Differential Rotation in Two RS CVn Systems: σ Gem and ζ And

Abstract

Abstract. The differentially rotating convective envelope is an indispensable element of the magnetic dynamo working in RS CVn-systems. Tidal coupling is responsible for maintaining fast rotation, and also the observed high level of magnetic activity. In this work, we compare the physical properties of two well known RS CVn-type binaries, that is the long-period system σ Gem and the ellipsoidal variable ζ And. For the comparison, we use the results obtained from processing time-series Doppler images. We also aim at understanding how differential rotation could be affected by tidal forces in such close binaries.

Rotation–differential rotation relationships for late‐type single and binary stars from Doppler imaging

“…Moreover, tidal effects may organize preferred longitudes, as well as latitudes of activity (Oláh ). Aspherical distortion of the active component in an RS CVn‐type binary caused by a close companion can explain the emergence of magnetic flux at preferred longitudes locked to the orbital frame; therefore, the degree of the deformation could also account for disparate rotation laws (Kővári et al ). Theoretical calculations by Scharlemann () demonstrated how physical parameters of such a close binary determine the developing corotation latitude, where rotation is locked to the orbital revolution.…”

“…In RS CVn‐type binary systems, tidal coupling is responsible for maintaining fast rotation. Also, the gravitational influence of a close companion yields different physical conditions inside a differentially rotating convective bulk, which may imply that dynamos work differently in single stars compared to components of RS CVn systems (Kővári et al ). Although the related background theory is still too complex in its predictive power, for now the observational database is wide enough to study the relationship between the rotation rate and the differential rotation.…”