  Recent studies of chemical abundances in metal-poor Halo stars show the
existence of different populations, which is important for studies of Galaxy
formation and evolution. Here we revisit the twin pair of chemically anomalous
stars HD 134439 and HD 134440, using high resolution (R $\sim 72 000$) and high
S/N ratio (S/N $\sim 250$) HDS/Subaru spectra. We compare them to the
well-studied Halo star HD 103095, using the line-by-line differential technique
to estimate precise stellar parameters and LTE chemical abundances. We present
the abundances of C, O, Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Sr,
Y, Ba, La, Ce, Nd, and Sm. We compare our results to the precise abundance
patterns of Nissen & Schuster (2010) and data from dwarf Spheroidal Galaxies
(dSphs). We show that the abundance pattern of these stars appears to be
closely linked to that of dSphs with [$\alpha$/Fe] knee below [Fe/H] $<-1.5$.
We also find a systematic difference of $0.06\pm0.01$ dex between the
abundances of these twin binary stars, which could be explained by the
engulfment of a planet, thus suggesting that planet formation is possible at
low metallicities ([Fe/H]=$ -1.4$).
