HST/COS Spectroscopy of H1504+65

TL;DR

This paper presents ultraviolet spectra of the peculiar white dwarf H1504+65, revealing its unique composition and potential origin as a naked core of a C--O or O--Ne--Mg white dwarf, possibly from single-star evolution.

Contribution

First ultraviolet spectra of H1504+65 obtained with HST/COS, providing insights into its unique composition and possible evolutionary origin.

Findings

H1504+65 is the hottest known white dwarf with Teff=200,000 K.

Its atmosphere is mainly composed of C, O, Ne, and Mg.

The observations suggest it may be a naked core of a C--O or O--Ne--Mg white dwarf.

Abstract

We present new ultraviolet spectra of the peculiar white dwarf (WD) H1504+65, obtained with COS on HST. H1504+65 is the hottest known WD (Teff= 200,000 K) and has an atmosphere mainly composed of C and O, augmented with high amounts of Ne and Mg. This object is unique and the origin of its surface chemistry is completely unclear. We probably see the naked core of either a C--O WD or even a O--Ne--Mg WD. In the latter case, this would be the first direct proof that such WDs can be the outcome of single-star evolution. The new observations were performed to shed light on the origin of this mysterious object.