Th-Ar lines - TemperatureLocation of Th-Ar lines - Temperature
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
72,5 73,5 74,5 75,5 76,5 77,5 78,5
Temperature [K]
Shift [pixel]
1124 nm1138 nm1124 nm pred1138 nm pred
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Conclusions - Physical ModelConclusions - Physical Model
Preserve know how about instrument Replace empirical wavelength calibration High quality input data is essential Predictive power Support instrument development
– assess expected performance– reduce risk
Calibration data is still required!
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Conclusions - Physical ModelConclusions - Physical Model
The resulting calibration is predictive and expected to be more precise
The process of optimising the model is somewhat more complex than fitting a polynomial
Understanding of physical properties and their changes
CRIRES will be the first ESO instrument to utilise this approach to calibration