AAO Fibre Instrument Data Simulator

10 October 2011

ROE Workshop 2011

Michael GoodwinTony FarrellGayandhi De SilvaScott Smedley

Australian Astronomical Observatory

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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

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.

Atmosphere

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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

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

Specifies the Anglo-Australian-Telescope (AAT) and the 2dF top-end corrector optics.

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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)

Distortion polynomials Aberration images (geometrical)

Zemax traces a matrix of slit field locations with wavelengths to determine detector locations (chief rays) and corresponding geometrical image (resolution element).

Matlab interpolates the detector locations in the spatial and wavelength dimensions and then fits characteristic polynomials (cubic) for fibres 1-400 tramlines

The data simulator approximates a spatial variant convolution by dividing detector into regions based on geometrical image matrix (resolution elements). The resolution element is convolved with ‘impulse’ tramline.

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EfficienciesData simulator imports realistic efficiency curves from detailed spreadsheet model.

HERMES

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Resolving Power (HERMES)

Data simulator resolving power at detector is determined by Zemax model.

R

wav

R=28,000

R=29,000

R=27,000

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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

Verification of model (solid line) with AAOmega observational data (image with dashed line).

model ~ observed

mechanical alignmentoptical tolerances

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)

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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

Scattering3% EnergySigma = 37 pixels

AAOmega Scattering1% EnergySigma = 37 pixels

Logarithmic scaling – flat field

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VPH Littrow Ghost Simulation

* Ghost analysis is still ongoing

HERMES

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Data Simulator Results (HERMES)

Gayandhi De SilvaAstronomer (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