Detection of Zinc in the Very Metal-Poor Post-AGB Star HR 4049

Abstract

Abstract We report on the detection of two Zn i lines at 4722.15 Å and 4810.53 Å in the high-quality spectrum of the very metal-poor post-AGB star HR 4049, which was obtained with the High Dispersion Spectrograph attached to the Subaru Telescope. The strengths of these lines indicate an appreciable underabundance of Zn by $ \sim-1.3 \,\mathrm{dex}$ relative to the Sun. The fact that this volatile element, similarly to others belonging to the same group (e.g., C, N, O, S), does not conform to the extreme depletion ($ \gt 4 \,\mathrm{dex}$) of refractory metals (e.g., Fe), strongly suggests that grain formation has something to do with the origin of the chemical peculiarity. This (not extremely but significantly) subsolar value of $ \mathrm{[Zn/H]}$ is quantitatively discussed in connection with those of other volatile species, especially with respect to S. We also detected a new Fe ii line at 5159.03 Å along with the already known Fe ii 4923.93 Å line; based on these two lines the Fe abundance of HR 4049 is determined to be $ \sim 2.8$ ($ \mathrm{[Fe/H]} \sim-4.7$).