Hinode/XRT stray light correction 2017

XRT Stray Light Study 2017 (phase 2).

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.
Link to the 2017 phase 3 page (after 27-May-2017).

(20 May, 2017 by Aki Takeda)
(13 Oct, 2017: After PREP plots corrected using MSU_XRT_PREP.)
(10 Oct, 2020: After PREP plots reprocessed.)

1. Purposes of the stray light measurement in 2017.

Judging from the intensity level of G-band images and FLD images (Ti-poly 8x8), we expect no further increase in stray light level since the end of last eclipse season (Aug-2015). The 2017 measurements are to confirm this with real data taken during eclipses.

2. Summary of Results.

The Ti-poly stray light intensities are not significantly changed since the end of 2015 eclipse season(after the 2nd pre-filter failure).
No change in the slight stray light patern detected in Al-mesh filter since last June. The intensity is still not significant (2 to 5 DN/sec).
The stray light components in Al-poly, thin-Be, med-Be, & med-Al are negligible.

3. Measurements 2017 at a glance.

ID No.	date & time (UT)	XOB	purposes (link: obtained plots & images)	memo
1	09-May-2017, 18:11:30	1B83	light curve, Ti-poly (1s) and Al-mesh (2.83s) at DC.	prev. bakeout + 14 days.
2	10-May-2017, 18:47:00	1B84	light curve, Al-poly (4s), Thin-Be (11.3s) at DC	prev. bakeout + 15 days.
3	11-May-2017, 17:41:30	1B85	light curve, med-Al (32s) at DC	prev. bakeout + 16 days.
4	12-May-2017, 18:17:00	1B86	light curve, med-Be (22s) at DC	prev. bakeout + 17 days.

[NOTE] X-ray light curves in 2017 measurement are low contrast(X-ray vs G-band) due to the lack of ARs in the monitoring area.

4. Stray light images 2017, at a glance.

Note: exposure times are different from 2015 measurements.
The Ti-poly "After PREP comparison" plot shows that the stray light intensity in 2017/05/09 is ~9 % larger than that of 2015/07/18. Considering the difference of the time past since their previous bakeout (+14 days for 2016 while +1 day for 2015), this increase can be explained by the increased contamination thickness (variable component cleared by every CCD bakeout and slightly increased persistent layer).

Ti-poly, 20150718(1.4s)	Ti-poly, 20170509(1.0s)	After PREP comparison	Ti-poly, 20160510(1.0s)

The Al-mesh "After PREP comparison" plot shows that the stray light intensity on 2017/05/09 is 10% smaller than that of 2015/07/18, in spite of the time difference since the previous CCD bakeout (+14 and +2 days, respectively). This suggests that the Al_mesh stray light intensities are affected by other factors than CCD contamination thickness. [old plot]

The Al-mesh "After PREP comparison" plot was reprocessed in 2020. The new plot shows that the stray light intensity on 2017/05/09 is the same level as that of 2015/07/18, which is different result from that obtained in 2017. The possible reason is that the data base for calibration (dark, contamination, etc.) was not ready at the time of previous study. It is also confirmed that the 2017 stray light is the same level as that of 2016.

Al-mesh, 20150718(1.0s) [bd+2d]	Al-mesh, 20170509(2.8s) [bd+14d]	After PREP comparison 2017 vs 2015	Al-mesh, 20160510(2.8s) [bd+8d]	After PREP comparison 2017 vs 2016

In plots below exposure difference is not corrected yet.

Al-poly,20150620(0.8s)	Al-poly,20175010(4.1s)

thin-Be,20150620(5.8s)	thin-Be,20170510(11s)

med-Be,20150508(32s)	med-Be,20160513(23s)

med-Al,20150509(23s)	med-Al,20170511(32s)