ATST Coronal Site Requirements ATST Background Induced Measurement
ATST Coronal Site Requirements “ATST Background Induced Measurement Errors in the Coronal Intensity, Density, Velocity and Magnetic Field” 17 Nov 2003 ATST SWG Mtg 1
ATST: Coronal Working Group • • • Aschwanden, Markus – Lockheed Buffington, Andrew – UCSD Elmore, David – HAO Hubbard, Rob – ATST Jackson, Bernie – UCSD Judge, Phil – HAO Kuhn, Jeff – If. A Lin, Hao. Sheng – If. A Rimmele, Thomas – NSO/Sac Peak 17 Nov 2003 ATST SWG Mtg 2
ATST: A coronal instrument 1. There are no space-based coronal spectroscopy instruments planned after Solar-B EIS (2008). 2. ATST 4 m aperture will resolve much of the coronal spatial structure. 3. ATST photon flux will allow direct coronal B measurements at interesting spatial / temporal scales. 17 Nov 2003 ATST SWG Mtg 3
ATST: Coronal SRD topics • • • Coronal magnetography (Judge, Lin) Coronal seismology (Aschwanden) Plasmoid observations (Penn) Coronal loop flows (Winebarger) Nanoflare search in loops (Penn, Judge) 17 Nov 2003 ATST SWG Mtg 4
ATST: Background limited • • Photon noise exists in ideal background subtraction Illustrative spectra: – – 40 millionths peak intensity coronal line Low background = 1 millionths High background = 100 millionths Only photon noise (ideal background and flat field corrections, no dark current nor read noise) 17 Nov 2003 ATST SWG Mtg 5
ATST: Background limited 17 Nov 2003 ATST SWG Mtg 6
ATST: Background limited 17 Nov 2003 ATST SWG Mtg 7
ATST: Background limited • • Given a background level, one can improve the S/N by longer integrations to collect more coronal photons Conversely, a higher background level has the same effect as if you collected fewer coronal photons – “Effective Coronal Aperture” (Lin): start with 4 m, 8 background, 40 corona – Telescope scatter or site sky brightness 17 Nov 2003 ATST SWG Mtg 8
ATST: Background limited 17 Nov 2003 ATST SWG Mtg 9
ATST: CWG conclusion For a 4 m ATST with a mirror roughness of 1. 2 nm RMS, with dust coverage 0. 036% at a site with sky brightness of 25 millionths at 1000 nm the magnetic sensitivity (1 σ) in a coronal loop with a brightness of 40 millionths at a height of 1. 1 RSUN will be 30 (+30/-15) Gauss for a 1 arcsec square pixel for a 1 second integration. 17 Nov 2003 ATST SWG Mtg 10
ATST: Site Goals 1. 480 hours annually below 25 (+/-10) millionths at R=1. 1 and λ=1000 nm 2. 40 annual 4 -hour blocks with sky brightness at or below this threshold 3. Sky brightness showing a radial slope of R-0. 8 or steeper during this time 17 Nov 2003 ATST SWG Mtg 11
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