Anatomy of the hyper-runaway star LP 40-365 with Gaia

TL;DR

This paper analyzes the hyper-runaway star LP 40-365 using Gaia data, confirming its origin as a supernova remnant and its high velocity escaping the Milky Way, providing insights into white dwarf supernovae remnants.

Contribution

It provides an updated kinematic analysis of LP 40-365 using Gaia data, confirming its supernova remnant origin and high-velocity escape trajectory from the Milky Way.

Findings

LP 40-365 is a subluminous star about 15 times larger than a white dwarf.

It is leaving the Milky Way at approximately 1.5 times the local escape velocity.

It was ejected from its progenitor binary with at least 600 km/s.

Abstract

LP 40-365 (aka GD 492) is a nearby low-luminosity hyper-runaway star with an extremely unusual atmospheric composition, which has been proposed as the remnant of a white dwarf that survived a subluminous Type Ia supernova (SN Ia) in a single-degenerate scenario. Adopting the Gaia Data Release (DR2) parallax, 1.58 +/- 0.03 mas, we estimate a radius of 0.18 +/- 0.01 Rsun, confirming LP 40-365 as a subluminous star that is ~ 15 times larger than a typical white dwarf and is compatible with the SN Ia remnant scenario. We present an updated kinematic analysis, making use of the Gaia parallax and proper motion, and confirm that Lp 40-365 is leaving the Milky Way at about 1.5 times the escape velocity of the Solar neighbourhood with a rest-frame velocity of 852 +/- 10 km/s. Integrating the past trajectories of LP 40-365, we confirm it crossed the Galactic disc 5.0 +/- 0.3 Myr ago in the direction of Carina, likely coming from beneath the plane. Finally, we estimate that LP 40-365 was ejected from its progenitor binary with a velocity of at least 600 km/s, which is compatible with theoretical predictions for close binaries containing a white dwarf and a helium-star donor.