On the Chemical Composition of the Evolved Very Bright Metal-Poor Star HD 1936

Abstract

We present chemical abundances of the very bright metal-poor star HD~1936 based on high-resolution and high SNR spectra from AUKR. We obtain the abundances of 29 atomic species with atomic numbers between 3 and 63. In this context, the derived lithium abundance of 1.01 is consistent with the thin Li plateau observed in lower red giant branch stars. The star is a carbon-normal with the ratio of -0.31, just like other low-luminosity red giants on the thin Li plateau. We find the ratios of [Eu/Fe]=0.43 and [Ba/Eu]=-0.64, indicating very little s-process contamination. These ratios allow us to classify the star as a moderately r-process-enhanced (r-I) metal-poor star for the first time. It is worth mentioning that the star has a metallicity of -1.74, a [Cu/Fe] of -0.74, a [Zn/Fe] of 0.04, and a [Mg/C] of 0.69. The results suggest that it may be a second-generation star formed in a multi-enriched environment, rather than being a descendant of very massive first-generation stars. A last point worth mentioning is the possibility that HD~1936 may host a sub-stellar component with a mass of 18.35$M_{\mathrm{J}}$. Although our study does not confirm or deny this, we briefly discuss the possibility of the star hosting a planet.

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