# Fluorine Abundances in the Globular Cluster M 4

## TL;DR

This study measures fluorine, carbon, and sodium abundances in red giants of globular clusters M 4 and $$ Centauri, revealing fluorine depletion correlated with sodium enhancement and comparing observations with stellar evolution models.

## Contribution

First detailed fluorine abundance analysis in M 4 and $$ Centauri red giants using high-resolution near-infrared spectra, highlighting abundance anti-correlations.

## Key findings

- Fluorine abundances are significantly lower than previous literature values.
- F abundance is anti-correlated with Na, consistent with globular cluster patterns.
- Models predict less F depletion than observed for Na enhancement.

## Abstract

We present chemical abundances for the elements carbon, sodium, and fluorine in 15 red giants of the globular cluster M 4, as well as six red giants of the globular cluster $\omega$ Centauri. The chemical abundances were calculated in LTE via spectral synthesis. The spectra analyzed are high-resolution spectra obtained in the near-infrared region around $\lambda$2.3$\mu$m with the Phoenix spectrograph on the 8.1m Gemini South Telescope, the IGRINS spectrograph on the McDonald Observatory 2.7m Telescope, and the CRIRES spectrograph on the ESO 8.2m Very Large Telescope. The results indicate a significant reduction in the fluorine abundances when compared to previous values from the literature for M 4 and $\omega$ Centauri, due to a downward revision in the excitation potentials of the HF(1-0) R9 line used in the analysis. The fluorine abundances obtained for the M 4 red giants are found to be anti-correlated with those of Na, following the typical pattern of abundance variations seen in globular clusters between distinct stellar populations. In M 4, as the Na abundance increases by $\sim$+0.4 dex, the F abundance decreases by $\sim$-0.2 dex. A comparison with abundance predictions from two sets of stellar evolution models finds that the models predict somewhat less F depletion ($\sim$-0.1 dex) for the same increase of +0.4 dex in Na.