Complete spectral energy distribution of the hot, helium-rich white dwarf RX J0503.9–2854^{⋆,⋆⋆,⋆⋆⋆,⋆⋆⋆⋆}

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 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
³ Physique Atomique et Astrophysique, Université de Mons – UMONS, 7000 Mons, Belgium
⁴ IPNAS, Université de Liège, Sart Tilman, 4000 Liège, Belgium

Received: 10 October 2016
Accepted: 17 October 2016

Abstract

Context. In the line-of-sight toward the DO-type white dwarf RX J0503.9–2854, the density of the interstellar medium (ISM) is very low, and thus the contamination of the stellar spectrum almost negligible. This allows us to identify many metal lines in a wide wavelength range from the extreme ultraviolet to the near infrared.

Aims. In previous spectral analyses, many metal lines in the ultraviolet spectrum of RX J0503.9–2854 have been identified. A complete line list of observed and identified lines is presented here.

Methods. We compared synthetic spectra that had been calculated from model atmospheres in non-local thermodynamical equilibrium, with observations.

Results. In total, we identified 1272 lines (279 of them were newly assigned) in the wavelength range from the extreme ultraviolet to the near infrared. 287 lines remain unidentified. A close inspection of the EUV shows that still no good fit to the observed shape of the stellar continuum flux can be achieved although He, C, N, O, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Cr, Ni Zn, Ga, Ge, As, Kr, Zr, Mo, Sn, Xe, and Ba are included in the stellar atmosphere models.

Conclusions. There are two possible reasons for the deviation between observed and synthetic flux in the EUV. Opacities from hitherto unconsidered elements in the model-atmosphere calculation may be missing, and/or the effective temperature is slightly lower than previously determined.