1. The Photometric Performance and Calibration of WFC3 • Quick Facts: • Wide field of view UVIS and IR cameras • Wavelength coverage of 0.2 – 1.7 microns • 62 UVIS filters + 1 grism • 15 IR filters + 2 grisms Nov 18th, 2009 SOC Committee Meeting, STScI

2. Calibration Goals 1.) Calibrate the WFC3 instrument throughput to 1%. 2.) Measure the temporal stability of the UVIS and IR cameras. 3.) Compute photometric zero points and transformations. The Photometric Performance and Calibration of WFC3 Method and Observational Design 4.) Target standard stars with S/N>>100. 5.) Construct EE curves out to >100 pixels. 6.) Synergy between _flt and _drz imaging. 7.) Employ subarrays to minimize readouts. July 2010 HST Calibration Meeting, STScI

3. Targets The Photometric Performance and Calibration of WFC3 SMOV WFC3/UVIS – GD153 SMOV WFC3/IR – GD153 and P330E Cycle 17 WFC3/UVIS – all stars Cycle 17 WFC3/IR – all stars July 2010 HST Calibration Meeting, STScI

4. The Photometric Performance and Calibration of WFC3 Photometric Stability WFC3 UVIS is temporally stable to <0.5% in W and M filters over its first year of science operations. WFC3 IR is temporally stable to <1% in W and M filters. July 2010 HST Calibration Meeting, STScI

5. UVIS: 5-10% efficiency boost at blue/red ’s, 15-20% at 400-700 nm IR: 10-15% boost in efficiency at all ’s ACS/WFC: Sirianni et al. (2002) The Photometric Performance and Calibration of WFC3 SMOV4 Throughput Calibration 1.) The HST OTA 2.) Pickoff mirror 3.) CSM 4.) Mirror reflectivity 5.) Filter throughputs 6.) Detector window 7.) Detector QE Calibration in TV3 July 2010 HST Calibration Meeting, STScI

6. The Photometric Performance and Calibration of WFC3 UVIS Throughput 1.) Published ZPs are accurate to within 1%. 2.) Upward revisions of l > 8500 Ang needed. 3.) GD153 and G191 self consistent to 0.25-50%. 4.) P330E trend is similar to ACS. IR Throughput 5.) Published ZPs are accurate to within 1%. General 6.) Flat field offsets are very important. July 2010 HST Calibration Meeting, STScI

7. The Photometric Performance and Calibration of WFC3 Implications WFC3 vs ACS: - 20% smaller pixels - 50% lower read noise - small CTE correction - much lower dark current A Look Forward to Cycle 18 1.) Observations of additional flux standards. 2.) Monitor Programs over wide baseline 3.) Absolute flux calibration of WDs. 4.) Photometric transformations. 5.) Testing the WFC3 flat field. For details: Kalirai et al. (2009, WFC3 ISR 2009-31) Kalirai et al. (2009, WFC3 ISR 2009-30) July 2010 HST Calibration Meeting, STScI