Download The Importance of Knowing

Physical Modelling of Instruments
Activities in ESO’s Instrumentation
Division
Florian Kerber, Paul Bristow
Our Partners
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INS, TEC, DMD, LPO, …
Instrument Teams (CRIRES, X-shooter …)
Space Telescope European Coordinating Facility (STECF)
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Atomic Spectroscopy Group (NIST)
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M.R. Rosa
J. Reader, G. Nave, C.J. Sansonetti
CHARMS (NASA, Goddard SFC)
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D.B. Leviton, B.J. Frey
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Outline
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Instrument Modelling - Concept
Instrument Modelling - Basics
Instrument Modelling - Details
Input for the Model
Discussion
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Building & Operating an Instrument
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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 Application
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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 Model
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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
Echelle, c  251.3 nm
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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
# of lines: Pt-Ne 258 vs Pt/Cr-Ne
7 1612
STIS
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STIS Science Demo Case: Result
10-4 nm
1 pixel
Standard: =(3.3 ± 1.9)
STIS Model: =(0.6 ± 1.7)9
Traditional Wavelength Calibration
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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 Approach
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Essentially same input as the polynomial:
– x,y location on detector
– Entrance slit position (ps) & wavelength ()
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Require that the model maps:
ps, 
x, y
for all observed features.
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CRIRES
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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 Kernel
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Model Kernel
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Speed
– Streamlined (simplistic) description
– Fast - suitable for multiple realisations
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Spectrograph (CRIRES - cold part only)
– Tips and tilts of principal components
– Dispersive behaviour of prism and grating
– Detector layout
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This is not a full optical model
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Operating Modes (foreseen)
1.
2.
3.
4.
General optimisation (calibration scientist,
offline)
Grating & prism optimisation (automatic)
Data reduction (pipeline)
Data simulation (interactive, offline)
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Operating Modes (foreseen)
1.
2.
3.
4.
General optimisation (calibration scientist,
offline)
Grating & prism optimisation (automatic)
Data reduction (pipeline)
Data simulation (interactive, offline)
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Operating Modes (foreseen)
1.
2.
3.
4.
General optimisation (calibration scientist,
offline)
Grating & prism optimisation (automatic)
Data reduction (pipeline)
Data simulation (interactive, offline)
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Operating Modes (foreseen)
1.
2.
3.
4.
General optimisation (calibration scientist,
offline)
Grating & prism optimisation (automatic)
Data reduction (pipeline)
Data simulation (interactive, offline)
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Simulated Stellar Spectrum
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Optimisation Strategy
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Take limits from design and construction
One order/mode - rich spectra
– Optimise detector layout
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Multiple order/modes (detector layout fixed)
– Optimise all except prism/grating
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All order/modes (all parameters fixed except prism/grating)
– Optimise prism/grating settings for each mode
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Near IR Wavelength Standards
1270–1290 nm
Ne
Kr
Th-Ar
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Th-Ar lamp:Visible and Near IR
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Established standard source in Visual
– Palmer & Engleman (1983) 278 - 1000 nm
– FEROS, FLAMES, HARPS, UVES, Xshooter
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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 ESO
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Intensity [normalised to 10 mA]
Spectrum - Operating Current
8
7
6
5
4
Argon
Thorium
3
2
1
0
2
6
10
14
18
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Lamp operating current [mA]
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Th-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 - ZnSe
n(,T)
from CHARMS,
(GSFC, NASA)
Leviton & Frey, 2004
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ZnSe Prism: Temperature 73 - 77 K
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Measured line
shifts
Physical Model
– Th-Ar line list
– n(,T) & dn/dT of
ZnSe
1124
Wavelength [nm]
1138
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Location of Th-Ar lines - Temperature
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4,5
4
Shift [pixel]
3,5
3
1124
1138
1124
1138
2,5
2
nm
nm
nm pred
nm pred
1,5
1
0,5
0
72,5
73,5
74,5
75,5
Temperature [K]
76,5
77,5
78,5
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Conclusions - Physical Model
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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
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Calibration data is still required!
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Conclusions - Physical Model
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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
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