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AR 17551 (Archival Research)

Sun Jul 14 20:33:17 GMT 2024

Principal Investigator: Benjamin Rackham
PI Institution: Massachusetts Institute of Technology
Investigators (xml)

Title: Unlocking the Stellar Treasure Trove: A Legacy Library of Stellar Hosts' Heterogeneities, Activity, and Spectral Contributions from HST Exoplanet Data
Cycle: 31

Abstract
Opening windows into the atmospheres of other worlds is undoubtedly among the most pivotal contributions to HST's scientific legacy. Exoplanetary transmission spectra have yielded insights into the their composition, temperatures, and pressures, providing a foundation for the new era of atmospheric characterization with JWST. However, it has recently become clear that host-star photospheric heterogeneities may limit the exoplanet legacy of HST - and even JWST - by giving rise to spectral features that mimic or mask those of planetary atmospheres, leading to erroneous inferences. Fortunately, the very same HST datasets provide exquisite out-of-transit stellar spectra that can be leveraged to mitigate this effect. While a few recent studies have shown the utility of studying out-of-transit HST stellar spectra, most remain untouched. Here we propose to thoroughly tap this stellar treasure trove via a large, uniform analysis of all 25,000 archival HST transit exposures to reveal the properties of hosts' photospheres. Through this analysis, we will establish an HST Legacy Library of time-dependent spectra of exoplanet host stars, constraints on their photospheric spectral components and covering fractions, and estimates of their spectral contributions to exoplanet transmission spectra. As Legacy Data Products, we will also release the tools we develop for the data reduction, stellar heterogeneity modeling, and transmission spectra corrections as open-source Python libraries. The insights and tools developed through this work will cement HST's legacy of revealing the properties of both exoplanets and their host stars and pave the way for future studies with both HST and JWST.