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The inhibition of small-scale convection in the Sun dominates the long-termradial velocity (RV) variability: it therefore has a critical effect on lightexoplanet detectability using RV techniques. We here extend our previousanalysis of stellar convective blueshift and its dependence on magneticactivity to a larger sample of stars in order to extend the Teff range, tostudy the impact of other stellar properties, and finally to improve thecomparison between observed RV jitter and expected RV variations. We estimate adifferential velocity shift for Fe and Ti lines of different depths and derivean absolute convective blueshift using the Sun as a reference for a sample of360 F7-K4 stars with different properties (age, Teff, metallicity). We confirmthe strong variation in convective blueshift with Teff and its dependence on(as shown in the line list in Paper I) activity level. Although we do notobserve a significant effect of age or cyclic activity, stars with a highermetallicity tend to have a lower convective blueshift, with a larger effectthan expected from numerical simulations. Finally, we estimate that for 71% ofthe stars in our sample the RV and LogR'HK variations are compatible with theeffect of activity on convection, as observed in the solar case, while for theother stars, other sources (such as binarity or companions) must be invoked toexplain the large RV variations. We also confirm a relationship between LogR'HKand metallicity, which may affect discussions of the possible relationshipbetween metallicity and exoplanets, as RV surveys are biased toward low LogR'HKand possibly toward high-metallicity stars. We conclude that activity andmetallicity strongly affect the small-scale convection levels in stars in theF7-K4 range, with a lower amplitude for the lower mass stars and a largeramplitude for low-metallicity stars.

astronomy and astrophysics

Variability in stellar granulation and convective blueshift with  spectral type and magnetic activity. II. From young to old main-sequence  K-G-F stars