# Partly burnt runaway stellar remnants from peculiar thermonuclear supernovae

## TL;DR

This paper reports the discovery of a new class of chemically peculiar, runaway stellar remnants from peculiar thermonuclear supernovae, providing insights into their composition, origins, and evolution.

## Contribution

It identifies and characterizes a new class of partly burnt white dwarf remnants from peculiar thermonuclear supernovae, with spectroscopic and kinematic evidence.

## Key findings

- Four stars have ONe-dominated atmospheres with nuclear ashes.
- At least two stars are unbound to the Galaxy.
- Estimated ~20 such stars brighter than 19 mag within 2 kpc.

## Abstract

We report the discovery of three stars that, along with the prototype LP40-365, form a distinct class of chemically peculiar runaway stars that are the survivors of thermonuclear explosions. Spectroscopy of the four confirmed LP 40-365 stars finds ONe-dominated atmospheres enriched with remarkably similar amounts of nuclear ashes of partial O- and Si-burning. Kinematic evidence is consistent with ejection from a binary supernova progenitor; at least two stars have rest-frame velocities indicating they are unbound to the Galaxy. With masses and radii ranging between 0.20-0.28 Msun and 0.16-0.60 Rsun, respectively, we speculate these inflated white dwarfs are the partly burnt remnants of either peculiar Type Iax or electron-capture supernovae. Adopting supernova rates from the literature, we estimate that ~20 LP40-365 stars brighter than 19 mag should be detectable within 2 kpc from the Sun at the end of the Gaia mission. We suggest that as they cool, these stars will evolve in their spectroscopic appearance, and eventually become peculiar O-rich white dwarfs. Finally, we stress that the discovery of new LP40-365 stars will be useful to further constrain their evolution, supplying key boundary conditions to the modelling of explosion mechanisms, supernova rates, and nucleosynthetic yields of peculiar thermonuclear explosions.