XRT CCD contaminantion uncorrected spots: location and growth.

(10 Apr 2017 by Aki Takeda)

0. Motivation.

In recent synoptic composite images, at least 4 relatively big contamination spots are noticable (an example) at the region between 0 and 20N degree latitude in the Eastern hemisphere. These spots are supposed to be cosmetically corrected by spot-correcting code, XRT_SPOTCOR, which is now included in XRT_PREP. The appearance of these uncorrected spots indicates that either (1) these spots are newly built up and thus not processed by the current code based on the old spot map, or (2) for some reason the current code started to fail to correct them.

1. Situation before August, 2016.

A big contamination spot became noticeable since January, 2015 at the North of CCD center (see center image below), in the synoptic composite images (i.e., images after PREP). This indicates the contamination spot correction program (XRT_SPOTCOR.PRO) started to fail to correct this spot. Since May 2016, this spot is corrected by XRT_ERASER.PRO, which is prepared to correct only this spot. The right image below is a successful example of XRT_ERASER applied to an Open/Al-mesh image taken on 5-Apr-2016.
Before PREP After PREP
(circle shows location of spot)
PREP + XRT_ERASER

2. Situation after August, 2016.

Since August, 2016, 4 new relatively big spots started to appear uncorrected by XRT_SPOTCOR. Location of these spots are shown by circles in the second image ("After PREP") below. The center coordinates of the circle (hopefully close enough to those of spot center) measured in this 1024x1024 image are (from East to West):
- [133,650]
- [234,595]
- [308,560]
- [482,560]

Before PREP After PREP
(circles show location of spots)
PREP + XRT_ERASER PREP + XRT_ERASER*2
(XRT_ERASER applied twice)

3. Growing history

Movie of level0 data (before PREP) obtained for the synoptic programs. (click image to see a java-script movie).

All uncorrected big spots (4 spots introduced in sec.2 as well as the big North spot introduced in sec.1) are NOT newly-born spots. They did exist at least as of 2013/02, but with smaller size. It seems that those spots grew so big that the current program (map of spot location) started to fail due to a mismatch between true and assumed size.

4. Quick-fix solution

On 11-Apr-2017, Trish Jibben (SAO) modifed the XRT_ERASER.PRO so that it handles additional 4 big spots to the original big one in North. Below images demonstrate the performance of the new XRT_ERASER.

Both image NOT processed with XRT_PREP before applying XRT_ERASER.
Solar image from 1-Apr-2017 17:03:37, by courtesy of T. Jibben. Click image to enlarge.

Before new XRT_ERASER After new XRT_ERASER

Performance check on synoptic images. Click image to enlarge.

with old XRT_ERASER with new XRT_ERASER