The solar photospheric abundance of hafnium and thorium. Results from CO5BOLD 3D hydrodynamic model atmospheres - AstrophysicsReport as inadecuate




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Abstract: Context: The stable element hafnium Hf and the radioactive element thoriumTh were recently suggested as a suitable pair for radioactive dating ofstars. The applicability of this elemental pair needs to be established forstellar spectroscopy. Aims: We aim at a spectroscopic determination of theabundance of Hf and Th in the solar photosphere based on a \cobold 3Dhydrodynamical model atmosphere. We put this into a wider context byinvestigating 3D abundance corrections for a set of G- and F-type dwarfs.Method: High-resolution, high signal-to-noise solar spectra were compared toline synthesis calculations performed on a solar CO5BOLD model. For the otheratmospheres, we compared synthetic spectra of CO5BOLD 3D and associated 1Dmodels. Results: For Hf we find a photospheric abundance AHf=0.87+-0.04, ingood agreement with a previous analysis, based on 1D model atmospheres. Theweak Th ii 401.9 nm line constitutes the only Th abundance indicator availablein the solar spectrum. It lies in the red wing of an Ni-Fe blend exhibiting anon-negligible convective asymmetry. Accounting for the asymmetry-relatedadditional absorption, we obtain ATh=0.09+-0.03, consistent with themeteoritic abundance, and about 0.1 dex lower than obtained in previousphotospheric abundance determinations. Conclusions: Only for the second time,to our knowledge, has am non-negligible effect of convective line asymmetrieson an abundance derivation been highlighted. Three-dimensional hydrodynamicalsimulations should be employed to measure Th abundances in dwarfs if similarblending is present, as in the solar case. In contrast, 3D effects on Hfabundances are small in G- to mid F-type dwarfs and sub-giants, and 1D modelatmospheres can be conveniently used.



Author: Elisabetta Caffau GEPI, L. Sbordone GEPI, Cifist, H.-G. Ludwig GEPI, Cifist, P. Bonifacio GEPI, Cifist, Inaf-Oat, M. Steffen AIP,

Source: https://arxiv.org/







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