First discovery of trans-iron elements in a DAO-type white dwarf (BD$-22{^\circ}3467$)

TL;DR

This study reports the first detection of trans-iron elements in a DAO-type white dwarf, revealing extreme overabundances driven by radiative levitation, and provides insights into the star's evolutionary history.

Contribution

First identification of trans-iron elements in a DAO white dwarf's ultraviolet spectrum, highlighting radiative levitation as the cause of overabundances without third dredge-up evidence.

Findings

Detected 484 lines of trans-iron elements in the white dwarf's spectrum.

Found overabundances of TIEs up to five dex, driven by radiative levitation.

Star's low mass suggests no third dredge-up occurred in its evolution.

Abstract

We have identified 484 lines of the trans-iron elements (TIEs) Zn, Ga, Ge, Se, Br, Kr, Sr, Zr, Mo, In, Te, I, Xe, and Ba, for the first time in the ultraviolet spectrum of a DAO-type WD, namely BD$-22{^\circ}3467$, surrounded by the ionized nebula Abell 35. Our TIE abundance determination shows extremely high overabundances of up to five dex -- a similar effect is already known from hot, H-deficient (DO-type) white dwarfs. In contrast to these where a pulse-driven convection zone has enriched the photosphere with TIEs during a final thermal pulse and radiative levitation has established the extreme TIE overabundances, {here the extreme TIE overabundances are exclusively driven by radiative levitation on the initial stellar metallicity. The very low mass ($0.533^{+0.040}_{-0.025}\,M_\odot$) of BD$-22{^\circ}3467$ implies that a third dredge-up with enrichment of s-process elements in the photosphere did not occur in the AGB precursor.