Constraining Exoplanet Compositions via Host Star Abundances

It is an open and actively researched question how/to what extent the presence and chemical compositions of planets correlate with those of their host stars, beyond the well-known giant planet-metallicity correlation. Particularly interesting is the relative importance of elements like C, O, Mg, or Si in the formation and heavy element enrichment of giant planets. The C/O ratio can be indicative of planetary formation history and location, and these are currently the most promising elements for measurement in both star and exoplanet atmospheres. Giant planet formation may be (more strongly) regulated by the presence of more refractory elements, like Si and/or Mg, if cores are dominated by rocky rather than icy material. The formation of small planets does not seem to show the same overall dependence on host star metallicity, but studies of solar twins and analogs suggest the formation of small planets may still imprint a signature on their host star abundances. I will present results of ongoing high resolution, high S/N spectroscopic studies of host star abundances to investigate how/to what extent planet composition, atmospheric and interior, is dependent on host star composition. I will also highlight why binary host stars are a valuable opportunity for disentangling how an individual star’s atmosphere may be affected by the formation of planets and its broader position in/motion through the Galaxy.