New insights on the relation between stellar metallicity and the architectures of planetary systems

Correlations between stellar and planetary properties provide important information about the processes of planet formation and evolution and the resulting architectures of planetary systems. Recent studies have provided evidence that higher stellar metallicities are connected to the presence of planets of certain sizes and orbital periods. In this work, we explored these relations further by focusing on planetary systems instead of individual planets. We derived independent and homogeneous iron abundances for a sample of 1005 planet hosting stars from the California-Kepler Survey (CKS) using a classical LTE spectroscopic analysis. Although we confirmed the well-known result that the metallicities of stars hosting large planets are significantly skewed to higher metallicities relative to systems with only small planets, we also found that the boundary between the large- and small-planet regimes occurs at Rp = 4.4 R_Earth. We observed that the previously reported differences between the host-star metallicity distributions for hot and warm planets also hold for planetary systems, with the former being more metal-rich. However, we show that planet multiplicity also plays an important role and these differences seem to be larger for multiple relative to single planet systems. The most significant difference is seen for systems hosting only Super-Earths and a similar result is not found for systems hosting only Sub-Neptunes, revealing an important distinction within the regime of small planets.