Binary Stars HD80606 & HD80607 Have an Interesting History for the Gas Giant's Migration Causing no Rocky Exoplanets to Form

Detailed Abundances of Planet-Hosting Wide Binaries. II. HD80606 + HD80607

Authors:

Mack et al

Abstract:

We present a detailed chemical abundance analysis of 15 elements in the planet-hosting wide binary system HD80606 + HD80607 using Keck/HIRES spectra. As in our previous analysis of the planet-hosting wide binary HD20782 + HD20781, we presume that these two G5 dwarf stars formed together and therefore had identical primordial abundances. In this binary, HD80606 hosts an eccentric (e≈0.93) giant planet at ∼0.5 AU, but HD80607 has no detected planets. If close-in giant planets on eccentric orbits are efficient at scattering rocky planetary material into their host stars, then HD80606 should show evidence of having accreted rocky material while HD80607 should not. Here we show that the trends of abundance versus element condensation temperature for HD80606 and HD80607 are statistically indistinguishable, corroborating the recent result of Saffe et al. This could suggest that both stars accreted similar amounts of rocky material; indeed, our model for the chemical signature of rocky planet accretion indicates that HD80606 could have accreted up to 2.5~M⊕ of rocky material---about half that contained in the Solar System and primordial asteroid belt---relative to HD80607 and still be consistent with the data. Since HD80607 has no known giant planets that might have pushed rocky planet material via migration onto that star, we consider it more likely that HD80606/07 experienced essentially no rocky planet accretion. This in turn suggests that the migration history of the HD80606 giant planet must have been such that it ejected any close-in planetary material that might have otherwise been shepherded onto the star.