Rocky planet engulfment in the binary system HIP 71726-37

TL;DR

This study investigates chemical differences in the binary system HIP 71726/37, providing evidence that planet engulfment can cause significant elemental and lithium abundance variations between stellar companions.

Contribution

It presents the first detailed chemical analysis of HIP 71726/37, demonstrating planet engulfment as a plausible explanation for observed abundance differences in a binary system.

Findings

HIP 71726 is more metal-rich than HIP 71737 in refractory elements.

HIP 71726 has a lithium abundance 1.03 dex higher than HIP 71737.

Engulfment of approximately 9.8 Earth masses of rocky material explains the observed chemical differences.

Abstract

Binary stars are supposed to be chemically homogeneous, as they are born from the same molecular cloud. However, high precision chemical abundances show that some binary systems display chemical differences between the components, which could be due to planet engulfment. In this work, we determine precise fundamental parameters and chemical abundances for the binary system HIP 71726/ HIP 71737. Our results show that the pair is truly conatal, coeval and comoving. We also find that the component HIP 71726 is more metal-rich than HIP 71737 in the refractory elements such as iron, with $\Delta$[Fe/H] $= 0.11 \pm 0.01$ dex. Moreover, HIP 71726 has a lithium abundance 1.03 dex higher than HIP 71737, which is the largest difference in Li detected in twin-star binary systems with $\Delta$ $T_{\rm eff}$ $\leq$ 50 K. The ingestion of $9.8^{+2.0}_{-1.6}$ M$_{\oplus}$ of rocky material fully explains both the enhancement in refractory elements and the high Li content observed in HIP 71726, thereby reinforcing the planet engulfment scenario in some binary systems.