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tokens: 6 are heavily driven by the differential abundances of the most volatile species, such as C, CH, O, and N (i.e., T Cond 200 K). In fact, the number of volatiles is much smaller than the number of refractory elements, as is visible in Figure 1 . In addition, the chemical abundances of volatile elements are often more uncertain than those of refractories. In the case of HIP 34407/HIP 34426, the chemical anomaly is extremely large compared to all the other pairs. The elements with an intermediate condensation temperature, such as Na, S, and Zn (i.e., 500 T Cond 1000 K) are well aligned by the Δ[X/H]– T Cond relation plotted in Figure 1 . This neat linear relation between elemental abundances and condensation temperature for this system may suggest that the anomaly was caused by a planetary engulfment event. Similar results were independently obtained by Ramirez et al. ( 2019 ). Interestingly, the HIP 34407/HIP 34426 system was determined to be the most chemically inhomogeneous system found to date among other pairs in binary systems or clusters, that show similar trends between abundances and condensation temperature (Tucci Maia et al. 2014 , 2019 ; Biazzo et al. 2015 ; Spina et al. 2015 , 2018 ; Teske et al. 2015 , 2016 ; Saffe et al. 2016 , 2017 ; Oh et al. 2018 ). Its median differential abundance in the refractory elements is 0.19 dex. In addition, we note that the results from the HIP 34407/HIP 34426 system involve similar but not identical volatile elemental abundances. Out of the four most volatile species measured (i.e., ), only one is consistent with zero, leading to the hypothesis that the slope is due to the engulfment of a gas giant. This is because such planets are capable of causing abundance changes in both volatiles (due to their gaseous outer layers) and refractories (due to their rocky cores and metallic inner layers). This hypothesis has been also proposed to explain a similar anomaly observed in the chemical composition of the 16 Cyg binary system (Tucci Maia et al. 2014 , 2019 ). 4. Conclusions The occurrence of chemically anomalous stars at the 0.01 dex precision level can be deduced from line-by-line differential analysis of twin stars in binary systems. Out of the 14 systems measured using UVES and HDS, 6 were found to exhibit chemical inhomogeneities (i.e., σ χ ), rendering chemical tagging on these systems inaccurate. However, only two pairs were chemically inhomogeneous at the precision level typical of large spectroscopic surveys (i.e., 0.05 dex). Of special note is that the HIP 34407/HIP 34426 system was determined to be the most chemically inhomogeneous system found to date. For this pair, the trend between differential abundances and condensation temperature is neat, and it may suggest that rocky material has polluted the atmosphere of HIP 34407. We speculated that the planet engulfed by the star was a giant gaseous planet, as HIP 34426 is also anomalously rich in the volatiles. The planet population around the