CCD Annealing

Radiation damage creates hot pixels in the STIS CCD Detector. Many of these hot pixels can be repaired by warming the CCD from its normal operating temperature near -83°C up to the ambient instrument temperature of about +5°C for several hours. Despite this annealing procedure, the number of permanently hot pixels has been increasing with time. These plots and reports document the evolution of hot pixels and the success of the annealing over time. Please note that STIS was shut down from mid 2004 to mid 2009, and so no data is available from that period. Further details of the annealing procedure are given in STIS ISR 98-06.

Plots From Anneal Monitor:

• Percentage of persistent pixels
• Post-anneal mean raw dark rate
• Post-anneal median dark rate
• Hot pixel growth rate
• Pre and Post-Anneal Hot Pixels (0.1 e/s Level)
• Ratio of Pre and Post-Anneal Hot Pixels
• Signal to noise ratio of flats taken with anneals

• Statistics on all anneals

Since the switch to Side-2 electronics, the STIS CCD has been operating without a working thermister. Instead of being operated at a constant temperature, it is now run at a constant current. This leads to fluctuations in the temperature of the ccd due to external sources such as the low-earth environment and the number of active instruments. Recent analysis has shown that the previously used temperature correction, used to scale the dark frames to a reference temperature, did not provide an accurate correction to the observed fluctuation in hot pixel count with temperature. By applying a new temperature scaling relation to just the number of hot pixels, we can see a more accurate representation of the effectiveness of the anneal process. Further information can be seen in an ISR in preparation.

Plots:

• Fluctuations in # hot pixels due to temperature
• Monthly anneals with temperature fluctuations removed