# The Potassium abundance in the globular clusters NGC104, NGC6752 and NGC6809

## TL;DR

This study measures potassium abundances in red giant stars across three globular clusters, finding limited intrinsic variation and correlations with other elements, supporting the idea that cluster multi-populations involve potassium enrichment linked to extreme oxygen and magnesium depletion.

## Contribution

It provides the first extensive potassium abundance analysis in these clusters, confirming limited spread and specific element correlations, and supports models of multi-population enrichment involving potassium.

## Key findings

- No significant intrinsic [K/Fe] spreads in the studied clusters.
- Marginal [K/Fe]-[O/Fe] anti-correlations in NGC104 and NGC6809.
- [K/Fe]-[Na/Fe] correlations observed in NGC104 and NGC6752.

## Abstract

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.