Query : 2015A&A...577A...6R

2015A&A...577A...6R - Astronomy and Astrophysics, volume 577A, 6-6 (2015/5-1)

Stellar laboratories. IV. New Ga IV, Ga V, and Ga VI oscillator strengths and the gallium abundance in the hot white dwarfs G191-B2B and RE 0503-289.


Abstract (from CDS):

For the spectral analysis of high-resolution and high-signal-to-noise (S/N) spectra of hot stars, advanced non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These atmospheres are strongly dependent on the reliability of the atomic data that are used to calculate them. Reliable GaIV-VI oscillator strengths are used to identify Ga lines in the spectra of the DA-type white dwarf G191-B2B and the DO-type white dwarf RE0503-289 and to determine their photospheric Ga abundances. We newly calculated GaIV-VI oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our NLTE stellar-atmosphere models for analyzing of Ga lines exhibited in high-resolution and high-S/N UV observations of G191-B2B and RE0503-289. We unambiguously detected 20 isolated and 6 blended (with lines of other species) GaV lines in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of RE0503-289. The identification of GaIV and GaVI lines is uncertain because they are weak and partly blended by other lines. The determined Ga abundance is 3.5±0.5x10–5 (mass fraction, about 625 times the solar value). The GaIV/GaV ionization equilibrium, which is a very sensitive indicator for the effective temperature, is well reproduced in RE0503-289. We identified the strongest GaIV lines (at 1258.801, 1338.129Å) in the HST/STIS spectrum of G191-B2B and measured a Ga abundance of 2.0±0.5x10–6 (about 22 times solar). Reliable measurements and calculations of atomic data are a prerequisite for stellar-atmosphere modeling. The observed GaIV-V line profiles in two white dwarf (G191-B2B and RE0503-289 ultraviolet spectra were well reproduced with our newly calculated oscillator strengths. For the first time, this allowed us to determine the photospheric Ga abundance in white dwarfs.

Abstract Copyright:

Journal keyword(s): atomic data - line: identification - stars: abundances - stars: individual: G191-B2B - stars: individual: RE0503-289 - virtual observatory tools

VizieR on-line data: <Available at CDS (J/A+A/577/A6): table7.dat table8.dat table9.dat>

Simbad objects: 2

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Number of rows : 2
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 RX J0503.9-2854 WD* 05 03 55.5148810152 -28 54 34.631077500 12.29 13.55 13.58     DO 100 0
2 BD+52 913 WD* 05 05 30.6180977592 +52 49 51.919301604 10.25 11.44 11.69 11.93 12.108 DA.8 1066 0

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