A Survey of Planet Engulfment Amongst Planet Host Systems

Dynamical evolution within planetary systems can cause planets to be engulfed by their host stars. Following engulfment, the stellar photosphere elemental abundance pattern will reflect accretion of rocky material by exhibiting refractory abundance enhancements. Abundance measurements have occasionally yielded such engulfment signatures, but few observations have targeted systems with known planets. Additionally, the lifetimes of such signatures are poorly constrained. To address these gaps, we took a combined observational and modeling approach by carrying out a Keck-HIRES survey of 36 solar-like planet host binaries, while examining the evolution of engulfment signatures with MESA stellar models that incorporate relevant interior mixing processes e.g., thermohaline instabilities. The modeling results explain the observations; among the 36 systems observed, none exhibit abundance patterns clearly indicative of engulfment events, and our models demonstrate that observable refractory enrichments corresponding to Late Heavy Bombardment (LHB) or rapid engulfment scenarios are depleted on timescales of ~1 Gyr for solar-like stars. This indicates that even if our observed binary systems underwent rapid engulfment or steady LHB-like accretion during the early stages of planetary system evolution, the resultant signatures would not last until the present day. We consider the implications of these results for planetary system dynamical evolution, as well as chemical homogeneity amongst bound stellar companions and assumptions that underpin galactic archaeology.