2018 Theses Doctoral

The Relationship Between Stellar Rotation and Magnetic Activity as Revealed by M37 and Alpha Persei

Núñez, Alejandro

In low-mass (≲1.2 M⊙) main-sequence stars, the combination of differential rotation and turbulent flows in the outer convective region generates strong magnetic fields. It has been observed that in these stars, the rotation rate and the strength of the magnetic field decrease over time. This is thought to result from a feedback loop in which magnetized winds carry angular momentum away from the star, braking its rotation and weakening the magnetic dynamo. A well-calibrated age-rotation-activity relation (ARAR) would be particularly valuable for low-mass stars. If we knew the dependence of rotation or magnetic activity on age, a measurement of one of these quantities could be used to determine an accurate age for any isolated field star. Empirical calibrations of the ARAR rely on observations of the co-eval populations of stars in open clusters. In this work, I characterize rotation and magnetic activity, using light curves for the former and X-ray and Hα emission for the latter, in two open clusters of different ages (Alpha Persei, ≈60 Myr, and Messier 37, ≈500 Myr) to analyze the relation between rotation and activity across the low-mass stellar range. I also compare coronal (X-rays) and chromospheric (Hα) activity to understand how magnetic heating varies across stellar atmospheric layers. My results inform models of angular momentum evolution in low-mass stars.