Keplercam Status

Created: 02/23/07 by EF
Updated: 09/08/13 by EF

  • Data acquired in Jan 2007 for the Kepler Input Catalog (KIC) project revealed a small jump in astrometry residuals in the DEC direction across the transition from amps 1 to 4 and 2 to 3. Mark Everett produced the plot shown here. The problem was discovered in Jan 2007, but it affects all Keplercam binned data through 01/31/07.

    After some detective work, Mark, TG and EF agreed that the symptom was that the top rows of amps 3 and 4 (abutting amps 1 and 2, respectively), when binned by 2, contained a sum of data and bias levels and therefore had unexpectedly low counts. These amps have a single overscan row at the top. Therefore, we concluded that there was an erroneous offset by 1 row in the row counters for amps 3 and 4, such that at the top, binning by 2 resulted in summing data and bias. Steve Amato in Cambridge was able to quickly correct the offset in the chip's signal and pattern files on 01/31/07. After a single iteration with TG, we verified with flats that the problem had been corrected. Mark confirmed that in subsequent KIC images.

  • After the 2006 August shutdown, Keplercam flats had changed. There was a drop in sensitivity in bands about 200-columns wide at the left and right edges of each quadrant. The drop was to about 10% of the original sensitivity. After discussions with John Geary and Dave Latham, we concluded that there was contamination on the chip. It was unclear how the contamination fell on the chip, because the usual procedure was used to warm up the dewar for the shutdown. Nothing was visible to the eye on the CCD, but the signs of contamination were unmistakable. Thus, we decided to bake the chip. We followed the careful prescription that JG put together, which involved warming the chip to up to +50C, pumping and N2 backfilling over a period of a little over 24 hours. WP conducted the bake-out starting 11/09/06. Subsequent flats revealed the bake-out recovered most, but not all of the sensitivity of the CCD that was seen before the shutdown. The results were deemed sufficient and not warranting additional baking. See Mark Everett's notes here.

  • Xuelong Mu analyzed Keplercam dome flats taken between 2005 and 2013, to establish the history of contamination of the CCD. See Xuelong's report here.