Prioritizing High-Precision Photometric Monitoring of Exoplanet and Brown Dwarf Companions with JWST -- Strategic Exoplanet Initiatives with HST and JWST White Paper

TL;DR

This paper emphasizes the importance of high-precision photometric monitoring of exoplanets and brown dwarfs using JWST to study their atmospheric features, rotation, and variability with unprecedented sensitivity and resolution.

Contribution

It advocates for strategic use of JWST's capabilities to monitor atmospheric variability and rotation in substellar companions, enhancing understanding of their atmospheric structures and dynamics.

Findings

JWST can monitor faint exoplanet companions over full rotation periods.

Photometric variability reveals atmospheric features and rotation periods.

Simultaneous multi-wavelength monitoring probes atmospheric layer differences.

Abstract

We advocate for the prioritization of high-precision photometric monitoring of exoplanet and brown dwarf companions to detect brightness variability arising from features in their atmospheres. Measurements of photometric variability provide not only an insight into the physical appearances of these companions, but are also a direct probe of their atmospheric structures and dynamics, and yield valuable estimates of their rotation periods. JWST is uniquely capable of monitoring faint exoplanet companions over their full rotation periods, thanks to its inherent stability and powerful high-contrast coronagraphic imaging modes. Rotation period measurements can be further combined with measurements of v sin i obtained using high-resolution spectroscopy to infer the viewing angle of a companion. Photometric monitoring over multiple rotation periods and at multiple epochs will allow both short- and long-term time evolution in variability signals to be traced. Furthermore, the differences between the layers in a companion's atmosphere can be probed by obtaining simultaneous photometric monitoring at different wavelengths through NIRCam dual-band coronagraphy. Overall, JWST will reach the highest sensitivities to variability to date and enable the light curves of substellar companions to be characterised with unprecedented cadence and precision at the sub-percent level.