New Time-Dependent WFC3/IR Inverse Sensitivities

TL;DR

This paper introduces updated, time-dependent inverse sensitivities for the WFC3/IR channel, improving photometric accuracy and accounting for sensitivity losses over 15 years, with an updated calibration tool to facilitate precise measurements.

Contribution

It provides the first time-dependent inverse sensitivities for WFC3/IR based on 15 years of data, enhancing photometric precision and updating calibration software.

Findings

Sensitivity losses of 1-2% over 15 years

Photometric precision better than 0.5% across filters

Updated calibration software (calwf3 v3.7.2) available

Abstract

We present new time-dependent inverse sensitivities for the WFC3/IR channel. These were calculated using the sensitivity change slopes measured by \citet{2024wfc..rept....6M} and photometry of five CALSPEC standards (the white dwarfs GRW+70~5824, GD~153, GD~71, G191B2B, and the G-type star P330E) collected from 2009 to 2023. The new inverse sensitivities account for losses of 1-2\% over 15 years, depending on wavelength, and provide an internal photometric precision better than 0.5\% for all wide--, medium--, and narrow-band filters. An updated version of \texttt{calwf3} (v3.7.2) has been developed for use with a new time-dependent image photometry table (IMPHTTAB) and will be used to update the image header photometric keywords following MAST reprocessing, expected in late-2024. Alternatively, the new inverse sensitivities may be computed by the user for a specific observation date by running \texttt{stsynphot}.