Host star metallicities are consistent with core accretion forming close-in Jupiter and low-mass brown dwarf companions

Core accretion is the likely formation process for close-in planets with masses similar to Jupiter; and the enhanced metallicity of the host stars provides strong evidence in favor of this mechanism. Considering the metallicities of stars hosting giant planets, Santos et al. (2017) reported evidence for two regimes of giant planet formation, with the separation occurring at around 4 Jupiter masses. We demonstrate that selection biases account for the metallicity differences seen in the two regimes. Our analysis shows that the metallicities of stars hosting companions from 1 to 50 Jupiter masses are not significantly different. Tentatively, we find that stars with low-mass brown dwarf companions, like those with Jupiter-mass planets, have greater metallicities than stars without giant companions.