Wednesday 09 Oct 2019[Seminar] The Effects of Stellar Magnetic Activity and Variability on Observations of Exoplanets

Dr Brett Morris - University of Bern

4th floor, Physics building 15:15-16:15

Stellar magnetic activity and variability at the stellar surface inject confounding time- and wavelength-dependent signals into the spectrophotometry of exoplanet host stars which complicate our interpretations of exoplanet radii, atmospheres and masses. We must understand heterogeneous stellar surfaces in order to accurately answer astrobiological questions such as: does this planet have a surface, and what might its atmosphere be composed of? We studied the magnetic activity of the Sun, and its impact on observations of Earth-like exoplanets orbiting Sun-like stars. We find that solar oscillations and granulation are a significant source of astrophysical noise in measuring exoplanet radii with precision, with applications to observations by the PLATO mission. Next, we present detailed studies of the magnetic activity of HAT-P-11, a K4V with a transiting hot-Neptune in a fortuitous orbit. The starspots of HAT-P-11 reveal that the star likely has a Sun-like dynamo, producing spots with a similar latitudinal distribution, though the spot coverage is two orders of magnitude larger. We then turn our attention to the magnetic activity of the very lowest mass planet-hosting star, TRAPPIST-1. We reason that TRAPPIST-1 likely has bright regions driving the stellar variability observed at optical wavelengths but not observed in the near infrared. We also find evidence that the presence of the bright regions seems to be associated with flare occurrence, perhaps indicating that the apparent rotational modulation observed at optical wavelengths may not be rotational modulation after all. Lastly, we prepare for observations of the systems of potentially habitable planets of TRAPPIST-1 with the James Webb Space Telescope (JWST) using NIRSpec's in Prism mode. We determine that TRAPPIST-1 may be one of the best known systems for follow-up with James Webb due largely to its brightness and the small size of its host star.

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