Title: "Detailed chemical abundances of distant RR Lyrae stars in the Virgo Stellar Stream"

Abstract:
RR Lyrae stars have proven to be excellent tracers of halo substructures, due to the quality of 
the distances that can be derived from them, and the relatively straight forward techniques that 
lead to their clean identification. They have been successfully used in the search and discovery 
of new over densities and streams (Virgo Stellar Stream, Pisces Stream, etc… ) as well as in 
the tracing of already known ones (Sgr Stream).  
However, even when they are excellent for phase-space tracing of the streams, they are 
generally never used to determine the detailed chemistry of the structures they reveal, since 
detailed abundance analysis is difficult for this rapidly pulsating variables. This is unfortunate, 
since the crucial chemical assessment of the substructures must then be derived from other 
stellar populations whose membership to the same substructure is less certain.
We present here the first detailed chemical abundance pattern for distant RR Lyrae stars 
defining the Virgo Stellar Stream, derived from X-Shooter spectra and comprising 15 elements 
from Carbon to Barium, thus sampling all main nucleosynthetic channels. This allows for the 
first time to compare in detail the chemical evolution of the Virgo Stellar Stream progenitor with 
those of local group dwarf galaxies as well as the one of the smooth halo.