Revisiting the Activity–Rotation Relation for Evolved Stars

Abstract The magnetic dynamo mechanism of giant stars remains an open question, which can be explored by investigating their activity–rotation relations with multiple proxies. By using the data from the LAMOST and Galaxy Evolution Explorer surveys, we carried out a comprehensive study of activity–rotation relations of evolved stars based on Ca ii H and K lines, H α lines, and near-ultraviolet (NUV) emissions. Our results show that evolved stars and dwarfs obey a similar power law in the unsaturated region of the activity–rotation relation, indicating a common dynamo mechanism in both giants and dwarfs. There is no clear difference in the activity levels between red giant branch stars and red clump stars, nor between single giants and those in binaries. Additionally, our results show that the NUV activity levels of giants are comparable to those of G- and K-type dwarfs and are higher than those of M dwarfs.