Potassium: a new actor on the globular cluster chemical evolution stage. The case of NGC 2808

TL;DR

This study reveals that potassium abundance varies among stars in NGC 2808 and correlates with other light elements, indicating a common self-enrichment process influencing globular cluster chemical evolution.

Contribution

It is the first to identify a Mg-K anti-correlation in NGC 2808, suggesting potassium's role in globular cluster chemical anomalies and self-enrichment processes.

Findings

Detected star-to-star spread in [K/Fe] in NGC 2808.

Found correlations of [K/Fe] with [Na/Fe] and [Al/Fe].

Observed anti-correlations of [K/Fe] with [O/Fe] and [Mg/Fe].

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.