Stellar laboratories

X. New Cu IV–VII oscillator strengths and the first detection of copper and indium in hot white dwarfs^{★,★★,★★★}

¹ Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Sand 1, 72076 Tübingen, Germany
e-mail: rauch@astro.uni-tuebingen.de
² Physique Atomique et Astrophysique, Université de Mons – UMONS, 7000 Mons, Belgium
³ IPNAS, Université de Liège, Sart Tilman, 4000 Liège, Belgium
⁴ Astronomisches Rechen-Institut (ARI), Centre for Astronomy of Heidelberg University, Mönchhofstraße 12-14, 69120 Heidelberg, Germany
⁵ NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA

Received: 3 September 2019
Accepted: 20 March 2020

Abstract

Context. Accurate atomic data is an essential ingredient for the calculation of reliable non-local thermodynamic equilibrium (NLTE) model atmospheres that are mandatory for the spectral analysis of hot stars.

Aims. We aim to search for and identify for the first time spectral lines of copper (atomic number Z = 29) and indium (Z = 49) in hot white dwarf (WD) stars and to subsequently determine their photospheric abundances.

Methods. Oscillator strengths of Cu IV–VII were calculated to include radiative and collisional bound-bound transitions of Cu in our NLTE model-atmosphere calculations. Oscillator strengths of In IV - VI were compiled from the literature.

Results. We newly identified 1 Cu IV, 51 Cu V, 2 Cu VI, and 5 In V lines in the ultraviolet (UV) spectrum of DO-type WD RE 0503−289. We determined the photospheric abundances of 9.3 × 10⁻⁵ (mass fraction, 132 times solar) and 3.0 × 10⁻⁵ (56 600 times solar), respectively; we also found Cu overabundances in the DA-type WD G191−B2B (6.3 × 10⁻⁶, 9 times solar).

Conclusions. All identified Cu IV-VI lines in the UV spectrum of RE 0503−289 were simultaneously well reproduced with our newly calculated oscillator strengths. With the detection of Cu and In in RE 0503−289, the total number of trans-iron elements (Z > 28) in this extraordinary WD reaches an unprecedented number of 18.