Paul Bristow (ESO Instrumentation)
Thanks to:
Andrea Modigliani, Joël Vernet & Florian
Kerber, Sabine Moehler (ESO)
Paolo Goldoni, Frédéric Royer & Régis
Haigron (APC-SAp/CEA)
Follow the Photons
–
Edinburgh
–
October 2011
Matrix Representation of
Optics
 ME is the matrix representation of the
order m transformation performed by an
Echelle grating with E at off-blaze angle
. This operates on a 4D vector with
components (wavelength, x, y, z).
Applications
Wavelength calibration
Simulations
Early DRS development
Effects of modifications/upgrades
Instrument monitoring/QC
Advanced ETC?
Some background
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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, CRIRES,
X-shooter – Bristow et al (Experimental
Astronomy 31, 131, 2011)
X-Shooter (300nm-2.5m)
Commissioned 2009
Vernet et al. 2011.
A & A. in press
Model for UVB, VIS
& NIR arms
Same model kernel
Independent
configuration files
Cross dispersed, medium res’n, single slit
Single mode (no moving components)
Cassegrain & heavy => Flexure
NIR Th-Ar HCL full slit
Solar like stellar point source and sky
X-shooter
Flexure
 Backbone flexure
 Causes movement of target
on spectrograph slits
 Corrected with Automatic
Flexure Compensation
exposures
 Spectrograph flexure
 Flexing of spectrograph
optical bench
 Can also be measured in
AFC exposures
 First order translation
automatically removed by
pipeline
UVB
VIS
NIR
Lab Measurements
• NIR arm
• Multi-pinhole
• Translational & higher order distortions
AFC Exposures
• Obtained with every science obs =>
large dataset ~300 exp from Jan –
May 2011
• Single pinhole, Pen-ray lamp
• Window:
• 1000x1000 win (UVB 12/VIS 14 lines)
• Entire array (NIR 160 lines)
NIR
UVB
VIS
Physical Model Optimisation
Default
configuration file
cal’ lamp line list
wavelengths
Simulated Annealing
X-Shooter
Physical Model
Output
Predicted positions
of spectral features
(pixels on detector
array)
Change configuration
No
Measured line
positions (pixels)
from cal’ exposure
Compare lists and
compute metric which
describes how well
they match
Satisfactory
match?
Yes
Simulated Annealing
Optimal
XSPM
parameters
for this cal’
exposure
Choosing “open” parameters
All parameters open
Slow
Optimal result
Degeneracy
Physically motivated:
Related to flexure
Constrained by data
In these results:
Prism orientation; Grating Orientation;
Grating constant; Camera focal length;
Detector position and orientation
NIR
NIR
NIR
NIR
(Product moment correlation)
VIS
VIS
VIS
UVB
UVB
UVB
Summary
Simple physical modelling approach:
wavelength calibration for a number of
instruments
Raw data simulation
Instrument monitoring
Application to X-shooter
Flexure monitoring
Allows identification of physical model
parameters that correlate with instrument
orientation
Physical Model Optimisation
Default
configuration file
Simulated Annealing
X-Shooter
Physical Model
cal’ lamp line list
wavelengths
QC Data
Output
Predicted positions
of spectral features
(pixels on detector
array)
Change configuration
9 pinhole mask, arc lamp:
No
Th-Ar (UVB 250 lines x 9 & VIS 390 lines x 9)
lists and
Measured
line 140 linesCompare
pen-ray
(NIR
x
9)
compute metric which
positions (pixels)
Daytime,
Zenith
(no
from cal’
exposure
Satisfactory
describes
how hysteresis)
well
match?
flexure
except
they match
Yes
1/week => small data set
Automatically processed by pipeline (ESO QC)
Simulated Annealing
Optimal
XSPM
parameters
for this cal’
exposure
Effective camera focal length (mm)
Effective camera focal length (mm)
UVB Camera temperature sensor reading (°C)
VIS Camera temperature sensor reading (°C)
Modified Julian Date (days)
Effective camera
focal length (mm)
Detector tip (°)
Detector tilt (°)
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Explain “our Physical Models”
 Compare to poly
 Uses
 Calibration
 Simulation
 Test DRS
 Investigate modifications/upgrades
 Monitor/understand instrument behaviour
 History (Ballester & Rosa)
Introduce X-shooter
 Overview
 Flexure
 Lab plots
 AFC
 Calibration exposures
Flexure Procedure
 Optimisation for 1 exposure
 Apply to all data
 Choosing open parameters
Flexure Results
 NIR
 Residuals
 Sin plot
 Linear plots
 Table – highlight interesting param combinations
 UVB
 Residuals
 Linear plots
 table
 VIS
 Residuals
 Linear plots
 table
Flexure conclusions