Instrument Science Report 2005-01:
Hot Pixels as a Probe of WFPC2 CTE Effects
J. Biretta and V. Kozhurina-Platais
July 15, 2005
Hot pixels provide a potentially useful probe of CTE effects, as they can be used to measure effects at the smallest scales -- at single pixel level. Herein we outline a method of using the tails on hot pixels to quantify CTE effects, and apply it to CTE tails in WFPC2 dark frames. As we show, many of the behaviors associated with photometric CTE are also found for hot pixel tails including the dependences on CCD row, epoch, and target brightness. The brightness distribution of the tails are well fit by a sum of exponential decays with scale-lengths of 0.6, 6, and 96 pixels, with the vast majority of the counts being in the longest decay component. The integrated counts in the tail are nearly equal to the expected photometric CTE, suggesting these tails are in fact the photometric deficit. We also find significant tails near row zero (y=0), and show these tails would cause effects quantitatively similar to the "long vs. short" effect. Finally we show evidence for chip-to-chip differences in CTE with WF4 having the least CTE.
The Complete Paper (PDF 0.3 MB) is available.