Fluorine in the Solar neighborhood: No evidence for the neutrino process

TL;DR

This study measures fluorine in nearby stars to determine its main cosmic sources, finding no evidence that type II supernovae are the dominant producers in the Solar neighborhood, thus challenging previous assumptions.

Contribution

It provides observational evidence against type II supernovae as the main fluorine source, favoring Asymptotic Giant Branch and Wolf-Rayet stars, and refines stellar production models.

Findings

Fluorine and alpha-elements do not evolve together.

Fluorine shows secondary behavior relative to oxygen.

Type II supernovae are unlikely the main fluorine producers.

Abstract

Asymptotic Giant Branch stars are known to produce `cosmic' fluorine but it is uncertain whether these stars are the main producers of fluorine in the Solar neighborhood or if any of the other proposed formation sites, type II supernovae and/or Wolf-Rayet stars, are more important. Recent articles have proposed both Asymptotic Giant Branch stars as well as type II supernovae as the dominant sources of fluorine in the Solar neighborhood. In this paper we set out to determine the fluorine abundance in a sample of 49 nearby, bright K-giants for which we previously have determined the stellar parameters as well as alpha abundances homogeneously from optical high-resolution spectra. The fluorine abundance is determined from a 2.3 $\mu$m HF molecular line observed with the spectrometer Phoenix. We compare the fluorine abundances with those of alpha elements mainly produced in type II supernovae and find that fluorine and the alpha-elements do not evolve in lock-step, ruling out type II supernovae as the dominating producers of fluorine in the Solar neighborhood. Furthermore, we find a secondary behavior of fluorine with respect to oxygen, which is another evidence against the type II supernovae playing a large role in the production of fluorine in the Solar neighborhood. This secondary behavior of fluorine will put new constraints on stellar models of the other two suggested production sites: Asymptotic Giant Branch stars and Wolf-Rayet stars.