Toward the Detection and Characterization of Sub-Neptune Exoplanets Orbiting Nearby M Dwarfs

Waalkes, William

Graduate Thesis Or Dissertation

Toward the Detection and Characterization of Sub-Neptune Exoplanets Orbiting Nearby M Dwarfs Público Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/6969z2547

Abstract

The last 20 years have seen a boom in the number of known exoplanetary systems, and many of the temperate sub-Neptune planets we study orbit low mass M stars. M dwarf stars can host temperate worlds with periods short enough for rapid followup and precise characterization but these stars are also extremely active, subjecting their planets to harsh XUV radiation and frequent flares that can sterilize and evaporate planetary atmospheres. Follow-up studies of potentially rocky planets in these systems have so far provided only tenuous evidence for their atmospheres and in some cases what are likely false positive detections caused by stellar active regions like starspots. Starspots are ubiquitous on M dwarf photospheres and introduce molecular features in the disk average stellar spectrum which, if uncorrected, can be mistaken for absorption of molecules like H2O and TiO in the planet’s atmosphere. With the successful launch of JWST and the promise of studying exoplanet atmospheres in greater detail than ever before, it is vital that we mitigate the problem of starspot contamination in exoplanet transmission spectra. How does stellar activity affect the atmospheres of short-period planets? Do temperate and warm sub-Neptune planets orbiting M dwarfs retain their atmospheres? To what extent do stellar active regions like starspots contaminate our observations and obscure the evidence of atmospheric absorption? How can we accurately measure spot characteristics and mitigate their effects on exoplanet observations? These questions have motivated the research I present in this thesis, where I describe how I used space and ground-based observations to validate new exoplanets found by TESS, search for atmospheric escape from a nearby terrestrial world, and characterize starspots on the young exoplanet host AU Microscopii.

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