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
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BrianCameron - 10 Nov 2006