Studying the Atmospheres and Magnetic Fields of Exoplanets

Transits of exoplanets observed in the near-UV have been used to study the absorption properties of their atmospheres and possible star-planet interactions. In total, 25 transiting exoplanets were observed either in the near-UV or optical with the 1.5-m Kuiper Telescope to constrain their atmospheres and determine if asymmetries are visible in their light curves. I find that none of the near-UV transits exhibit any asymmetries. These observations suggest that asymmetries are not common in ground-based transits. With these observations I also conclude that 15 of the exoplanets have clouds, 5 have some type of scattering, and 3 may have TiO absorption in their atmospheres.

Next, I used the plasma photoionization code CLOUDY to explore whether there is a UV absorbing species in the stellar wind that can cause an early UV ingress in the transits of close-in exoplanets due to the presence of a bow shock compressing the coronal plasma. For all UV wavelengths, I find under realistic physical conditions for the corona that there are no species that can cause absorption with sufficient opacity. These conclusions suggest that UV asymmetry observations are not a suitable approach for exoplanet magnetic field detection. I also simulated escaping planetary gas in ionization and thermal equilibrium with the stellar radiation field with CLOUDY. From this model, I find species with strong absorption lines previously observed in exoplanet upper atmospheres but also make predictions for many species and lines not yet observed from X-rays to the radio domain.

Detection of radio emission from exoplanets can provide information on the star-planet system that is difficult to study otherwise, such as the planetary magnetic field, magnetosphere, rotation period, interior structure, atmospheric dynamics and escape, and star-planet interactions. Such a detection in the radio domain would open up a whole new field in the study of exoplanets. I created a pipeline for Low-Frequency Array (LOFAR) beam-formed observations that mitigates radio frequency interference, calibrates the time-frequency response of the telescope, and searches for bursty planetary radio signals in the data. Next, I investigate the radio emission from Jupiter, scaled such that it mimics emission coming from an exoplanet, with low-frequency radio observations using the LOFAR. The goal is to determine up to what distance and with what strength radio emission from exoplanets can be detected using LOFAR. This is the first time that the sporadic nature of expected radio emission from exoplanets has been simulated. I find that radio bursts from an exoplanet located at 20 pc (encompassing tens of known exoplanets) could be detected if the flux is a million times stronger than the peak level of Jupiter’s radio emission. This finding is consistent with theoretical models that predict such strong radio emission can exist. The present study can be used as a guide to search for radio emission from exoplanets and to produce more reliable upper-limits for non-detections.