CNO and F abundances in the globular cluster M22 (NGC 6656)

Recent studies have confirmed the long standing suspicion that M22 shares a metallicity spread and complex chemical enrichment history similar to that observed in omega Cen. To further constrain the chemical diversity of M22, necessary to interpret its nucleosynthetic history, the authors seek to measure relative abundance ratios of key elements carbon, nitrogen, oxygen, and fluorine best studied, or only available, using high-resolution spectra at infrared wavelengths. Chemical abundances were calculated through a standard 1D local thermodynamic equilibrium analysis using Kurucz model atmospheres. The authors derive Fe/H = -1.87 to -1.44, confirming at infrared wavelengths that M22 does present a Fe/H spread. They also find large C and N abundance spreads, which confirm previous results in the literature but based on a smaller sample. Their study confirms and expands upon the chemical diversity seen in this complex stellar system. All elements studied to date show large abundance spreads which require contributions from both massive and low mass stars.