Hinode/XRT stray light correction 2020

XRT Stray Light Study 2020 -- phase 4 (after 29-May-2018).

Link to the 2014 summary page.
Link to the 2015 phase 1 summary. (after 9-May-2012 ← 1st pre-filter failure event)
Link to the 2015 phase 2 summary. (after 14-Jun-2015 ← 2nd failure event)
Link to the 2016 page and 2017 phase 2 page.
Link to the 2017 phase 3 page (after 27-May-2017 ← 3rd event).
Link to the 2018 phase 4 page (after 29-May-2018 ← 4th event).
Link to the 2019 phase 4 page.
Link to the 2021 phase 4 page.

(14 Aug, 2020 by Aki Takeda)

1. Purposes of the stray light measurement in 2020.

Hinode operation was in "emergency focus mode" due to the COVID-19 pandemic at the beginning of the 2020 eclipse season (early- to mid-May), which is the most suitable period for XRT's stray light measurements. Therefore, we minimized the measurements by taking stray light images only with 3 main filters for the regular synoptic programs (Al_mesh, Al_poly, and thin_Be) and only at the Disk Center pointing (note: one AR pointing was added on the 12-July measurement).

Judging from the intensity level of G-band images and FLD images (Al-poly 8x8), we have not seen further increase of stray light level since the start of the phase 4 (Aug-2018). The 2020 measurements are to confirm this by taking real stray light images. The same measurements were performed before and after the CCD bakeout performed 10-13 May, to see the effect of growing contamination layer on CCD to the stray light level.

2. Summary of Results.

It was fortunate that we didn't see a new pre-filter failure event during this eclipse season. The 2020 measurements were spent all for taking data for the phase 4.
[Al_mesh] No change in the stray light component (pattern & intensity level) since the beginning of the phase 4 (Aug-2018). Comparison of the stray light images taken before and after CCD bakdout shows ~2% increase of the stray light level in 14 days.
[Al_poly] No change in the stray light component either, since Aug-2018. The West-pointing anomaly (significant increase of visible light component noticed near West-limb pointing) was reproduced. The stray light intensity before the CCD bakeout turned out ~4% smaller than the image taken after the bakeout, indicating that there are other factors that determine the stray light intensities of Al_poly (e.g., slight change of pointing) than the CCD contamination layers.
[thin_Be] Stray light component is still in a negligible level.
[med_Be, med_Al & thick_Al filters] No measurements this year.

3. Measurements 2020 at a glance.

ID No.	date & time (UT)	XOB	purposes (link: obtained plots & images)	memo
1	7-May-2020, 18:37:30	1C81	light crv., Al-mesh (1.4s) and Al-poly (2.0s) at DC.	previous bakeout + 14 day.
2	8-May-2020, 18:54:30	1C82	light crv., thin_Be (11.3s) at DC.	prev. b.o. + 15 day.
3	13-May-2020, 18:22:00	1C83	light crv., Al-mesh (1.4s) and Al-poly (2.0s) at DC.	prev. b.o. + 0 day. Many lost frames.
4	14-May-2020, 19:08:00	1C84	light crv., thin_Be (11.3s) at DC.	prev. b.o. + 1 day.
5	12-Jul-2020, 01:16:30	1C88	light crv., Al-mesh (1.4s) and Al-poly (2.0s) on AR.	prev. b.o. + 21 days.

4. Stray light images 2020, at a glance.

Al_mesh filter

No change in the stray light component included in the Al_mesh filter (no new pattern found). Observed no increase of the stray light level since the 2018 July data. Comparison of the stray light images taken before and after CCD bakdout shows ~2% increase of the stray light level in 14 days.

- DC pointings
[NOTE] pnt. indicates the satellite pointing at the time of data acquisition, i.e., (index.xcen, index.ycen) corrected by the the coalignment DB.

Al-mesh, 20200507(1.4s) [bd+14d] pnt.(-18.5, 7.4)	Al-mesh, 20200513(1.4s) [bd+0d] pnt.(-17.6, 12.5)	Al-mesh, 20180712(1.4s) [bd+2d] pnt.(-22.1,19.8)	After PREP comparison 1 comparison with 2018	After PREP comparison 2 before/after bakeout

- Other pointings

Al-mesh, 20200712(1.4s)
[bd+21d]
pnt.(881.0, 73.5)

Al_poly filter

No change in the stray light component included in the Al_poly filter. No change in the stray light intensity since 2018. The stray light intensity before the CCD bakeout turned out ~4% smaller than the image taken after the bakeout, indicating that there are other factors that determine the stray light intensities of Al_poly (e.g., slight change of pointing) than the growing CCD contamination layers. The West pointing anomaly (significant increase of stray light intensity near West-limb pointing) was reproduced.

- DC pointings

Al-poly, 20200507(2.0s) [bd+14d] pnt.(-18.5, 7.4)	Al-poly, 20200513(2.0s) [bd+0d], pnt.(-17.6, 12.5)	Al-poly, 20180712(2.0s) [bd+2d], pnt.(-22.2,19.8)	After PREP comparison 1 comparison with 2018	After PREP comparison 2 before/after bakeout