Ultraviolet spectroscopy of the supernova Ia hypervelocity runaway white dwarf J0927‑6335

Abstract

The hot white dwarf (WD) J0927‑6335 (Gaia DR3 5250394728194220800 with an effective temperature of T_eff = 60 000 K and a surface gravity of logg = 7) was detected as the fastest known Galactic hypervelocity star with a space velocity of ≈2800 km s^‑1 and an atmosphere dominated by carbon and oxygen. It is thought to be the surviving WD donor predicted by the so-called dynamically driven double-degenerate double-detonation (D⁶) type Ia supernova formation model. We analysed an ultraviolet spectrum of J0927‑6335 that was recently obtained with the Hubble Space Telescope and found very high abundances of iron and nickel. This might originate in the pollution of the remnant by the supernova Ia explosion, but it is uncertain to which extent atomic diffusion altered the chemical composition of the accreted material.