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arXiv · 2308.13368

Helioseismic determination of the solar metal mass fraction

G. Buldgen·A. Noels·V. A. Baturin·A. V. Oreshina·S. V. Ayukov·R. Scuflaire·A. M. Amarsi·N. Grevesse
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Abstract

Context. The metal mass fraction of the Sun Z is a key constraint in solar modelling, but its value is still under debate. The standard solar chemical composition of the late 2000s have the ratio of metals to hydrogen Z/X = 0.0181, with a small increase to 0.0187 in 2021, as inferred from 3D non-LTE spectroscopy. However, more recent work on a horizontally and temporally averaged <3D> model claim Z/X = 0.0225, consistent with the high values of twenty-five years ago based on 1D LTE spectroscopy. Aims. We aim to determine a precise and robust value of the solar metal mass fraction from helioseismic inversions, thus providing independent constraints from spectroscopic methods. Methods. We devise a detailed seismic reconstruction technique of the solar envelope, combining multiple inversions and equations of state to accurately and precisely determine the metal mass fraction value. Results. We show that a low value of the solar metal mass fraction corresponding to Z/X = 0.0187 is favoured by helioseismic constraints and that a higher metal mass fraction corresponding to Z/X = 0.0225 are strongly rejected by helioseismic data. Conclusions. We conclude that direct measurement of the metal mass fraction in the solar envelope favours a low metallicity, in line with the 3D non-LTE spectroscopic determination of 2021. A high metal mass fraction as measured using a <3D> model in 2022 is disfavoured by helioseismology for all modern equations of state used to model the solar convective envelope.

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G. Buldgen, A. Noels, V. A. Baturin, A. V. Oreshina, S. V. Ayukov, R. Scuflaire, A. M. Amarsi, N. Grevesse. 2023-08-25. Helioseismic determination of the solar metal mass fraction. https://arxiv.org/abs/2308.13368

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