Stars & Planets Seminar - Allison Youngblood (NASA GSFC)


Monday, November 26, 2018, 12:00pm to 1:00pm


Title: Observing Lyman alpha Emission from Exoplanet Host Stars

Abstract: UV stellar radiation can control chemistry and mass-loss in planetary atmospheres due to the large, wavelength-dependent photoionization cross sections of common atmospheric molecules. Thus, characterizing the UV spectral energy distribution of an exoplanet host star is critical for evaluating the origin of any atoms or molecules detected in planets. H I Lyman alpha (1215.67 Å) dominates the far-UV spectrum of cool dwarf stars, especially M dwarfs, but strong absorption from neutral hydrogen in the interstellar medium and Earth’s Lyman alpha airglow makes direct observations of the intrinsic Lyman alpha emission from even the closest stars challenging. I describe the techniques used to recover this important emission line from Hubble Space Telescope STIS and COS spectroscopy, including as part of the MUSCLES (Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems) and FUMES (Far Ultraviolet M-dwarf Evolution Survey) surveys, and how the strength of Lyman alpha evolves with stellar age and activity.
See also: Seminars, 2018 - 19