Volume 600, April 2017
|Number of page(s)||8|
|Section||Galactic structure, stellar clusters and populations|
|Published online||06 April 2017|
The potassium abundance in the globular clusters NGC 104, NGC 6752 and NGC 6809⋆
1 Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Viale Berti Pichat, 6/2, 40127 Bologna, Italy
2 INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
3 Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP.226, Boulevard du Triomphe, 1050 Brussels, Belgium
Received: 9 January 2017
Accepted: 9 February 2017
We derived potassium abundances in red-giant-branch stars in the Galactic globular clusters NGC 104 (144 stars), NGC 6752 (134 stars), and NGC 6809 (151 stars) using high-resolution spectra collected with FLAMES at the ESO – Very Large Telescope. In the samples we consider, we do not find significant intrinsic spreads in [K/Fe], which confirms the previous findings, but which is at variance with the cases of the massive clusters NGC 2419 and NGC 2808. Additionally, marginally significant [K/Fe]−[O/Fe] anti-correlations are found in NGC 104 and NGC 6809, and [K/Fe]−[Na/Fe] correlations are found in NGC 104 and NGC 6752. 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 also implies 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 so far only been found in clusters harbouring some Mg-poor stars, while the other globulars, without a Mg-poor sub-population, show small or null [K/Fe] spreads.
Key words: techniques: spectroscopic / globular clusters: individual: NGC 104 / globular clusters: individual: NGC 6752 / globular clusters: individual: NGC 6809 / stars: abundances
Full Table 1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/600/A104
© ESO, 2017
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