Difference: 061110Telecon ( vs. 1)

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META TOPICPARENT
Telecon 11/10/06

Attendees: Jessica, Claire, Chris, Rich, Matthew and Brian

Identify two goals for this project

  • Technical report describing key factors for better astrometry (Performance Budget)
  • Numerical tool for evaluating the performance (Excel Spreadsheet)

Astromety Methodology (Jessica)

  • Short exposures (1 min, 3 per dither position)
  • Small dithers (< 1 arcsec) to minimize optical distortion
  • Drizzle to combine images
  • Starfinder for photometry and astrometry (3000 stars/10 arcsec field)
  • Uses a single PSF for the field
  • RMS based on 3 (equal quality) subsets reaches a floor of ~ 250 uas for brighter stars
  • Second order transformations between epochs yields similar precision
  • Goal is 100 uas precision to measure GR effects

Astrometry Methodology (Brian)

  • Similar observational technique to GC
  • Objects of interest are much fainter (K' ~ 19.5-22.5 mag), requires coadding data
  • Concentrated mainly on 40 arcsec field, which contains fewer stars
  • Spatially variable PSF

Key Drivers

  • Current limit for GC is confusion in the inner 1-2 mas and differential tilt jitter
  • For Brian it's SNR
  • Andrea has been runnign simulations with 170nm WFE to compare with the current system

Action Items/Error term investigation

  • Differential atmospheric tilt jitter -- Matthew
  • Geometric Distortion -- Jessica (w/ Brian)
  • Confusion -- Andrea to do trade studies vs. WFE (Chris to provide PSFs)
  • SNR and centroiding preceision for isolated stars -- Brian
  • Differential chromatic refraction (DCR) and achromatic effects -- Brian

End of meeting comments

  • Suggestion from Chris to correlate the high-altitude turbulence data
  • GC is so extincted all the stars are the same color -- no DCR, but achromatic effects are apparent
  • GC observations cover only 1.5-1.7 airmasses

Plan is to meet every 3 weeks

-- BrianCameron - 10 Nov 2006

 
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