An HST exclusive look at two rising stars: high-energy spectra of the two closest M dwarfs to host transiting terrestrial exoplanets

Diamond-Lowe, Hannah, King, George, Buchhave, Lars A., Corrales, Lia, Kozakis, Thea, Kreidberg, Laura, Medina, Amber, Mendonca, Joao Manuel and Winters, Jennifer (2021) An HST exclusive look at two rising stars: high-energy spectra of the two closest M dwarfs to host transiting terrestrial exoplanets.

Abstract

As we build towards robustly detecting and characterizing the atmospheres of terrestrial exoplanets with JWST, we cannot forget to take a close look at the low-mass stars they orbit. Complete coverage of M dwarf ultraviolet spectra are needed to determine the photochemical production rates of molecular species in terrestrial planet atmospheres, which will alert us to when disequilibrium chemistry, a sign of surface processes or even life, is present. High-energy spectra from the UV to X-ray are also needed to calculate mass loss rates from planetary atmospheres, which can explain the lack of atmospheres around highly-irradiated terrestrial worlds. LTT 1445Ab and GJ 486b are two of the most spectroscopically accessible terrestrial exoplanets we will ever find, and their M dwarf hosts are similarly at the top of their class in terms of observability. We will use the unique ultraviolet capabilities of HST, supplemented by X-ray observations, to provide complete short-wavelength spectral coverage for the stars LTT 1445A and GJ 486. Both planets, LTT 1445Ab and GJ 486b, will be observed in JWST Cycle 1 with the aim of detecting their atmospheres. If we do not take the opportunity to make UV measurements of their host stars while HST is still operational, this crucial input to understanding the atmospheres of these planets will be lost. We request 18 orbits with HST (COS and STIS) to capture complete UV spectra of LTT 1445A and GJ 486.

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Contributors

Author: Joao Manuel Mendonca

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