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Using DELPHI for Weak Lensing Measurements: Science Return and Mirror Size. Jes Ford, JPL, UNR SURF 2007 8/21/07 Mentor: Jason Rhodes Co-mentor: David Johnston. Orbit: 600 km Sun Synchronous, 97.79 ° Estimated observatory mass (spacecraft plus instruments): 205 kg
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Using DELPHI for Weak Lensing Measurements: Science Return and Mirror Size Jes Ford, JPL, UNR SURF 2007 8/21/07 Mentor: Jason Rhodes Co-mentor: David Johnston
Orbit: 600 km Sun Synchronous, 97.79° Estimated observatory mass (spacecraft plus instruments): 205 kg Estimated payload power consumption: < 50 W Mission duration and launch constraints: 2 years / Pegasus Sky coverage: 21,000 deg2 over two years Frequency: Visible Temperature: Telescope – ambient, Detectors – 170 K Pointing requirements: ~ milliarcseconds Data rate to ground: 54 GB/day TRADEOFFS: Orbit Selection L2 vs. Sun-Synchronous Thermally stable orbits Telecommunications requirements increase subsytem mass for L2 mission Pegasus does not have the performance to place a s/c in an L2 halo orbit Scanning Strategy Drifting vs. Step-and-Stare Drifting strategy works best with L2 orbit Combination of integration time and sun-synchronous orbit require step-and-stare scanning DELPHI: BackgroundOriginally a midex mission planned by Jason Rhodes
DELPHI: Trade Studies • Telescope Design • Mirror diameter • 0.5 m, 0.75 m • Three-mirror anastigmat vs. Cassegrain • Plate scale and focal length • 15 m, 20 m • Detector / Pixel Sizes • NIR HgCdTe Hawaii 2RG • E2V visible, frame transfer CCDs • Buses • Ball Aerospace • STP-IV • Orbital Science Corp. • MicroStar MIRROR SIZE IS A COST DRIVER!
DELPHI: Current Status • NASA recently announced small midex (SMEX) mission opportunity - not MIDEX • DELPHI cannot fit tight budget constraints • However, since Mirror size is main factor in the cost of a telescope, it is important to know how small of a mirror is still worthwhile to launch • MY PROJECT: what is the minimum mirror size that can recover weak lensing data reliably?
Image Simulation Parameters • Created using Shapelets • Pixels: 4096 x 4096 pix • Optical Filter: Wide filter centered on I-band • Input Shear: , no shear • PSF shape: roughly circular PSF, based on SNAP’s telescope design • PSF size: 2 pixels per FWHM • Throughput: peak throughput ~70%
Image Variations • Mirror Sizes:range from 20 cm - 2.4 m in diameter, in 20 cm increments • 2 sets: - constant exposure time (1500s) -constant photon flux (varying exposure times, 1500s at 1.2 m) • Separate Galaxy and Stellar images created • Total of 23 star/galaxy image pairs
Sample Images 2.0 m mirror, 1500s exposure 40 cm mirror, 1500s exposure
Steps of Analysis • Objects detected and catalogue created using Source Extractor • Object moments recalculated using RRG method • Stellar images used to measure the PSF moments • PSF is removed from the galaxy images (RRG) • Bad galaxies are cut based on: moments, ellipticity, size compared to PSF size, signal-to-noise ratio (RRG) • Shear and shear error are measured from the galaxy images (RRG) • Plots created to analyze number of useful galaxies (those that make the cuts) as a function of mirror size • Plots created to analyze measured shear and error as a function of mirror size
RESULTS 1: Number of useful galaxies as a function of mirror size Diamonds: constant exposure time simulations Crosses: constant flux simulations • Useful galaxies are those that survive the cuts and are used to measure the shear • Number of galaxies has been normalized to number per square arcminute of sky
Continuing Research • Currently processing set of 143 simulations with non-zero input shear: - = 0, = -5, -3, -1, 0, 1, 3, 5 % - = 0, = -5, -3, -1, 0, 1, 3, 5 % - Mirror Sizes: 0.4 m - 2.4 m in 40 cm increments - one set at constant exposure time (1500s) - one set at constant flux • Images need to be analyzed by others using methods other than RRG… contact Jason Rhodes.
AcknowledgementsMany many thanks to: • Dr. Jason Rhodes, my mentor • Dr. David Johnston, co-mentor • Dr. Richard Massey, writer of Shapelets simulation pipeline