Evolved stars and the origin of abundance trends in planet hosts
  Tentative evidence that the properties of evolved stars with planets may be
different from what we know for MS hosts has been recently reported. We aim to
test whether evolved stars with planets show any chemical peculiarity that
could be related to the planet formation process. We determine in a consistent
way the metallicity and individual abundances of a large sample of evolved
(subgiants and red giants) and MS stars with and without known planetary
companions. No differences in the <[X/Fe]> vs. condensation temperature (Tc)
slopes are found between the samples of planet and non-planet hosts when all
elements are considered. However, if the analysis is restricted to only
refractory elements, differences in the Tc-slopes between stars with and
without known planets are found. This result is found to be dependent on the
stellar evolutionary stage, as it holds for MS and subgiant stars, while there
seem to be no difference between planet and non-planet hosts among the sample
of giants. A search for correlations between the Tc-slope and the stellar
properties reveals significant correlations with the stellar mass and the
stellar age. The data also suggest that differences in terms of mass and age
between MS planet and non-planet hosts may be present. Our results are well
explained by radial mixing in the Galaxy. The sample of giant contains stars
more massive and younger than their MS counterparts. This leads to a sample of
stars possibly less contaminated by stars not born in the solar neighbourhood,
leading to no chemical differences between planet and non planet hosts. The
sample of MS stars may contain more stars from the outer disc (specially the
non-planet host sample) which might led to the differences observed in the
chemical trends.
