Evidence of differential surface rotation in the solar-type star HD 114710

Abstract

Observations of the chromospheric Ca II H and K emission variability of the intermediate-age solar-type star HD 114710 (β Comae Berenices, GO V) obtained at Mount Wilson Observatory over the past 10 years reveal a secular change in the seasonal rotation period that can be interpreted as surface differential rotation. The dependence of rotation period on chromospheric flux (i.e., activity-cycle phase) suggests that the star may have two latitudinal zones of activity: one in which changes in rotation period appear to follow the starspot activity cycle, and another confined to a narrow range of periods that does not. The pattern of rotation that depends on stellar cycle phase is opposite that of the Sun: the rotation period increased as activity declined during the last activity cycle. Active region growth and decay is ruled out as the explanation for the systematic change of the seasonal rotation periods.