  Binary star systems are assumed to be co-natal and coeval, thus to have
identical chemical composition. In this work we aim to test the hypothesis that
there is a connection between observed element abundance patterns and the
formation of planets using binary stars. Moreover, we also want to test how
atomic diffusion might influence the observed abundance patterns. We conduct a
strictly line-by-line differential chemical abundance analysis of 7 binary
systems. Stellar atmospheric parameters and elemental abundances are obtained
with extremely high precision (< 3.5%) using the high quality spectra from
VLT/UVES and Keck/HIRES. We find that 4 of 7 binary systems show subtle
abundance differences (0.01 - 0.03 dex) without clear correlations with the
condensation temperature, including two planet-hosting pairs. The other 3
binary systems exhibit similar degree of abundance differences correlating with
the condensation temperature. We do not find any clear relation between the
abundance differences and the occurrence of known planets in our systems.
Instead, the overall abundance offsets observed in the binary systems (4 of 7)
could be due to the effects of atomic diffusion. Although giant planet
formation does not necessarily imprint chemical signatures onto the host star,
the differences in the observed abundance trends with condensation temperature,
on the other hand, are likely associated with diverse histories of planet
formation (e.g., formation location). Furthermore, we find a weak correlation
between abundance differences and binary separation, which may provide a new
constraint on the formation of binary systems.
