Magnetic activity in stars causes surface features such as starspots (regions of strong magnetic field that supresses convection and are therefore cooler than the surrounding photosphere) and plage (bright regions in the chromosphere). These different features will vary with time, both on short and long timescales, and will affect exoplanet observations including planet discovery work as well as characterisation of their atmospheres.
First, as stellar active regions rotate across the observed face of the star, they cause spurious radial velocity shifts as well as distortions in the shape of the stellar line profile. On relatively short timescales (weeks to months) these changes are typically correlated to the stellar rotation period, but on longer timescales the magnetic activity cycle of the star can cause the underlying magnetic field structure to change, causing long-term variations in the observed radial velocity measurements. This can have a severe impact on the discovery and confirmation of low-mass (especially terrestrial) planets.
Second, the varying starspot coverage can cause wavelength dependent brightness variations. These variations can cause issues for (spectro)photometric transit observations, as they can make it more difficult to combine data taken on different nights, as well as introduce spurious effects in the planet’s transmission spectrum. This can lead to an incorrect interpretation of the physical conditions on the planet’s surface and in its atmosphere.
Therefore, detailed understanding and modelling of the impact of stellar activity is very important.
The aim of this project is to model stellar activity, fitting both spectroscopic and photometric data of exoplanet systems to help mitigate and correct for these effects. This work will build on the expertise developed within the exoplanet group at the Astrophysics Research Centre at Queen’s University Belfast.