Detailed abundances of the planet-hosting TOI-1173 A/B system: Possible evidence of planet engulfment in a very wide binary

TL;DR

This study investigates chemical signatures in the wide binary system TOI-1173 A/B, providing evidence of planet engulfment in the planet-hosting star, and explores the implications for planetary system evolution.

Contribution

It presents the first detailed chemical abundance analysis of a wide binary with a known exoplanet, suggesting planet engulfment as a key process in planetary system development.

Findings

TOI-1173 A shows refractory element enhancement indicating planet engulfment.

The system's dynamics support planet migration and engulfment scenarios.

Evidence of rocky material accretion (~18 Earth masses) in star A.

Abstract

Over the last decade, studies of large samples of binary systems identified chemical anomalies, and showed that they might be attributed to planet formation or planet engulfment. However, both scenarios have primarily been tested in pairs without known exoplanets. In this work, we explore these scenarios in the newly detected planet-hosting wide binary TOI-1173 A/B (projected separation $\sim 11,400$ AU) using high-resolution MAROON-X and ARCES spectra. We determined photospheric stellar parameters both by fitting stellar models and via the spectroscopic equilibrium approach. Both analyses agree and suggest that they are cool main sequence stars located in the thin disc. A line-by-line differential analysis between the components (B$-$A) displays an abundance pattern in the condensation temperature plane where the planet-hosting star TOI-1173 A is enhanced in refractory elements such as iron by more than 0.05 dex. This suggests the engulfment of $\sim$18 M$_{\oplus}$ of rocky material in star A. Our hypothesis is supported by the dynamics of the system detailed in our companion paper Yana Galarza et al. 2024, which suggest that the Super-Neptune TOI-1173 A $b$ might have been delivered to its current short period ($\sim7$ days) through circulatization and von Zeipel-Lidov-Kozai mechanisms, thereby triggering the engulfment of inner rocky exoplanets.