AAO Fibre Instrument
Data Simulator
ROE Workshop 2011
Michael Goodwin
Tony Farrell
Gayandhi De Silva
Scott Smedley
10 October 2011
Australian Astronomical Observatory
Data Simulator Goal
• Construct an end-to-end
software simulation tool that
produces detector images (flat,
arc and object) based on the
fibre-fed instrument designs.
• A verification tool for the
engineers, instrument
scientists and astronomers
HERMES 4-channel, N=392, R~28,000, S/N=100
(late 2012) is a complex astronomical spectrograph
requiring a simulation tool to assist in the early
performance and design verification.
Samuel C. Barden, et al.
Proc. SPIE 7735, 773509 (2010).
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Data Simulator Overview
Pre-computed optical
data & efficiency
response data
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Simulator Components
Atmosphere
The data simulator system
model abstracts the physical
design of the fibre instrument.
This is achieved by translating
the data simulator requirements
and specifications into suitable
model components.
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Specifications – Science Object (HERMES)
•
high resolution (0.02Å) synthetic stellar spectra from 300nm to 1.8μm
with solar and alpha-enhanced composition by P. Coelho et. Al (2005)
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Specifications – Atmosphere (HERMES)
•
sky background is modelled as reflected solar spectra from the Moon [Krisciunas,
K. and Schaefer, PASP 103, 1033–1039 (1991)]
•
sky emission is modelled from observations with the HIRES echelle spectrograph
on the Keck I telescope. [Osterbrock, D. E. et al., PASP 108, 277 (1996)]
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Specifications - Telescope
Specifies the Anglo-Australian-Telescope (AAT)
and the 2dF top-end corrector optics.
Mirror diameter
3.8m
Central obstruction
1.5m
Efficiency response
Default efficiency response of telescope
mirrors and corrector optics as a function of
wavelength – spreadsheet model
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Specifications - Instrument
Instrument - Fibre Optics
parameters such as the fibre efficiency response, fibre layout,
fibre diameter, fibre mapping to object spectra and number of
fibres
Instrument - Calibration &
Efficiency
• calibration arc lamp data for wavelength calibration, 2dFdr
line lists & ThAr lines for UVES compiled by M. Murphy et. al
[MRAS 378, 221–230 (2007)]
• calibration lamp data for flat fielding calibration is theoretical
blackbody curve of T=3000K to model a Quartz lamp
• efficiency response models each four channels
Instrument - Cameras
Specifies the optical aberration and distortion configuration for
the particular camera (four spectrograph channels) as well as
parameters for the simulation of the spectrograph ghosting and
scattering.
Instrument - Detector
Specifies the detector properties such as the bias, bias width,
image window, read noise, dark current, ADU gain, bad pixels,
pixel size, pixel variance, charge transfer efficiency, cosmic ray
intensity, cosmic ray rates, fixed pattern noise, read-out
window, QE response.
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Model Data (HERMES)
Zemax traces a matrix of slit field locations with wavelengths to determine detector
locations (chief rays) and corresponding geometrical image (resolution element).
Distortion polynomials
Matlab interpolates the detector locations in the spatial
and wavelength dimensions and then fits characteristic
polynomials (cubic) for fibres 1-400 tramlines
Aberration images (geometrical)
The data simulator approximates a spatial variant
convolution by dividing detector into regions based on
geometrical image matrix (resolution elements). The
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resolution element is convolved with ‘impulse’ tramline.
Efficiencies
HERMES
Data simulator imports realistic
efficiency curves from detailed
spreadsheet model.
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Resolving Power (HERMES)
R
R=29,000
R=28,000
R=27,000
wav
Data simulator resolving power at
detector is determined by Zemax model.
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Implementation Verification
Verification of data simulator
implementation (Linux) with that
of the simulator model, Zemax /
Matlab (solid line).
implementation = model
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Verification with AAOmega
Model can be fitted (mean error
~0.34 pixels) to real data
(dashed line) with a simple
transformation:
y-offset
= 5.5 pixels;
scale factor = 0.994;
Rotation
= -0.17 degrees
(i.e. clockwise)
model ~ observed
Verification of model (solid line) with
AAOmega observational data (image with
dashed line).
mechanical alignment
optical tolerances
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Simulated Output (HERMES)
exposure time of 1800s
using (fibers 391-400)
assigned synthetic stellar
spectra having
Teff=4750K and
brightness mv=12.5
using (fibers 381- 390)
assigned spectra
Teff=4250K and
brightness mv=15.0.
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Scattering Simulation (HERMES)
No Scattering
Logarithmic scaling – flat field
Scattering
3% Energy
Sigma = 37 pixels
AAOmega Scattering
1% Energy
Sigma = 37 pixels
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VPH Littrow Ghost Simulation
HERMES
* Ghost analysis is still ongoing
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Data Simulator Results (HERMES)
Gayandhi De Silva
Astronomer (HERMES project scientist)
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Data Simulator (SAMI)
The Sydney-AAO Multi-object IFS (SAMI). N=13,
R~1800-4500, hexabundles (61-element) deployed 1
degree FoV (Commission run #1 : 1-4 July 2011)
AAO Observer, August
2011, Edition #120
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Data Simulator Results (SAMI - FLAT)
Simulated
Actual – First Light
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Conclusions
Data simulator producing detector images for
HERMES and SAMI instrument projects
Simulated detector images have been used in
developing the data reduction software
Science analysis of simulated data in progress
by the HERMES project scientist
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