The James Webb Space Telescope Absolute Flux Calibration. I. Program Design and Calibrator Stars

TL;DR

This paper details the design of JWST's absolute flux calibration program, which aims to ensure precise and consistent calibration across all instruments and modes using well-vetted calibration stars of different types.

Contribution

It introduces a comprehensive calibration program for JWST that includes multiple star types, instrument modes, and calibration checks to improve flux measurement accuracy.

Findings

Calibration stars vetted with HST, Spitzer, TESS data

Instrument mode calibration covering all configurations

Quantification of systematic and statistical uncertainties

Abstract

It is critical for James Webb Space Telescope (JWST) science that instrumental units are converted to physical units. We detail the design of the JWST absolute flux calibration program that has the core goal of ensuring a robust flux calibration internal to and between all the science instruments for both point and extended source science. This program will observe a sample of calibration stars that have been extensively vetted based mainly on Hubble Space Telescope, Spitzer Space Telescope, and Transiting Exoplanet Survey Satellite observations. The program uses multiple stars of three different, well understood types (hot stars, A dwarfs, and solar analogs) to allow for the statistical (within a type) and systematic (between types) uncertainties to be quantified. The program explicitly includes observations to calibrate every instrument mode, further vet the set of calibration stars, measure the instrumental repeatability, measure the relative calibration between subarrays and full frame, and check the relative calibration between faint and bright stars. For photometry, we have set up our calibration to directly support both the convention based on the band average flux density and the convention based on the flux density at a fixed wavelength.