Starspots

摘要

Starspots are created by local magnetic fields on the surfaces of stars,just as sunspots. Their fields are strong enough to suppress the overturning convectivemotion 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 theyet unknown internal dynamo activity and allow a glimpse into the complex inter-nal stellar magnetic field structure. Starspots also enable the precise measurement ofstellar rotation which is among the key ingredients for the expected internal magnetictopology. But whether starspots are just blown-up sunspot analogs, we do not knowyet. This article is an attempt to review our current knowledge of starspots. A compar-ison of a white-light image of the Sun (G2V, 5 Gyr) with a Doppler image of a youngsolar-like star (EK Draconis; G I .5V, age 100Myr, rotation 10 xΩ_(sun) and with amean-field dynamo simulation suggests that starspots can be of significantly differentappearance and cannot be explained with a scaling of the solar model, even for a star ofsame mass and effective temperature. Starspots, their surface location and migrationpattern, and their link with the stellar dynamo and its internal energy transport, mayhave far reaching impact also for our understanding of low-mass stellar evolution andformation. Emphasis is given in this review to their importance as activity tracers inparticular in the light of more and more precise exoplanet detections around solar-like,and therefore likely spotted, host stars.