Exoplanet transit photometry for stellar activity and exomoon research

Exoplanet transit photometry for stellar activity and exomoon research

Photometry underlies important discoveries in observational astronomy, from the detection of stellar magnetic phenomena unveiling dynamic dynamo processes to the much sought-after identification of exomoons. Transit light curves contain
a wealth of information on planet-hosting stars and the celestial bodies orbiting them.

This body of work presents an analysis and interpretation of transit light curves of solar-type stars. Periodic flux dimming signals the transit of an exoplanet, with the degree of dimming indicative of the exoplanet’s radial size. Small scale flux modulations within the transit duration, or dimming, appear as bumps and dips and are attributed to starspots and faculae on an unresolved stellar face. From the size and location of these photospheric features, much can be learned about the host star: differential rotation, active longitudes, and magnetic activity cycles.

For this thesis, two stars were selected as targets from the more than 150,000 stars observed by the Kepler telescope, Kepler-71 and Kepler-45. Both are solar-type stars, as defined by having a radiative core surrounded by a convective envelope. Kepler-71 is a G star somewhat younger than the Sun and orbited by a single hot Jupiter. The analysis of Kepler-71 transits presents the first use of faculae to measure stellar rotation period at the transit latitude. The difference between the mean stellar rotation period and the latitudinal rotation period indicate an almost rigid rotation. Acomplete analysis is presented in Chapter 2.

Kepler-45 is a young M dwarf, also orbited by a single hot Jupiter. The inspection of transit light curves revealed two distinct types of small-scale amplitude variations - temporally confined flux changes due to starspots and faculae, and extended decreases in flux due to a possible satellite of the hot Jupiter Kepler-45b. For the former case, Chapter 3 presents the first analysis of stellar activity for an M1V dwarf.

Investigation of the latter type of flux modulations revealed interesting evidence for an exomoon companion to Kepler-45b. A method for analyzing this evidence for a super-Earth exomoon is discussed in Chapter 4. The discovery of the first super-Earth exomoon would provide an important observational constraint for theories of planetary formation and evolution, and exomoon orbital stability. This potential exomoon candidate is expected to become an observational target and the subject of many future studies.