Linking chromospheric activity and magnetic field properties for late-type dwarf stars

Spectropolarimetric data allow for simultaneous monitoring of stellar chromospheric logR′_HK activity and the surface-averaged longitudinal magnetic field, B_l, giving the opportunity to probe the relationship between large-scale stellar magnetic fields and chromospheric manifestations of magnetism. We present logR′_HK and/or B_l measurements for 954 mid-F to mid-M stars derived from spectropolarimetric observations contained within the PolarBase database. Our magnetically active sample complements previous stellar activity surveys that focus on inactive planet-search targets. We find a positive correlation between mean logR′_HK and mean log |B_l|, but for G stars the relationship may undergo a change between logR′_HK∼−4.4 and −4.8. The mean logR′_HK shows a similar change with respect to the logR′_HK variability amplitude for intermediately-active G stars. We also combine our results with archival chromospheric activity data and published observations of large-scale magnetic field geometries derived using Zeeman Doppler Imaging. The chromospheric activity data indicate a slight under-density of late-F to early-K stars with −4.75≤logR′_HK≤−4.5⁠. This is not as prominent as the original Vaughan–Preston gap, and we do not detect similar under-populated regions in the distributions of the mean |B_l|, or the B_l and logR′_HK variability amplitudes. Chromospheric activity, activity variability and toroidal field strength decrease on the main sequence as rotation slows. For G stars, the disappearance of dominant toroidal fields occurs at a similar chromospheric activity level as the change in the relationships between chromospheric activity, activity variability and mean field strength.