Assessing Mg I Activity with Rotation and Age for FGK Stars

A thorough understanding of how stellar activity, age, and rotation are connected is crucial for accurately modeling and predicting the underlying physical processes present in all types of stars. In general, we observe that a star's rotation slows down as it ages due to magnetic braking. This spin down relationship is relatively predictable for certain classes of stars (e.g. F and G stars), but K stars have an interesting stalling period where they rotate at a constant rate for up to 1.4 Gyr before resuming their spin down. To better understand age-activity-rotation relations and how this unique K star behavior contributes, we build on previous observational work focused on measuring the activity of the corona, transition region, and upper chromosphere of K stars by examining the activity of the lower chromosphere. We accomplished this by analyzing the Mg I line at 8809.2 angstroms of 49 K star targets; we then compared our results to the measured Mg I activity of young F and G stars found in a similar observational study by Yamashita et al. (2022). We found that while the Mg I emission line is a good activity marker in young F and G stars, it is an absorption feature and therefore a poor activity marker in older K star targets. We plan to observe young K star targets to see if a trend exists between lower chromospheric activity and age. If not, this may suggest that K stars have a less-active lower chromosphere than other types of stars.