Abundance Differences Between Exoplanet Binary Host Stars XO-2N and XO-2S -- Dependence on Stellar Parameters

TL;DR

This study analyzes the chemical abundance differences between binary star hosts of exoplanets, highlighting how stellar parameters influence observed elemental variations and identifying elements consistently enhanced in one star.

Contribution

It provides a differential abundance analysis of the XO-2 binary system, exploring how stellar parameters affect abundance differences and emphasizing the importance of binary systems in planet formation studies.

Findings

Fe, Si, and potentially Ni are consistently enhanced in XO-2N.

Abundance differences depend heavily on stellar parameter choices.

Binary star analysis helps isolate effects of planet formation on stellar composition.

Abstract

The chemical composition of exoplanet host stars is an important factor in understanding the formation and characteristics of their orbiting planets. The best example of this to date is the planet-metallicity correlation. Other proposed correlations are thus far less robust, in part due to uncertainty in the chemical history of stars pre- and post-planet formation. Binary host stars of similar type present an opportunity to isolate the effects of planets on host star abundances. Here we present a differential elemental abundance analysis of the XO-2 stellar binary, in which both G9 stars host giant planets, one of which is transiting. Building on our previous work, we report 16 elemental abundances and compare the $\Delta$(XO-2N-XO-S) values to elemental condensation temperatures. The $\Delta$(N-S) values and slopes with condensation temperature resulting from four different pairs of stellar parameters are compared to explore the effects of changing the relative temperature and gravity of the stars. We find that most of the abundance differences between the stars depend on the chosen stellar parameters, but that Fe, Si, and potentially Ni are consistently enhanced in XO-2N regardless of the chosen stellar parameters. This study emphasizes the power of binary host star abundance analysis for probing the effects of giant planet formation, but also illustrates the potentially large uncertainties in abundance differences and slopes induced by changes in stellar temperature and gravity.