Influence of Stellar Metallicity on Occurrence Rates of Planets and Planetary Systems

Abstract

We study the influence of stellar metallicity on the fraction of stars with planets (i.e., the occurrence rate of planetary systems) and the average number of planets per star (i.e., the occurrence rate of planets). The former directly reveals the planet formation efficiency, whereas the latter reveals the final product of formation and evolution. We show that these two occurrence rates have different dependences on stellar metallicity. Specifically, the fraction of stars with planets rises gradually with metallicity, from $\sim$25% to $\sim$36% for 0.4 dex of [Fe/H] for all Kepler-like planets (period $P<400$ days and radius $R_{\rm p}\gtrsim R_\oplus$). The average number of planets per star reaches a plateau (or possibly starts declining) at [Fe/H]$\gtrsim0.1$. This is plausibly caused by the emergence of distant giant planets at high metallicities, given that the close-in small planets and the distant giants preferentially co-exist in the same system.