K faculae as tracers of the solar differential rotation

Abstract

Daily angular velocities of K-faculae are measured in terms of differences in Carrington longitudes deduced from daily spectroheliograms obtained in the Ca II K line over an eight-year period. The angular velocities are then averaged in order to determine mean solar rotation rates as a function of latitude for different compactnesses and areas. It is found that the equatorial angular velocities of faculae with corrected areas less than 2500 millionths of a solar hemisphere and with compactness 4 are about the same as that deduced from sunspot measurements and about 5 percent higher than that of the photospheric gas; faculae with larger corrected areas and compactness 3 are found to have an equatorial angular velocity which tends to approach that of the photospheric gas. These results are taken as an apparent confirmation of the conjecture that newly emerged magnetic fields (associated with the smaller and more compact faculae) in active regions are still mechanically coupled to a subphotospheric layer rotating with higher angular velocity and consequently exhibit an angular velocity higher than that of the photospheric gas.