Background

Here we present previous calibrations for the WFC3/UVIS instrument.

 

Previous UVIS Zeropoints

2017 Solution

The inverse sensitivity values written to the PHOTFLAM image header keyword are the CORRECT values for flux calibration for all except the UV filters observed on UVIS2. The IMPHTTAB carries the values for UVIS1 via the keywords PHOTFLAM and PHTFLAM1, and these are identical with the exception of the UV filters. Inverse sensitivity values for UVIS2 are written to the keyword PHTFLAM2 but should not be used for flux calibration with calibrated data products retrieved from MAST, since calwf3 by default will scale the UVIS2 chip by the chip sensitivity ratio to match UVIS1. 
 

Changes from 2012

  • Flat fields: Improved low-frequency in-flight corrections to the ground flats were computed in 2016 using CTE-corrected observations of Omega Centauri. The flats are normalized to the median value of each detector and no longer correct for sensitivity differences between CCDs. The photometric repeatability of white dwarf standards stepped across the field of view is better than 1% r.m.s. and 3% peak-to-peak over the full wavelength range of the detector (ISR 2016-04 and 2016-05).
  • Inverse Sensitivity: The current chip-dependent inverse sensitivity values are systematically ~3.7% brighter than the 2012 solutions. Using the default AstroDrizzle configuration parameters when combining images with different signal to noise and telescope orientation on the sky can result in ‘clipping’ of pixel values in the PSF wings. This effect was discovered in the 2012 solutions and was corrected in the 2016 implementation.

zeropoints

2012

2012 zeropoints

2009

2009 zeropoints

Previous Quad Filters Zeropoints

Here we present the 2012 Infinite Aperture and 0.4 arcsec inverse sensitivity values for the quad filters. These values still make use of the pre-flight flats that contain the flare. See ISR 2011-16 for the geometric model of the flare, and ISR 2013-10 for the  inflight corrections to the flats.

For general information on the quad filters, see the WFC3 Instrument Handbook.

2012 Quad Filter Zeropoints

Previous UVIS Encircled Energies

2009 Encircled Energies

After WFC3's installation in 2009, deep observations in F275W and F625W were obtained in 5 positions across the UVIS array, and these were used to revise the pre-flight EE. EE fractions for all remaining filters were interpolated from the revised 2009 optical model. See ISR 2009-38 for more details.

The tables listed below can also be downloaded as a DAT file.

uvis_ee_model_smov.dat

2009 ee

Last Updated: 08/03/2023

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