kitt peak vacuum telescope -- raw to synoptic map j. harvey

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

• Skylab prompted start of daily observations in 1973 & construction of KPVT

First KP Synoptic Map – CR 1558

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

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

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

Synoptic Map Basic Recipe

1. 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

2. 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

Recipe – con’t.

3. 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

4. Pole correction

5. Publish– Done for B and |B|

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

Variants

1. Snapshot maps started in 1998 until Y2K2. Polar projections3. Daily difference maps4. CR difference maps5. Neutral line and AR summaries6. Movies7. Butterfly diagrams8. Coronal holes

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

Status

• Old KPVT mags have been cleaned up

• New set of synoptic maps from CR 1625-2007 about to be prepared