Hinode/XRT stray light correction 2018

XRT Stray Light Study 2018 -- phase 3 (before 29-May-2018).

Link to the 2014 summary page.
Link to the 2015 phase 1 summary.
Link to the 2015 phase 2 summary.
Link to the 2016 page and 2017 phase 2 page.
Link to the 2017 phase 3 page (after 27-May-2017).
Link to the 2018 phase 4 page (after 29-May-2018).

(15 May, 2018 by Aki Takeda)
(2-jul-2018, summary added.)
(18-aug-2018, added pointing information).

1. Purposes of the stray light measurement in 2018.

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-2017). The 2018 measurements are to confirm this with real data taken during eclipses.

The 2018 measurements fortunately 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, so that we can estimate the amount of stray light included in the images with non-DC, non-limb pointings.

We will re-take med_Be and med_Al stray light images, to confirm the stray light level (last year's observation suggested that med_Al, which is thicker than med_Be, has more stray light component.

2. Summary of Results.

[Al_mesh] No change in the stray light component since the end of last eclipse season (Aug-2017). 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] Stray light component is still in a negligible level.
[med_Be & med_Al] Stray light component is still in a negligible level. It was confirmed that the stray light level of med_Al filter is slightly higher than that of med_Be filter.

3. Measurements 2018 at a glance.

ID No.	date & time (UT)	XOB	purposes (link: obtained plots & images)	memo
1	8-May-2018, 21:36:00	1BF5	light crv., Al-mesh (1.41s) and Al-poly (2.00s) at DC.	prev. bakeout + 0 day. CCD temp ~-54C.
2	9-May-2018, 17:16:30	1BF5	light crv., Al-mesh (1.41s) and Al-poly (2.00s) at N-pole.	prev. b.o. + 1 day. Large pnt shift to W.
3	9-May-2018, 18:55:00	1BF5	light crv., Al-mesh (1.41s) and Al-poly (2.00s) at DC.	prev. b.o. + 1 day. Large pnt shift to W.
4	9-May-2018, 20:33:00	1BF5	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on AR.	prev. b.o. + 1 days. Large pnt shift to W.
5	10-May-2018, 12:56:30	1BF7	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on S-pole.	prev. b.o. + 2 days.
6	10-May-2018, 14:35:00	1BF6	light crv., Al-poly (2.83s) and thin-Be (11.3s) on S-pole.	prev. b.o. + 2 days.
7	10-May-2018, 17:51:30	1BF6	light crv., Al-poly (2.83s) and thin-Be (11.3s) at DC.	prev. b.o. + 2 days.
8	11-May-2018, 18:27:00	1BF6	light crv., Al-poly (2.83s) and thin-Be (11.3s) on N-pole.	prev. b.o. + 3 days.
9	11-May-2018, 20:05:00	1BF7	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on AR.	prev. b.o. + 3 days.
10	15-May-2018, 17:31:00	1BF8	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on E-limb.	prev. b.o. + 7 days.
11	15-May-2018, 22:24:00	1BFA	light crv., med-Al (32.0s) at DC.	prev. b.o. + 7 days.
12	16-May-2018, 18:06:30	1BF8	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on W-limb.	prev. b.o. + 8 days.
13	16-May-2018, 22:59:30	1BFB	light crv., med-Be (22.6s) at DC	prev. b.o. + 8 days.
14	17-May-2018, 00:37:30	1BFA	light crv., med-Al (32.0s) at DC	prev. b.o. + 9 days.
15	17-May-2018, 13:46:30	1BF8	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on HOP79.	prev. b.o. + 9 days.
16	17-May-2018, 15:25:00	1BF8	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on HOP79.	prev. b.o. + 9 days.
17	18-May-2018, 17:38:30	1BF8	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on N-pole.	prev. b.o. + 10 days.
18	18-May-2018, 19:17:00	1BF8	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on AR.	prev. b.o. + 10 days.
19	18-May-2018, 22:33:30	1BF8	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on S-pole.	prev. b.o. + 10 days.
20	19-May-2018, 18:13:30	1BF8	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on SW.	prev. b.o. + 11 days.
21	20-May-2018, 17:10:30	1BF8	light crv., Al-mesh (1.41s) and Al-poly (2.00s) on SE.	prev. b.o. + 12 days.

[NOTE]
1) Hinode pointing system configuration change occurred for the period 5/6 -- 5/11.
* 2018/05/06 22:36: UFSS-A,-B →→→ UFSS-A,NSAS
* 2018/05/08 22:17: UFSS-A,NSAS →→→ NSAS only
--------- large pointing shift (to the West) observed. ---------
* 2018/05/10 07:38: NSAS only →→→ UFSS-B,NSAS
* 2018/05/11 07:43: UFSS-B,NSAS →→→ UFSS-A,-B
* pointing shifts observed outside the above period are due to imperfect values of "SOT offset", which is often the case with eclipse season.
2) The stray light measurements on 5/12-14 were canceled due to the ROI errors at the "check_rois" program.

4. Stray light images 2018, 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.

- 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, 20180508(1.4s) [bd+0d] pnt.(-13.7, -24.9)	Al-mesh, 20180509(1.4s) [bd+1d] pnt.(-137.8, -21.3)	Al-mesh, 20170808(1.4s) [bd+1d]	After PREP comparison

- Limb pointings

Al-mesh, 20180509(1.4s) [bd+1d] pnt.(-148.2, 870.5)	Al-mesh, 20180510(1.4s) [bd+2d] pnt.(-45.9, -887.8)	Al-mesh, 20180515(1.4s) [bd+7d] pnt.(-988.7, -1.4)	Al-mesh, 20180516(1.4s) [bd+8d] pnt.(951.5, 14.3)	Al-mesh, 20180518(1.4s) [bd+10d] pnt.(-40.6, -898.1)

- Other pointings

Al-mesh, 20180509(1.4s) [bd+1d] pnt.(-449.9, 176.2)	Al-mesh, 20180511(1.4s) [bd+3d] pnt.(-541.9, 145.2)	Al-mesh, 20180517(1.4s) [bd+9d] pnt.(-43.8, -549.1)	Al-mesh, 20180517(1.4s) [bd+9d] pnt.(-45.2, -249.1)	Al-mesh, 20180518(1.4s) [bd+10d] pnt.(793.0, 134.4)

Al-mesh, 20180519(1.4s) [bd+11d] pnt.(-543.9, -522.9)	Al-mesh, 20180520(1.4s) [bd+12d] pnt.(512.3, -512.1)

Al_poly filter

No change in the stray light component included in the Al_poly filter. The anomaly (significant increase of visible light component) noticed last year near West-limb pointing was reproduced.

- DC pointings

Al-poly, 20180508(1.4s) [bd+0d] pnt.(-13.8, -25.2)	Al-poly, 20180509(1.4s) [bd+1d] pnt.(-138.0, -21.4)	Al-poly, 20180510(2.8s) [bd+2d] pnt.(-24.6, 24.6)	Al-poly, 20170809(2.8s) [bd+2d]	After PREP comparison

- Limb pointings

Al-poly, 20180509(1.4s) [bd+1d] pnt.(-158.9, 885.1)	Al-poly, 20180510(1.4s) [bd+2d] pnt.(-45.9, -887.7)	Al-poly, 20180510(2.8s) [bd+2d] pnt.(-47.0, -887.9)	Al-poly, 20180511(2.8s) [bd+3d] pnt.(-59.4, 889.0)	Al-poly, 20180515(1.4s) [bd+7d] pnt.(-988.7, -1.4)

Al-poly, 20180516(1.4s) [bd+8d] pnt.(951.5, 14.3)	Al-poly, 20180518(1.4s) [bd+10d] pnt.(-40.6, -898.1)

- Other pointings

Al-poly, 20180509(1.4s) [bd+1d] pnt.(-450.4, 177.3)	Al-poly, 20180511(1.4s) [bd+3d] pnt.(-541.8, 145.0)	Al-poly, 20180517(1.4s) [bd+9d] pnt.(-43.8, -549.1)	Al-poly, 20180517(1.4s) [bd+9d] pnt.(-45.2, -249.1)	Al-poly, 20180518(1.4s) [bd+10d] pnt.(793.0, 134.4)

Al-poly, 20180519(1.4s) [bd+11d] pnt.(-543.9, -522.9)	Al-poly, 20180520(1.4s) [bd+12d] pnt.(512.3, -512.1)

thin_Be filter

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

thin-Be,20180510(11s) DC	thin-Be,20170510(11s) DC - phase 2 -	thin-Be,20180510(11s) S-pole	thin-Be,20180511(11s) N-pole	after PREP comparison

med_Be & med_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,20180516(23s)	med-Al,20180517(32s)	After exp. normalization