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Inelastic e plus Mg collision data and its impact on modelling stellar and supernova spectra
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
Instituto de Astrofísica de Canarias, vía Láctea.; Universidad de La Laguna, Departamento de Astrofísica.; Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg.
Curtin Institute for Computation, Kent Street.; Department of Physics, Astronomy and Medical Radiation Science, Kent Street.
Curtin Institute for Computation, Kent Street.; Department of Physics, Astronomy and Medical Radiation Science, Kent Street.
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 606, article id A11Article in journal (Refereed) Published
Abstract [en]

Results of calculations for inelastic e+Mg effective collision strengths for the lowest 25 physical states of Mg I (up to 3s6p P-1), and thus 300 transitions, from the convergent close-coupling (CCC) and the B-spline R-matrix (BSR) methods are presented. At temperatures of interest, similar to 5000 K, the results of the two calculations differ on average by only 4%,with a scatter of 27%. As the methods are independent, this suggests that the calculations provide datasets for e+Mg collisions accurate to this level. Comparison with the commonly used dataset compiled by Mauas et al. (1988, ApJ, 330, 1008), covering 25 transitions among 12 states, suggests the Mauas et al. data are on average similar to 57% too low, and with a very large scatter of a factor of similar to 6.5. In particular the collision strength for the transition corresponding to the Mg I intercombination line at 457 nm is significantly underestimated by Mauas et al., which has consequences for models that employ this dataset. In giant stars the new data leads to a stronger line compared to previous non-LTE calculations, and thus a reduction in the non-LTE abundance correction by similar to 0.1 dex (similar to 25%). A non-LTE calculation in a supernova ejecta model shows this line becomes significantly stronger, by a factor of around two, alleviating the discrepancy where the 457 nm line in typical models with Mg/O ratios close to solar tended to be too weak compared to observations.

Place, publisher, year, edition, pages
2017. Vol. 606, article id A11
Keywords [en]
atomic data, atomic processes
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-337751DOI: 10.1051/0004-6361/201730864ISI: 000412874000002OAI: oai:DiVA.org:uu-337751DiVA, id: diva2:1170875
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationAvailable from: 2018-01-04 Created: 2018-01-04 Last updated: 2018-01-04Bibliographically approved

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