Hinode/XRT CCD contamination

The XRT team has recently provided information on the status of the XRT CCD camera and calibration software. The following is a message sent by Ed DeLuca to SolarNews on August 30, 2007.

The XRT CCD has experienced some degradation due to contamination that appeared after a short CCD bake-out in July. The contamination is manifest by small (~5 pixel diameter) spots on the detector. The spots cover somewhat less than 4% of the CCD area.They are seen in G-band images and in the thinner x-ray filters (Al_mesh, Al_poly, Ti_poly, C_poly and Be_thin, with decreasing effect in the order listed).
The origin of the contamination is not understood at this time.

The XRT team is modifying the software in the SSWIDL tree to give scientists two ways of analyzing XRT data taken after the contamination event:

1. a "touch-up" program that will replace the affected pixels with an average signal from near-by unaffected pixels.
2. a "bad-pixel" map that allows scientists to avoid using the affected pixels in their analysis.

The touch-up program is applied to the quick-look images that are being distributed to web-pages and should be used when constructing movies and studying morphological changes. This same program will be available as a switch to the XRT_PREP code that converts level 0 data to level 1 data.

The XRT team is working to develop a cleaning program that will preserve the photometric information available below the spots. This programs will be distributed to the XRT user community through the SSWIDL distribution.

In addition the XRT team will develop programs that correct for the decrease in "filter-dependent" transmission between Nov-2006 and July-2007 caused by the accumulation of contaminants on the CCD. These corrections are particularly important for scientists using XRT data to estimate temperatures (e.g. via filter ratios).

The XRT team has setup an email distribution for users of XRT data. To subscribe to this list send an email to: xrt_users-request@head.cfa.harvard.edu

To reduce the amount of spam on this list, users are accepted by positive confirmation at SAO. Please include your signature file when requesting admission to this list. The XRT team will use the list to keep the community up-to-date on the latest analysis tools and developments. Users may use this list to ask questions about analysis, report bugs and discuss analysis techniques with other users.
Email to this list will be archived at: http://xrt.cfa.harvard.edu/community/xrt_users