How Planets Affect Cool Stars
Creators: name: Poppenhaeger, Katja
Publisher: name: Zenodo
Year: 2018

description: All cool stars display magnetic phenomena including flares, spots, and coronal high-energy emission, collectively called magnetic activity. Cool stars also spin down over time by shedding a magnetized wind which couples to the stellar magnetic field; these magnetic effects therefore fade over timescales of gigayears. Cool stars with exoplanets in close orbits may be a fundamental exception from the age-activity-rotation relationships which govern other cool stars. In analogy to close stellar binaries, a planet and its star are thought to interact tidally and magnetically. If the planetary orbit is shorter than the stellar rotation period, angular momentum transfer from the orbit to the stellar spin can take place. This can lead to a spin-up (or inhibited spin-down) of the host stars and a shrinking planetary orbit. In addition to this long-term evolution, planets have also been speculated to trigger stellar flares or other changes in the stellar atmosphere through magnetic interaction or accretion of evaporating exoplanetary material. Observational searches for such enhanced rotation or activity of Hot-Jupiter host stars are not straightforward due to the presence of selection effects and the stochastic nature of stellar activity itself; however, there has been progress over the past years which I will report on. I will also highlight the influence these effects can have on exoplanets themselves.
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