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
8
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
10
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.
11
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
12
Model Kernel
13
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
22
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
24
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]
28
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
29
CRIRES pre-disperser prism - ZnSe
n(,T)
from CHARMS,
(GSFC, NASA)
Leviton & Frey, 2004
30
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
31
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
32
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!
33
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
34