Further insight on the hypervelocity white dwarf, LP 40-365 (GD 492): a nearby emissary from a single-degenerate Type Ia supernova

TL;DR

This study confirms that the hypervelocity white dwarf GD 492 likely originated from a single-degenerate Type Ia supernova, based on its unique spectral features and elemental abundances, especially its high manganese-to-iron ratio.

Contribution

The paper provides new spectroscopic evidence and atmospheric modeling that support GD 492's origin from a single-degenerate SN Ia, highlighting its unique elemental composition.

Findings

GD 492 has a helium-dominated, hydrogen-deficient atmosphere.

Detected traces of eleven elements, including sulfur, chromium, manganese, and titanium.

Manganese-to-iron ratio is seven times larger than Solar, indicating nuclear processing.

Abstract

The recently discovered hypervelocity white dwarf LP 40-65 (aka GD 492) has been suggested as the outcome of the failed disruption of a white dwarf in a sub-luminous Type Ia supernova (SN Ia). We present new observations confirming GD 492 as a single star with unique spectral features. Our spectroscopic analysis suggests that a helium-dominated atmosphere, with ~ 33 percent neon and 2 percent oxygen by mass, can reproduce most of the observed properties of this highly unusual star. Although our atmospheric model contrasts with the previous analysis in terms of dominant atmospheric species, we confirm that the atmosphere of GD 492 is strongly hydrogen deficient, log(H/He) < -5, and displays traces of eleven other alpha- and iron-group elements (with sulfur, chromium, manganese, and titanium as new detections), indicating nuclear processing of carbon and silicon. We measure a manganese-to-iron ratio seven times larger than Solar. While the observed abundances of GD 492 do not fully match any predicted nuclear yields of a partially-burned supernova remnant, the manganese excess strongly favors a link with a single-degenerate SN Ia event over alternative scenarios.