The Photometric Performance and Calibration of WFC3

Nov 18th, 2009 SOC Committee Meeting, STScI

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

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.

July 2010 HST Calibration Meeting, STScI

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.

Targets

Star B V J H Temp (K) Log(g)

G191B2B 11.45 11.77 12.55 12.66 61,193 7.492

GD153 13.06 13.35 14.07 14.19 38,686 7.662

GD71 12.78 13.03 13.74 13.86 32,747 7.683

GRW+70d5824 12.68 12.77 ------- ------- ------- -------

P330E 13.62 13.00 11.88 11.60 G0V G0V

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

The Photometric Performance and Calibration of WFC3

Photometric StabilityWFC3 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

The Photometric Performance and Calibration of WFC3

UVIS: 5-10% efficiency boost at blue/red ’s, 15-20% at 400-700 nm

IR: 10-15% boost in efficiency at all ’sACS/WFC: Sirianni et al. (2002)

SMOV4 Throughput Calibration1.) The HST OTA2.) Pickoff mirror3.) CSM4.) Mirror reflectivity5.) Filter throughputs6.) Detector window7.) Detector QE Calibration in TV3

July 2010 HST Calibration Meeting, STScI

The Photometric Performance and Calibration of WFC3

July 2010 HST Calibration Meeting, STScI

The Photometric Performance and Calibration of WFC3

UVIS Throughput1.) Published ZPs are accurate to within 1%.2.) Upward revisions of 8500 Ang needed. 3.) GD153 and G191 self consistent to 0.25-50%.4.) P330E trend is similar to ACS.

IR Throughput5.) Published ZPs are accurate to within 1%.

General6.) Flat field offsets are very important.

For details: Kalirai et al. (2009, WFC3 ISR 2009-31) Kalirai et al. (2009, WFC3 ISR 2009-30)

July 2010 HST Calibration Meeting, STScI

The Photometric Performance and Calibration of WFC3

ImplicationsWFC3 vs ACS: - 20% smaller pixels - 50% lower read noise - small CTE correction - much lower dark current

A Look Forward to Cycle 181.) Observations of additional flux standards.2.) Monitor Programs over wide baseline3.) Absolute flux calibration of WDs.4.) Photometric transformations.5.) Testing the WFC3 flat field.