Stellar laboratories

Abstract

Context. For the spectral analysis of high-resolution and high-signal-to-noise (S/N) spectra of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These are strongly dependent on the reliability of the atomic data that is used for their calculation.Aims. Reliable Ba v-vii oscillator strengths are used to identify Ba lines in the spectra of the DA-type white dwarf G191−B2B and the DO-type white dwarf RE 0503−289 and to determine their photospheric Ba abundances.Methods. We newly calculated Ba v-vii oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our NLTE stellar-atmosphere models for the analysis of Ba lines exhibited in high-resolution and high-S/N UV observations of G191−B2B and RE 0503−289.Results. For the first time, we identified highly ionized Ba in the spectra of hot white dwarfs. We detected Ba vi and Ba vii lines in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of RE 0503−289. The Ba vi/Ba vii ionization equilibrium is well reproduced with the previously determined effective temperature of 70 000 K and surface gravity of log g = 7.5. The Ba abundance is 3.5 ± 0.5 × 10 −4 (mass fraction, about 23 000 times the solar value). In the FUSE spectrum of G191−B2B, we identified the strongest Ba vii line (at 993.41 Å) only, and determined a Ba abundance of 4.0 ± 0.5 × 10−6 (about 265 times solar). Conclusions. Reliable measurements and calculations of atomic data are a pre-requisite for stellar-atmosphere modeling. Observed Ba vi-vii line profiles in two white dwarfs' (G191−B2B and RE 0503−289) far-ultraviolet spectra were well reproduced with our newly calculated oscillator strengths. This allowed to determine the photospheric Ba abundance of these two stars precisely.

Stellar laboratories

“…For both stars, the final models of Rauch et al (2014b) are adopted as start models for our calculations. For G191−B2B and RE 0503−289, the statistics of our model atoms are summarized in Tables 11 and 12, the model abundances in Tables 13 and 14. The SEDs calculated for this analysis are available via the registered Theoretical Stellar Spectra Access (TheoSSA 8 ) Virtual Observatory (VO) service.…”

“…These enabled us to measure the Zn (Rauch et al 2014a), Ge , and Ba (Rauch et al 2014b) abundances in RE 0503−289 and the hydrogen-rich DA-type WD G191−B2B (T eff = 60 000 K, log g = 7.6, Rauch et al 2013). The Sn abundance in G191−B2B was determined based on existing atomic data (Rauch et al 2013).…”

Stellar laboratories

“…The abundance analysis of these species is hampered by the lack of atomic data for their higher ionization stages, i.e., iv-vii. While Werner et al (2012b) could measure only the Kr and Xe abundances, further abundance determinations (Zn, Ge, Ga, Xe, and Ba by Rauch et al 2014aRauch et al , 2012Rauch et al , 2014bRauch et al , 2015b were always initiated by new calculations of reliable transition probabilities.…”

Overview of recent advances performed in the study of atomic structures and radiative processes for the lowest ionization stages of heavy elements

“…To fill this lack of atomic data, we recently started to compute transition rates for spectral lines belonging to three-through six-times ionized elements of interest using the HFR + CPOL + CPEN method. These studies allowed us to provide a large number of new reliable gf-values in Zr IV-VII [181], Mo IV-VII [182], Xe IV-VII [181,183], and Ba IV-VII [184] fifth-and sixth-row ions, in addition to Zn IV-VII [185], Ga IV-VII [186], Ge IV-VII [187], and Kr IV-VII [188] lighter ions. All these analyses, performed in collaboration with the Institute for Astronomy and Astrophysics of Eberhard Karls University in Tübingen, Germany, showed that, without exception, the abundances of those heavy metals in RE 0503-289 are unexpectedly strong supersolar (up to about 5 dex).…”

“…Mainly based on experimental energy levels, these were calculated with the semi-empirical HFR + CPOL + CPEN approach in accordance with the procedures described in detail in our different papers related to the search (and identification) of trans-iron elements in the hot white dwarfs G191-B2B and RE0503-289 [181][182][183][184][185][186][187][188]. More precisely, new radiative parameters for tens of thousands spectral lines in moderately charged fifth-and sixth-row ions, such as Zr IV-VII, Mo IV-VII, Tc IV-VII, Xe IV-VII, and Ba IV-VII, in addition to new atomic data obtained for the lighter ions Zn IV-VII, Ga IV-VII, Ge IV-VII, and Kr IV-VII are currently available in the database.…”