Using DELPHI for Weak Lensing Measurements: Science Return and Mirror Size

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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

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DELPHI BackgroundOriginally a midex mission
planned by Jason Rhodes

• 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

• Orbit 600 km Sun Synchronous, 97.79
• Estimated observatory mass (spacecraft plus
  instruments) 205 kg
• Estimated payload power consumption lt 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

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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!
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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?

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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 SNAPs
  
• telescope design
• PSF size 2 pixels per FWHM
• Throughput peak throughput 70

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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

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Sample Images

• 2.0 m mirror, 1500s exposure
  40 cm mirror, 1500s exposure

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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

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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

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RESULTS 2 Measured Shear as a function of
Mirror size
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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,
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• - 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.

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AcknowledgementsMany many thanks to

• Dr. Jason Rhodes, my mentor
• Dr. David Johnston, co-mentor
• Dr. Richard Massey, writer of Shapelets
• simulation pipeline

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Questions?