Fluorine in the solar neighborhood - is it all produced in AGB-stars?

TL;DR

This study investigates the origin of fluorine in the solar neighborhood, using new infrared spectral lines to determine its abundance and suggesting AGB stars as the primary source based on chemical evolution models.

Contribution

It introduces the first use of the 12.2 μm pure rotational HF line for fluorine abundance analysis and compares it with vibrational-rotational lines, supporting AGB stars as the main fluorine source.

Findings

Abundances from the two HF diagnostics agree.

Chemical models with AGB star production match observed fluorine levels.

12 μm HF lines are effective for studying fluorine in different environments.

Abstract

The origin of 'cosmic' fluorine is uncertain, but there are three proposed production sites/mechanisms: AGB stars, $\nu$ nucleosynthesis in Type II supernovae, and/or the winds of Wolf-Rayet stars. The relative importance of these production sites has not been established even for the solar neighborhood, leading to uncertainties in stellar evolution models of these stars as well as uncertainties in the chemical evolution models of stellar populations. We determine the fluorine and oxygen abundances in seven bright, nearby giants with well-determined stellar parameters. We use the 2.3 $\mu$m vibrational-rotational HF line and explore a pure rotational HF line at 12.2 $\mu$m. The latter has never been used before for an abundance analysis. To be able to do this we have calculated a line list for pure rotational HF lines. We find that the abundances derived from the two diagnostics agree. Our derived abundances are well reproduced by chemical evolution models only including fluorine production in AGB-stars and therefore we draw the conclusion that this might be the main production site of fluorine in the solar neighborhood. Furthermore, we highlight the advantages of using the 12 $\mu$m HF lines to determine the possible contribution of the $\nu$-process to the fluorine budget at low metallicities where the difference between models including and excluding this process is dramatic.