Code of Conduct
Klaus-Peter Schroeder (Mexico)
By contrast to coronal X-ray detections, chromospheric emission measures seem to be a less biased indicator for magnetic activity among cool giant stars. We review the legacy of Mount Wilson "S-index" observations, and together with our own chromospheric activity monitoring data of bright, cool giants (obtained by the robotic telescope project TIGRE in Guanajuato, MEX) we put magnetic activity among giant stars into context with stellar evolution. We show that (1) despite huge -compered to the Sun- convective envelopes, activity is a common phenomenon among cool giant stars, too. (2) After magnetic breaking on the main sequence and a first revival in the Hertzsprung gap, giant activity suffers from magnetic breaking again during central Helium burning (as the 4 Hyades K giants demonstrate), (3) on the AGB then chromospheric emission is, surprisingly, again on the rise. Consequently, activity revivals seem to coincide in the HRD with phases of fast core contraction.
