Lyman α wing absorption in cool white dwarf stars

Autores
Rohrmann, René; Althaus, Leandro Gabriel; Kepler, S. O.
Año de publicación
2011
Idioma
inglés
Tipo de recurso
artículo
Estado
versión publicada
Descripción
Kowalski & Saumon identified the missing absorption mechanism in the observed spectra of cool white dwarf stars as the Lyman α red wing formed by the collisions between atomic and molecular hydrogen and successfully explained entire spectra of many cool DA-type white dwarfs. Owing to the important astrophysical implications of this issue, we present here an independent assessment of the process. For this purpose, we compute free-free quasi-molecular absorption in Lyman α due to collisions with H and H2 within the one-perturber, quasi-static approximation. Line cross-sections are obtained using theoretical molecular potentials to describe the interaction between the radiating atom and the perturber. The variation in the electric dipole transition moment with the interparticle distance is also considered. Six and two allowed electric dipole transitions due to H-H and H-H2 collisions, respectively, are taken into account. The new theoretical Lyman α line profiles are then incorporated in our stellar atmosphere program for the computation of synthetic spectra and colours of DA-type white dwarfs. Illustrative model atmospheres and spectral energy distributions are computed, which show that Lyman α broadening by atoms and molecules has a significant effect on the white dwarf atmosphere models. The inclusion of this collision-induced opacity significantly reddens spectral energy distributions and affects the broad-band colour indices for model atmospheres with Teff < 5000K. These results confirm those previously obtained by Kowalski & Saumon. Our study points out the need for reliable evaluations of H3 potential energy surfaces covering a large region of nuclear configurations, in order to obtain a better description of H-H2 collisions and a more accurate evaluation of their influence on the spectrum of cool white dwarfs.
Facultad de Ciencias Astronómicas y Geofísicas
Instituto de Astrofísica de La Plata
Materia
Ciencias Astronómicas
Atomic processes
Line: profiles
Molecular processes
Stars: atmospheres
White dwarfs
Nivel de accesibilidad
acceso abierto
Condiciones de uso
http://creativecommons.org/licenses/by-nc-sa/4.0/
Repositorio
SEDICI (UNLP)
Institución
Universidad Nacional de La Plata
OAI Identificador
oai:sedici.unlp.edu.ar:10915/84021

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oai_identifier_str oai:sedici.unlp.edu.ar:10915/84021
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network_name_str SEDICI (UNLP)
spelling Lyman α wing absorption in cool white dwarf starsRohrmann, RenéAlthaus, Leandro GabrielKepler, S. O.Ciencias AstronómicasAtomic processesLine: profilesMolecular processesStars: atmospheresWhite dwarfsKowalski & Saumon identified the missing absorption mechanism in the observed spectra of cool white dwarf stars as the Lyman α red wing formed by the collisions between atomic and molecular hydrogen and successfully explained entire spectra of many cool DA-type white dwarfs. Owing to the important astrophysical implications of this issue, we present here an independent assessment of the process. For this purpose, we compute free-free quasi-molecular absorption in Lyman α due to collisions with H and H<SUB>2</SUB> within the one-perturber, quasi-static approximation. Line cross-sections are obtained using theoretical molecular potentials to describe the interaction between the radiating atom and the perturber. The variation in the electric dipole transition moment with the interparticle distance is also considered. Six and two allowed electric dipole transitions due to H-H and H-H<SUB>2</SUB> collisions, respectively, are taken into account. The new theoretical Lyman α line profiles are then incorporated in our stellar atmosphere program for the computation of synthetic spectra and colours of DA-type white dwarfs. Illustrative model atmospheres and spectral energy distributions are computed, which show that Lyman α broadening by atoms and molecules has a significant effect on the white dwarf atmosphere models. The inclusion of this collision-induced opacity significantly reddens spectral energy distributions and affects the broad-band colour indices for model atmospheres with T<SUB>eff</SUB> < 5000K. These results confirm those previously obtained by Kowalski & Saumon. Our study points out the need for reliable evaluations of H<SUB>3</SUB> potential energy surfaces covering a large region of nuclear configurations, in order to obtain a better description of H-H<SUB>2</SUB> collisions and a more accurate evaluation of their influence on the spectrum of cool white dwarfs.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plata2011info:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersionArticulohttp://purl.org/coar/resource_type/c_6501info:ar-repo/semantics/articuloapplication/pdf781-791http://sedici.unlp.edu.ar/handle/10915/84021enginfo:eu-repo/semantics/altIdentifier/issn/0035-8711info:eu-repo/semantics/altIdentifier/doi/10.1111/j.1365-2966.2010.17716.xinfo:eu-repo/semantics/openAccesshttp://creativecommons.org/licenses/by-nc-sa/4.0/Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)reponame:SEDICI (UNLP)instname:Universidad Nacional de La Platainstacron:UNLP2025-09-29T11:16:10Zoai:sedici.unlp.edu.ar:10915/84021Institucionalhttp://sedici.unlp.edu.ar/Universidad públicaNo correspondehttp://sedici.unlp.edu.ar/oai/snrdalira@sedici.unlp.edu.arArgentinaNo correspondeNo correspondeNo correspondeopendoar:13292025-09-29 11:16:10.356SEDICI (UNLP) - Universidad Nacional de La Platafalse
dc.title.none.fl_str_mv Lyman α wing absorption in cool white dwarf stars
title Lyman α wing absorption in cool white dwarf stars
spellingShingle Lyman α wing absorption in cool white dwarf stars
Rohrmann, René
Ciencias Astronómicas
Atomic processes
Line: profiles
Molecular processes
Stars: atmospheres
White dwarfs
title_short Lyman α wing absorption in cool white dwarf stars
title_full Lyman α wing absorption in cool white dwarf stars
title_fullStr Lyman α wing absorption in cool white dwarf stars
title_full_unstemmed Lyman α wing absorption in cool white dwarf stars
title_sort Lyman α wing absorption in cool white dwarf stars
dc.creator.none.fl_str_mv Rohrmann, René
Althaus, Leandro Gabriel
Kepler, S. O.
author Rohrmann, René
author_facet Rohrmann, René
Althaus, Leandro Gabriel
Kepler, S. O.
author_role author
author2 Althaus, Leandro Gabriel
Kepler, S. O.
author2_role author
author
dc.subject.none.fl_str_mv Ciencias Astronómicas
Atomic processes
Line: profiles
Molecular processes
Stars: atmospheres
White dwarfs
topic Ciencias Astronómicas
Atomic processes
Line: profiles
Molecular processes
Stars: atmospheres
White dwarfs
dc.description.none.fl_txt_mv Kowalski & Saumon identified the missing absorption mechanism in the observed spectra of cool white dwarf stars as the Lyman α red wing formed by the collisions between atomic and molecular hydrogen and successfully explained entire spectra of many cool DA-type white dwarfs. Owing to the important astrophysical implications of this issue, we present here an independent assessment of the process. For this purpose, we compute free-free quasi-molecular absorption in Lyman α due to collisions with H and H<SUB>2</SUB> within the one-perturber, quasi-static approximation. Line cross-sections are obtained using theoretical molecular potentials to describe the interaction between the radiating atom and the perturber. The variation in the electric dipole transition moment with the interparticle distance is also considered. Six and two allowed electric dipole transitions due to H-H and H-H<SUB>2</SUB> collisions, respectively, are taken into account. The new theoretical Lyman α line profiles are then incorporated in our stellar atmosphere program for the computation of synthetic spectra and colours of DA-type white dwarfs. Illustrative model atmospheres and spectral energy distributions are computed, which show that Lyman α broadening by atoms and molecules has a significant effect on the white dwarf atmosphere models. The inclusion of this collision-induced opacity significantly reddens spectral energy distributions and affects the broad-band colour indices for model atmospheres with T<SUB>eff</SUB> < 5000K. These results confirm those previously obtained by Kowalski & Saumon. Our study points out the need for reliable evaluations of H<SUB>3</SUB> potential energy surfaces covering a large region of nuclear configurations, in order to obtain a better description of H-H<SUB>2</SUB> collisions and a more accurate evaluation of their influence on the spectrum of cool white dwarfs.
Facultad de Ciencias Astronómicas y Geofísicas
Instituto de Astrofísica de La Plata
description Kowalski & Saumon identified the missing absorption mechanism in the observed spectra of cool white dwarf stars as the Lyman α red wing formed by the collisions between atomic and molecular hydrogen and successfully explained entire spectra of many cool DA-type white dwarfs. Owing to the important astrophysical implications of this issue, we present here an independent assessment of the process. For this purpose, we compute free-free quasi-molecular absorption in Lyman α due to collisions with H and H<SUB>2</SUB> within the one-perturber, quasi-static approximation. Line cross-sections are obtained using theoretical molecular potentials to describe the interaction between the radiating atom and the perturber. The variation in the electric dipole transition moment with the interparticle distance is also considered. Six and two allowed electric dipole transitions due to H-H and H-H<SUB>2</SUB> collisions, respectively, are taken into account. The new theoretical Lyman α line profiles are then incorporated in our stellar atmosphere program for the computation of synthetic spectra and colours of DA-type white dwarfs. Illustrative model atmospheres and spectral energy distributions are computed, which show that Lyman α broadening by atoms and molecules has a significant effect on the white dwarf atmosphere models. The inclusion of this collision-induced opacity significantly reddens spectral energy distributions and affects the broad-band colour indices for model atmospheres with T<SUB>eff</SUB> < 5000K. These results confirm those previously obtained by Kowalski & Saumon. Our study points out the need for reliable evaluations of H<SUB>3</SUB> potential energy surfaces covering a large region of nuclear configurations, in order to obtain a better description of H-H<SUB>2</SUB> collisions and a more accurate evaluation of their influence on the spectrum of cool white dwarfs.
publishDate 2011
dc.date.none.fl_str_mv 2011
dc.type.none.fl_str_mv info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Articulo
http://purl.org/coar/resource_type/c_6501
info:ar-repo/semantics/articulo
format article
status_str publishedVersion
dc.identifier.none.fl_str_mv http://sedici.unlp.edu.ar/handle/10915/84021
url http://sedici.unlp.edu.ar/handle/10915/84021
dc.language.none.fl_str_mv eng
language eng
dc.relation.none.fl_str_mv info:eu-repo/semantics/altIdentifier/issn/0035-8711
info:eu-repo/semantics/altIdentifier/doi/10.1111/j.1365-2966.2010.17716.x
dc.rights.none.fl_str_mv info:eu-repo/semantics/openAccess
http://creativecommons.org/licenses/by-nc-sa/4.0/
Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)
eu_rights_str_mv openAccess
rights_invalid_str_mv http://creativecommons.org/licenses/by-nc-sa/4.0/
Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)
dc.format.none.fl_str_mv application/pdf
781-791
dc.source.none.fl_str_mv reponame:SEDICI (UNLP)
instname:Universidad Nacional de La Plata
instacron:UNLP
reponame_str SEDICI (UNLP)
collection SEDICI (UNLP)
instname_str Universidad Nacional de La Plata
instacron_str UNLP
institution UNLP
repository.name.fl_str_mv SEDICI (UNLP) - Universidad Nacional de La Plata
repository.mail.fl_str_mv alira@sedici.unlp.edu.ar
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