The Chemical Abundances of Tycho G in Supernova Remnant 1572

TL;DR

This study analyzes the chemical composition of Tycho G, a star near supernova remnant 1572, revealing overabundances of Ni and Co likely from supernova ejecta, and a high lithium level unexpected for its evolutionary stage.

Contribution

It provides detailed chemical abundance measurements of Tycho G, supporting its potential role as a supernova companion star with unique elemental signatures.

Findings

Ni overabundant relative to Fe

High Li abundance detected

Chemical patterns suggest supernova ejecta pollution

Abstract

We present an analysis of the chemical abundances of the star Tycho G in the direction of the remnant of supernova (SN) 1572, based on Keck high-resolution optical spectra. The stellar parameters of this star are found to be those of a G-type subgiant with $T_{\mathrm{eff}} = 5900 \pm 100$ K, \loggl $ = 3.85 \pm 0.30$ dex, and $\mathrm{[Fe/H]} = -0.05 \pm 0.09$. This determination agrees with the stellar parameters derived for the star in a previous survey for the possible companion star of SN 1572 (Ruiz-Lapuente et al. 2004). The chemical abundances follow the Galactic trends, except for Ni, which is overabundant relative to Fe, $[{\rm Ni/Fe}] $ $=$ 0.16 $\pm$ 0.04. Co is slightly overabundant (at a low significance level). These enhancements in Fe-peak elements could have originated from pollution by the supernova ejecta. We find a surprisingly high Li abundance for a star that has evolved away from the main sequence. We discuss these findings in the context of companion stars of supernovae.