Journal Article

The total and relative contribution of the relevant absorption processes to the opacity of DB white dwarf atmospheres in the UV and VUV regions

Lj. M. Ignjatović, A. A. Mihajlov, N. M. Sakan, M. S. Dimitrijević and A. Metropoulos

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 396, issue 4, pages 2201-2210
Published in print July 2009 | ISSN: 0035-8711
Published online July 2009 | e-ISSN: 1365-2966 | DOI: https://dx.doi.org/10.1111/j.1365-2966.2009.14870.x
The total and relative contribution of the relevant absorption processes to the opacity of DB white dwarf atmospheres in the UV and VUV regions

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The main aim of this work is to estimate the total contribution of the processes of molecular ion photodissociation and collisional absorption charge exchange to the opacity of DB white dwarf atmospheres, and compare this with the contribution of and other relevant radiative absorption processes included in standard models.

The method for the calculations of the molecular ion photodissociation cross-sections is based on the dipole approximation and quantum-mechanical treatment of the internuclear motion, while the quasi-classical method for describing absorption processes in collisions is based on the quasi-static approximation.

Absorption coefficients are calculated in the region 50 nm ≤λ≤ 850 nm and compared with the corresponding coefficients of other relevant absorption processes; the calculations of the optical depth of the atmosphere layers considered are performed in the far-UV and VUV regions; the contribution of the relevant absorption processes to the opacity of DB white dwarf atmospheres is examined.

We examined the spectral ranges in which the total and absorption processes dominate in particular layers of DB white dwarf atmospheres. In addition, we show that in the region of λ≲ 70 nm the process of atom photoionization is also important, in spite of the fact that the ratio of hydrogen and helium abundances in the DB white dwarf atmosphere considered is 1:105.

Keywords: atomic processes; molecular processes; radiation mechanisms: general; radiative transfer; stars: atmospheres

Journal Article.  4847 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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