A cool R Coronae Borealis star Z UMi

TL;DR

This paper analyzes the high-resolution spectra of the R Coronae Borealis star Z UMi, determining its atmospheric parameters, confirming its hydrogen deficiency, and revealing its elemental abundances, including low iron and high lithium levels.

Contribution

It provides detailed spectroscopic analysis and atmospheric parameters for Z UMi, a cool R CrB star, and characterizes its elemental composition.

Findings

Z UMi is among the coolest R CrB stars.

Confirmed hydrogen deficiency in Z UMi.

Detected very low iron and high lithium abundance.

Abstract

The high resolution spectra of a R CrB type star Z UMi are analysed. The atmospheric parameters of Z UMi are estimated: Teff=5250+/-250K and log g=0.5+/-0.3. This places Z UMi among the coolest R CrB stars. The hydrogen deficiency of Z UMi is confirmed. The abundances of other elements resemble those found for the minority group of R CrB stars. We note very low iron abundance, [Fe/H]=-1.85, and an excess of lithium, [Li/Fe]=+1.9.