Host--Non-host Differences in Stellar Chemistry, Activity, and Birth Radius: Hints of Distinct Formation Environments for Earth-like Planets and Sub-Neptunes

Abstract

Host-star properties provide important clues to planet formation and evolution, yet it remains unclear whether the observed differences between planet-hosting stars and stars without detected planets reflect genuine signatures of planet formation or underlying differences in stellar populations. Using a homogeneous sample of 28,383 Kepler-LAMOST-Gaia dwarf and subgiant stars, including 629 host stars with 865 planets, we compare host stars with age-mass matched non-host stars after correcting for distribution-induced matching biases. Most host-non-host differences disappear when the full planet sample is considered. However, separating planets by radius reveals distinct trends. At the high-abundance end of the [O/Fe], [Mg/Fe], and [Si/Fe] distributions, Earth-like hosts tend to be more O-rich but more Mg-poor and Si-poor than their age-mass matched non-host stars, whereas sub-Neptune hosts tend to show the opposite behavior. Sub-Neptune hosts also tend to exhibit lower chromospheric activity and smaller birth radii than comparable non-host stars. These results suggest that host-non-host differences become apparent primarily after separating planets by size and that Earth-like planets and sub-Neptunes may be associated with distinct formation environments and evolutionary pathways. We also find that hot-Jupiter hosts are tentatively more metal-rich, chromospherically active, and formed at smaller Galactic birth radii than hosts of longer-period Jupiters.