Rocky planet engulfment in the binary system HIP 71726-37

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.