Correlations between Ca II H&K Emission and the Gaia M dwarf Gap

Abstract

The Gaia M dwarf gap, also known as the Jao Gap, is a novel feature discovered in the Gaia DR2 G vs. BP-RP color magnitude diagram. This gap represents a 17 percent decrease in stellar density in a thin magnitude band around the convective transition mass ($\sim 0.35 M_{\odot}$) on the main sequence. Previous work has demonstrated a paucity of Hydrogen Alpha emission coincident with the G magnitude of the Jao Gap in the solar neighborhood. The exact mechanism which results in this paucity is as of yet unknown; however, the authors of the originating paper suggest that it may be the result of complex variations to a star's magnetic topology driven by the Jao Gap's characteristic formation and breakdown of stars' radiative transition zones. We present a follow up investigating another widely used magnetic activity metric, Calcium II H\&K emission. Ca II H\&K activity appears to share a similar anomalous behavior as H$\alpha$ does near the Jao Gap magnitude. We observe an increase in star-to-star variation of magnetic activity near the Jao Gap. We present a toy model of a stars magnetic field evolution which demonstrates that this increase may be due to stochastic disruptions to the magnetic field originating from the periodic mixing events characteristic of the convective kissing instabilities which drive the formation of the Jao Gap.