Spectroscopic Studies of Extremely Metal-Poor Stars with the Subaru High Dispersion Spectrograph. V. The Zn-Enhanced Metal-Poor Star BS 16920-017

TL;DR

This study measures zinc abundances in very metal-poor stars, revealing a high [Zn/Fe] in one star possibly linked to hypernova explosions, and confirms a trend of increasing [Zn/Fe] with decreasing metallicity.

Contribution

First detailed zinc abundance analysis of extremely metal-poor stars including the peculiar star BS 16920-017, suggesting hypernova influence on its chemical pattern.

Findings

Most stars show increasing [Zn/Fe] with decreasing [Fe/H]

BS 16920-017 has exceptionally high [Zn/Fe] = +1.0

This star exhibits deficiency in alpha and neutron-capture elements

Abstract

We report Zn abundances for 18 very metal-poor stars studied in our previous work, covering the metallicity range -3.2 < [Fe/H] < -2.5. The [Zn/Fe] values of most stars show an increasing trend with decreasing [Fe/H] in this metallicity range, confirming the results found by previous studies. However, the extremely metal-poor star BS 16920-017 ([Fe/H] = -3.2) exhibits a significantly high [Zn/Fe] ratio ([Zn/Fe] = +1.0). Comparison of the chemical abundances of this object with HD 4306, which has similar atmospheric parameters to BS 16920-017, clearly demonstrates a deficiency of alpha elements and neutron-capture elements in this star, along with enhancements of Mn and Ni, as well as Zn. The association with a hypernova explosion that has been proposed to explain the high Zn abundance ratios found in extremely metal-poor stars is a possible explanation, although further studies are required to fully interpret the abundance pattern of this object.