  Terzan 5 is a stellar system located in the inner Bulge of the Galaxy and has
been historically catalogued as a globular cluster. However, recent photometric
(Ferraro et al. 2009) and spectroscopic (Origlia et al. 2011; Origlia et al.
2013) investigations have shown that it hosts at least three stellar
populations with different iron abundances (with a total spread of
Delta[Fe/H]>1 dex) thus demonstrating that Terzan 5 is not a genuine globular
cluster. In addition, the striking similarity between the chemical patterns of
this system and those of its surrounding environment, the Galactic Bulge, from
the point of view of both the metallicity distribution and the alpha-element
enrichment, suggests that Terzan 5 could be a pristine fragment of the Bulge
itself.

Astrophysics of Galaxies