Hinode/XRT stray light correction 2019

XRT Stray Light Study 2019 -- 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 2020 phase 4 page (after 29-May-2018 ← 4th event).

(15 Jul, 2019 by Aki Takeda)
(10 Aug, 2019, measurements in late July added.)

1. Purposes of the stray light measurement in 2019.

Judging from the intensity level of G-band images and FLD images (Al-poly 8x8), we expect no further increase in stray light level since the end of last eclipse season (Aug-2018). The 2019 measurements are to confirm this with real data taken during eclipses.

The 2019 measurements started right after the CCD bakout. This allows us to obtain the best stray light images, least affected by the accumulating contamination on the CCD.

We will take the stray light images at various pointings with Al_mesh and Al_poly filters, so that we can estimate the amount of stray light included in the images with non-DC, non-limb pointings.

[requested by T. Jibben in July 2019] : It turned out that some synoptic images were taken at the focus position for the active region obervation (-361). It is therefore useful to check if the stray light pattern will change with different focus position (i.e., -361 v.s. -86).

2. Summary of Results.

It was fortunate that we didn't see a new pre-filter failure event during this eclipse season. The 2019 measurements were spent all for taking data for the phase 4.
[Al_mesh] No change in the stray light component since the end of last eclipse season (Aug-2018). As noticed in the past years, a bright short arc appears in the upper-right quadrant when it is illuminated by the solar disk.
[Al_poly] No change in the stray light component either, since the last eclipse season. The anomaly (significant increase of visible light component) noticed last year near West-limb pointing was reproduced.
[thin_Be, med_Be, med_Al & thick_Al filters] Stray light component is still in a negligible level.
[focus position comparison] The stray light images with the focus position at -361 were taken for Al_mesh and Al_poly filters on 30-Jul-2019. There found no significant difference in the stray light pattern between those taken at the focus points -361(for AR) and -86(synoptics). The increase of stray light level due to the CCD contamination layer growth is larger.

3. Measurements 2019 at a glance.

ID No.	date & time (UT)	XOB	purposes (link: obtained plots & images)	memo
1	8-May-2019, 13:37:30	1C46	light crv., Al-mesh (1.4s) and Al-poly (2.0s) at DC.	prev. bakeout + 0 day. CCD temp ~-54C.
2	8-May-2019, 20:10:30	1C46	light crv., Al-mesh (1.4s) and Al-poly (2.0s) at N-pole.	prev. b.o. + 0 day.
3	9-May-2019, 17:29:00	1C48	light crv., thin_Be (11.3s) at DC.	prev. b.o. + 1 day.
4	10-May-2019, 13:09:00	1C46	light crv., Al-mesh (1.4s) and Al-poly (2.0s) at S-pole.	prev. b.o. + 2 days.
5	10-May-2019, 18:04:00	1C49	light crv., med-Be (22.6s).	prev. b.o. + 2 days.
6	11-May-2019, 18:39:00	1C4B	light crv., med-Al (32.0s).	prev. b.o. + 3 days.
7	12-May-2019, 17:36:00	1C4A	light crv., thick-Al (32.0s).	prev. b.o. + 4 days.
8	13-May-2019, 18:11:00	1C4C	light crv., Al-mesh (1.4s) and Al-poly (2.0s) at W-limb.	prev. b.o. + 5 days.
9	13-May-2019, 23:06:00	1C4C	light crv., Al-mesh (1.4s) and Al-poly (2.0s) on AR.	prev. b.o. + 5 days.
10	14-May-2019, 18:46:00	1C4E	light crv., Al-mesh (1.4s) and Al-poly (2.0s) at E-limb.	prev. b.o. + 6 days.
11	15-May-2019, 17:43:00	1C4F	light crv., thin-Be (11.3s) at W-limb.	prev. b.o. + 7 days.
12	16-May-2019, 11:45:00	1C4E	light crv., Al-mesh (1.4s) and Al-poly (2.0s) with HOP79.	prev. b.o. + 8 days.
13	16-May-2019, 13:23:00	1C4E	light crv., Al-mesh (1.4s) and Al-poly (2.0s) with HOP79.	prev. b.o. + 8 days.
14	16-May-2019, 15:01:30	1C4E	light crv., Al-mesh (1.4s) and Al-poly (2.0s) with HOP79.	prev. b.o. + 8 days.
15	16-May-2019, 23:13:30	1C4E	light crv., Al-mesh (1.4s) and Al-poly (2.0s) with HOP79.	prev. b.o. + 8 days.
16	17-May-2019, 00:51:30	1C4E	light crv., Al-mesh (1.4s) and Al-poly (2.0s) with HOP79.	prev. b.o. + 9 days.
17	17-May-2019, 15:37:00	1C4E	light crv., Al-mesh (1.4s) and Al-poly (2.0s) on AR.	prev. b.o. + 9 days.
18	17-May-2019, 18:53:30	1C4F	light crv., thin-Be (11.3s) at E-limb.	prev. b.o. + 9 days.
19	18-May-2019, 19:29:00	1C4F	light crv., thin-Be (11.3s) at S-pole.	prev. b.o. + 10 days.
20	30-Jul-2019, 18:08:30	1C4C	light crv., Al-mesh (1.4s) and Al-poly (2.0s) at DC.	prev. b.o. + 9 days. Focus position: -361.
21	30-Jul-2019, 19:47:00	1C4C	light crv., Al-mesh (1.4s) and Al-poly (2.0s) at DC.	prev. b.o. + 9 days.
22	1-Aug-2019, 17:41:00	1C4F	light crv., thin-Be (11.3s) at N-pole.	prev. b.o. + 11 days.

4. Stray light images 2019, at a glance.

Al_mesh filter

No change in the stray light component included in the Al_mesh filter. As noticed in the past years, a bright short arc appears in the upper-right quadrant of the image when it is illuminated by the solar disk. No significant change found in the stray light pattern with different focus position.

- 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, 20190508(1.4s) [bd+0d] pnt.(-17.2, 0.30)	Al-mesh, 20190730(1.4s) [bd+9d], focus -361 pnt.(-19.6, 10.7)	Al-mesh, 20190730(1.4s) [bd+9d] pnt.(-19.6, 10.7)	Al-mesh, 20180710(1.4s) [bd+1d]	After PREP comparison

Focus posision comparison 1	Focus posision comparison 2

- Limb pointings

Al-mesh, 20190508(1.4s) [bd+0d] pnt.(-41.5, 857.8)	Al-mesh, 20190510(1.4s) [bd+2d] pnt.(-32.3, -942.2)	Al-mesh, 20190513(1.4s) [bd+5d] pnt.(903.7, -3.4)	Al-mesh, 20190514(1.4s) [bd+6d] pnt.(-986.2, -15.7)

- Other pointings

Al-mesh, 20190513(1.4s) [bd+5d] pnt.(693.8, 85.3)	Al-mesh, 20190516(1.4s) [bd+8d] pnt.(-32.6, -887.8)	Al-mesh, 20190516(1.4s) [bd+8d] pnt.(-33.6, -688.0)	Al-mesh, 20190516(1.4s) [bd+8d] pnt.(-34.5, -487.9)	Al-mesh, 20190516(1.4s) [bd+8d] pnt.(-39.0, 202.1)

Al-mesh, 20190517(1.4s) [bd+9d] pnt.(-39.0, 402.1)	Al-mesh, 20190517(1.4s) [bd+9d] pnt.(815.8, 59.5)

Al_poly filter

No change in the stray light component included in the Al_poly filter. (PREP behaves different from last year regarding 2018 data. Reason not identified. Comparison was made by manualy subtracting the closest dark and devided by the exposure time.) The anomaly (significant increase of visible light component) noticed last year near West-limb pointing was reproduced. No significant change found in the stray light pattern with different focus position.

- DC pointings

Al-poly, 20190508(2.0s) [bd+0d] pnt.(-17.2, 0.30)	Al-poly, 20190730(2.0s) [bd+9d], focus -361 pnt.(-19.6, 10.7)	Al-poly, 20190730(2.0s) [bd+9d] pnt.(-19.6, 10.7)	Al-poly, 20180710(2.0s) [bd+1d]

After PREP comparison	After dark sub comparison	Focus posision comparison 1	Focus posision comparison 2

- Limb pointings

Al-poly, 20190508(2.0s) [bd+0d] pnt.(-41.5, 857.8)	Al-poly, 20190510(2.0s) [bd+2d] pnt.(-32.3, -942.2)	Al-poly, 20190513(2.0s) [bd+5d] pnt.(903.7, -3.42)	Al-poly, 20190514(2.0s) [bd+6d] pnt.(-986.2, -15.7)

- Other pointings

Al-poly, 20190513(2.0s) [bd+5d] pnt.(903.7, -3.4)	Al-poly, 20190516(2.0s) [bd+8d] pnt.(-32.6, -877.8)	Al-poly, 20190516(2.0s) [bd+8d] pnt.(-33.6, -688.0)	Al-poly, 20190516(2.0s) [bd+8d] pnt.(-34.5, -487.9)	Al-poly, 20190516(2.0s) [bd+8d] pnt.(-38.1, -60.1)

Al-poly, 20190517(2.0s) [bd+9d] pnt.(402.1, -60.1)	Al-poly, 20190517(2.0s) [bd+9d] pnt.(815.8, 59.5)

thin_Be filter

Stray light included in thin_Be images is still in negligible level.

thin-Be,20190509(11s) DC	thin-Be,20180711(11s) DC	after PREP comparison

thin-Be,20190515(11s) W-limb	thin-Be,20190517(11s) E-limb	thin-Be,20190518(11s) S-pole	thin-Be,20190801(11s) N-pole

med_Be, med_Al & thick_Al filters

It turned out that the stray light level of med_Al filter is slightly higher than that of med_Be filter, but absolute values are negligible (less than 0.3 DN/sec for both filters).

med-Be,20190510(23s)	med-Al,20190511(32s)	thick-Al,20190512(32s)	After exp. normalization