Physical Modelling of Instruments Activities in ESO’s Instrumentation Division Florian Kerber, Paul Bristow.
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Transcript Physical Modelling of Instruments Activities in ESO’s Instrumentation Division Florian Kerber, Paul Bristow.
Physical Modelling of Instruments
Activities in ESO’s Instrumentation
Division
Florian Kerber, Paul Bristow
Our Partners
INS, TEC, DMD, LPO, …
Instrument Teams (CRIRES, X-shooter …)
Space Telescope European Coordinating Facility (STECF)
–
Atomic Spectroscopy Group (NIST)
–
M.R. Rosa
J. Reader, G. Nave, C.J. Sansonetti
CHARMS (NASA, Goddard SFC)
–
D.B. Leviton, B.J. Frey
2
Outline
Instrument Modelling - Concept
Instrument Modelling - Basics
Instrument Modelling - Details
Input for the Model
Discussion
3
Building & 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
4
From 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
5
Physical Model
Optical Model (Ray trace)
High quality Input Data
Simulated Data
Close loop between Model
and Observations
Optimizer Tool (Simulated
Annealing)
6
STIS-CE Lamp Project
Echelle, c 251.3 nm
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
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
Essentially same input as the polynomial:
– x,y location on detector
– Entrance slit position (ps) & wavelength ()
Require that the model maps:
ps,
x, y
for all observed features.
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CRIRES
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
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
14
Operating Modes (foreseen)
1.
2.
3.
4.
General optimisation (calibration scientist,
offline)
Grating & prism optimisation (automatic)
Data reduction (pipeline)
Data simulation (interactive, offline)
15
16
Operating Modes (foreseen)
1.
2.
3.
4.
General optimisation (calibration scientist,
offline)
Grating & prism optimisation (automatic)
Data reduction (pipeline)
Data simulation (interactive, offline)
17
Operating Modes (foreseen)
1.
2.
3.
4.
General optimisation (calibration scientist,
offline)
Grating & prism optimisation (automatic)
Data reduction (pipeline)
Data simulation (interactive, offline)
18
Operating Modes (foreseen)
1.
2.
3.
4.
General optimisation (calibration scientist,
offline)
Grating & prism optimisation (automatic)
Data reduction (pipeline)
Data simulation (interactive, offline)
19
20
Simulated Stellar Spectrum
21
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Optimisation 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
23
Near IR Wavelength Standards
1270–1290 nm
Ne
Kr
Th-Ar
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Th-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)
25
26
Measurements with FTS at ESO
27
Intensity [normalised to 10 mA]
Spectrum - Operating Current
8
7
6
5
4
Argon
Thorium
3
2
1
0
2
6
10
14
18
22
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
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
5
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
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 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
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