Potassium: A New Actor on the Globular Cluster Chemical Evolution Stage. The Case of NGC 2808

Journal
Date Issued
2015
Author(s)
•
•
Merle, Thibault
•
Plez, Bertrand
•
•
Ibata, Rodrigo
DOI
Description
We warmly thank the anonymous referee for suggestions in improving the paper. M.B. acknowledges the financial support from PRIN MIUR 2010-2011 project “The Chemical and Dynamical Evolution of the Milky Way and Local Group Galaxies,” prot. 2010LY5N2T. T.M. is supported by the FNRS-F.R.S. as a temporary post-doctoral researcher under grant No. 2.4513.11.
Abstract
We derive [K/Fe] abundance ratios for 119 stars in the globular cluster NGC 2808, all of them having O, Na, Mg, and Al abundances homogeneously measured in previous works. We detect an intrinsic star-to-star spread in the potassium abundance. Moreover [K/Fe] abundance ratios display statistically significant correlations with [Na/Fe] and [Al/Fe], and anti-correlations with [O/Fe] and [Mg/Fe]. All the four Mg deficient stars ([Mg/Fe] < 0.0) discovered so far in NGC 2808 are enriched in K by ~0.3 dex with respect to those with normal [Mg/Fe]. NGC 2808 is the second globular cluster, after NGC 2419, where a clear Mg-K anti-correlation is detected, albeit of weaker amplitude. The simultaneous correlation/anti-correlation of [K/Fe] with all the light elements usually involved in the chemical anomalies observed in globular cluster stars strongly support the idea that these abundance patterns are due to the same self-enrichment mechanism that produces Na-O and Mg-Al anti-correlations. This finding suggests that detectable spreads in K abundances may be typical in the massive globular clusters where the self-enrichment processes are observed to produce their most extreme manifestations.

Based on data obtained at the ESO Very Large Telescope under the programs 072.D-0507 and 091.D-0329.

Volume
801
Issue
1
Start page
68
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...801...68M
Rights
open.access
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