  We conducted a high-precision elemental abundance analysis of the twin-star
comoving pair HIP34407/HIP34426. With mean error of 0.013 dex in the
differential abundances (D[X/H]), a significant difference was found: HIP34407
is more metal-rich than HIP34426. The elemental abundance differences correlate
strongly with condensation temperature, with the lowest for the volatile
elements like carbon around 0.05+/-0.02 dex, and the highest up to about
0.22+/-0.01 dex for the most refractory elements like aluminum. Dissimilar
chemical composition for stars in twin-star comoving pairs are not uncommon,
thus we compile previously-published results like ours and look for
correlations between abundance differences and stellar parameters, finding no
significant trends with average effective temperature, surface gravity, iron
abundance, or their differences. Instead, we found a weak correlation between
the absolute value of abundance difference and the projected distance between
the stars in each pair that appears to be more important for elements which
have a low absolute abundance. If confirmed, this correlation could be an
important observational constraint for binary star system formation scenarios.

Solar and Stellar Astrophysics