XRT Stray Light Study 4 -- Measurement and Correction.
Link to the 3rd test page.
Link to the 5th & 6th tests page.
(05 July, 2014 by Aki Takeda)
1. Stray light correction project -- the 4th test.
1.1 Purposes of the 4th test.
- collect more light curves of the XRT eclipses.
- obtain Ti-poly stray-light images to compare with previous images.
- first attempt to obtain Thin-Be stray-light images.
1.2 Test sequence.
The fourth test was performed on 03-July-2014, 18:30 -- 18:50UT.
- 18:18:00 -- s/c pointing to disk center (0,0)
- 18:21:00 -- regular synoptic program.
- 18:32:30 -- test sequence started (until ~18:40).
- -----------------------------------------------------------------------------------------------------------------------------------------------
- 128x128 pix, 2" resol., every 10 sec on AR12104, Ti-poly + G-band(VLS close).
- 1024x1024 pix, 2" resol., every 60 sec, Full-Sun, Ti-poly + Thin-Be.
- detailed parameters of the sequence (XOB#1A29).
- -----------------------------------------------------------------------------------------------------------------------------------------------
- 18:33:00 ------ XRT entering twilight zone.
- 18:38:30 ------ XRT s/c night entry.
- 18:54:30 ------ XRT SAA entry.
- 18:58:30 ------ XRT s/c night exit.
- 19:03:30 ------ XRT exiting from twilight.
- 19:17:30 ------ XRT SAA exit.
2. Result of the test observation.
2.1 Solar condition
2.2 Sunset light curves
2.3 Stray light images
Thin-Be stray light images obtained (movie).
No significant stray light detected.
Ti-poly stray light images obtained (movie).
2.4 Comparison of the Stray-light images (2nd and 4th tests).
If the stray light images (taken at the same pointing) do not(or only a little)
vary with time, you can use a single stray image to correct images taken outside
eclipse season. The Ti-poly stray-light images taken on 15-May-2014(2nd test)
and 3-Jul-2014(4th test) were compared.
The left image is the difference image of the stray-light images taken
at the 2nd and 4th tests:
dd1: stray light image from the test 2 (15-May-2014, 18:25:03, exp. 1440msec)
ii1: index(FITS header) structure of dd2
dd2: stray light image from the test 4 (03-Jul-2014, 18:36:59, exp. 1440msec)
ii2: index(FITS header) structure of dd2
[diff_img] = [dd2] - [dd1]
Their difference image is almost featueless, with stripes (as we see in
dark frames) and subtle trace of solar disk.
Their intensity level on the average is zero with noise roughly
± 5 DN.
