The Impact of Stellar Activity on the Detection and Characterization of Exoplanets

At the level of a stellar photosphere, stellar magnetic fields manifest themselves as the stellar equivalents of sunspots and faculae. The dark, localized spots give rise to a rotationally modulated background signal that both increases the fractional depth of exoplanet transits and increases the variability of the background against which they are detected. The convective motions of the electrically conducting photospheric gas are inhibited in spots and in facular regions, again producing rotationally modulated variability in spectral line shapes as the star rotates. Discussed here is the physical phenomena that give rise to these forms of variability, their impact on the detection and characterization of extrasolar planets, and proxy indicators and observing strategies that can mitigate this impact.