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

Abstract

Spectropolarimetric data allow for simultaneous monitoring of stellar chromospheric log R 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 log R 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 surv e ys that focus on inactive planet-search targets. We find a positive correlation between mean log R HK and mean log | B l | , but for G stars the relationship may undergo a change between log R HK ∼−4 . 4 and −4.8. The mean log R HK shows a similar change with respect to the log R HK variability amplitude for intermediately active G stars. We also combine our results with archi v al chromospheric acti vity data and published observ ations 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 ≤log R 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 log R HK variability amplitudes. Chromospheric activity, acti vity v ariability, and toroidal field strength decrease on the main sequence as rotation slo ws. For G stars, the disappearance of dominant toroidal fields occurs at a similar chromospheric acti vity le vel as the change in the relationships between chromospheric acti vity, acti vity v ariability, and mean field strength.