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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 -- Main.BrianCameron - 10 Nov 2006
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Topic revision: r1 - 2006-11-10
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BrianCameron
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