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

Abstract

We report on the detection of two Zn I lines at 4722.15Å and 4810.53Å 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 under abundance of Zn by ~-1.3 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 (>4dex) 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 [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 5159.03Å along with the already known Fe II 4923.93Å line; based on these two lines the Fe abundance of HR 4049 is determined to be ~2.8 ([Fe/H] ~-4.7).