The Potassium abundance in the globular clusters NGC104, NGC6752 and
  NGC6809
  We derived Potassium abundances in red giant branch stars in the Galactic
globular clusters NGC104 (144 stars), NGC6752 (134 stars) and NGC6809 (151
stars) using high-resolution spectra collected with FLAMES at the ESO - Very
Large Telescope. In the considered samples we do not find significant intrinsic
spreads in [K/Fe] (confirming the previous findings by Carretta et al.), at
variance with the cases of the massive clusters NGC2419 and NGC2808.
Additionally, marginally significant [K/Fe]-[O/Fe] anti-correlations are found
in NGC104 and NGC6809, and [K/Fe]-[Na/Fe] correlations are found in NGC104 and
NGC6752. No evidence of [K/Fe]-[Mg/Fe] anti-correlation are found. The results
of our analysis are consistent with a scenario in which the process leading to
the multi-populations in globular clusters implies also enrichment in the K
abundance, the amplitude of the associated [K/Fe] enhancement becoming
measurable only in stars showing the most extreme effects of O and Mg
depletion. Stars enhanced in [K/Fe] have been found so far only in clusters
harbouring some Mg-poor stars, while the other globulars, without a Mg-poor
sub-population, show small or null [K/Fe] spreads.
