The internal magnetic fields of cool stars are known to power activity in stellar chromospheres, but there is still much to discover about the relationship between the large-scale magnetic field and chromospheric activity. We have revisited this relationship by surveying the chromospheric activity (logR'HK) and surface-averaged longitudinal magnetic field strength (Bl) for 954 mid-F to mid-M dwarf stars using observations from 3 the PolarBase spectropolarimetric database. We computed the mean logR'HK, mean Bl and their variability amplitudes from time-series observations, and found that for F, K and M stars, the mean logR'HK declines fairly smoothly with the mean logBl and also the amplitude of logR'HK variability. Meanwhile, for G stars on the main sequence, chromospheric activity appears to drop from logR'HK ~ -4.4 to -4.8, with minimal change in the logBl and the amplitude of logR'HK variability. At a similar logR'HK level, we also see a switch from mixed magnetic field geometries to dominantly poloidal magnetic field geometries, as shown by published large-scale magnetic field maps derived using Zeeman Doppler Imaging. These results support a change in the magnetic surface properties of G stars that occurs on the main sequence.

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