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

TL;DR

This study presents ultraviolet spectroscopic analysis of the hypervelocity white dwarf J0927-6335, revealing high iron and nickel abundances that suggest supernova pollution, supporting its identification as a surviving donor in a Type Ia supernova event.

Contribution

First ultraviolet spectrum of J0927-6335 analyzed, providing evidence of supernova pollution and supporting its role as a surviving donor in the D6 Type Ia supernova model.

Findings

High iron and nickel abundances detected in the spectrum.

Possible pollution from supernova explosion inferred.

Uncertainty remains regarding atomic diffusion effects.

Abstract

The hot white dwarf (WD) J0927-6335 (Gaia DR3 5250394728194220800, effective temperature T$_{\rm eff}$ = 60,000 K, surface gravity log g = 7) was detected as the fastest known Galactic hypervelocity star with a space velocity of $\approx$2800 km s$^{-1}$ and an atmosphere dominated by carbon and oxygen. It is thought to be the surviving WD donor predicted by the "dynamically driven double-degenerate double-detonation" (D$^6$) type Ia supernova formation model. We analysed an ultraviolet spectrum of J0927-6335 obtained recently with the Hubble Space Telescope and found very high abundances of iron and nickel. This could originate in the pollution of the remnant by the SN Ia explosion but it is uncertain to what extent atomic diffusion altered the chemical composition of the accreted material.