A phylogenetic approach to chemical tagging. Reassembling open cluster
  stars
  Context. The chemical tagging technique is a promising approach to
reconstruct the history of the Galaxy by only using stellar chemical
abundances. Different studies have undertaken this analysis and they raised
several challenges.
  Aims. Using a sample of open clusters stars, we wish to address two issues:
minimize chemical abundance differences which origin is linked to the
evolutionary stage of the stars and not their original composition; evaluate a
phylogenetic approach to group stars based on their chemical composition.
  Methods. We derived differential chemical abundances for 207 stars (belonging
to 34 open clusters) using the Sun as reference star (classical approach) and a
dwarf plus a giant star from the open cluster M67 as reference (new approach).
These abundances were then used to perform two phylogenetic analyses,
cladistics (Maximum Parsimony) and Neighbour-Joining, together with a
partitioning unsupervised classification analysis with k-means. The resulting
groupings were finally confronted to the true open cluster memberships of the
stars.
  Results. We successfully reconstruct most of the original open clusters when
carefully selecting a subset of the abundances derived differentially with
respect to M67. We find a set of eight chemical elements that yields the best
result, and discuss the possible reasons for them to be good tracers of the
history of the Galaxy.
  Conclusions. Our study shows that unraveling the history of the Galaxy by
only using stellar chemical abundances is greatly improved provided that i) we
perform a differential spectroscopic analysis with respect to an open cluster
instead of the Sun, ii) select the chemical elements that are good tracers of
the history of the Galaxy, and iii) use tools that are adapted to detect
evolutionary tracks such as phylogenetic approaches.
