On the Metal-Richness of M Dwarfs with Planets

Knowledge of the metallicities of M dwarfs rests predominantly on the photometric calibration of Bonfils and collaborators, which predicts that M dwarfs in the solar neighborhood, including those with known planets, are systematically metal-poor compared to their higher-mass counterparts. We test this prediction using a volume-limited sample of low-mass stars, together with a subset of M dwarfs with high-metallicity, F, G amd K wide binary companions. We find that the Bonfils et al. photometric calibration systematically underestimates the metallicities of our high-metallicity M dwarfs by an average of 0.32 dex. We derive a new photometric metallicity calibration and show that M dwarfs with planets appear to be systematically metal-rich, a result that is consistent with the metallicity distribution of FGK dwarfs with planets.

💡 Research Summary

The paper addresses a long‑standing problem in the determination of metallicities for M‑type dwarfs (M dwarfs). For more than a decade the community has relied on the photometric calibration introduced by Bonfils et al. (2005), which uses the V–K colour and absolute K‑band magnitude (M_K) to estimate