Detection of Fluorine in the Halo Planetary Nebula BoBn 1: Evidence For a Binary Progenitor Star

We have found the fluorine lines [F IV] 3996.92A,4059.90A in the extremely metal-poor ([Ar/H] = -2.10+/-0.21) halo planetary nebula (PN) BoBn 1 in high-dispersion spectra from the 8.2-m VLT/UVES archive. Chemical abundance analysis shows that the fluorine abundance is [F/H] = +1.06+/-0.08, making BoBn 1 the most fluorine-enhanced and metal-poor PN among fluorine-detected PNe and providing new evidence that fluorine is enhanced by nucleosynthesis in low mass metal-poor stars. A comparison with the abundances of carbon-enhanced metal-poor (CEMP) stars suggests that BoBn 1 shares their origin and evolution with CEMP-s stars such as HE1305+0132. BoBn 1 might have evolved from a binary consisting of ~2 Msun primary and ~0.8 Msun secondary stars.