Joint HST/Chandra Accepted Cycle 23 Targets & Abstracts

Proposal Number Subject Category PI Name Chandra Time Title
23100674 SOLAR SYSTEM AND EXOPLANETS Allison Youngblood 180.00ks Essential Ultraviolet Stellar Characterization for Cycle 1 JWST Transiting Planet Targets

Proposal Number: 23100674
Title: Essential Ultraviolet Stellar Characterization for Cycle 1 JWST Transiting Planet Targets
PI Name: Allison Youngblood
Abstract: Atmospheric spectroscopy of an exciting array of exoplanets (warm rocky planets, sub-Neptune, and Jupiter-mass planets) will be obtained during JWST's Cycle 1. To accurately model and interpret observations of these planets' atmospheres, we must understand the high-energy SED of their host stars: FUV and NUV-driven photochemistry shapes an atmosphere's molecular abundances and the formation of hazes, EUV irradiation can erode a planet's gaseous envelope, and flares can affect long term atmospheric stability. A number of recent surveys have used HST's UV capabilities to characterize the energetic irradiance spectra across a range of stellar masses, ages, and activity levels. While these surveys have proven invaluable for predicting photochemical tracers and evolution of an exoplanet's atmosphere, they have also shown scatter in UV irradiance properties for stars of similar type. As a result, direct UV observations remain the gold standard for understanding the effects of the stellar irradiance on a specific exoplanet. We propose to obtain temporally-resolved UV (1150-3200 A) and X-ray stellar spectroscopy of the 23 JWST Cycle 1 targets without UV characterization data in the HST archive. Our proposed observations will provide the high-energy context necessary to determine the likelihood of atmospheric formation and retention, the identification and interpretation of atmospheric chemistry, and the impacts of stellar activity on the exoplanet atmospheric stability.