A chemo-dynamical search for planet-candidate hosts of possible extragalactic origin

Abstract: To date, all known exoplanetary systems have been identified around stars currently residing in the Milky Way, whereas planets formed in external galaxies remain largely unexplored. Such systems would offer a unique probe of planet formation in galactic environments distinct from the Milky Way. We combine a literature-compiled sample of Kepler, K2, and TESS planet-candidate host stars with Gaia DR3 astrometry and radial velocities, and incorporate metallicities and [Mg/Fe] abundances from the LAMOST DR9 DD-Payne catalogue, to search for candidate accreted-halo planet hosts. We identify 11 planet-candidate hosts with halo-like kinematics, five of which have reliable chemical abundance measurements. Among these, four systems exhibit low metallicities ([Fe/H]<-0.7) and low [Mg/Fe] ratios that are inconsistent with the canonical Milky Way thick-disc sequence, indicative of enrichment histories characteristic of accreted dwarf galaxies. We further carry out a uniform false-positive assessment using Gaia RUWE, Gaia DR3 neighbourhood checks, odd--even transit-depth comparisons, secondary-eclipse searches, independent BLS period recovery, and comparison with ExoFOP and available follow-up information. This vetting identifies EPIC~211407755 and TIC~239541449 as the most plausible, although still unvalidated, planet-candidate systems. TIC~293432942 is more likely associated with a blended or otherwise binary-related false positive, whereas TIC~184739529 remains a high-risk giant-companion candidate whose planetary nature is uncertain. If confirmed, EPIC~211407755 and TIC~239541449 would suggest that planetary systems can form in dwarf-galaxy environments and subsequently survive accretion into the Milky Way.