The chemical abundances of Tycho G in supernova remnant 1572

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 Teff = 5900 ± 100 K, log(g/cms2) = 3.85 ± 0.30 dex, and [Fe/H] = -0.05 ± 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.). The chemical abundances follow the Galactic trends, except for Ni, which is overabundant relative to Fe, [Ni/Fe] = 0.16 ± 0.04. Co is slightly overabundant (at a low significance level). These enhancements in Fe-peak elements could have originated from pollution by the SN 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 SNe.