2016MNRAS.461.4071S

We have derived elemental abundances of a remarkable star, HD 179821, with unusual composition (e.g. [Na/Fe]=1.0±0.2 dex) and extra-ordinary spectral characteristics. Its metallicity at [Fe/H]=0.4 dex places it among the most metal-rich stars yet analysed. The abundance analysis of this luminous star is based on high-resolution and high-quality (S/N ≃ 120-420) optical echelle spectra from McDonald Observatory and Special Astronomy Observatory. The data includes five years of observations over 21 epochs. Standard 1D local thermodynamic equilibrium analysis provides a fresh determination of the atmospheric parameters over all epochs: T_eff=7350±200 K, log g= +0.6±0.3, and a microturbulent velocity ξ=6.6±1.6 km/s and [Fe/H]=0.4±0.2, and a carbon abundance [C/Fe]=-0.19±0.30. We find oxygen abundance [O/Fe]=-0.25±0.28 and an enhancement of 0.9 dex in N. A supersonic macroturbulent velocity of 22.0±2.0 km/s is determined from both strong and weak Fe i and Fe iilines. Elemental abundances are obtained for 22 elements. HD 179821 is not enriched in s-process products. Eu is overabundant relative to the anticipated [X/Fe] ≃ 0.0. Some peculiarities of its optical spectrum (e.g. variability in the spectral line shapes) is noticed. This includes the line profile variations for H α line. Based on its estimated luminosity, effective temperature and surface gravity, HD 179821 is a massive star evolving to become a red supergiant and finally a Type II supernova.