DETAILED ABUNDANCES OF PLANET-HOSTING WIDE BINARIES. I. DID PLANET FORMATION IMPRINT CHEMICAL SIGNATURES IN THE ATMOSPHERES OF HD 20782/81?

Abstract

Using high-resolution echelle spectra obtained with Magellan/MIKE, we present\na chemical abundance analysis of both stars in the planet-hosting wide binary\nsystem HD20782 + HD20781. Both stars are G dwarfs, and presumably coeval,\nforming in the same molecular cloud. Therefore we expect that they should\npossess the same bulk metallicities. Furthermore, both stars also host giant\nplanets on eccentric orbits with pericenters $\\lesssim 0.2\\,$ AU. We\ninvestigate if planets with such orbits could lead to the host stars ingesting\nmaterial, which in turn may leave similar chemical imprints in their\natmospheric abundances. We derived abundances of 15 elements spanning a range\nof condensation temperatures ($T_{C}\\approx 40-1660\\,$ K). The two stars are\nfound to have a mean element-to-element abundance difference of $0.04\\pm0.07\\,$\ndex, which is consistent with both stars having identical bulk metallicities.\nIn addition, for both stars, the refractory elements ($T_{C} > 900\\,$ K)\nexhibit a positive correlation between abundance (relative to solar) and\n$T_{C}$, with similar slopes of $\\approx$ $1\\times10^{-4}\\,$ dex K$^{-1}$. The\nmeasured positive correlations are not perfect; both stars exhibit a scatter of\n$\\approx$ $5\\times10^{-5}\\,$ dex K$^{-1}$ about the mean trend, and certain\nelements (Na, Al, Sc) are similarly deviant in both stars. These findings are\ndiscussed in the context of models for giant planet migration that predict the\naccretion of H-depleted rocky material by the host star. We show that a simple\nsimulation of a solar-type star accreting material with Earth-like composition\npredicts a positive---but imperfect---correlation between refractory elemental\nabundances and $T_{C}$. Our measured slopes for HD 20782/81 are consistent with\nwhat is predicted for the ingestion of 10--20 Earths by both stars.\n