Starspots |
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Authors: | Klaus G Strassmeier |
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Institution: | (1) Astrophysikalisches Institut Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany |
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Abstract: | Starspots are created by local magnetic fields on the surfaces of stars, just as sunspots. Their fields are strong enough
to suppress the overturning convective motion and thus block or redirect the flow of energy from the stellar interior outwards
to the surface and consequently appear as locally cool and therefore dark regions against an otherwise bright photosphere
(Biermann in Astronomische Nachrichten 264:361, 1938; Z Astrophysik 25:135, 1948). As such, starspots are observable tracers
of the yet unknown internal dynamo activity and allow a glimpse into the complex internal stellar magnetic field structure.
Starspots also enable the precise measurement of stellar rotation which is among the key ingredients for the expected internal
magnetic topology. But whether starspots are just blown-up sunspot analogs, we do not know yet. This article is an attempt
to review our current knowledge of starspots. A comparison of a white-light image of the Sun (G2V, 5 Gyr) with a Doppler image
of a young solar-like star (EK Draconis; G1.5V, age 100 Myr, rotation 10 × Ω
Sun) and with a mean-field dynamo simulation suggests that starspots can be of significantly different appearance and cannot
be explained with a scaling of the solar model, even for a star of same mass and effective temperature. Starspots, their surface
location and migration pattern, and their link with the stellar dynamo and its internal energy transport, may have far reaching
impact also for our understanding of low-mass stellar evolution and formation. Emphasis is given in this review to their importance
as activity tracers in particular in the light of more and more precise exoplanet detections around solar-like, and therefore
likely spotted, host stars. |
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Keywords: | Starspots Stars: activity Stars: imaging Sunspots Magnetic fields Techniques: polarimetric Stars: rotation Exoplanets |
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