Fluorine Abundance Variations in Red Giants of the Globular Cluster M4 and Early‐Cluster Chemical Pollution

We present fluorine abundances in seven red-giant members of the globularcluster M4 (NGC 6121). These abundances were derived from the HF (1--0) R9 lineat 2.3357 microns in high-resolution infrared spectra obtained with the Phoenixspectrograph on Gemini-South. Many abundances in the target stars have beenstudied previously, so that their overall abundance distributions arewell-mapped. The abundance of fluorine is found to vary by more than a factorof 6, with the F-19 variations being correlated with the already establishedoxygen variations, and anti-correlated with the sodium and aluminiumvariations. In this paper we thus add fluorine to the list of elements known tovary in globular cluster stars, and this provides further evidence thatH-burning is the root cause of the chemical inhomegeneities. The fact that F-19is found to decrease in the M4 stars, as the signature of H-burning appears,indicates that the polluting stars must have masses greater than about 3.5solar masses, as less massive stars than this should produce, not destroy,fluorine.Comment: Astrophysical Journal, accepted and in-pres