Fluorine in R Coronae Borealis Stars

TL;DR

This study detects fluorine in R Coronae Borealis stars, revealing significant overabundances that suggest fluorine synthesis, and compares these findings with other stellar objects to understand stellar evolution.

Contribution

First measurement of fluorine abundance in R Coronae Borealis stars, providing evidence for fluorine synthesis and implications for stellar evolution models.

Findings

Fluorine is enriched by factors of 800 to 8000 in some RCBs.

F I lines are not detected in Sakurai's object, a final He-shell flash product.

Results support fluorine synthesis during RCB star formation.

Abstract

Neutral fluorine (F I) lines are identified in the optical spectra of several R Coronae Borealis stars (RCBs) at maximum light. These lines provide the first measurement of the fluorine abundance in these stars. Fluorine is enriched in some RCBs by factors of 800 to 8000 relative to its likely initial abundance. The overabundances of fluorine are evidence for the synthesis of fluorine. These results are discussed in the light of the scenario that RCBs are formed by accretion of an He white dwarf by a C-O white dwarf. Sakurai's object (V4334 Sgr), a final He-shell flash product, shows no detectable F I lines.