Searching for TESS Photometric Variability of Possible JWST Spectrophotometric Standard Stars

TL;DR

This study uses TESS data to evaluate the photometric stability of potential JWST spectrophotometric standards, identifying some variability that could affect calibration accuracy and establishing most candidates as suitable standards.

Contribution

It provides the first systematic assessment of TESS photometry for JWST standard stars, setting upper limits on variability and highlighting stars suitable for calibration.

Findings

15 out of 37 stars show measurable variability.

Four stars vary by more than 1%, potentially impacting calibration.

Stars brighter than magnitude 12 have variability limits below 0.5%.

Abstract

We use data from the Transiting Exoplanet Survey Satellite (TESS) to search for, and set limits on, optical to near-infrared photometric variability of the well-vetted, candidate James Webb Space Telescope (JWST) spectrophotometric standards. Our search of 37 of these candidate standards has revealed measurable periodic variability in 15 stars. The majority of those show variability that is less than half a percent; however, four stars are observed to vary photometrically, from minimum to maximum flux, by more than 1% (the G dwarf HD 38949 and three fainter A dwarfs). Variability of this size would likely impact the error budget in the spectrophotometric calibration of the science instruments aboard JWST. For the 22 candidate standards with no detected variability, we report upper limits on the observed changes in flux. Despite some systematic noise, all stars brighter than 12 magnitude in the TESS band show a 3 sigma upper limit on the total change in brightness of less than half a percent on time scales between an hour and multiple weeks, empirically establishing their suitability as spectrophotometric standards. We further discuss the value and limits of high-cadence, high-precision photometric monitoring with TESS as a tool to vet the suitability of stars to act as spectrophotometric standards.