The new IR inverse sensitivities are based on observations of the four white dwarf standard stars, namely GD153, G191B2B, GD71, GRW+70D5824, and the G-type star, P330E, collected between 2009 and 2019. Changes relative to the 2012 values are described below.
New 2020 solution:
- Models: Models for the CALSPEC standard white dwarfs were improved and the Vega reference flux was increased (Bohlin et al. 2020). As a consequence, the standard white dwarf fluxes increase ~1.5% in the range 1-1.6 micron covered by the IR detector.
- Flat fields: the updated 'pixel to pixel' flats correct for spatial sensitivity residuals up to 0.5% in the center of the detector and up to 2% at the edges (ISR 2021-01). A new set of 'delta' flats correct for low-sensitivity artifacts known as 'blobs' in six filters (F098M, F105W, F110W, F125W, F140W, and F160W), as new blobs appear over time (ISR 2021-10).
IR Inverse Sensitivity (Zeropoint) Tables
Please note that we only provide values for an infinite aperture of radius 6 arcsec.
|Å||Å||Mag||Mag||Mag||Mag||erg cm-2 Å-1 e-1||erg cm-2 Å-1 e-1|
The repeatability of photometric measurements stars over the course of one to a handful of orbits is found to be approximately +/- 1.5%, despite Poisson noise terms being quite a bit smaller than 1%.
Previous analyses have shown that WFC3-IR suffers a count-rate dependent non-linearity of about 1% per dex, an order of magnitude smaller than the prior HgCdTe detector, NICMOS, flown on HST, but large enough to potentially limit the accuracy of photometry. In Riess et al. 2019 (ISR 2019-01) we present new and more precise measurements of count-rate non-linearity (CRNL) through a combination of comparisons of cluster star photometry between WFC3-IR and WFC3-UVIS and by using observed and synthetic magnitudes of white dwarfs. We further extend the measured range of CRNL to higher count rates by comparing magnitudes between the ground and WFC3-IR for LMC and Milky Way Cepheids. Combining these results with all previous measurements and those from the WFC3 grism provides a consistent and improved characterization of the CRNL of WF3-IR, of 0.75% +/- 0.06% per dex, with no apparent wavelength dependence, measured across 16 astronomical magnitudes. To illustrate the value of the precision reached for the CRNL, we show it is sufficient to compare the photometry of sources along a distance ladder calibrated by Gaia parallaxes and produce a 1% determination of the Hubble constant.
Due to the difficulty of measuring CRNL for WFC3-IR on orbit, a broad set of approaches have been used. The initial, on-orbit calibration of CRNL was produced by Riess (2010) who compared the magnitudes of stars in clusters between two overlapping passbands, one from an instrument without CRNL (the CCDs of ACS WFC) or corrected for CRNL (NICMOS) and WFC3-IR.
In Riess et al. (2019) we present additional sets of measurements which provide greater precision in the on-orbit determination of the WFC3-IR CRNL. First we present new measurements comparing cluster star magnitudes in bands where CCD’s overlap with WFC3-IR, F850LP, and F098M using a combination of deep and shallow frames to extend the dynamic range. We also provide calibrations of the CRNL at brighter magnitudes (F160W=6-14) using comparisons between the ground and WFC3-IR of the photometry of Cepheids in the Large Magenallanic Cloud and the Milky Way. We then use an independent approach where we compare the near-infrared photometry of hot, DA White Dwarf (WD) to models constrained by optical measurements.
We find the CRNL in WFC3-IR to be 0.0077 +/- 0.0008 mag/dex (or 0.0075 +/- 0.006 mag/dex including the grism measurements), characterized over 16 magnitudes with no apparent wavelength dependence and independent corroboration. This result is consistent with the initial determination by Riess (2010) of 0.010 +/- 0.002 mag/dex but the present results are much more precise. This result may be used to correct IR photometry by using the difference in apparent flux (in dex) between where the WFC3-IR zeropoint is set (~12th mag) and the target source (fainter sources appear even fainter and thus are corrected to be brighter).
Nov 19, 2012
First IMPHTTAB for IR
|wbj1825ri_imp.fits||HSTCAL replaces calls to STSDAS/synphot in calwf3 to populate PHOT keywords|
Mar 06, 2012
Revised Zeropoints (Infinite and 3 pix)
GD153, GD71, G191B2B, P330E
Master DRZ frames, per filter
ISR 2011-08: The Photometric Performance of WFC3/IR: Temporal Stability Through Year 1
Dec 7, 2010
Ground flats corrected by a 'grey' delta-flat
Computed from average sky flat for all filters
|+/- 2% correction||
ISR 2011-11: Sky Flats: Generating Improved WFC3 IR Flat-fields
Nov 10, 2009
F098M, F105W and F160W
Other filters from optical models
ISR 2009-37: WFC3 SMOV Programs 11437/9: IR On-orbit PSF Evaluation
Nov 18, 2009
In-flight Zeropoints (infinite)
Polynomial correction with wavelength
GD 153, P330E
|10-15% higher sensitivity than ground test data||
ISR 2009-30: WFC3 SMOV Proposal 11451: The Photometric Performance and Calibration of WFC3/IR
|Dec 10, 2008||Ground Flats||s*pfl.fits||Thermal vacuum data||ISR 2008-28: WFC3 IR Ground P-Flats|