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Kitt Peak Vacuum Telescope -- Raw to Synoptic Map

Kitt Peak Vacuum Telescope -- Raw to Synoptic Map. J. Harvey. Pre-History. KP 40-channel collected daily FD maps in March 1970 to compare with corona at eclipse Randy Levine worked with Marty Altschuler at HAO to make synoptic map and extrapolations; did it again in 1972

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Kitt Peak Vacuum Telescope -- Raw to Synoptic Map

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  1. Kitt Peak Vacuum Telescope --Raw to Synoptic Map J. Harvey

  2. Pre-History • KP 40-channel collected daily FD maps in March 1970 to compare with corona at eclipse • Randy Levine worked with Marty Altschuler at HAO to make synoptic map and extrapolations; did it again in 1972 • Skylab prompted start of daily observations in 1973 & construction of KPVT

  3. First KP Synoptic Map – CR 1558

  4. More History • Synoptic map algorithm was basically derived from Randy’s HAO work • 1974: 40-chan replaced with 512-chan • 1974: Started doing helium 10830 maps • 1993: 512-chan replaced by SPMG • 2003: KPVT replaced by SOLIS VSM

  5. 512-ch Calibration • It was an array of Babcock magnetographs • Calibrated with circular polarizer + known displacement • 8688 Å linear response to ~9000 G • Not much center – limb variation • Calibration done very rarely • Observations sensitive to I & vel crosstalk

  6. SPMG Calibration • Used TV images of polarized spectra • Still used 8688 Å (small disk variation) • Uses whole line profile so Zeeman displacement measured directly • Vulnerable to modulator efficiency being less than 100% • Did a cross-comparison between 512 for ~9 months

  7. Synoptic Map Basic Recipe • Clean up full-disk image • Filter noisy pixels • Geometric fit (P-angle, disk center and radius) • Adjust zero point (if needed) • Multiply by sec ρ • Map to Carrington coordinates (sin B, CMD) • 3 resolutions: 180 x 180, 360 x 360, 900 x 900 • 2 maps: sum and weight • Flux conserved

  8. Recipe – con’t. • Weighted merge of images • Cos4 CMD for low resolution • 1-D gaussians in CMD for higher resolution • Build sum and weight merged images • Divide merged sum by weight • Pole correction • Publish • Done for B and |B|

  9. Pole Correction • Remap pole region to polar coordinates • Iterative fit of 2-D 5th-order cubic spline to measured data (rejects wild points) • Replace missing and noisy pixels with fit • Map back to Carrington grid • Latitude-dependent blend with original map • Tested by absence of annual signal

  10. Variants • Snapshot maps started in 1998 until Y2K • Polar projections • Daily difference maps • CR difference maps • Neutral line and AR summaries • Movies • Butterfly diagrams • Coronal holes

  11. Problems • Assumes each image is instantaneous • Except for the snapshot maps, does not represent the full solar surface at any specific time • Dubious polar correction • Dark umbras poorly handled • Leaves a small monopole • Radial correction is bad in AR • Bad in quiet photosphere, too

  12. Status • Old KPVT mags have been cleaned up • New set of synoptic maps from CR 1625-2007 about to be prepared

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