Following the recovery of ACS with the side-2 electronics in July 2006, the temperature of the WFC detector was lowered from -77C to -80C in an effort to mitigate the impact of CTE and hot pixels. As predicted, the temperature change caused a slight loss in detector sensitivity. By using relative photometry of 47 Tuc before and after the temperature change, corrections to the WFC photometric zeropoints have been computed. The largest change is 0.026 mag at F435W, decreasing with wavelength to 0.011 mag at F625W. Beyond ~7000A, the sensitivity losses increase, reaching 0.024 mag for F850LP. A revised detector QE curve and a new set of photometric zeropoints have been computed for all WFC observations obtained at the new operating temperature. These zeropoints must be applied manually until the new QE curves are implemented in SYNPHOT.
Instrument Science Report ACS 2007-02
- Pub Date:
- May 2007
- Hubble Space Telescope;
- Space Telescope Science Institute;
- Wide Field Camera;
- Photometric Techniques