ORCID Profile
0000-0003-4936-4211
Current Organisation
Stockholms Universitet
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Publisher: American Astronomical Society
Date: 12-11-2013
Publisher: EDP Sciences
Date: 06-2013
Publisher: EDP Sciences
Date: 07-2012
Publisher: EDP Sciences
Date: 19-12-2016
Publisher: Springer Science and Business Media LLC
Date: 13-02-2014
Publisher: American Astronomical Society
Date: 10-07-2013
Publisher: EDP Sciences
Date: 07-2010
Publisher: American Astronomical Society
Date: 10-07-2013
Publisher: EDP Sciences
Date: 02-2020
DOI: 10.1051/0004-6361/201936104
Abstract: Context. The pursuit of more realistic spectroscopic modelling and consistent abundances has led us to begin a new series of papers designed to improve current solar and stellar abundances of various atomic species. To achieve this, we have begun updating the three-dimensional (3D) non-local thermodynamic equilibrium (non-LTE) radiative transfer code, MULTI3D, and the equivalent one-dimensional (1D) non-LTE radiative transfer code, MULTI 2.3. Aims. We examine our improvements to these codes by redetermining the solar barium abundance. Barium was chosen for this test as it is an important diagnostic element of the s -process in the context of galactic chemical evolution. New Ba II + H collisional data for excitation and charge exchange reactions computed from first principles had recently become available and were included in the model atom. The atom also includes the effects of isotopic line shifts and hyperfine splitting. Methods. A grid of 1D LTE barium lines were constructed with MULTI 2.3 and fit to the four Ba II lines available to us in the optical region of the solar spectrum. Abundance corrections were then determined in 1D non-LTE, 3D LTE, and 3D non-LTE. A new 3D non-LTE solar barium abundance was computed from these corrections. Results. We present for the first time the full 3D non-LTE barium abundance of A (Ba) = 2.27 ± 0.02 ± 0.01, which was derived from four in idual fully consistent barium lines. Errors here represent the systematic and random errors, respectively.
Publisher: EDP Sciences
Date: 07-2023
DOI: 10.1051/0004-6361/202346724
Abstract: Context. The shapes of Stokes profiles contain a great deal of information about the atmospheric conditions that produced them. However, a variety of different atmospheric structures can produce very similar profiles. Thus, it is important for a proper interpretation of the observations to have a good understanding of how the shapes of Stokes profiles depend on the underlying atmosphere. An excellent tool in this regard is forward modeling, namely, computing and studying synthetic spectra from realistic simulations of the solar atmosphere. Modern simulations routinely produce several hundred thousand spectral profiles per snapshot. With such numbers, it becomes necessary to use automated procedures in order to organize the profiles according to their shape. Here, we illustrate the use of two complementary methods, k -means and k -Shape, to cluster similarly shaped profiles and demonstrate how the resulting clusters can be combined with knowledge of the simulation’s atmosphere to interpret spectral shapes. Aims. We aim to showcase the use of clustering analysis for forward modeling. In particular, we wish to introduce the k -Shape clustering method to the solar physics community as a complement to the well-known k -means method. Methods. We generated synthetic Stokes profiles for the Ca II 854.2 nm line using the Multi3D code from a Bifrost simulation snapshot. We then applied the k -means and k -Shape clustering techniques to group the profiles together according to their shape and investigated the within-group correlations of temperature, line-of-sight velocity, and line-of-sight magnetic field strengths. Results. We show and compare the classes of profile shapes we retrieved from applying both k -means and k -Shape to our synthetic intensity spectra. We then show the structure of the underlying atmosphere for two particular classes of profile shapes retrieved by the clustering and demonstrate how this leads to an interpretation for the formation of those profile shapes. We applied both methods to the subset of our profiles containing the strongest Stokes V signals and we demonstrate how k -Shape can be qualitatively better than k -means at retrieving complex profile shapes when using a small number of clusters.
Publisher: Oxford University Press (OUP)
Date: 02-12-2016
Publisher: American Astronomical Society
Date: 17-06-2013
No related grants have been discovered for Jorrit Leenaarts.