Accounting for differential rotation in calculations of the Sun’s angular momentum-loss rate

Vol. 674
9. The Sun and the Heliosphere

Accounting for differential rotation in calculations of the Sun’s angular momentum-loss rate

The rotation rate of solar-type stars provides a clock for estimating their age and that of any cluster in which they reside, separate from other nuclear evolutionary chronometers. However, this requires careful calibration because the rate could depend on the differential rotation of the star and its magnetic dynamo cycle. This study aims to provide a sensitivity study of the effect of these assumptions on the spindown torque for a particular, rather nearby star for which the braking torque on the solid body rotation shifts in latitude during the magnetic cycle. The authors used a semi-empirical approach for the solar wind, reconstructing the topology of the field from 15 years of surface magnetograms and computing the braking variation over a complete solar cycle. They find that, for at least this slow rotator, the open field line outflows in the solar wind are not strongly connected to or influenced by the differential rotation. The implications for spindown of sola! r-type and low-mass stars, and possible modifications of the Skumanich law, are extremely interesting and will have a resonance in the "Sun as a star" community.