Discovery of Carbon/Oxygen depleted Blue Straggler Stars in 47 Tucanae:   the chemical signature of a mass-transfer formation process
  We use high-resolution spectra obtained with the ESO Very Large Telescope to measure surface abundance patterns of 43 Blue Stragglers stars (BSS) in 47 Tuc. We discovered that a sub-population of BSS shows a significant depletion of Carbon and Oxygen with respect to the dominant population. This evidence would suggest the presence of CNO burning products on the BSS surface coming from a deeply peeled parent star, as expected in the case of mass-transfer process. This is the first detection of a chemical signature clearly pointing to a specific BSS formation process in a globular cluster. 
F.R. Ferraro, E. Sabbi, R. Gratton, G. Piotto, B. Lanzoni, E.   Carretta, R.T. Rood, A. Sills, F. Fusi Pecci, S. Moehler, G....